DEPARTMENT OF THE INTERIOR
UNITED STATES GEOLOGICAL SURVEY
Informal Notes:
WORKSHOP ON THE APPLICATION OF ISOTOPE SYSTEMS TO GEOLOGICAL PROBLEMS
Robert Ayuso and Klaus Schulz Convenors
September 14-16, 1992 Auditorium National Center Reston, Virginia 22092
Open-File Report 92-525 September 1992
This report is preliminary and has not been edited or reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. Any use of trade names is for descriptive purposes only and does not imply endorsement by the uses. List of Titles, Presenters, and Authors Page
Introduction 1
Schedule of meeting 3
Innovative uses ofPb isotopic measurements: Dating stromatolites and tracing sand dunes by J. N. Aleinikoff (U.S. Geological Survey, Box 25046, Mail Stop 963, Denver Federal Center, Denver, CO 80225) 7
Pb-Nd-O isotopic compositions of igneous rocks: Implications for petrogenesis and terrane correlation, Cape Breton Island, Nova Scotia, Canada by R. Ayuso (U.S. Geological Survey, 954 National Center, Reston, VA 22092), S. Barr, F. Longstaffe, and E. Hegner 15
The use ofK-Ar and ^Ar/^Ar techniques to date multiple thermal events: An example from the Bayan Obo Fe-Nb-REE ore deposit, China by J. E. Conrad (U.S. Geological Survey, 345 Middlefield Road, Mail Stop 901, Menlo Park, CA 94025) 24
Lead isotopic composition of galena from Malaysia, an S-type granite terrane by B. R. Doe (U.S. Geological Survey, 104 National Center, Reston, VA 22092) 28
Mass spectrometric measurements of234^!/23^ and 230Th/238U and dating late Quaternary carbonates by R. L. Edwards (University of Minnesota, Department of Geology and Geophysics, Minneapolis, MN 55455) 63
Nd isotopes as tracers of the origin and evolution of the continental lithosphere by G. L. Farmer (CIRES, University of Colorado, Department of Geological Sciences, Boulder, CO 80302) 65
Paragenetic constraints on the Pb isotopic and trace element character ofAu-Ag mineralized rocks of the North Amethyst vein, Mineral County, Colorado by N. K. Foley (U.S. Geological Survey, 959 National Center, Reston, VA 22092) and R. A. Ayuso 74
Direct dating of ductile deformation fabrics: An integrated microstructural/ geochronologic approach by S. R. Getty (Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138) 83 Recent developments in dating ancient crustal fluid flow by A. N. Halliday (University of Michigan, Department of Geological Sciences, 1006 C. C. Little Building, Ann Arbor, MI 48109-1063), M. Ohr, K. Mezger, J. T. Chesley, S. Nakai, and C. P. DeWolf 92
Re and Os isotopic study of Ni-Mo-PGE-rich sulfide layers and black shales, Yukon territory, Canada and south China by M. F. Horan (U.S. Geological Survey, 981 National Center, Reston, VA 22092), J. W. Morgan, and R. I. Grauch 100
Modern applications of precise V-Pb geochronology by T. E. Krogh (Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada) 102
Pb isotopic composition of Paleozoic sediments derived from the Appalachian orogen by E. J. Krogstadt (University of Maryland, Department of Geology, College Park, MD 20742) 106
Alleghanian cleavage and acadian diagenesis in the Martinsburg Formation, eastern Pennsylvania: 40Ar/39Ar whole-rock data and geological constraints by M. J. Kunk (U.S. Geological Survey, 981 National Center, Reston, VA 22092), R. Wintsch, and J. Epstein 107
Radiogenic isotopes in seawater and sedimentary systems by J. D. Macdougall (University of California, Scripps Institution of Oceanography, A-008, Geological Research Division, La Jolla, CA 92093) 108
4OAr/39Ar studies offluid inclusions in vein quartz from Battle Mountain, Nevada by E. H. McKee (U.S. Geological Survey, 345 Middlefield Road, Mail Stop 941, Menlo Park, CA 94025) 116
Isotopic provinciality in the shallow mantle, on-craton and off-craton volcanism, and implications for lithospheric growth in the western USA by M. A. Menzies (Department of Geology, University of London, Royal Holloway & Bedford New College, Egham, Surrey TW20 OEX, United Kingdom) 121
Geochronology in granulites by K. Mezger (Max-Planck Institute fur Chemie, Abteilung Geochemie, Postfach 3060, D-6500 Mainz, West Germany) 129
The nature of the crust in western Alaska as inferred from the chemical and isotopic composition of Late Cretaceous to early Tertiary magmatic rocks in western Alaska by E. Moll-Stalcup (U.S. Geological Survey, 959 National Center, Reston, VA 22092) and T. Frost 149
Rhenium and osmium isotope systematics in meteorites by J. W. Morgan (U.S. Geological Survey, 981 National Center, Reston, VA 22092) 153 Nd and Pb isotopic evolution of basalts of the 1.1 Ga Midcontinent rift: Evidence for a region-wide model for plume-lithosphere-asthenosphere interaction by S. W. Nicholson (U.S. Geological Survey, 954 National Center, Reston, VA 22092) and S. B. Shirey 155
The Rb-Sr, Sm-Nd and Re-Os isotopic systems and the cosmochronology and geochronology of igneous rocks by S. B. Shirey (Carnegie Institution of Washington, Department of Terrestrial Magnetism, Washington, DC 20015) 162
The hydrothermal stability of zircon: Preliminary experimental and isotopic studies by A. K. Sinha (Virginia Polytechnic Institute and State University, Department of Geological Sciences, Blacksburg, VA 24061), D. M. Wayne, and D. A. Hewitt 193 and Crustal evolution ofGrenville terranes in the central and southern Appalachians: The Pb isotope perspective for Grenville tectonics by J. E. Parks, P. J. Jenks, and A. K. Sinha 196
Argon thermochronology of mineral deposits by L. W. Snee (U.S. Geological Survey, Box 25046, Mail Stop 963, Denver Federal Center, Denver, CO 80225) 197
Rhenium-osmium data for sulfides and oxides from climax-type granite-molybdenum systems: ML Emmons, Colorado by H. J. Stein (U.S. Geological Survey, 981 National Center, Reston, VA 22092), J. W. Morgan, R. J. Walker, and M. F. Koran 211
^Ar/^Ar thermochronology: Applications to stratigraphy, tectonics, and mineralization by J. Sutter (U.S. Geological Survey, Reston, VA 22092) 212
Isotopic reference materials - absolute or otherwise by R. D. Vocke, Jr. (National Institute of Standards and Technology, Center for Analytical Chemistry, 823 Physics Building, Gaithersburg, MD 20899) 225
Applications of the rhenium-osmium isotope system to geologic problems by R. J. Walker (Department of Geology, University of Maryland, College Park, MD 20742) 327
The Pb-Sr-Nd isotopic troika Theory and applications by R. E. Zartman (U.S. Geological Survey, Box 25046, Mail Stop 963, Denver Federal Center, Denver, CO 80225) 329
in INTRODUCTION About the Workshop: The intended audience of this workshop is the general geological community at the Survey and interested faculty and graduate students from nearby universities. The main objective of the discussions is to provide a broad introduction for a non- isotope geologist audience into modern methods of geochronology and isotope tracer studies and to gi've examples of their application to solve complex problems in stratigraphy, petrology, ore petrogenesis, and tectonics. The participants will be, for the most part, from the Geologic Division at the Survey, and consequently they have varying levels of understanding about isotope systems and their uses. The sessions will start with general talks on the general systematics of the isotope techniques to be illustrated that day. Note that the oral presentations are scheduled for 45 minutes and that 15 minutes are reserved for discussion after each talk. During the first day, we will discuss modern applications of precise U-Pb geochronology and common Pb isotope studies. The contributors will illustrate how these techniques have been applied to solve stratigraphic problems in the northern Appalachians, date high grade metamorphism and stromatolites, tracing sand dunes, study the hydrothermal stability of zircon, and to establish the crustal evolution of the central and southern Appalachians. The second day will start with an introduction into the Rb- Sr, Nd-Sm, and Re-Os dating techniques. Practical illustrations of the use of these systems will also be given, including examples of dating ductile deformation fabrics in New England, the application of Re-Os systematics for dating ultramafic rocks and to study the petrogenesis of these and associated ore deposits, and the use of Nd isotopes as tracers of continental lithosphere evolution. This session will end with a presentation on the isotopic provinciality in the mantle, on-craton and off- craton volcanism and implications for lithospheric growth in the western USA. The third day will begin with an introduction to Ar thermochronology and applications to stratigraphy, tectonics, and mineralization. Recent results of Ar studies on fluid inclusions from Battle Mountain (Nevada) will be reported, as well as dating of multiple events in the Bayan Obo deposit (China) and examples of Ar dating of ore deposits from the western United States, England, and Portugal. The rest of the day will be devoted to an introduction to U-Th disequilibria and dating of young rocks, a discussion of radiogenic isotopes in seawater and sedimentary systems, and to recent developments in dating ancient crustal fluid flow. Due to the number of non-USGS speakers and the length of the workshop, USGS contributors from Reston have prepared posters instead of oral presentations. The posters will be shown in the Exhibit Hall Afternoon Session 1:00-1:45 PM JOHN ALEINIKOFF: Innovative uses of Pb isotopic measurements: Dating stromatolites and tracing sand dunes 1:45-2:00 PM Discussion 2:00-2:45 PM KRISHNA SINHA: The hydrothermal stability of zircon: Preliminary experimental and isotopic studies KRISHNA SINHA: Crustal evolution of Grenville terranes in the central and southern Appalachians: The Pb isotope perspective for Grenville tectonics 2:45-3:00 PM Discussion 3:00-3:15 PM Break 3:15-5:00 PM Posters: To be displayed through Wednesday ROBERT AYUSO, SANDRA BARR, FRED LONGSTAFFE, and ERNST HEGNER: Pb-Nd-O isotopic compositions of igneous rocks: Implications for petrogenesis and terrane correlation, Cape Breton Island, Nova Scotia, Canada BRUCE DOE: Lead isotopic composition of galena from Malaysia, an S-type granite terrane 3 NORA FOLEY and ROBERT AYUSO: Paragenetic constraints on the Pb isotopic and trace element character of Au-Ag mineralized rocks of the North Amethyst vein, Mineral County, Colorado MARY KORAN: Re and Os isotopic study of Ni-Mo-PGE-rich sulfide layers and black shales, Yukon territory, Canada and south China EIRIK KROGSTADT: Pb isotopic composition of Paleozoic sediments derived from the Appalachian orogen MICK KUNK: Alleghanian cleavage and acadian diagenesis in the Martinsburg Formation, eastern Pennsylvania: 40Ar/39Ar whole-rock data and geological constraints ELIZABETH MOLL-STALCUP: The nature of the crust in western Alaska as inferred from the chemical and isotopic composition of Late Cretaceous to early Tertiary magmatic rocks in western Alaska JOHN MORGAN: Rhenium and osmium isotope systematics in meteorites SUZANNE NICHOLSON and STEVE SHIREY: Nd and Pb isotopic evolution of basalts of the 1.1 Ga Midcontinent rift: Evidence for a region-wide model for plume-lithosphere-asthenosphere interaction HOLLY STEIN, JOHN MORGAN, RICHARD WALKER, and MARY KORAN: Rhenium-osmium data for sulfides and oxides from climax-type granite-molybdenum systems: Mt. Emmons, Colorado ROBERT VOCKE: Isotopic reference materials - absolute or otherwise Tuesday, September 15, 1992 Morning Session 8:30-9:30 AM STEVE SHIREY: The Rb-Sr, Sm-Nd and Re-Os isotopic systems and the cosmochronology and geochronology of igneous rocks 9:30-9:45 AM Discussion 9:45-10:30 AM STEVE GETTY: Direct dating of ductile deformation fabrics: An integrated microstructural/geochronologic approach 10:30-10:45 AM Discussion 10:45-11:00 AM Break 11:00-11:45 AM RICH WALKER: Applications of the rhenium- osmium isotope system to geologic problems 11:45-12:00 AM Discussion 12:00-1:00 PM Lunch Afternoon Session 1:00-1:45 PM LANG FARMER: Nd isotopes as tracers of the origin and evolution of the continental lithosphere 1:45-2:00 PM Discussion 2:00-2:45 PM ROBERT ZARTMAN: The Pb-Sr-Nd isotopic troika Theory and applications 2:45-3:00 PM Discussion 3:00-3:15 PM Break 3:15-4:00 PM MARTIN MENZIES: Isotopic provinciality in the shallow mantle, on-craton and off-craton volcanism, and implications for lithospheric growth in the western USA 4:00-4:15 PM Discussion Wednesday, September 16, 1992 Morning Session 8:00-8:45 AM JOHN SUTTER: 40Ar/39Ar thermochronology: Applications to stratigraphy, tectonics, and mineralization 8:45-9:00 AM Discussion 9:00-9:45 AM TED MCKEE: 40Ar/39Ar studies of fluid inclusions in vein quartz from Battle Mountain, Nevada JAMES CONRAD: The use of K-Ar and 40Ar/39Ar techniques to date multiple thermal events: An example from the Bayan Obo Fe-Nb-REE ore deposit, China 9:45-10:00 AM Discussion 10:00-10:15 AM Break 10:15-11:00 AM LARRY SNEE: Argon thermochronology of mineral deposits 1:00-11:15 AM Discussion 11:15-12:00 AM LARRY EDWARDS: Mass spectrometric measurements of 234U^238U and 230Th/238u and dating late Quaternary carbonates 12:00-12:15 PM Discussion 12:15-1:00 PM Lunch Afternoon Session 1:00-1:45 PM J. MACDOUGALL: Radiogenic isotopes in seawater and sedimentary systems 1:45-2:00 PM Discussion 2:00-2:45 PM ALEX HALLIDAY: Recent developments in dating ancient crustal fluid flow 2:45-3:00 PM Discussion Innovative Uses of Pb Isotopic Measurements: Dating Stromatolites and Tracing Sand Dunes John N. Aleinikoff U.S.Geological Survey Denver, CO 80225 U-Pb geochronology historically has involved measuring radiogenic Pb isotopic compositions and U and Pb concentrations in minerals such as zircon, monazite, and sphene to calculate crystallization ages of igneous rocks. Over the past several decades, the technique has been gready modified and improved (mostly by T. Krogh and colleagues) to allow dating of very tiny samples (of single grains or even pans of single grains). The application of the method has been diversified to now include dating of a wide variety of minerals for the determination of the timing of metamorphism, ore deposition, provenances of sedimentary rocks, and faulting. Another important facet of U-Pb geochronology is the measurement of the initial Pb isotopic compositions of igneous rocks, usually determined by analyzing U-deficient minerals (those in which there is very little in situ growth of radiogenic Pb) such as K-feldspar and plagioclase. Initial Pb isotopic compositions are used to calculate geochronologic data, and are also useful in discerning petrologic and tectonic origins of specific rocks and in modeling the geochemical evolution of the earth (Aleinikoff and others, 1987; Plumbotectonics models such as Zartman and Haines, 1988). Two relatively new and rarely utilized applications of Pb isotopic analyses are the direct dating of stromatolitic limestones and dolomites and determination of provenances of Holocene sand dunes. The first study describing the dating of stromatolites by the Pb-Pb method (Moorbath and others, 1987) produced an isochron of 2839 ± 33 Ma for the Mushandike stromatolitic limestone in Zimbabwe. The method is predicated on the assumption that carbonate incorporates small amounts of uranium during deposition and over long periods of time, the uranium decays to its stable daughter product, lead. Despite the potential broad appeal of the technique for dating sedimentary sequences, a surprisingly few number of papers have been published using this method (see bibliography for references). Some of the problems of this technique include the somewhat difficult chemical procedure, possible contamination of the carbonate by detrital material, partial silicification of the dolomite, measurement of very small quantities of U, Th, and Pb (in the 10-500 ppb range), scatter in the data, small radiogenic growth of Pb because of the low concentrations of U and Th, and, perhaps most important, questions related to the interpretation of the data (i.e. does the calculated age represent a depositional (or diagenetic) age or were the isotopic systematics reset by metamorphism?). In the Hartville uplift of eastern Wyoming, we have collected preliminary data from a stromatolitic dolomite, currently at garnet metamorphic grade, that indicates an age of 1.9 ± 0.1 Ga (Fig. 1). This age is in conflict with interpretations of the regional geology (Fig. 2), based on cross-cutting relationships and lithologic correlations, that suggest an age of >2.6 Ga for the sequence ( cf. Hofmann and Snyder, 1985). At this time, we are unable to establish if the regional interpretations are incorrect or if the date on the stromatolite is a metamorphic age. Two other samples of stromatolitic dolomite (Kona Dolomite, MI and Nash Formation, Medicine Bow iVItns, WY), containing beautifully preserved algal structures, do not yield colinear data (Fig. 3). Pb concentrations and isotopic compositions suggest addition of large quantities of Pb, obliterating the subtle radiogenic signature. Thus, Pb-Pb dating of stromatolitic limestone and dolomite appears to be a method of some promise for determining the age of sedimentary sequences; however, with the wide variety of possible complications, the technique presently has limited appeal. The identification of provenances of Holocene eolian sands of the central Great Plains is critical for developing models of regional paleoclimate changes and for understanding the origin and evolution of midlatitude sand seas. Prevailing winds have deposited vast quantities of sand-sized material in dunes (of several geomorphologic types) and sand sheets in northeastern Colorado and the Sand Hills of western Nebraska (Muhs, 1985; Swinehart, J.B., 1990). As part of a multidisciplinary effort by the U.S. Geological Survey to understand the relationships between climatic variability, development of surficial deposits, and environmental changes in arid and semi- arid regions (cf. Muhs and Maat, in press), we have attempted to determine the bedrock sources of eolian sands using Pb isotopic ratios in detrital K-feldspar as a fingerprint. Interpretations of the isotopic data will be combined with existing sedimentologic, geochemical, and meteorological data to derive a model for prevailing wind directions in the recent past (up to about 5000 years BP). The objective of this study is to identify the source of K-feldspar (and, by inference, quartz) in Holocene eolian sands of the northern Great Plains. North of the Cheyenne belt in northern Colorado and southern Wyoming, most of the crystalline rocks are Late Archean (-2.7 Ga), whereas to the south throughout Colorado most of the igneous rocks are 1.7 and 1.4 Ga; the basement rocks are intruded by small Cretaceous and Tertiary stocks. Sanidine, a significant component of the K-feldspar in the Holocene eolian sands, probably was derived from a number of Tertiary volcanic centers in the western U.S. The different provenances of the K-feldspars are easily distinguished because Archean, Proterozoic and Tertiary rocks have distinctly different Pb isotopic compositions. In northeastern Colorado, Pb isotopic compositions from bulk fractions plot in a fairly tight array, slightly more radiogenic than Pb in 1.4-Ga plutonic rocks from the Colorado province (Fig. 4a). Analyses of individual grains (distinguished by color and clarity) suggest that the bulk fractions are composed of feldspars from 1.7- and 1.4-Ga igneous rocks, plus Tertiary sanidine, with no obvious evidence for an Archean (Wyoming) component (Fig. 4b). We conclude that materials in Holocene eolian sand dunes of northeastern Colorado were derived from Early and Middle Proterozoic crystalline rocks of the Colorado province and from Tertiary volcaniclastic rocks, were deposited along major fluvial systems, and were redeposited by prevailing northwesterly (and sometimes southeasterly) winds (Fig. 5). In contrast, Pb isotopic compositions of bulk K-feldspar fractions from the Sand Hills of northwestern Nebraska plot as a broad field with ratios that are more radiogenic than ratios from Colorado sands (Fig. 6a). Analyses of individual grains indicate that these eolian sediments had Archean, Proterozoic and Tertiary sources (Fig. 6b). Thus, as previously suggested by sedimentologic studies, the materials that comprise the Sand Hills were derived from both the Wyoming and Colorado provinces. Selected Bibliography Aleinikoff, J. N., Dusel-Bacon, C, Foster, H. L., and Nokleberg, W. J., 1987, Lead isotopic fingerprinting of tectonostratigraphic terranes, east-central Alaska: Canadian Jour, of Earth Science, v. 24, p. 2089-2098. Hofmann, H.J., and Snyder, G.L., 1985, Archean stromatolites fromt he hartville Uplift, eastern Wyoming: Geological Society of America Bulletin, v. 96, p.842-849. Jahn, Bor-ming, 1988, Pb-Pb dating of young marbles from Taiwan: Nature, v. 332, p. 429-432. Jahn, Bor-ming, Bertrand-Sarfati, J., Morin, N., and Mace, J., 1990, Direct dating of stromatolitic carbonates fromt eh Schmidtsdrif Formation (Transvaal dolomite), South Africa, with implications on the age of the Venterdorp Supergroup: Geology, v. 18, p. 1211-1214. Moorbath, S., Taylor, P.N., Orpen, J.L., Tneloar, P., and Wilson, J.F., 1987, First direct radiometric dating of Archaean stromatolitic limestone: Nature, V. 326, p. 865-867. Muhs, D.R., 1985, Age and paleoclimatic significance of Holocene sand dunes in northeastern Colorado: Annals of the Association of American Geographers, v. 75, p. 566-582. Muhs, D.R., and Maat, P.B., The potential response of eolian sands to greenhouse warming and precipitation reduction on the Great Plains of the UnitedStates: Journal of Arid Environments (in press). Smith, P.E., and Farquhar, R.M., 1989, Direct dating of Phanerozoic sediments by the 238U- 2°6pb method: Nature, v. 341, p. 518-521. Swinehart, J.B., 1990, Wind-blown deposits: in Bleed, A., and Flowerday, C. (eds.), An atlas of the Sand Hills, Resource Atlas No. 5a, University of Nebraska-Lincoln, p. 29-42. Taylor, P.N., and Kalsbeek, F., 1990J)ating the metamorphism of Precambrian marbles: examples from the Proterozoic mobile belts in Greenland: Chemical Geology (Isotope Geoscience Section), v. 86, p. 21-28. Zartman, R.E., and Haines, S.M., 1988, The plumbotectonic model for Pb isotopic systematics among major terrestrial reservoirs-A case for bi-directional transport: Geochimica Cosmochimica Acta, v. 52, p. 1327-1339. 25 Stromatolitic dolomite, HartviBe dump, Hartvifle uplift, Wyoming 23 Figure 1. .0 21 0. 0. § 19 age- 1919 ±98 Ma 17 (MSWD - 83) 15 20 40 60 80 STROMATOLITES UNIT UTHOLOGY Locality Tnu GftAMTt Of > f -t -t KAWMM UTTES (2 M G«. ftb-Sr wfcoM toekl > * -t » CoUumnar/arta UNIT D CmiMria ^. / Slrali/rr> dated stromatolite / =»/ (5) W*»e« Hrfte 0-tOO m / -s/1 1 Oi&67JI)H«n*ill« ; Sp*rk« C*nven 5wf^ UNIT C 0 2KX) m 1ARCHEAN (*v«r*e« 1200 ml [GROUPWHALEN Figure 2 (From Hofmann and Snyder, 1985) UNIT B 170 1SOO m ( vw«g« 7SO ml * " * 4 / ""f^ / / . Lae^ / 0(|)A«»«M*« Canyon UNIT A Si' / * Hadrop/irc*M « / / , 900-ISOO m / / ^$" ' 4 - ^ . / . m M AMI MI iDOMd . TF^. I I Figure 3. \ ' I ' I ' I 17.4 _ Stromatolites silicate residues i . i 17.0 carbonate 16.6 - i i ... -i n Q. v ^\1.70±.12 Ma j 3 M . ' A i 16.2 ~ .-' ' ~! Q. ^. ' on Kona Dokxnrte, J 15.8 Marquette. Ml - i-»o«h Formation, 15.4 ~ CMedicine Bow Mtns., WY 15.0 1,1,1,1,1 1 4 18 22 26 30 3^ \\ 15.6 Northeastern Colorado Bulk K-feldspar fractions Ogallala Fm., Colo. 15.5 .a Figure 4a Q_ 15.4 N n CL 15.3 15.2 15.4 15.8 16.2 16.6 17.0 17.4 16.0 Northeastern Colorado Bulk fractions and single grains 15.8 O Figure 4b O .a a. 400 \ 15.6 15.4 O sanidine A microcline (pink) -1.4-Gaplutons A microcline (white) O bulk K-feldspar 1.7-Gaplutons 15.2 15 16 17 18 19 206 Pb/^Pb no- 0 100 TOO 300 «OOKIIOMET£RS I____I I I____I Figure 5. (compiled by D. Muhs, 1990) 15.8 I Sand Hills, Western Nebraska Bulk K-feldspars Figure 6a 15.6 samples a..Q S JOa. 15.4 1.4-Ga plutons 1.7-Ga plutons 15.2 15 16 17 18 19 206 Pb/ 2M Pb single K-feldspars, 16.0 NE-10. Sand Hills, Nebraska north-central Nevada, 15.8 (RyeetaJ., 1974) Middle-Late Archean rocks, Granite Mountains. WY (Fischer and Stacey, 1986) Figure tb JO 0. San Juan Voteanics, CO 15.4 (Lipmanetal., 1978) 39-mile Vokanics, CO 15.2 15.0 14 15 16 17 18 19 206 Pb/ 2M Pb I Mr Workshop on the Application of Isotope Systems to Geological Problems Pb-Nd-O ISOTOPIC COMPOSITIONS OP IGNEOUS ROCKS: IMPLICATIONS FOR PETROGENESIS AND TEHRANE CORRELATION, CAPE BRETON ISLAND, NOVA SCOTIA, CANADA AYUSO, R., U.S. Geological Survey, Reston, VA 22092, USA; BARR, S. f Acadia University, Wolfville, Nova Scotia, Canada BOP 1X0; LONGSTAFFE, F., University of Western Ontario, London, Ontario, Canada N6A 5B7; and HEGNER, E., Universitat Tubingen, 7400 Tubingen, Germany The geochemical nature of the lower continental crust is difficult to determine directly because for the most part these rocks are not exposed. One important but indirect source of information regarding the type and age of unexposed crustal rocks, however, can be obtained by establishing the isotopic compositions of igneous source regions (e.g., Zartman, 1974; Farmer and DePaolo, 1983; Ayuso, 1986; Aleinikoff and others, 1987). In an effort to test whether Pb, Nd (Barr and Hegner, 1992), and O isotopic data of plutonic rocks in Cape Breton Island can be used to correlate with plutons within terranes in mainland North America (Ayuso and Bevier, 1991), the present study uses isotopic data on 20 well-characterized (petrography, major- and trace element geochemistry) felsic units ranging from Precambrian to Paleozoic, and representing the pre-Carboniferous tectonic blocks in Cape Breton Island proposed by Barr and Raeside (1989). The Pb and Nd isotopic data in general show variations in agreement with a subdivision of the Island into magmatic source regions which may be related to unique terranes; the O isotopic data do not allow for the definition of distinct terranes. In the New England and Canadian Appalachians, use of geochemical data for characterizing crustal segments is complicated by tectonic events which resulted in superposition and juxtaposition of crustal blocks. This kind of structural complexity has led to the recognition that magmatic rocks exposed at the surface may now be part of thrust slices or dismembered blocks which have separated the magmatic rocks from their source rocks (Ayuso and Bevier, 1991). Even in this case, however, geochemical information can be of help to identify magmas that had a common source region. In fact, the isotopic data can assist in characterizing plutonic rocks within dismembered slices which ultimately belonged to unique crustal blocks. Pb isotope compositions in Cape Breton Island are consistent with a source in the Northwest Highlands which resulted in a relatively unradiogenic group of Grenville-age syenites and anorthosites (Blair River Complex) (feldspar measured values of 206pb/204pb = 17.408-17.850; 207pb/204pb = 15.504-15.522; 208pb/204pb = 36.689-37.329); this source is similar to that inferred for plutonic rocks in northern New England. Plutons from the Blair River Complex plot below the Pb evolution curve, consistent with derivation from source rocks with generally low U/Pb (and low n) and Th/Pb ratios (Fig. 1). Syenite from the Blair River Complex has an initial £Nd value of +0.4 (Fig. 2) and a depleted mantle model age (TDM) of 1.66 Ga, reflecting a major component of older crust during its evolution; initial £Nd values in the Complex at 400 Ma range from -6 to -1.5. Highly variable 8l8o values are found in granitic rocks from Cape Breton Island, from about +2.3 to +10.8 permil; if all of these values are magmatic, they would be consistent with an origin from widely different source rocks (Fig. 3). The narrowest range in 818o values is in the Blair River Complex (~ +8 permil). A few of the plutons in the terranes to the south of the Northwest Highlands Aspy, Bras D'Or, and Mira, have exceptionally low 818o values (as low as 2 permil) , implying that these are not magmatic, or alternatively, if the values are magmatic, that the source rocks must have undergone hydrothermal alteration prior to melting. The Pb isotopic values of plutons from terranes to the south of the Northwest Highlands are more radiogenic (206pb/204pb = 18.192-18.644; 207pb/204pb = 15.584-15.712; 208pb/204pb = 37.815- 38.495). In the Aspy and Bras D f Or terranes the plutons had source regions containing more evolved components (higher U/Pb) than in the Northwest Highlands, and virtually all of the results plot higher than the Pb evolution curve. Granite and rhyolite (Devonian?) associated with Grenville-age rocks in the Northwest Highlands appear to have been derived from the same type of crustal sources as Devonian plutons in the Aspy terrane which contain initial values of SNd from -1.2 to +2.8 (8Nd at 400 Ma from -1.8 to +2.4). In the Bras D'Or terrane plutonic rocks (mostly 565-555 Ma) have values of 6Nd from -1.8 to +1.4 (6Nd at 400 Ma from 0 to -3.8). The Nd isotopic data do not provide clear evidence for distinction between the Aspy and Bras D'Or terranes; the range in initial 6Nd values (+2.8 to -1.8) and the depleted mantle model ages (0.7 to l.l. Ga) are similar. Granitic rocks from the Bras D'Or terrane have a wide range in 518o values (~+4 to +11 permil), overlapping the range in the Aspy (~+7.5 to +9). In general, isotopic data for plutons from the Aspy and Bras D'Or terranes reflect a source region similar to that for plutons in the Central and Southern groups (Gander and Avalonian zones) in mainland North America (Ayuso and Bevier, 1991). Pb isotopic compositions of Devonian plutons from the Mira terrane (206pb/204pb = 18.243-18.460; 207pb/204pb = 15.587- 15.640; 208pb/204pb = 37.922-38.174) overlap that of plutons in the Aspy and Bras D'Or terranes. However, older granitic rocks (Precambrian?) in the Mira terrane are distinctly more radiogenic than in all the other units (206pb/204pb = 18.832-18.874; 207pb/204pb = 15.590-15.608; 208pb/204pb = 38.155-38.200). In the Mira terrane, the plutonic rocks (ca. 620 Ma and Devonian) range in initial 8Nd values from +0.8 to +5 (ewd at 400 Ma from -1.1 to +3.7). In the Mira terrane, the older plutons (ca. 620 Ma) previously distinguished by their relatively high 206pb/204pb values, also contain unusually low 518o values (<6 permil?) relative to the younger group of granites (ca. 380 Ma) (>6 permil). The isotopic data in the Mira terrane are consistent with a source region for the granitic rocks similar to that in the Avalonian of Newfoundland and mainland North America (Ayuso and Bevier, 1991; Whalen and others, 1989; Fryer and others, 1991). Igneous rocks from Cape Breton Island, except for those in the Blair River Complex, have relatively young Nd model ages (<1.1 Ga), in agreement with the suggestion that the magmas do not reflect merely the type of older component found in the Blair River Complex. Pb and Nd isotopic data are consistent with a source region characterized by generally unradiogenic Pb and with 6Nd values < 0 in the Northwest Highlands (Blair River Complex); the source region of the plutons in the terranes to the south contained increasingly more radiogenic Pb and higher values of 6Nd« Pb and Nd isotope data are thus in agreement with the idea that the Aspy and Bras D'Or terranes cannot be uniquely defined, and that they may represent crustal reworking of mixtures ultimately derived from unradiogenic Grenville-type sources and more radiogenic Proterozoic Avalonian basement rocks. The fact that both the Aspy and Bras D'Or terranes probably overlie the same deep crustal block as suggested by seismic reflection data (Marillier and others, 1989; Loncarevic and others, 1990) permit the suggestion that the plutons may have had a common source region. The results imply that at least two blocks or terranes were present in Cape Breton Island by the beginning of the Paleozoic: the Grenvillian Blair River Complex, and the Avalonian Mira terrane. Moreover, the Pb isotope data are not consistent with the idea that the Blair River Complex is merely a different level of exposure of the Mira terrane because the Blair River Complex does not contain a 620 Ma granite or metamorphic event, and because the Pb isotopic compositions of the 620 Ma granites do not lie along the estimated Pb evolution from 1040 Ma to 620 Ma. The isotopic contributions could have been made by including both blocks (or sedimentary debris obtained thereof) in the source region of the Bras D'Or magmas. In this case, the results imply that by ~565 Ma the Blair River Complex and the Mira terranes had already been amalgamated or that the two blocks were geographically close enough to have contributed sedimentary material that ultimately melted to produce the granitic magmas. Younger Devonian granitic magmas produced at ~400-360 Ma in the Aspy terrane, and at ~380 Ma in the Mira terrane are also in agreement with a process involving melting of similar source materials as those in the 565 Ma granitic magmas or remelting of the ~565 Ma rocks themselves previously derived from a combination of the Grenvillian and Avalonian blocks. Pb, Nd, and 0 isotopic compositions of plutonic rocks can help in delineating regional characteristics of the magmas and this information can be of assistance in more detailed terrane correlations in conjunction with geological and geophysical observations. REFERENCES Aleinikoff, J.N, Dusel-Bacon, C., Foster, H.L., and Nokleberg, W., 1987, Pb isotopic fingerprinting of tectonostratigraphic terranes, east-central Alaska: Canadian J. Earth Sciences, v. 24, p. 2089-2098. Ayuso, R.A., 1986, Pb isotopic evidence for distinct sources of granite and for distinct basements in the northern Appalachians: Geology, v. 14, p. 322-325. Ayuso, R.A., and Bevier, M.L. 1991, Regional differences in Pb isotopic compositions of feldspars in plutonic rocks of the northern Appalachian Mountains, U.S.A. and Canada: A geochemical method of terrane correlation: Tectonics, v. 10, p. 191-212. Barr, S.M., and Raeside, 1989, Tectonostratigraphic terranes in Cape Breton Island, Nova Scotia: implications for the configuration of the northern Appalachian Orogen: Geology, V. 17, p. 822-825. Barr, S.M., and Hegner, E., 1992, Nd isotopic compositions of felsic igneous rocks in Cape Breton Island, Nova Scotia: Canadian J. Earth Sciences, v. 29, p. 650-657. Doe, B.R., Delevaux, M., and Albers, J.P., 1985, The plumbotectonics of the West Shasta mining district, Eastern Klamath Mountains, California, Economic Geology, v. 80, p. 2136-2148. Farmer. L., and DePaolo, D.J., 1983, Origin of Mesozoic and Tertiary granite in the western U.S. and implications for pre-Mesozoic crustal structure. I. Nd and Sr isotopic studies in the geocline of the northern Great Basin: J. Geophysical Research, v. 80. p. 3379-3401. Fryer, B.J., Jenner, G.A., and Longstaffe, F.J., 1991, Isotopic compositions of granitoid rocks in the Appalachians: clues to crustal structure?: European Union of GeoSciences, Abstracts, v. 3, p. 35. Loncarevic, D.B., Barr, S.M., Raeside, R.P., and others, 1989, Northeastern extension and crustal expression of terranes from Cape Breton Island, Nova Scotia, based on geophysical data: Canadian J. Earth Sciences, v. 26, p. 2255-2267. Marillier, F., Keen, C.E., Stockmal, G.S., and others, 1989, Crustal structure and surface zonation of the Canadian Appalachians: implications of deep seismic reflection data: Canadian J. Earth Sciences, v. 26, p. 305-321. Stacey, J.S., and Kramers, J.D., 1975, Approximation of terrestrial Pb isotope composition by a two-stage model: Earth and Planetary Sciences Letters, v. 26, p. 207-222. Whalen, J.B., Hegner, E., and Jenner, G.A., 1989, Nature of Canadian basement terranes as inferred from a Nd isotopic transect: Geological Society of America, Abstracts: v. 22, p. A201. Zartman, R.E., 1974, Lead isotopic provinces in the Cordillera of the western United States and their geologic significance: Economic Geology, v. 69, p. 160-175. Zartman, R.E., and Wasserburg, G.J., 1969, The isotopic composition of Pb in potassium feldspars from igneous rocks: Geochimica et Cosmochimica Acta, v. 33, p. 901-942. FIGURES Figure 1. 206pb/204pb-207pb/204pb evolution plots showing isotopic compositions of feldspars from granitic rocks in Cape a (3 Breton Island. Pb isotope data for granites from the Aspy, Bras D'O, and Mira terranes in New Brunswick (NB), equivalent to terranes in Nova Scotia, are from Ayuso and Bevier (1991) and are shown for comparison. Grenville data are from Zartman and Wasserburg (1969), and the composition of the Devonian mantle is from Doe and others (1985). Symbols are as follows: BRC, Blair River Complex (Northwest Highlands)-; ASP, Aspy terrane; EDO, Bras D'Or terrane; MIR, Mira terrane; S&K, Stacey and Kramers (1975) Pb evolution curve (tick marks at intervals of 250 m.y. before the present). Figure 2. Initial 8Nd values plotted against age for samples from Cape Breton Island; Nd data from Barr and Hegner (1992) . Figure 3. 206pb/204pb-518o plot for granitic rocks from Cape Breton Island. Symbols as in figure 1. Cape Breton island, Nova Scotia Granitic Rocks at 400 Ma 15.9 15 17.0 17.5 18.0 18.5 19.0 19.5 19.5 pb 206/pb 204 Figure 1 10 Patchett and Ruiz (19891 M / i f / / '. / / >/ *2 ! |7 j / X^y^ Aspy 7 tP: ' x/ / ****/ ""'-Tr-*-^' A7 CHUR 0 / / / iO^Bras d'Or / -2 / / A Bloir River Complex w «spy -4 / / envelope for , Q Bras d'Or / Grenville- ' Mira / age rocks v / -6 __L- _____ I I x/ I l I I L_ 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Age (Ga) Figure 2 Cape Breton Island, Nova Scotia Granitic Rocks at 400 Ma 12 Mira, 10 - 380 Ma Aspy 8 - Northwest Bras d'Or co 6 - Highlands 4 - 2 - 620 Ma 17.5 18.0 18.5 19.0 19.5 Pb 206/Pb204 Figure 3 The use of K-Ar and 40Ar/39Ar techniques to date multiple thermal events: An example from the Bayan Obo Fe-Nb-REE ore deposit, China James E. Conrad U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 Bayan Obo in Inner Mongolia, northern China, is the world's largest known rare- earth element ore deposit and a major iron and niobium producer as well. The Bayan Obo ore bodies are in Middle Proterozoic dolomite that is pan of a 2,000 m thick sequence of quartzite, carbonate rock, and shale.' These sedimentary rocks are thought to represent a platform sequence deposited in east-trending grabens along the north edge of the Archean crystalline Sino-Korean craton. They are variably metamorphosed, cut by numerous veins and (likes, and complexly deformed by a system of south vergent thrust faults. The entire sequence of faulted metasedimentary rocks and Archean basement is intruded by granite of Permian age. K-Ar and 40Ar/39Ar studies have established four significant thermal events: amphibole veining at about 1,260 and 820 Ma, 460-400 Ma regional metamorphism, and a 300-225 Ma intrusive event. In general, the 460-400 and 300-255 Ma thermal events are easily dated by K-Ar and 40Ar/39Ar techniques because these rocks have relatively simple cooling histories. The 1,260 and 820 Ma thermal events, however, are largely overprinted by the younger thermal events and minerals of this age often give spurious partially or fully reset ages. ^Ar/^Ar incremental heating techniques are usually necessary to evaluate the degree of disturbance and help identify samples giving reliable cooling ages. For example, the 820 Ma event appears to be represented by samples giving apparently disturbed ages in the range 560-800 Ma. These include discordant K-Ar ages, variable ages by ^Ar/^Ar single-grain total-fusion techniques, and 40Ar/39Ar incremental heating analyses that give complexly disturbed spectra. A single grain from a sample that exhibited all these characteristics yielded a plateau age of 820 Ma using laser-heated age- spectrum techniques. This indicates that samples showing considerable thermal disturbance may contain occasional grains that preserve an original cooling age. This grain-to-grain variation in apparent age within a single sample is poorly understood, however. The 1,260 Ma thermal event is suggested by a 40Ar/39Ar incremental heating analysis that shows significant argon loss. The age spectrum shows a steady increase in apparent age from a minimum of about 640 Ma to an apparent plateau at 1,180 Ma. This apparent plateau includes the last 4 steps and comprise about 20 percent of the toiai 39Ai release. This pattern represents a disturbed spectrum indicating a loss of radiogenic argon during a subsequent heating event, so the apparent plateau age of 1,180 Ma must be considered a minimum age. To assess the degree of resetting, this spectrum was compared to model diffusion curves that suggest that the plateau age has been lowered by about 6 percent by later heating of the sample, suggesting original crystallization at about 1,260 Ma. References on the age and origin of the Bayan Obo Fe-Nb-REE ore deposit Chao, E.C.T., Minkin, J.A., Back, J.M., Erickson, R.I., Drew, L.J., Okita, P.M., McKee, E.H., Conrad, I.E., Turrin, B., Tatsumoto, M., Wang Junwen, Edwards, C.A., Buden, R.V., Hou Zonglin, Ren Yingzhen, Meng Qingren, and Sun Weijun, 1989a, Epigenetic hydrothermal-metasomatic origin of the Bayan Obo Fe-Nb-REE ore deposit of Inner Mongolia, China [abs]: 28th International Geologic Congress Abstracts, Washington, D.C., v. 1, p 1-262. Chao, E.C.T., Minkin, J.A., Back, J.M., Okita, P.M., McKee, E.H., Tosdal, R.M., Tatsumoto, M., Wang Junwen, Edwards, C. A., Ren Yingchen, and Sun Weijun, 1989b, The H8 dolomite host rock of the Bayan Obo iron-niobium-rare-earth- element ore deposit of Inner Mongolia, China-Origin, episodic mineralization, and implications [abs]: U.S. Geological Survey, Fifth Annual V.E. McKelvey Forum on mineral and energy resources-Program and abstracts, p. 8-10. Chao, E.C.T., Tatsumoto, Mitsunobu, Erickson, R.L., Minkin, J.A., Back, J.M., Buden, R.V., Okita, P.M., Hou Zonglin, Meng Qingrun, Ren Yingchen, Sun Weijun, McKee, E.H., Turrin, B.D., Wang Junwen, Li Xibin, and Edwards, C.A., 1990, Origin and ages of mineralization of Bayan Obo, the world's largest rare earth ore deposit, Inner Mongolia, China: U.S. Geological Survey Open-File Report 90-538, lip. Conrad, J.E., and McKee, E.H., 1992, 40Ar/-*9Ar dating of vein amphibole from the Bayan Obo iron-rare-earth element-niobium deposit, inner Mongolia, China: Constraints on mineralization and deposition of the Bayan Obo Group: Economic Geology, v. 87, no. 1, p. 185-188. Conrad, J.E., McKee, E.H., and Turrin, B.D., 1991, Laser-microprobe single-grain 40Ar/39Ar age-spectrum analysis of riebeckite from Bayan Obo, China: Implications for dating disturbed minerals [abs.]: Geological Society of America Abstracts with Programs, v. 23, no. 2, p. 15. Drew, L.J., and Meng Qingrun, 1990, Geologic map of the Bayan Obo area, Inner Mongolia, China: U.S. Geological Survey Miscellaneous Investigations Series Map 1-2057. Drew, L.J., Meng Qingrun, and Sun Weijun, 1990, The Bayan Obo iron-rare-earth- niobium deposits, Inner Mongolia, China, in A.R. Woolley and M. Ross, eds., Alkaline igneous rocks and carbonatites: Lithos, v. 26, p 43-65. Philpotts, J.A., Tatsumoto, M., Hearn, P.P., and Fan, P-F., 1988, On the petrography, chemistry, age and origin of the Bayan Obo rare-earth iron deposit and resulting insight on the mid-Proterozoic earth [abs.]: EOS, Transactions, American Geophysical Union, v. 69, no. 16, p. 517. PROBABILITY C/) n DO< 0-n DO m Si "0m o m O DO z o m o CD O August 26, 1992 LEAD ISOTOPIC COMPOSITION OF GALENA FROM MALAYSIA, AN S-TYPE GRANITE TERRANE Bruce R. Doe, U.S. Geological Survey, 923 National Center, Reston, VA 22092 Abstract Seven new samples of galena trpn Malaysia have Pb isotope ratios of 18.609 to 19.057 for 206.PJ3/204J?t>, 15.704 to 15.765 for mPb/m?b, and 38.950 to 39.385 for 2L°Pb/""Pb. Both the tin- bearing East and West Belts of Hosking (1977) and the Au- and base- metal-bearing Central Belt are represented. The East and West Belts coincide with the East Coast (ECP) and West Coast (WCP) Provinces of batholiths of Bignell and Snelling (1977) . The range in isotope ratios is surprisingly small in that the WCP plutons are Late Triassic in age, are exclusively S-type, and have a concealed basement age of 1500-1700 Ma, whereas the ECP plutons are Permo- Triassic, are both I- and S-type, and have a concealed basement age of 1100-1400 Ma (Liew and McCulloch, 1985). Although all their values of 87 Sr/"Sr^ are at least somewhat high for mantle ratios O0.705), the WCP has some of the highest values known (up to 0.7512) . Probably the most distinguishing feature of the Pb isotopes is the high value of 207Pb/ 204 Pb, which has a distinct continental upper- crust nature. Because the Stacey-Kramers model Pb ages range from ~260 Ma (close to the age of the deposits) to -450 Ma , there is no indication of cratonized crust (values of U/Pb and Th/Pb reduced by Uigh-cnrade metamorphism in the Precambrian) , The high values of 207Pb/ Pb in the galenas require an extended Precambrian history for the Malay Peninsula, as concluded by Liew and McCulloch (1985) from neodymium isotopes and U-Th-Pb isotopic dating of zircons. Similar Pb-isotope ratios are known from tin-bearing Belitung Island of Indonesia, which is included in an extension of the Malaysian tin belt to the SE by Hosking (1970) . Appropriate ratios are not known from adjacent Sumatra; however, Pb isotope ratios similar to Malaysia are also known in Java. The other major tin province, Bolivia, also has many high values of 207 Pb/ Pb (Tilton et al., 1981) . A model is presented in which a lead-isotope source was established 3700-Ma ago with values normalized to the present day of 10 - 10.3 for 238U/209 Pb and 3.79 - 4.05 for 232 Th/238U. At some intermediate time, e.g. 1600-Ma. ago, the values of 238 U/204Pb were altered to higher values, e.g., up to approximately 12. Doe, B.R., 1990, Lead-isotope composition of galena from Malaysia: 7th International Conference on Geochronology, Cosmochronolo- gy, and Isotope Geology, Canberra, September 24-29, Geological Society of Australia, Abstracts, p. 28. a-T September 13 , 1990 LEAD ISOTOPIC COMPOSITION OF GALENA FROM MALAYSIA, AN S-TYPE GRANITE TERRANE Bruce R. Doe, U.S. Geological Survey, 923 National Center, Reston, VA 22092 Abstract Seven new samples of galena from Malaysia *have Pb isotope ratios of 18.609 to 19.057 for 206Pb/204Pb, 15.704 to 15.765 for 207Pb/204Pb, and 38.950 to 39.385 for. 208Pb/204Pb. Both "the tin- bearing East and West Belts of Hosking (1977) and the Au- and base- metal-bearing Central Belt are represented. The East and West Belts coincide with the East Coast (ECP) and West Coast (WCP) Provinces of batholiths of Bignell and Snelling (1977). The range in isotope ratios is surprisingly small in that the WCP plutons are Late Triassic in age, are exclusively S-type, and have a concealed basement age of 1500-1700 Ma, whereas the ECP plutons are Permo- Triassic, are both I- and S-type, and have a concealed basement age of 1100-1400 Ma (Liew and McCulloch, 1985). Although all their values of ^Sr/^Sr. are at least somewhat high for mantle ratios (>0.705), the WCP has some of the highest values known (up to 0.7512). Probably the most distinguishing feature of the Pb isotopes is the high value of 207Pb/204Pb, which has a distinct continental upper- crust nature. Because the Stacey-Kramers model Pb ages range from 260 Ma (close to the age of the deposits) to -450 Ma, there is no indication of cratonized crust (values of U/Pb and Th/Pb reduced by high-grade metamorphism in the Precambrian). The high values of 207Pb/204Pb in the galenas require an extended Precambrian history for the Malay Peninsula, as concluded by Liew and McCulloch (1985) from neodymium isotopes and U-Th-Pb isotopic dating of zircons. Similar Pb-isotope ratios are known from tin-bearing Belitung Island of Indonesia, which is included in an extension of the Malaysian tin belt to the SE by Hosking (1970) . Appropriate ratios are not known from adjacent Sumatra; however, Pb isotope ratios similar to Malaysia are also known in Java. The other major tin province, Bolivia, also has many high values of 207Pb/204Pb (Tilton et al., 1981). A model is presented in which a lead-isotope source was established 3700-Ma. ago with values normalized to the present day of 10 - 10.3 for 238U/204Pb and 3.79 - 4.05 for ^Th/23^. At some intermediate time, e.g. 1600-Ma. ago, the values of 238u/204pb were altered to higher values, e.g., up to approximately 12. INTRODUCTION General Tin is an element that has become of increasing geochemical interest over the last 15 years since the classification of granites into S-type (generated by melting of sedimentary sources) and I-type (by melting of igneous sources)(Chappell and White, 1974). Tin in the largest geochemical anomalies is associated with S-type or two-mica granites, although the mined deposits are usually in placers eroded from the granites rather than in lode deposits in the granites themselves. Tin is an unusual element in that to be commercial, it must be in the form of the mineral cassiterite. Tin-bearing fluids appear to have an igneous origin with deposition of cassiterite by a number of methods, in many cases through replacement of carbonate rocks (Heinrich, 1990). Southeast Asia accounts for at least 65 percent of the Western world's tin production. Malaysia has long been the largest individual producer of tin; yet no lead-isotope data is known for this area. This paper presents new data on seven samples of galena from Malaysia. A model is presented in which a lead-isotope source was established 3700-Ma. ago with values normalized to the present day of 238U/204Pb between 10.0 and 10.3 and ^Th/23^ between 3.79 and 4.05 (Fig. 5). At some intermediate time, e.g., 1600-Ma. ago, the values of 23SU/204Pb were altered to higher values, e.g., up to approximately 12. , Terrane classification Malaysia is included in the Southeast Asian Tin Belt that^ extends from Thailand to Sumatra, Indonesia (Fig. 1). Provincial terminology used for Malaysia is confusing but bears on interpretations in this paper. Thus a rather complete discussion follows. Hosking (1977) separates Indonesia into East, Central, and West Belts, which are mineral belts. The East and West Belts contain the tin mineralization and the Central Belt has gold, barite, and base-metal sulfides dominant. The West Belt is further subdivided into parts I (to the west) and II (to the East) . Mitchell (1976, 1977) classifies Malaysia into four stratigraphic- structural zones from west to east. Zone 4 is essentially Hosking's East Belt whereas zone 3 is largely in Hosking's Central Belt; Mitchell*s zone 2 mainly is in Hosking's West Belt (within part II) with zone 1 overlapping part I but extending westward from Malaysia. The mineral belt classification of Hosking (1977) mainly will be accepted in this report because galenas are analyzed from each of these mineral belts. In addition, his East and West Belts, which are mineral belts, coincide with the East Coast, central, and West Coast Provinces for granite batholiths of Bignell and Snelling (1977) as cited in Liew and McCulloch (1985). Mitchell's 31 classification is valuable, however, because of his extensive tectonic interpretations. For example zone 2 contains the "ophiolite-melange association" or medial "ophiolite line" of Hutchison (1977) that might represent a former convergent plate margin. The geologic section of Malaysia consists entirely of Phanerozoic rocks; no outcrops of Precambrian rocks are known from the entire region. It is a matter of some interest that Belitung Island of Indonesia is placed in the Eastern Belt by Hosking, but Mitchell (1977) puts it in Hosking's West Belt. One objective of the present study was to see if lead isotopes could solve this difference in classification. Unfortunately, a somewhat different classification also has been given by Mitchell (1977) who separated Malaysia into Eastern, Central and Western Tin-bearing Granite Belts. Although Hosking's and Mitchell's Eastern Belts are the same, Mitchell has no equivalent to Hosking's Central Belt, a gold and base-metal belt (Mitchell refers to it as tin-barren). Mitchell's Central Belt then is Hosking's West Belt (and Hosking sometimes also refers to his West Belt as a West Tin Belt). Mitchell f s Western Belt, which is further west than anything considered by Hosking, has no equivalent in the Hosking classification. This second classification of Mitchell will not be referred to further because of the confusion it introduces. Where necessary, Mitchell's terminology will be converted to the Hosking system. 32. Tectonic hypothesis Mitchell (1976) gives an interesting plate tectonic interpretation for Southeast Asia. He hypothesizes that his zones 3 and 4 (Hosking East and Central Belts) were emplaced above an eastward dipping subduction zone during the Carboniferous to Triassic Periods. Zone 2 of flysch-type sediments, radiolarian ^cherts, Devonian shales and ultrabasic bodies formed the outer arc. The tin-barren granites of zone 3 were emplaced to the ocean .side and the tin-bearing granites of zone 4 were emplaced in the continental crust side of the overriding plate. As the ocean closed at the end of the Triassic, zone 1, a continental shelf covered with platform carbonate rocks, was subducted producing the tin-bearing granites of zone 1 (Hosking's West Belt). Granite batholiths The following discussion is an abstract of discussions of the Eastern and Western Provinces from Liew and McCulloch (1985). They did not work on the Central Province: The batholiths in the East Coast Province intrude Carboniferous to Triassic sedimentary rocks which include volcanic rocks of the andesite stem with calcalkaline affinities. Intrusive rocks can range from gabbro to potassic granite with biotite ± hornblende 33 granodiorite of I-type dominant. Minor peraluminous intrusions of S-type are present. Zircon concordia intercept ages range from 227 Ma to 264 Ma for both I-type and S-type granites, ages in general agreement with K-Ar biotite and Rb-Sr ages. Samples containing inherited zircons give upper intercept ages of 800 to 1350 Ma. I- type granites have values of 87Sr/86Sri of 0.7054 to 0.7092 whereas S-type granites range from 0.708 to 0.714. Both I-type and S-type granites have values of U3Nd/144Nd epsilon initial values^ in the range of -0.7 to -6.2 (or ratios of 0.51150 to 0.51118) with the S- type granites values only near the more negative values, Model H3Nd/ 144Nd source ages are 900-1400 Ma, with the age range 1100-1400 Ma. interpreted to be the best value. The model source ages are interpreted to estimate the time at which the crust separated from a depleted mantle. The batholiths of the West Coast Province are S-type granodiorites to granites of Triassic age that contain biotite, muscovite, tourmaline and, rarely, a high-Mn almandine garnet. [The batholiths are intruded into Mitchell's (1977) zones 1 and 2 which are upper Permian to Middle Triassic limestones to the west and metamorphosed Devonian to Triassic turbidites and flysch towards the east.] These granites are enriched in K, Rb, Th, U, and Pb. Concordant zircon ages are 198-215 Ma. K-Ar ages range from 40 Ma to 210 Ma and are younger than Rb-Sr whole-rock ages of 200-220 Ma. Discordant zircons give upper intersect ages on concordia of 1500- 1700 Ma. Values of ^Sr/^Sr. range broadly from 0.716 to 0.751 whereas H3Nd/ luNd is more restricted with epsilon initial values of -6 to -10 (or ratios of 0.51128 to 0.51106). Model U3Nd/ luNd source ages are 1300-1700 Ma including two metasedimentary rocks, in general agreement with the zircon upper intercept ages, especially when considering modeling uncertainties. ANALYTICAL METHODS The lead-isotope compositions were measured by two different but comparable mass 'spectrometric methods. Sample G-l, G-2, p-4, and G-6 were analyzed by the thermal ionization (triple filament) method and samples G-7 and G-9 were analyzed by the surface emission ionization method (silica gel). Both were standard methods, normalized to absolute ratios using the NBS 981 lead- isotope standard, and yielded ratios within 0.1 percent of absolute. LEAD-ISOTOPE DATA Seven new samples of galena from Malaysia have Pb isotope ratios of 18.609 to 19.057 for 206Pb/204Pb, 15.704 to 15.765 for 207Pb/204Pb, and 38.950 to 39.385 for 208Pb/204Pb (Table 1, Fig. 2). Represented are both the East (two samples) and West Belts (three samples) of Hosking (1977) that are tin-bearing and the Central Belt (two samples) containing Au and base metal deposits. The data are shown on Fig. 3 with selected lead-isotope data from Indonesia. Although the samples were collected from as much as 250 km apart and from three diverse tectonic terranes, the spread in data is small. The samples from the West Belt, however, are seen to have slightly greater values of 208Pb/204Pb than the samples from the East and Central Belt. Samples from the East Belt are seen to have slightly greater values of 206Pb/204Pb than the Central Belt. Probably the most distinguishing feature of the Pb isotopes is the high values for 207Pb/204Pb. In this regard, it is interesting that lead-isotope data on ores from Bolivia (Tilton et al., 1981), the second largest tin producing province, overlap the data from the Malaysian/Belitung area (Fig. 4). The data from the tin deposits of Belitung Island (Jones et al.,1977) some 800 km to the southeast, also have isotope ratios similar to Malaysian deposits. The best isotopic match is with the Central Belt of Malaysia, the tin-barren zone. With such sparse data, such large distances, and such a small isotopic spread, the significance of the match can be questioned. The data on Southeast Asia deposits suggest some kind of provincial tie between Belitung and Malaysia, however, because a few galenas from adjacent Sumatra (Doe and Zartman, 1979) have lead-isotope compositions with more average values of 207Pb/204Pb. One of these samples is from the Sungei Tuboh prospect near Palembang, which is near the southeast Asian Tin Belt. Lead-isotope data are known from Java (Doe and Zartman, 1979) that are isotopically similar to data from the Southeast Asian Tin Belt, although the relations between the deposits in Java and the Tin Belt are not known. LEAD-ISOTOPE SYSTEMATICS Although the systematics of lead isotopes have been described many times, some modeling bears on the interpretations contained herein. In modeling neodymium isotopes, Liew and McCulloch (1985) form an Earth at 4500 Ma. (T^ with chrondritic initial neodymium-isotope ratios and values for Sm/Nd. They propose the mantle was ^depleted in samarium relative to neodymium, arbitrarily, at 2700 Ma (T2 ) . Their subsequent interpretations are not sensitive to this age. They then present an interpretation of neodymium isotopes and zircon U-Th-Pb isotope dating that the crust of the East Province was formed about 1100-1400 Ma. ago, and the crust of the West Province was formed about 1400-1700 Ma. ago (T3 ) which existed to the time of formation of the granite batholiths 200-250 Ma. ago. A somewhat parallel argument has long been proposed regarding common-lead isotopes. The most sophisticated of these is the multi-stage plumbotectonic model IV given by Zartman and Haines (1988); however, for the purposes of this paper, the two-stage model of Stacey and Kramers (1975) is a sufficient beginning point. They developed a model in which the Earth was formed at T, (4500 Ma.) with a lead-isotope composition similar to the troilite phase of iron meteorites. In the first stage of lead-isotope evolution, an average 238U/204Pb (normalized to the present day for radioactive decay) of 7.19 existed until 3700 Ma. ago (T2) . At this time, the continental crust (the orogene of Doe and Zartman, 1979) was estimated to have formed with an average 238U/2WPb of 9.74, which exists down to the present. During the past 15 years, there has been little change in these average global values. Improvements have been made by considering more complex Earth models (e.g., Doe and Zartman, 1979, separated the crust into upper and lower crust as well as the orogene; Zartman, 1984, separated the lithospheric mantle from the asthenosphere.). But for present purposes modification of' the models of Stacey and Kramers (1975) will suffice. DISCUSSION The great values of 207Pb/204Pb rule out young mantle sources. For example, Doe and Zartman (1979) model the average mantle today as having values for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb of 18.08, 15.42, and 37.68, respectively, instead of the observed ratios for the Malaysian ores of 18.609 to 19.057 for 206Pb/204Pb, 15.704 to 15.765 for 207Pb/204Pb, and 38.950 to 39.385 for 2oaPb/204Pb. Further more, the source of the ores also would have values of 207Pb/204Pb too great to be representative of pelagic sediments, which would average today about 18.70, 15.63, and 38.62 for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, respectively (Stacey and Kramers, 1975). The conclusion is that the sources are continental crust that includes Precambrian material, and adds to the evidence in favor of this environment from other studies, . Indeed, the observed ratios are remarkably similar to the modeled ratios of average upper crust by Doe and Zartman (1979) of 19.0, 15.7, 38.9, adjusted to 250 Ma. ago. Because the spread in Malaysian isotopic data is so small, the source of the lead appears to be from sediments in all cases because sedimentation is the best mixer. For example, the range in 206Pb/204Pb for volcanic rocks of Hawaii Island over a distance of only 40 km greatly exceeds what is seen in the Malaysian Tin Belt. It should be noted, however, that a small percentage of lead-rich continental sediment assimilated into a basaltic parent melt would dominate the lead-isotope ratios, but might not influence the neodymium- or strontium-isotope ratios. Liew and McCulloch (1985) , however, do find convincing evidence of incorporation of sediments in the batholiths in the strontium isotope data. The Stacey-Kramers model-lead-isotope ages range from 260 Ma (close to the age of the deposits) to -450 Ma. Thus there is little indication of cratonized crust where values of U/Pb and Th/Pb have been reduced by high-grade metamorphism in the Precambrian. Cratonization would result in non-radiogenic values of 206Pb/204Pb and great model values of Th/U (Doe and Zartman, 1979) in young melts. For example, great values of 207Pb/204Pb are known in present-day ratios of Archean rocks (Goldich et al., 1975), but the spread in ratios is greater than for Malayan samples and values of apparent Th/U are also greater. When younger Precambrian periods are considered, cratonized crust can be harder to recognize (Doe and Delevaux, 1980), because of a lack of time for reduced values of U/Pb to take effect. However, if the source is Middle Precambrian as estimated by Liew and McCulloch (1985) and if the mineralization age is young (around 200-250 Ma.) as determined, it seems most likely that we are not dealing with cratonized Precambrian crust, although "normal" Precambrian crust is quite possible. Liew and McCulloch (1985) present an interpretation^ of the neodymium isotope data in which a mantle depleted in neodymium relative to samarium formed' at the time of presumed major global continent formation 2500-3000 Ma. ago. They estimate the formation of the Malaysian arcs to have occurred at 1100-1400 Ma. in the East Province and 1500-1700 Ma. in the West Province, based on both neodymium isotope modeling and inherited zircon U-Pb dating. At these times, the value of Sm/Nd increased during crust formation. Granites then formed 200-250Ma. ago from this enriched source material. Lead-isotope data likewise indicate pre-history for the source materials involved in ore formation related to the igneous activity. Some source enriched in uranium relative to lead must have developed a long-time ago to produce the observed ratios. The time cannot be determined by these means, but the youngest time at which any of the galena isotopic compositions could have been produced from a source that evolved with a 238U/204Pb = 9.74 (The mean orogene value of Stacey and Kramers, 1975, for a system beginning at 3700 Ma. ago.) is about 2000 Ma. ago. The average 238U/2?4Pb must have been greater to obtain the larger observed values of 207Pb/204Pb for many of the samples. A 238U/204Pb a 10.3 beginning at 3700 Ma. (T2) , for example, would produce the greatest observed value of 207Pb/204Pb and its -accompanying 206Pb/204Pb at about 250 Ma. ago, the presumed age of mineralization (sample G-6)(Fig. 5). Values of 207Pb/204Pb between 10.0 and 10.3 can satisfactorily explain the two galenas from the Central Belt. Such an undisturbed old source, however, cannot explain the more radiogenic 206Pb/204Pb values of the two samples from the East Belt and one sample from the West belt (G-l,G-5, and G-7). To generate such ratios beginning with the lead-isotope ratios at 3700 Ma. of Stacey and Kramers (1975) (T2) , a second stage is needed with values of 238U/204pb between the orogene value of 9.74 and 10.3, and then a third stage beginning at time (T3 ) with variable higher values. Adopting an age of 1600 Ma. for the time of beginning of the third stage, which is in the range estimated by Liew and McCulloch (1985) for the Precambrian source material, a 238U/204Pb of about 12 would be needed to explain the most radiogenic ratios. A parallel agrument can be developed for 208Pb/204Pb and ^Th/238!! (Fig 5). A value of 10.3 is all right for 238U/204Pb if ^h/238!! is increased to 4.05 in order to bring the model 208Pb/204Pb age of G-2 into agreement with the uranium system. No change in ^^h/238!! is needed to model the galenas with the greates values of 206Pb/204Pb so a 23aU/204Pb of 10 in the second stage and a 238U/204Pb of 12 in the third stage beginning at 1600 Ma. is adequate. There is a good deal of flexibility in the ages and 238U/204Pb values of the stages, but there must be a stage of high 238U/204Pb beginning before 2000 Ma. ago and another, generally higher, stage since. Adequate models can be developed beginning the third stage at 2700 Ma. to be more compatible with Liew and McCulloch (1985) or having a "mantle second stage" between 3700 and 2700 Ma., but then a fourth stage is 'needed to explain the observed lead-isotope data. In addition some values of 207Pb/204Pb will need to be decreased and some increased. Thus the three-stage model is attractive because it is simpler and values of 207Pb/204Pb and ^h/238*! in the second stage are either adequate or are increased. CONCLUSIONS 1. There is a tectonic tie between the Southeast Asian Tin Belt in Malaysia with Belitung Island in Indonesia. The best lead- isotope match is for Belitung Island is with the Central Belt of mineralization in Malaysia. 2. The values of 207Pb/204Pb for galenas of the Southeast Asian Tin Belt are unusually high, and cannot be the result of any kind of mixture of mantle and pelagic sediment lead-isotope compositions. 3. The history of the Malay Peninsula is estimated to have begun in the Precambrian, much older than the oldest observed rocks of Early Paleozoic age. This conclusion agrees with the inter pretation of Liew and McCulloch (1985) based on neodymium isotopes and U-Th-Pb dating of zircons. 4. The simplest lead-isotope models begin at 3700 Ma. with the lead-isotope values of Stacey and Kramers (1975). Second « stages are formed with values of 238u/204Pb between 10.0 and 10.3 to explain some of the lead-isotope data rather ^than the global value of 9.74 used by Stacey and Kramers (1975). Some samples require a third stage (e.g., beginning at 1600 Ma.) to explain the most radiogenic values of 206Pb/204Pb. 5. The values of 207pb/204Pb for galenas from Malaysia are overlapped by ratios found in ore samples from the other largest tin province, Bolivia. Although the sample size is small, there might be some connection between major geochemical anomalies of tin and 207Pb/204Pb found in major tin districts. Acknowledaements The samples were obtained from Melvin Jones of the University of Adelaide, Australia, and collected by K.F.G. Hosking and Ee Beng Yeap of the University of Malaya. Sample locations and descriptions were provided by Ee Beng Yeap. M.H. Delevaux and A.A. Afifi made the excellent lead-isotope analyses. Discussions with Bruce L. Reed of the U.S. Geological Survey were most helpful. References Bignell J.D. and Snelling N.J. (1977) Geochronology of Malayan granites. Overseas Geology and Mineralogy 47, Institute of Geological Science, London. Doe B.R. (1985)' The plumbotectonics of the West Shasta Mining district, Eastern Klamath Mountains, California. Economic Geology. 80, 2136-2148* Doe B.R., and Delevaux M.H. (1980) Lead-isotope investigations in the Minnesota River Valley Late-tectonic and posttectonic granites. Geological Society of America Special Paper 182. 105-112. Doe B.R. and Zartman R.E. (1979) Chapter 2. Plumbotectonics I, The Phanerozoic, in H. L. Barnes, ed. , Geochemistry of Hvdrother- mal Ore Deposits. 2nd edition. New York, John Wiley and Sons Publishers, 22-69. Goldich S.S., Doe B.R., and Delevaux M.H. (1975) Possible further evidence for 3.8 b.y.-old rocks in the Minnesota River Valley of southwestern Minnesota. U.S. Geological Survey Open File Report 75-65 r lip. L|. If Hosking K.F.G. (1977) Known relationships between the "hard rock" tin deposits and the granites of southeast Asia. Geological Society of Malaysia Bulletin, 9, 141-157. Hutchison C.S.(1977) Granite emplacement and tectonic subdivisions of Peninsular Malaysia. Geological Society of Malaysia Bulletin. 9, 187-207. Jones M.T., Reed B.L. , Doe B.R. and Lanphere M.A. (1977) Age of tin mineralization and plumbotectonics, Belitung, Indonesia. Economic Geology f 72, 745-752. Mitchell A.H.G. (1976) Southeast Asian tin granites: Magmatism and mineralization in subduction and collision related setting. CCOP Newsletter Reports, Bangkok, 3, numbers 1 & 2, p. 10-19. Mitchell A.H.G. (1977) Tectonic settings for emplacement of Southeast Asian tin granites. Bulletin Geological Society of Malaysia Bulletin, 9, 123-140. Tilton G.R., Pollak R.J., Clark A.H., and Robertson R.C.R. (1981) Isotopic composition of Pb in Central Andean ore deposits. Geological Society of America Memoir 154. 791-816. Zartman R.E. (1984) Lead, strontium, and neodymium isotopic characterization of mineral deposits relative to their geologic environments. In Metallogenesis and Mineral Ore Deposits. Vol. 12 f Proceedings 27th International Geological Congress, Moscow 4-14 August, 1984, pp. 83-106, VNU Science ,Press. Zartman R.E. and Haines S.M. (1988) The plumbo tectonic model for Pb isotopic systematics among major terrestrial reservoirs A case for bi-directional transport. Geochimica et Cosmochimica Acta. 52, 1327-1339. APPENDIX: SAMPLE LOCATIONS AND DESCRIPTIONS (From Ee Beng Yeap) Gl. N 4* QUO", E 103"40'50". Bandi area, Trengganu. Replacement sulfide body of post Mid-Carboniferous age in Mid-Carbon iferous (?) marble. Galena with pyrite, chalcopyrite, magne tite and other minerals. G2. N 3* 10'30"; E 101 "42'40". Ban Hock Hin mine, Setapak, Selangor. Vein of estimated post-Triassic age cutting dolomite of the Kuala Lumur Limestone (Lower to Middle Silurian). Galena with trace quartz collected from an ore vein. G4. N 5*33'40", E 101'59'30". Manson Lode, Sungei Ketabong area, Sokor Kelanton. Galena-rich ore cutting metavolcanic rocks of Triassic age. Coarse-grained galena with associated coarse grained sphalerite. G5. N 3"53 f 40", E 103" 4' 5". PCCL Sungei, Gakak area, Sungei Lembing, Pahang. Sulfide-rich part of tin lodes cutting Lower Carboniferous shale, mudstone and other fine-grained clastic rocks. Galena-chlorite-chalcopyrite-sphalerite ore. Galena replaces chlorite, quartz and other minerals. G6. N 4*32', E 101* 9'. Krawat Pulai area, Perak. Galena-rich vein of estimated post-Upper Triassic age in marble in Paleozoic(?) marble and metasediment. Coarse galena replacing .sphalerite. G7. N 3' 4'50", E 101'35' 5". Melor Syndicate mine, Sungai Way, Selangor. Galena-sphalerite-chalcopyrite vein of estimated post-Triassic age cutting Lower to Middle silurian marble. Galena-quartz-sphalerite-chalcopyrite ore. Coarse galena « filling voids and replacing quartz, shalerite and chalco- pyrite. G9. N 3'37', E 103' 55'. Maran Lode, Kuantan vicinity, central Phang. Galena-rich lode of estimate post-Carboniferous age cutting argillaceous rocks. Galena-pyrite-chalcopyrit- chlorite ore. Medium-grained galena replacing pyrite, chalcopyrite, and chlorite. Table 1: 206Pb/204Pb f ^Pb/^Pb, and 208Pb/204Pb for galenas from Malaysia and selected data from other areas. Sample No. Deposit or Province Name 206Pb/204Pb 207Pb/2WPb 208Pb/204Pb Reference Malaysia i G-lgn-E Bandi 19 .023 15. 714 38 .998 (1) G-5gn-E PCCL Sungei 19 .048 15. 739 39 .064 M CD G-9gn-E Maran Lode 18 .644 15. 738 38 .972 CD G-6gn-W Kramat Pulai 18 .731 15. 765 39 .097 CD G-2gn-W Ban Hock Hin 18 .875 15. 729 39 .385 CD G-7gn-W Melor Synd. 19 .057 15. 711 39 .191 CD G-4gn-W Ketabong 18 .676 15. 704 38 .951 (1) Indonesia Belitung Kelapa Kampit 18 .61 15. 71 38 .95 (2) Belitung Selumar 18 .50 15. 71 38 .88 (2) Sumatra S. Tuboh 18 .36 15. 58 38 .41 (3) Sumatra Simau Gold 18 .42 15. 58 38 .46 (3) Sumatra M. Sipongi 18 .66 15. 63 38 .85 (3) Java G. Sawal 18 .70 15. 72 38 .96 (3) Java S . Banten 18 .79 15. 70 39 .19 (3) Java Cikondang 18.60 15.62 38.73 (3) Bolivia Tin Belt Monolito 18.41 15.64 38.51 (4) Tin Belt Mercedes 18.80 15.81 39.20 (4) Tin Belt Don Carlo 18.43 15.67 38.62 (4) Tin Belt Chojlla 18.52 15.69 38.64 (4) Tin Belt Urania 18.60 15.69 38.76 (4) Tin Belt Urania 18.73 15.69 38.94 (4) Tin Belt Viloco 18.76 15.67 38.96 (4) Tin Belt Argentina 18.77 15.70 39.05 (4) Tin Belt Pacuni 18.69 15.65 38.87 (4) (1) This paper, (2) Jones et al. (1977), (3) Doe and Zartman, (4) Tilton et al. (1981) FIGURES Fig. 1. Map of Malaysia and part of Indonesia showing sample locations of the galenas analyzed for this study and principal tectonic zones. Fig. 2. 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb plots for galenas from Malaysia. Letters designate mineral belts: E is East Belt, C « is Central Belt, and W is West Belt. (A) 207Pb/204Pb vs. 206Pb/204Pb plot including the Stacey-Kramers (1975) curve with ^fy/^Pb of 9.74 beginning at 3700-Ma. ago. Curve (1) has the same starting point for lead-isotope ratios as the Stacey- Kramers curve 3700-Ma. ago; however, curve (1) evolves with a ^fy/^Pb of 10.0 and curve (2) 10.3. (B) 208Pb/204Pb vs. 206Pb/204Pb plot including the Stacey- Kramers curve with ^ZTh/238!! of 3 ^ 78 and 238U/204PJ3 of 9.74. curve (1) has a 232Th/238u of 3 ^ 78 and a 23^/20^ of 10 .o; curve (2) has a of 4 ^ 05 and a zsSu/ZMpk of 10-3- Ticks on the curved line are in Ma. Fig. 3. 206Pb/20APb, 207Pb/20APb, and 208Pb/20APb plots comparing galenas from Malaysia (this study) with Indonesia (Doe and Zartman, 1979; Jones et al., 1977). The symbols represent: Malaysian mineral belts E - East Belt, C- Central Belt, W -West Belt; Indonesia B - Belitung, J - Java, S - Sumatra. See Fig. 2 for further explanation. Fig. 4. 206Pb/204Pb, 207Pb/204Pb, and ^Pb/^Pb plots for galenas from Malaysia (this study) and Bolivia (Tilton et al. f 1981). See Fig. 2 for additional explnation. Fig. 5. (A) 207Pb/204Pb versus 206Pb/204Pb evolution diagram to model lead-isotope ratios for galenas from Malaysia. The Stacey- Kramers model begins a second stage at 3700 Ma. with values of 11.152 for 206Pb/204Pb and 12.998 for 207Pb/204Pb with a value for 238U/204Pb of 9.74 (normalized to the present day) for the second stage. Curve (1) represents lead-isotope evolution for a second stage with 238u/204Pb = 10.0 and curve (2) a second stage with 238u/204pb = 3.0.3. Curve 3 represents a change of ^V204^ from 10.0 to 12 ( 206Pb/204Pb = 16.100, 207Pb/204Pb - 15.426) at 1600-Ma. ago to show third-stage lead-isotope evolution. (B) 208Pb/204Pb vs 206Pb/204Pb plot to model lead- isotope ratios for galenas from Malaysia. The Stacey-Kramers curve for 208Pb/204Pb vs 206Pb/204Pb uses a value of 3.79 for ^Th/238!!; the curve is omitted for clarity. Curve (2) begins at the second stage ratios ( 208Pb/204Pb = 31.23) adopted by Stacey-Kramers at 3700 Ma. and evolves with a 238U/204Pb of 10.3 as for curve (2) in plot A but with a ^^h/238!! of 4.05 to give sample G-2 a model 208Pb/204Pb age in approximate agreement with its known age. Curve (3) is parallel to curve (3) in plot A. Lead isotopes evolve with a ^fy/^Pb of 10.0 and ^h/238!! « 3.79 until 1600-Ma. ago. These conditions would evolve a curve (1) that is omitted for clarity here (see Fig. 2). At 1600 Ma. ago, the value of ^fy/^Pb changes to 12 with no 53. change in ^^h/23^, which gives approximate model 208pb/204Pb ages for the samples with the greatest values of 206pb/204Pb (e.g., East Belt galenas). 108 o in 15.86 15.82 C2) 15.78 15.74 w 207 Pb w 204 pb 15.70 15.66 100 15.62 200 STACEY-KRAWERS CURVE 15.58 15.54 18.2 18.4 18.6 18.8 19.0 19.2 206 pb/ 204 pb 33.7 39.5 W 39.3 20B pb 39.1 204 Pb 36.9 38.7 STACEY-KRAMERS 0 CURVE 38.5 38.3 18.2 18.6 18.8 19.0 19.2 206 pb/ 204 pb 15.9 15.8 W 207 Pb W B B 204 pb 15.7 STAGEY-KRMrfEHS CURVE 15.6 ss 13.5 17.0 17.4 17.8 18.2 18.6 13.0 19. 206 pb/ 2(Mpb h'.^ ^ 39.8 39.4 W W 39.0 208 Pb 38.E 204 Pb 38.2 37.8 37.4 37.0 17.0 17. 4 17.8 18.2 18.6 13.0 19. 206 pb/ 2CH pb 15.9 15.8 M M 207 Pb M 204 pb 15.7 15.6 - STAGEY-KBAUERS CUBVE 15.5 /___i 17.0 17.4 17.8 18.2 18.6 13.0 19.4 206 pb/ 204 pb 39.8 39.4 M B M "B M 39.0 M 208 Pb 38. E 204 Pb 38.2 200 37.8' 400 37.1 600 37.0 i 17.0 17.4 17.8 18.2 18.6 19.0 19.4 ro ro CJ c=> TJ TJ CT cr ~oen cr -a cr 40 39 38 208 Pb 204 Pb 37 36 35 15 16 17 18 19 20 206 pb/ 204 pb Mass Spectrometric Measurements of 234u/238u and 230jh/238u and Dating Late Quaternary Carbonates R. Lawrence Edwards, University of Minnesota Thermal ionization mass Spectrometric (TIMS) methods for measuring 23°Th (Edwards et al., 1987a) and 234U (Chen et al., 1986) have provided improved precision and sensitivity over earlier techniques. This allows us to obtain precise 238U - 234U - 230Th ages of carbonates younger-"than 500 ka (Edwards et al., 1987b). Two sigma precisions range from ±3 y for materials younger than 1000 y, to ±25 y at 10 ka, to ±1 ka at 130 ka. For corals younger than 8 ka, comparisons with other chronometers show that 238U - 234U - 230Th ages are accurate (Edwards et al., 1988; 1992). For corals older than 100 ka, 234u/238U ratios are sometimes consistent with closed system evolution from sea water and other times indicate diagenetic shifts to higher values (even for aragonitic samples that retain their original Sr and Mg concentrations). The sensitivity of 234y/238u to diagenetic shifts makes it an important indicator of alteration, and provides a criterion for selecting materials that are likely to record accurate ages (e.g. Edwards et al. 1987b; Banner et al., 1991; Gallup et al., 1991; 1992). The detailed timing of part of the late Quaternary sea level curve (e.g. Edwards et al., 1987b; Li et al., 1989; Gallup et al., 1991; 1992) has been determined via application of these techniques to corals and cave deposits. The results have a bearing on the causes of Quaternary climate shifts. A second application focuses on extracting regional climate records from inorganically precipitated calcite. This approach has produced some of the first continuous high resolution regional climate records longer thanIO5 years (Winograd et al., 1990, Ludwig et al., 1990, Richards et al., 1992a, b). Such records are important, particularly within the context of the high- resolution sea level curve. By comparing regional and sea level records, one may resolve leads and lags between regional and global climate shifts. A third application involves combined 238U - 234U - 230Th and 14C analyses on the same corals. As 238U - 234y . 230Th ages are at |east as precise as 14C ages, they provide the opportunity to calibrate the 14C chronometer for times earlier than the dendrochronology calibration (Edwards et al., 1988). Results show offsets between 14C and 238U - 234U - 230Th ages (Bard et al., 1990) indicating large shifts in atmospheric CP 2C, particularly between 10,900 and 12,300 B.P., when differences between conventional 14C and 238U - 234U - 230Th ages jump from 800 to 2100 years (Edwards et al., 1992). The jump appears to result from shifts in the ocean - atmosphere carbon cycle. Here, I discuss the TIMS measurements, as well as improvements in these measurements that have recently been made at the University of Minnesota. I then discuss data that have a bearing on the accuracy of the ages, and finally some of the applications discussed above. References Banner, J.L, Wasserburg, G.J., Chen, J.H., and Humphrey, J.D. 1991. Uranium-series evidence on diagenesis and hydrology in Pleistocene carbonates of Barbados, West Indies. Earth Planet. Sci. Lett. 107, 129 -137. Bard. E., Hamelin. B., Fairbanks, R.G., and Zindler, A. T 1990. Calibration of the C-14 timescale over the past 30,000 years using mass spectrometric U-Th ages from Barbados corals. Nature 345, 405 - 409. Chen, J.H., Edwards, R.L and Wasserburg, G.J., 1986. U-238, U-234, and Th- 232 in seawater. Earth Planet. Sci. Lett., 80, 241-251. Edwards, R.L, Chen, J.H. and Wasserburg, G.J., 1987a. U-238, U-234, Th- 230, Th-232 systematics and the precise measurement of time over the past 500,000 years. Earth Planet. Sci. Lett., 81, 175-192. Edwards, R.L, Chen, J.H., Ku, T.-L and Wasserburg, G.J., 1987b. Precise timing of the last interglacial period from mass spectrometric determination of Th-230 in corals. Science, 236, 1547-1553. Edwards, R.L, Taylor, F.W. and Wasserburg, G.J., 1988. Dating earthquakes with high precision thorium-230 ages of very young corals. Earth Planet. Sci. Lett., 90, 371-381. Edwards, R.L, Beck, J.W., Burr, G.S., Gray, S.C., Taylor, F.W., Donahue, D.J., and Druffel, E.R.M. 1992. Calibrating C-14 ages with Th-230 ages of corals from New Guinea and Vanuatu. Fourth International Conference on Paleooceanography, Kiel, Germany, September 21 - 25. Gallup, C.D., Edwards, R.L, and Johnson, R.G., 1991. The timing of the interglacial before last. EOS, 72, 271. Gallup, C.D., Edwards, R.L , and Johnson, R.G. 1992. The precise timing and amplitude of sea levels between 85 and 230 ka from Th-230 ages of fossil corals from Barbados, West Indies. Fourth International Conference on Paleooceanography, Kiel, Germany, September 21 - 25. Li, W.X., Lundberg, J., Dickin, A.P., Ford, D.C., Schwarcz, H.P., McNutt R., and Williams, D. 1989. High-precision mass-spectrometric uranium-series dating of cave deposits and implications for palaeoclimate studies. Nature 339, 534-536. Ludwig, K.R., Simmons, K.R., Szabo, B.J., and Riggs, A.C. 1990. Mass spectrometric Th-230 - U-234 - U-238 dating of Devils Hole calcite vein: a precise record of continuous growth from 566 ka to 60 ka. Geol. Soc. Amer. abstracts with programs 22:7, A310. Richards, D.A., Smart, P.L, and Edwards, R.L. 1992a. Late Pleistocene sea- level change based on high-precision, mass spectrometric Th-230 ages of submerged speleothems from the Bahamas. EOS, 73, 172. Richards, D.A., Smart, P.L, and Edwards, R.L 1992b. Sea levels for the last glacial period based on 238(j_234|j_230Th ages Of submerged cave deposits from the Bahamas. In review, Nature. Winograd, I.J., Coplen, T.B., Ludwig, K.R., Szabo, B.J., Riggs, A.C., and Revesz, K.M. 1990. Continuous 500,000 year climatic record from Great Basin vein calcite: 1. the 6 180 time series. Geol. Soc. Amer, abstracts with programs 22:7, A209. c^o 4T Nd Isotopes as Tracers of the Origin and Evolution of the Continental Lithosphere G. L. Fanner, CIRES and Dept. of Geological Sciences, Campus Box 216, Univ. of Colorado, Boulder, CO 80309 Abstract Over the past 15 years, neodymium isotopic data have provided important constraints regarding the formation, tectonic modification, and subsequent degredation of the continental lithosphere. The technique is based on the fact that the Earth's crust and mantle have, over time, developed discretely different Nd isotopic compositions, due to the a-decay of ^'Sm to ^^Nd combined with the small differences in Sm/Nd that have developed in the Earth primarily as a result of magmatic processes. The Nd isotopic compositions of continental igneous, metamorphic, or sedimentary rocks can then be used to determine the sources involved in the rock formation if the isotopic compositions of the potential source rocks are known and are distinguishable. However, continental rocks often contain Nd derived from a variey of different sources and so it is often difficult to extract unambiguous information regarding the origin of a given rock from its Nd isotopic compositions alone. Instead, the Nd isotopic compositions of continental rocks are best interpreted in conjunction with other isotopic, geochemical, and geologic information. In many continental regions, particularly in North America, extensive Nd isotope data bases exist for the Precambrian crust which can be used not only to study crustal genesis but also to study magmatic and tectonics events that subsequently modified the continental lithosphere. In the U.S., the Nd data reveal that the Precambrian crust can be divided into distinct provinces which define distinct arrays (pseudoisochrons) on conventional isochron plots. These arrays have implications for how the Precambrian crust was generated and assembled and also provide convenient templates against which to compare the isotopic compositions of younger rocks which may have been formed, at least in part, from Precambrian components. The comparsion between the isotopic compositions of Mesozoic and younger peraluminous granites in the western U.S. and the Precambrian crust clearly demonstrate that these granites were derived solely from anatexis of pre-existing felsic to intermediate composition Precambrian crust. The Nd isotopic compositions of large-volume Cenozoic rhyolites in the western U.S., on the other hand, show that these rhyolites are not simple crustal melts, as commonly assumed, but instead differentiated from mafic magmas derived from the upper mantle that interacted extensively with the crust. Other studies of Cenozoic volcanic rocks in the western U.S. have shown that Nd isotopic data can distinguish between lithosphere and asthenospheric mantle derived basalts. As a result, temporal and spatial variations in the isotopic compositions of syn-extensional basalts can be used to track the physical response of the deep continental lithosphere to extension. Nd isotopic data have also proved useful in constraining the provenance of marine siliciclastic sediment shed from North America. One example is the recent demonstration that the large volumes of Cenozoic flysch accreted to the southern margin of Alaska represent detritus derived from the unroofing of the northern portions of the Coast Ranges Plutonic Complex in SE Alaska and British Columbia. General Svstematics Surface V/G PG O4 P 4 , Crust 3 3 - 2 j^^H CD = 1 1 -^l^sn 5 g c Mantle Endmember OJ 0.1 70 A 0.5 0.9 130 D 0.9 0.9 70 cu 15 F-0.1 Crustal Endmember 0.71 87Sr/86Sr Precambrian of Continental U.S. Western U.S. Province 2 Provinces Q Province » z CO 0.5 Age (Ga) PROTEROZOIC O 1 ' Granites M t 4 Granites A Basafls Province 2&3 1 7 Granites x 1 4 Granites A Basalts PHANEROZOIC PeraJununous Granites Arizona D Nevaoa/SE California Anzona Nevada/ SE Calif 147Sm/ 144Nd 0.90 X * 015 X* H XX PRQTEROZQIC x i 7 Ga Granites M 1 4 Ga Granites 0.80 O 1 0 Ga Granites O Metaseaimentary rocxs OO^ + Gabtoros oo * Basalts 00 A Intermediate 0.75 Pcraluirunous Granites volcanic rocKs PHANEROZOIC Peraluntlnous Granites H Arizona O Nevaoa/SE California 0.70 87Rb/86Sr Grenviile crust ince 2&3 crust C3 O -10 p . -IS Precambnan sedimentary rocks GrenviUe province S. margin of Wyoming/Superior provinces Wvommg/Supenor orovmccs 0.25 OJO OJS l47Sm/ 144Nd Oriein of Rhvolite 90 95 '00 I -'OS .tio i 5 20 301 002 303 306 1 /Nd (pom) Timber Mountain Tuff TR HSR O 9 Ammonia Tanks Member 0 ^ Rainier Mesa Member Paintbrush Tuff LSR A A A Tiva Canyon Member Q Topopah Spmg member "MCv asn now iu«i c ^ ' i5 50 55 60 65 '0 '5 30 SO2 (wt. %) Continental Extension Pure Shear Aatfacnosphere On-Aria /^ S V u) / / V -" LUhosphene Time Simple Shear Time NEW MEXICO 2 ,,-«, 00 (14) t COLORADO PLATEAU TRANSITION/^ ZONE BASIN AND RANGE RIO GRANDE RIFT 0-, 100 BASALT Nd BOTOWC COMPOSfTIONS REFERENCE LIST Nd Isotopes as Tracers of the Origin and Evolution of the Continental Lithosphere- G. L. Fanner Overview 1) General systematics: Arndt, N.T., and S.L. Goldstein, 1987, Use and abuse of crust-formation ages: Geology, v. 15, p. 893-895. DePaolo, D.J., 1988, Neodymium Isotope Geochemistry: An Introduction, Springer-Verlag, Berlin- Heidelberg, 187 pp. 2) Mixing Systematics: DePaolo, D.J., 1981b, Trace element and isotopic effects of combined wall-rock assimilation and fractional crystallization: Earth Planet. Sci. Lett., v. 53, p. 189-202. Gray, CM, 1984, An isotopic mixing model for the origin of granitic rocks in southeastern Australia: Earth Planet. Sci. Lett., v. 70, p. 47-60. 1 Q -If. Taylor, J., H.P., 1980, The effects of assimilation of country rocks by magmas on i0O/ i0O and 87Sr/ 86Sr systematics in igneous rocks: Earth Planet. Sci. Lett., v. 36, p. 359-362. Nd tracer studies 1) Magmatic processes/ Origin of rhyolite: Cameron, K.L., and M. Cameron, 1985, Rare earth element, 87Sr/86Sr, and 143Nd/144Nd compositions of Cenozoic erogenic dacites from Baja California, northwestern Mexico, and adjacent West Texas: evidence for the predominance of a subcrustal component: Contrib. Mineral. Petrol., v. 91, p. 1-11. Farmer, G.L., D.E. Broxton, R.G. Warren , and W. Pickthom, 1991, Nd, Sr, and O isotopic variations in metaluminous ash-flow tuffs and related volcanic rocks at the Timber Mountain/Oasis Valley caldera complex, SW Nevada: implications for the origin and evolution of large-volume silicic magma bodies: Contrib. Mineral. Petrol., v. 109, p. 53-68. Hildreth, W., Halliday, A. N., and R. L. Christiansen, 1991, Isotopic and chemical evidence concerning the genesis and contamination of basaltic and rhyolitic magma beneath the Yellowstone Plateau volcanic field, ]. Petrol., v. 29, p. 63-138. Johnson, C.M., 1989, Isotopic zonations in silicic magma chambers: Geology, v. 17, p. 1136-1139. Johnson, C.M., 1991, Large-scale crust formation and lithosphere modification beneath middle to late Cenozoic calderas and volcanic fields, western North America: J. Geophys. Res., v. 96, p. 13485-13507. Tegtmeyer, KJ., and G.L. Farmer, 1990, Nd isotopic gradients in upper crustal magma chambers: Evidence for in situ magma-wall rock interaction: Geology, v. 18, p. 5-9. 2) Continental growth and tectonism: Precambrian continental growth of continental U.S.: Bennett, V.C., and D.J. DePaolo, 1987, Proterozoic crustal history of the western United States as determined by neodymium isotopic mapping: Geol. Soc. Am. Bull., v. 99, p. 674-685 Condie, K.C., 1990, Growth and accretion of continental crust: Inferences based on Laurentia: Chem. Geol., v. 83, p. 183-194 Patchett, P.J., and N.T. Arndt, 1986, Nd isotopes and tectonics of 1.9-1.7 Ga crustal genesis: Earth Planet. Sci. Lett., v. 78, p. 329-338. Mechanisms of continental extension: Farmer, G.L., F.V. Perry, S. Semken, B. Crowe, D. Curtis , and DJ. DePaolo, 1989, Isotopic evidence on the structure and origin of subcontinental lithospheric mantle in southern Nevada: J. Geophys. Res., v. 94, p. 7885-7898. Ormerod, D.S., C.J. Hawkesworth, N.W. Rogers, W.P. Leeman , and M.A. Menzies, 1988, Tectonic and magmatic transitions in the western Great Basin: Nature, v. 333, p. 349-353. Perry, F., W.S. Baldridge , and DJ. DePaolo, 1988, Chemical and isotopic evidence for lithospheric thinning beneath the Rio Grande rift, Nature, .v. 332, p. 432-434. 4) Sedimentary provenance Frost, C.D., and D. Winston, 1987, Nd isotope systematics of clastic sediments: Sedimentary fractionation processes and implications for provenance studies and models of crustal evolution: J. Geol., v. 95, p. 309-327. McLennan, S.M., M.T. McCulloch, S.R. Taylor, and J.B. Maynard, 1989, Grain size and provenance: Evidence from Nd-isotopes in deep-sea turbidites: Nature, v. 337, p. 547-549. Nelson, B.K., and D J. DePaolo, 1988, Comparison of isotopic and petrographic provenance indicators in sediments from Tertiary continental basins of New Mexico: J. Sed. Petrol., v. 58, p. 348-357. 1 PARAGENETIC CONSTRAINTS ON THE PB ISOTOPIC AND TRACE ELEMENT CHARACTER OF Au-Ag MINERALIZED ROCKS OF THE NORTH AMETHYST VEIN, MINERAL COUNTY, COLORADO by Nora K. Foley and Robert A. Ayuso U.S. Geological Survey, National Center, Reston, Virginia 22092 Chemical redistribution as a result of alteration and mineralization in the North Amethyst vein illustrates the combined effects of metasomatism, dissolution, and crystallization of new minerals. The vein is hosted by the 27.6 Ma (Lanphere, 1988) Carpenter Ridge Tuff (CRT), which consists of dacites and rhyodacites related to the evolution of the central cluster of calderas in the San Juan volcanic field (Lipman, 1976; Lipman and Sawyer, 1988). The vein is located ~7 km north of the Creede mining district (Bethke and Lipman, 1987). The vein system has an older mineral association that consists of quartz, rhodonite, Mn-carbonates, hematite, magnetite, electrum, Au-Ag-sulfides, Ag-sulfosalts, and base metal sulfides and a younger mineral association (-25 Ma, M. Lanphere, 1987) that crosscuts the Mn- and Au-bearing assemblages and consists of quartz, cakate, sericite, chlorite, hematite, adularia, fluorite, base metal sulfides, and Ag-tetrahedrite (figure 1; Foley, 1990). A stage of brecciation and deposition of sediment in veins separates the two mineral associations. Samples of least altered wallrock, more highly altered wallrock, and early vein material have geochemical patterns that reflect the amount of vein material incorporated into the wallrock and the mobility of REE's and other elements in the hydrothermal fluid (Foley and Ayuso, 1992). In general, REE's and trace incompatible elements (e.g., Th, Ta) in the volcanic wallrock were relatively immobile during the alteration events that preceded or were concurrent with mineralization. In contrast, the relative mobility of base and precious metal elements was an important factor controlling the evolving chemical composition of the altered wallrock. Potassium-metasomatized CRT that constitutes the least altered and unbleached host of the vein (samples located 3-10 m from vein, and consist of wallrock >97%, vein material <3%) has ratios of incompatible element abundances (table, WR97) that match those in regionally potassium-metasomatized rocks of CRT (K-m CRT, e.g., Krause-Webber, 1988) for Th/Ta, although other ratios show large discrepancies (Th/Hf). Least altered wallrocks also have rare earth element (REE) contents and chondrite-normalized patterns (at SiO2 =66-74%) characterized by Ce/Yb ratios that range from 8 to 12 and small negative Eu anomalies (Eu/Eu* =0.47-0.81) in the range of volcanic rocks of the central San Juan calderas (e.g., Lipman, 1987). In addition, the least altered wallrocks have values of Zn/Ta that are similar to regionally K-metasomatized rocks of CRT (table 1, K-m CRT). With increasing alteration, primarily as a result of metasomatism produced by vein mineralization, the wallrocks are systematically bleached, silicified, and (or) chloritized (wallrock =90-95%, vein material =5-10%), with higher Na/K values proximal to the vein (figure 2; Foley and Ayuso, 1992; this study). Contents of trace elements of widely different geochemical behavior in the more bleached rocks overlap the content values of least altered wallrocks. This overlap suggests that vein mineralization and metasomatism did not significantly disturb the composition of wallrocks a few meters away from the veins (table, WR90). The most obvious effect of the vein mineralization is the increased abundance of base and precious metals relative to immobile elements for the altered rocks compared to the least altered wallrocks (table, WR97). Silicified, bleached, and chloritized wallrocks, for the most part, retained the original REE signature of the CRT volcanic rocks. The REE pattern of the K-metasomatized volcanic rocks also is preserved in more highly altered wallrocks (wallrock =70-85%, vein material =15-30%) that have not retained their volcanic fabric and have a higher density of quartz veining. These rocks have relatively undisturbed incompatible element ratios (table, WR70), but vein effects are enhanced and so produce significantly higher base-and-precious metal to immobile-element ratios. Feldspar-stable altered wallrocks have overlapping or slightly lower REE contents and patterns that match those of the unaltered patterns. Although highly metasomatized wallrocks adjacent or within a few centimeters of vein, having a high density of veining (wallrock = 50%, vein material = 50%) and resorbed feldspars, have trace element ratios that are similar to those of the least altered hostrocks (table, WR50); these wallrocks have high abundances of base and precious metals compared to abundances in least altered wallrocks. Initial Pb isotopic values for -40 samples of galenas and feldspars from the North Amethyst vein system and associated host rocks have a narrow compositional range, but significant differences exist among volcanic wallrock, older vein assemblages, and younger vein assemblages (figure 3, Foley and Ayuso, in prep.). Pb isotopic compositions of paragenetically early galenas associated with Au mineralization are relatively less radiogenic (206Pb/ 204Pb, 18.826-18.881; 207Pb /204pb, 15.588-15.602; and 208Pb/204Pb, 37.790-37.926) compared to compositions of galenas associated with the younger mineralization (206pb/204pb, 19.041-19.115; 207Pb/204Pb, 15.627-15.672; and 208pb/204Pbr 37.829-38.057). Pb isotopic compositions of galenas from the North Amethyst vein are comparable to those of galenas from the southern part of the Creede mining district, located ~5 km to the south (Doe and others, 1979; Foley, 1990; Foley and Ayuso, in prep.). Pb isotopic compositions of the vein system are more radiogenic than the compositions of host volcanic rocks (e.g., 206Pb/204Pb, 18.501 to 18.742; 207Pb/ 204Pb, 15.564 to 15.607; and 208pb/204pb, 37t886 to 38.183; Lipman and others, 1978; Matty and others, 1987; D. Matty, written commun., 1987; this study). The older assemblage may represent the product of a hydrothermal system that interacted with a source having a slightly different Pb isotopic character than that of the younger mineralization, or it may represent an increasing and variable mixture of volcanic rock with ore-fluid lead as characterized by galena in the later mineralization. Pb isotopic compositions correlate with bulk chemical variations (e.g., Au, Ag, As, Cu contents); however, neither the Pb isotopic ratios nor the metal abundance ratios permit the ores to have been derived solely from local wallrock (Foley and Ayuso, 1992). The geochemical profile of the vein material requires the addition of Pb and other base and precious metals from mineralizing fluids that originated at depth. Table. Geochemical data for mineralized rocks of North Amethyst Au-Ag vein. Rock K-mCRT1 WR97 WR90 WR70 WR50 Th/Ta 14.9-8.9 13.1-9.4 13.6-11.5 13.3-8.9 12.6-10.6 Th/Hf 8.2-7.3 3.3-1.7 3.4-3.0 3.3-2.3 3.4-1.4 Zn/Ta 70 45-197 29-2102 45-1503 864-5327 Pb/HF 6-34 3.7-214 5-380 409-902 Pb/Ta 24-136 15-877 17-1421 1534-6034 Ag/Ta 1.5-35 0-25 6-148 35-2431 1 K-m = K-metasomatized; percentage of wallrock (WR) varies from 97 to 50%. References Cited Bethke and Lipman, 1989, Mineralization in silicic calderas: Questa, New Mexico and the San Juan Mountains, Colorado: American Geophysical Union, 28th International Geological Congress, Field trip guidebook T320, 75p Doe, B.R., Steven, T.A., Delevaux, M.H., Stacey, J.S., Lipman, P.W., and Fisher, F.S., 1979, Genesis of ore deposits in the San Juan volcanic field: Econ. Geol., v. 74, pp. 1-26. Foley, N.K., 1990, Petrology of gold-, silver-, and base-metal-bearing ores of the North Amethyst vein system, Mineral County, Colorado: unpub. Ph.D thesis, Virginia Polytechnic Institute and State University, 325p. Foley, N.K., and Ayuso, R.A., 1992, The geochemical character of mineralized rocks of the North Amethyst vein, Mineral County, Colorado [abs]: V.M. Goldschmidt conference Program and Abstracts, Reston, Virginia, p. A36. Foley, N.K., and Ayuso, R.A., in prep., Paragenetic constraints on Pb isotopic evolution of the North Amethyst Au-Ag vein system, Creede mining district, San Juan volcanic field, Colorado, in, W. Elston and G. Plumlee, eds., Volcanic Centers as Targets for Mineral Exploration, Economic Geology, Spec. Issue, 36p. Krause-Webber, K.L., 1988, The Mammoth Mountain and Wason Park Tuffs: Magmatic evolution in the central San Jaun volcanic field, southwestern Colorado: unpub. Ph.D thesis, Rice University, Houston, Texas, 244p. Lanphere, M.A., 1987, High-resolution ^Ar/^Ar geochronology, central San Juan caldera complex, Colorado [abs]: Geol. Soc. America Abs. with Programs, v. 19, no. 5, p. 288. Lanphere, M.A., 1988, High resolution ^Ar/^Ai chronoly of Oligocene volcanic rocks, San Juan Mountains, Colorado: Geochimica cosmochimica acta, v. 52, pp. 1425-1434. Lipman, P.W., 1976, Caldera-collapse breccias in the western San Juan Mountains, Colorado: Geological Society of America Bulletin, v. 87, p. 1387-1410. Lipman, P.W., 1987, Rare-earth-element compositions of Cenozoic volcanic rocks in the Southern Rocky Mountains and adjecent areas: U.S. Geological Survey Bulletin No. 1668, 23 p. Lipman, P.W., and Sawyer, D.A., 1988, Preliminary geology of the San Luis Peak quadrangle and adjacent areas, San Juan volcanic field, southwestern Colorado: U.S. Geological Survey Open-file report 88-359, 32p. Lipman, P.W., Doe, B.R., Hedge, C.E., and Steven, T.A., 1978, Petrologic evolution of San Juan volcanic field, southwestern Colorado: Pb and Sr evidence: Bull. Geol. Soc. Amer., v.89, pp. 59-82. Matty, D.M., Lipman, P.W., and Stormer, J.C., 1987, Common-Pb isotopic characteristics of central San Juan ash flow tuffs [abs]: Geol. Soc. America Abstracts with Programs, v. 19, no. 5, p. 319. NORTH AMETHYST VEIN SYSTEM 3 Mn-Calcite»Quartz>Pyrite 2 Quartz>Mn-Calcite>Rhodocrosite>Aduairia> Fluorite>Chlorite~Pyrite>Mn-siderite Q>Sphalerite>Galena>Pyrite>Chalcopyrite> ~Hematite~Chlorite>Tetrahedrite Breccia Chaicedonic Quartz cement Sphalerite>Galena>Chalcopyrite>Pyrite> Tetrahedrited>Ag-Au minerais>Electrum {Hematite>Magnetite} a Rhodocrosite~Quartz>Mn-Calcite~Rhodonite> K-feldspar»Sphaierite>Pyrite>Galena [Barite] Figure 1. Paragenetic sequence for mineralized rocks of the North Amethyst vein system (Foley, 1990). Stages 2 and p are the main sulfide-bearing assemblages. LEAST ALTERED. HIGHLY ALTERED SAMPLES UNBLEACHED SAMPLES SiO2% Stmpl* SAMPLE SIO2% AR-44 663 -»- DMV-0 783 -*- TIL) 641 -a- EO-17U 724 BN-66 661 ~~~ DMV-26827 -<.- M-13 743 M-13U 743 DMV52965 -*- DMV-11 74 5 AG-33 750 ~*y- DMV-16 764 t J L»a«t atorvd. unU**dt«d ample* CHLORIDZED WALLROCK. 00 BLEACHED AND SILJCIRED WALLROCK, METASOMATIZED WALLROCK VOLCANIC FABRIC RETAINED VOLCANIC FABRIC RETAINED -5 AV-488X Samel* SiO2% Sampl* SO2% -i- AV-APRQ Figure 2. Samples of least altered wallrock (A), more highly altered wallrock (B, C), and early vein material (D) have geochemical patterns which reflect the amount of vein material incorporated into the wallrock and the mobility of REE's and other elements in the hydrothermal fluid. Samples are normalized to least altered Carpenter Ridge Tuff. The most obvious effect of the vein mineralization is the increased abundance of base and precious metals relative to immobile elements. 39.0. Central San Juan Mountains, Colorado North Amethyst base-metal Southern Amethyst 38.5- Alpha-Corsair 38.0- Q. oo BoodhoWer 8 37.5 - Midwest Carpenter Ridge and Nelson Mountain Turfs 37.0 18 18.25 13.5 18.75 19 19.25 15.8. North Amethyst base-metal Southern Amethyi 15.7- .o aa. 1.7Ga rS- 15.6- 8 Bondholder Midwest North Amethyst 15.5 - alpha Carpenter Ridge and Nelson o Galenas Mountain Tuffs 15.4 18 18.25 18.5 18.75 19 19.25 206, Figure 3. Lead isotope values for galenas and adularia from mineralized structures (Doe and others, 1979; Foley and Ayuso, 1992) compared to data for feldpars from volcanic rocks of the central cluster of the San Juan volcanic center (Lipman and others, 1978; Matty and others, 1987; D. Matty, written commun., 1987; this study). The data straddle but are more radiogenic than the secondary isochron at 1.78 Ga defined by the volcanic rocks from the central caldera cluster (Lipman and others, 1978; Matty and others, 1987). Dashed line (S&K) is average lead evolution line for Stacey and Kramer's (1975) two-stage Pb evolution model. Direct Dating of Ductile Deformation Fabrics: An Integrated Microstructural/Geochronologic Approach Getty, S.R., Earth and Planetary Sciences, Harvard Univ, 20 Oxford St, Cambridge, MA, 02138 The ages of deformational fabrics in regionally metamorphosed rocks are typically constrained by dating bracketing events such as pre- or post-tectonic plutonism or mineral cooling. In some cases, however, ductile deformational fabrics can be dated directly with mineral isochrons by integrating structural, microstructural, and geochronologic observations. This approach is based upon experimental data indicating that extensive chemical exchange can occur among deforming minerals by the ductile deformation mechanisms of dislocation creep and grain boundary diffusion creep (i.e., pressure solution), even if metamorphic temperatures are too low to permit significant exchange by volume diffusion through the crystal lattice. In naturally deformed rocks, these two deformation mechanisms are intimately related to the development of recrystallized textures and mesoscopic deformation fabrics. Thus, detailed field and petrographic observations can be used to identify samples likely to have undergone chemical and isotopic exchange by these two deformation mechanisms. Several criteria are used to identify samples where deformation fabrics can be directly dated with mineral isochrons. Constituent minerals should (1) define part of the mesoscopic fabric of the tectonite (e.g., foliation, lineation), (2) exhibit microstructures in thin section indicating that ductile deformation and metamorphic processes have eliminated relict grains (i.e., complete recrystallization has occurred), and (3) remain unaffected by post-tectonic diffusive exchange or retrogression. Minerals that do not satisfy these three criteria yield scatter on isotope diagrams. Coexisting minerals that do satisfy these criteria constitute a deformationai mineral assemblage. By analogy with the concept of a metamorphic mineral assemblage, minerals of a deformational assemblage undergo chemical and isotopic exchange during ductile deformation under a given set of conditions (e.g., P, T, bulk composition). For a given deformational assemblage, constructing isochrons with three or more minerals in multiple radiometric systems provides a rigorous test of whether equilibration was achieved during deformation, and whether mineral isotope systems were disturbed after that time. Two examples from the late Proterozoic crystalline rocks of the New England Appalachians (Willimantic dome) illustrate the principles described above. At one locality, mylonitic amphibolites were totally recrystallized during dynamic recrystallization and grain boundary diffusive mass transfer at 500-550°C in a major shear zone. Virtually identical Sm-Nd, Rb-Sr, and U-Pb mineral isochrons (272±7 Ma, 274±15 Ma, 258±6 Ma, respectively) plus structural and geochronologic relations within neighboring samples indicate that the minerals achieved complete equilibration by these ductile deformation processes, and underwent only very limited isotopic exchange during cooling. In a porphyroclastic gneiss (i.e., incompletely recrystallized) structurally beneath the mylonitized amphibolite, U-Pb analyses of sphene reveal rare sphene porphyroclasts with late Precambrian radiogenic signatures, and a dominant population of clear sphene euhedra that grew during gneiss formation at 304±2 Ma. Rb-Sr and Sm-Nd mineral compositions form scattered arrays due to relict, pre-300 Ma radiogenic components (within fragments of sphene, allanite, and feldspar porphyroclasts) and to partial exchange during the later, non-penetrative deformational overprint during mylonitization in the overlying amphibolite at -270 Ma. Combined with isotopic and structural studies in the overlying sequence of metasediments, the ability to identify discrete ductile deformation events at the Willimantic dome constrains the age of tectonism along map-scale structures and the amalgamation of distinct rock groups in this region. Selected References Ductile deformation mechanisms: Drury, M.R., and Urai, J.L., 1990, Deformation-related recrystallization processes: Tectonophysics, v. 172, p. 235-253. Poirier, J.P., 1985,Creep of crystals; high temperature deformation processes in metals, ceramics, and minerals, Cambridge University Press, Cambridge, U.K., 260 pps. (chapters 2, 4, 6, 7) Suppe, J., 1985, Principles of structural geology, Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 537 pps. (chapters 4 and 10) Tullis, J., and Yund, R.A., 1985, Dynamic recrystallization of feldspar: A mechanism for ductile shear zone formation: Geology, v. 13, p. 238-241. Tullis, J., and Yund, R.A., 1991, Diffusion creep in feldspar aggregates: experimental evidence: Journal of Structural Geology, 13,987-1000. Chemical / isotopic exchange during ductile deformation: Getty, S.R., and Gromet, L.P., 1992, Geochronologic constraints on ductile deformation, crustal extension, and doming about a basement-cover boundary, New England Appalachians, American Journal of Science, 292:359-397. Gromet, L.P., 1991, Direct dating of deformational fabrics, in Heaman, L., and Ludden, J.N., editors, Applications of Radiogenic Isotope Systems to Problems in Geology: Toronto, Mineralogical Association of Canada, Short Course Handbook 19, p. 167-189. Yund, R.A., and Tullis, J., 1991, Compositional changes of minerals associated with dynamic recrystallization: Contributions to Mineralogy and Petrology, v. 108, p. 346-355. Radiogenic isotopes and mctamorphic mineral growth: Burton, K.W., and O'Nions, R.K., 1991, High-resolution chronometry and the rates of metamorphic processes, Earth and Planetary Science Letters, 107:649-671. Christensen, J.N., Rosenfeld, J., and DePaolo, D.J., 1989, Rates of tectonometamorphic processes from Rubidium and Strontium isotopes in garnet, Science, 244:1465-1469. Mezger, K., Hanson, G.N., and Bohlen, S.R., 1989, U-Pb systematics of garnet: dating the growth of garnet in the late Archean Pikwitonei granulite at Cauchon and Natawahunan Lakes, Manitoba, Canada, Contributions to Mineralogy and Petrology, 101:136-148. Selected Figures Figures are adapted from Getty and Gromet (1992), except for table of isotope exchange mechanisms and underlying compositional profile of "recrystallized" feldspar grain (Fig. 3). Figures 1. Generalized geologic map of central and southern New England with sample locality at the Willimantic dome, Connecticut Figure 2. Schematic diagram of structural relations at the Willimantic dome, and approximate structural positions of mylonitized amphibolite (1) and augen gneiss (2) discussed in abstract. Isotopic data for two metasediment samples (3 & 4) are shown in Figure 6. Figure 3. Profile of feldspar compositional variations across "recrystallized" matrix grain. Figure 4. Sm-Nd, Rb-Sr, and U-Pb relations in the mylonitized amphibolite. Figure 5. Sm-Nd and U-Pb relations in the porphyroclastic gneiss. Figure 6. U-Pb and Sm-Nd relations from two metasediment samples (3&4) structurally overlying the mylonitized amphibolite and porphyroclastic gneiss (see fig. 2). Figure 7. Summary diagram of structural and metamorphic events at the Willimantic dome. AVALONIAN BASEMENT (Esmond-Oedham) AVALONIAN BASEMENT (Hope Valley) t 50 km NW SE f/f- pinch-and-swell zone high-angle low-angle normal shear normal shear cross-section to stretching direction Distinctions among Mechanisms of Isotopic Exchange Volume Diffusion: - random motion of atoms through a crystal lattice. - in general, diffusivities are variable for different radiometric systems in a given mineral. - isotopic exchange is strongly temperature-dependent and favored by fine grain sizes. - no rock fabric modification. Dynamic Recrystallization: - strain accommodated by dislocation glide. - driven by differences in strain energy (i.e., variable dislocation densities) either between adjacent grains or within«different portions of a grain. - affects all radiometric systems equally in recrystallizing grains. - isotopic exchange is controlled by rate and extent of recrystallization. - characterized by grain-size reduction, polygonal grains, highly variable dislocation densities. Grain Boundary Diffusion Creep: - strain accommodated by dissolution, grain boundary diffusion, and reprecipitation. - driven by chemical potential gradients. - affects all radiometric systems equally in dissolving grains. - isotopic exchange is strongly favored by fine grain sizes and grain boundary fluid phase. - characterized by evidence for grain growth and grain dissolution, low average dislocation densities. 50 X anorthite Mylonitized Amphibolite (mole %) "recrystallized" matrix 45 feldspar grain 40 35 30 rim core rim 25 20 40 60 80 100 120 140 Distance (fim) 0.51320- 0.51300- Sphene 0.51280- Hornblende Apatite 0.51260- Plagioclase (3) whole rock Epidote 0.51240- 147 Sm/ 144Nd 0.51220. i i r 0.10 0.20 0.30 0.40 0.50 0.70855- 87Sr/ 86Sr Mylonitic Amphibolile 0.70755- Hornblende 0.70655- whole rock 0.70555- Spltene Plagioclase 0.70455- Epidote Apatite 87Rb/ 86 Sr 0.70355- 0.20 0.40 0.60 0.80 206 pb/ 204 pb 60 Mylonitic Amphibolite 40 20 Plagioclase Epidote 200 400 600 800 1000 0.51320- 143Nd/ 144Nd 0.51300- Basement Gneiss Sphene 0.51280- I Apatite Hornblende 0.51260- Plagioclase whole rock 0.51240- ' I Allanite Epidote 147Sm/ 144Nd 0.51220- 0 0.10 0.20 0.30 0.40 0.070 206 Pb/ 238U 420 Ma 0.065 - Basement gneiss \ Sphene 380 Ma large, brown 0.060 - sphene porphyroclasts Intercepts 300±4 and 625±30 Ma 0.055 - 340 Ma (mswd = .86) 0.050- 300 Ma 500-800 Jim \ clear euhedra 0.045 - and bulk sphene 150 Jim ,£^7 bulk sphene 207 Pb/ 235U (^ clear, euhedral sphene 0.040 1 I I r i i i I r 0.280 0.330 0.380 0.430 0.480 0.530 lozenge interior high-grade pelitic gneiss sample 3 lozenge-bounding shear mylonitic schist -2m sample 4 206pb/ 238u Pinch-and-Swell Zone 0.065- 400 Ma Monazite -250 |im ^ Pelitic Gneiss (lozenge interior) ^ Mylonitic Schist (shear zone) 375 Ma 0.060- 350 Ma Intercepts (monazite) 392±7 Ma to 286+20 Ma 0.055- (mswd = .18) 325 Ma 207 Pb/ 235U 0.050- 0.37 0.40 0.43 0.46 0.49 0.51250- 143Nd/ 144Nd Pinch-and-Swell Zone 0.51230- Pelitic Gneiss (lozenge interior) <& Garnet 0.51210- Monazite "Feldspar" 0.51190- 147Sm/ 144Nd 0.51170- - 0 0.050 0.100 0.150 0.200 0.250 ljtp^ Intense Mylonitization Formation of Cooling / Avalonian Crust Felsic Plutonism Uplift Gneissic Deformation Avalonian Basement Complex Metamorphism 1 1 1 600 500 400 300 250 200 Age (Ma) RECENT DEVELOPMENTS IN DATING ANCIENT CRUSTAL rLUID FLOW Alex N. Halliday, Matthias Ohr, Klaus Mezger, John T. Chesley, Shun'ichi Nakai, and Charles P. DeWolf Department of Geological Sciences University of Michigan, Ann Arbor Abstract. Several isotopic techniques have recently been and Rb-Sr dating of sulfides, ^Ar-^Ar and Rb-Sr dating developed or substantially improved, allowing the accurate of fluid inclusions, and U-Pb dating of ilmenite/magnetite, determination of the timing of fluid-related processes. sphene, and rutile. While many of these techniques require These include K-Ar, Rb-Sr, and Sm-Nd dating of further evaluation, some have already resulted in new diagenetic minerals in clastic rocks, U-Pb dating of constraints on a variety of crustal fluid flow models. carbonates, Sm-Nd dating of fluorite and uraninite, Re-Os INTRODUCTION The development of reliable geochronology for the growth of specific mineral phases in low-temperature envi The movement of crustal fluids in the geological past is ronments has been slow for several reasons. not easily studied, because the products of such activity 1. The number of minerals demonstrated to have suit generally preserve only partial evidence of the scale of able parent/daughter element ratios for precise geochronol circulation, origins of fluid, and mechanisms responsible ogy was relatively small until recently. for migration. Such fluid movement leads to the redistribu 2. Many of the processes of interest are recorded in mix tion of significant amounts of certain components in the tures of inherited assemblages formed at different times. crust, including hydrocarbons [Burst, 1969], and the As such these phases were not in isotopic or chemical formation of economic concentrations of metals (Cu, Pb, equilibrium. Zn, U) and other raw materials (such as barite and fluorite) 3. Several of the traditional techniques are subject to [Bethke: 1986; Bethke and Marshak, 1990; Sverjensky, resetting or disturbance, particularly those involving meta- 1986; Oliver, 1986; Duane andDeWit, 1988]. Fluids are of stable phases. more fundamental significance than this, however, since 4. The development of some methods has required tech they exercise a critical control on the processes of nical improvements in blanks and mass spectrometry. diagenesis, metamorphism, metasomatism, and melting. As a direct consequence of these problems there has As such, the timing and scale of fluid movements in the been a lack of tightly constrained models for the timing crust are of interest to a far broader range of scientists than and ultimate cause of large-scale fluid movements. those concerned with economic geology per se. Furthermore, the complexity of the systems and ambiguity Our understanding of large-scale crustal fluid flow has of some of the isotopic data that do exist have resulted in been hampered by the paucity of constraints on the timing equivocal interpretations. and magnitude of migration and interaction. Radiogenic isotope geochemistry provides tracers to quantify the interaction between fluids and various crustal reservoirs as GLOSSARY well as methods of dating the products of fluid flow. This Blanks: Analytical backgrounds that must be corrected paper is concerned with the latter of these two applications for or reduced to negligible levels in order for the data to and attempts to point out both the potential and limitations truly represent the composition of the analyzed sample of most of the new techniques, as applied to hydrothermal material. mineralization, diagenesis, and low-grade metamorphism Closure Temperature: Temperature below which (<300°Q. diffusion of the radioactive and radiogenic nuclides is Copyright 1991 by the American Geophysical Union. Reviews of Geophysics, 29,4 / November 1991 pages 577-584 8755-1209/91/91RG-01813 $15.00 Paper number 91RG01813 577* 578 Halliday et al.: DATING ANCIENT CRUSTAL FLUID FLOW 29, 4 / REVIEWS OF GEOPHYSICS effectively negligible or, more strictly, the temperature that 1979; Warden et al., 1990; Walker, 1990] and presents a a slowly cooling mineral had at the time defined by its age severe difficulty to those attempting to infer loss properties [Dodson, 1913]. of feldspars in the low-temperature fluid-rich environments Diagenesis: Chemical and mineralogical changes in a of diagenesis and hydrothermal activity. sediment that take place after deposition including those Such ambiguities surround the often cited conclusion involved in lithification, for example, compaction, loss of that widespread formation of K-feldspar overgrowths and water, low-temperature recrystallization, and later illite in early Paleozoic sedimentary rocks in the Ap replacement. The term is used by some in the context of palachians took place during the Alleghanian Orogeny at processes that occur within a few million years of deposi circa 300 Ma [Hearn and Sutler. 1985; Hearn et al., 1987; tion but more broadly by others. It does not include Elliot and Aronson, 1987]. The data can also be interpreted metamorphic and metasomatic reactions. in terms of partial resetting during burial and deformation Metasomatism: Chemical and, in some instances, [CraddockandvanderPluijm, 1989]. mineralogical modification of rocks via medium- to The ^Ar-^Ar dating of feldspars and K-Ar dating of high-temperature fluids. clays are clearly useful for studying thermal histories [Harrison and McDougall, 1982; Harrison and Be, 1983], for determining minimum ages and timing of hydrothermal TRADITIONAL APPROACHES overprinting [Halliday and Mitchell, 1984; Jackson et al., 1982], or for dating the growth of diagenetic minerals The major problem with traditional chronometers of formed during or immediately following lithification in cmstal-scale fluid flow is that those which are most young sedimentary rocks for which a low-temperature commonly deployed reset easily with mild heating (<100°C) thermal history can be established with some (<200°C), chemical exchange with hydrothermal fluids, or confidence [Aronson and Hower, 1976; Aronson and stress-activated recrystallization. For example, it has long Douthitt, 1986; Lee et al., 1989]. The most reliable K-Ar been known that K-Ar and ^Ar-^Ar dating of hydrother geochronology of ore deposits utilizes 40Ar-39Ar dating of mal feldspars and clays suffer from the problem of coarsely crystallized micas [Snee et al., 1988], combines low-temperature resetting [Halliday, 1977; Halliday and the data with Rb-Sr studies of the same minerals [Jackson Mitchell, 1976, 1984]. While it is well established that et al.. 1982; Bohlke and Kistler, 1986], or is undertaken on these minerals retain argon at temperatures below 100°C a variety of different minerals in a young setting [Bethke et [Ineson and Mitchell, 1972; Bonhomme et al., 1983; al.. 1976]. Aronson and Lee, 1986], it is doubtful that such minerals The U-Th-Pb dating of fine-grained U and Th rich completely retain AT for long periods at higher tempera minerals such as pitchblende and coffinite can suffer tures or in hydrothermal environments. If the thermal analogous problems of Pb loss, although it may be possible history is not well established, as for example in many to discern the original history from the Pb isotopic older rocks, it will be difficult to discern whether clays and compositions [Sluckless et al., 1979; Cunningham et al., feldspars have lost Ar during burial and deformation (in 1982; Ludwig et al., 1984; Hon et al., 1985]. the case of sedimentary rocks) or repeated hydrothermal Model ages offer another rather limited approach in activity (in the case of vein systems) and hence yield ages which an "age" is calculated assuming a specific source for that merely date the last tectonic or thermal disturbance. the components (hence initial isotopic composition). Such Such a disturbance could be of interest and may cor approaches have been used for Pb, Sr, and Nd isotopic respond to fluid flow [Macintyre, 1986], but it is difficult ages [Godwin and Sinclair, 1982; Ruiz et al., 1984; Kesler to be certain whether the apparent ages correspond to the et al., 1988; Halliday et al., 1986, 1990]. However, in growth of the mineral, to later deformation or heating, or many situations the source of components is poorly are geologically meaningless because of partial resetting. constrained, and as a consequence, the results are depend A major problem with feldspars and clays is that there ent on the model chosen. Even if source reservoirs have does not exist at this time a clear understanding of the been characterized in detail, it needs to be established that transport paths for AT loss and why some feldspars are the fluids equilibrated isotopically with the bulk lithologies more retentive than others. Some early models based on rather than with a select assemblage of minerals that were the assumption that the width of alkali feldspar exsolution more susceptible to leaching and reaction with the fluids lamellae defines the effective grain size for diffusion [Halliday etal., 1990]. [Harrison and Be, 1983] have largely been superseded by models that consider argon loss properties to be dominated by submicroscopic pores and domain (or subgrain) NEW APPROACHES boundaries [Parsons et al., 1988; Lovera et al., 1989; Kelley et al., 1989], Certainly, evidence for fluid-related The most promising new techniques generally involve microcracks and. micropores in feldspars is abundant small samples, necessitating low blanks and high- [Montgomery and Brace, 1975; Rodgers and Holland, sensitivity mass spectrometry but utilize decay systems 29, 4 / REVIEWS OF GEOPHYSICS Halliday et al.: DATING ANCIENT CRUSTAL FLUID FLOW 579 that have been studied for some time including 87Rb-87Sr, develop. Kelley et al. [1989] report the presence of a ^Sm-M3 Nd.«°K<3»Ar)-«0 Ar, 23I U-206 Pb. and 187Re- component of excess argon in alkali feldspars which can be r i87 0s. degassed easily by mild heating at low temperatures but Of these the 187Re-187Os system has been least studied otherwise results in meaningless total degassing ages using because of difficulties with the chemical preparation and a pulsed laser. These effects need to be carefully evaluated the ionization of Os, traditionally tackled using secondary before further progress can be made. ionization or resonance ionization mass spectrometry. It Some recent studies of fluid-induced clay diagenesis in has recently been shown that Os isotopic compositions can clastic sedimentary sequences have highlighted the be determined relatively simply and at much higher potential usefulness of Rb-Sr dating of authigenic illite, sensitivity using negative thermal ionization mass provided great care is exercised in eliminating older spectrometry [Creaser et al., 1991]. This has greatly mineral grains that were part of the original sedimentary helped to pave the way for a variety of interesting new detritus and removing nonradiogenic Sr by acid leaching studies using Os isotope geochemistry. Reconnaissance [Clauer, 1976, 1979, 1982; Chauduri and Brootins, 1979; studies of hydrothermal ores and clastic sediments [Luck Ohr et al., 1991]. A more controversial approach has been andAllegre, 1982; Ravizza and Turefdan, 1989; Walker et to use the combined Rb-Sr data for the leachate and for the al.. 1989] indicate considerable fractionation of Re/Os residue from leaching, to define the age of illite growth ratios in fluid-related crustal processes and precipitation of [Erwin and Long, 1989], assuming that exchangeable Sr sulfides, offering potential as a chronometer of crustal fluid has not reequilibrated with later pore fluids since crystal flow. lization of the illite. In certain cases it can be shown that Even though the uses of the other decay schemes have such late reequilibration has in fact occurred and such ages been appraised more fully, the most exciting developments would be meaningless [Ohr et al., 1991]. In contrast, the with respect to dating crustal fluid flow are still in their residues from leaching of fine-grained clay fractions infancy and need to be evaluated carefully on a mineral- (assumed to be pure diagenetic illite) commonly display a by-mineral basis, to determine the closure temperatures reasonable spread in Rb/Sr (possibly inherited from the and general robustness to resetting. In all of these systems rock-dominated pore fluid). The Rb-Sr isotopic data for it is critical that the ratio of the parent element to the such leached diagenetic clays sampled over a considerable daughter element should be relatively high and/or display a depth range (> 1,000 m) can define an apparent isochron, considerable range among a cogenetic suite of minerals thought to define the age of growth of the authigenic illite. and that the amount of radiogenic daughter isotope should Results obtained in this manner have been interpreted in be high relative to background levels (be they "common" terms of simultaneous fluid movement over several inherited components or analytical blank). thousand meters of sediment [Morton, 1985a, b; Ohr et al., In many of the techniques that we now discuss the exact 1991]. host of Ihe parent and daughter elements and the factors There are some critical questions to be addressed in this controlling the fractionation of parent/daughter ratio are ill type of work. For example, what exactly is happening to defined. This is because a number of the new techniques the clay grains during the leaching procedure? Is utilize host minerals into which the radioactive parent "exchangeable Sr" absorbed in some way on the clay element does not readily substitute. For many of these it is surfaces or does it represent submicroscopic growth of far from obvious whether the parent element is hosted in soluble low-temperature phases? Is the exchangeable Sr defects, strained sites, or submicroscopic inclusions of irrelevant or does it record an important aspect of the some minor phase, distinct from the major host mineral. It fluid-mineral interaction history? What controls the is then even more difficult to assess what factors are variations in Rb/Sr in the leached residues of fine-grained controlling the parent/daughter ratios. In certain instances authigenic illite; is it protolith variations in Rb/Sr? If so, this may be of little consequence, but in low-temperature there must surely be some heterogeneity in initial 87Sr/86Sr nonequilibrium environments it is critical to know which in such a rock-dominated diagenetic system. Despite phase and process in the potentially complex, multistage considerable efforts, these important aspects remain largely history is being dated. unresolved. Awwiller and Mack [1989, 1991] have argued that Dating Diagenesis Sm/Nd can be fractionated during diagenesis of fine K-Ar dating of illite and diagenetic K-feldspar over grained clastic sediment. This has been confirmed by the growths have been used very effectively to date the findings of Ohr and Halliday [1990] who have shown that diagenesis of clastic sediments and migration of hydrocar leaching of fine-grained authigenic illite fractions from bons in young sedimentary basins [Lee et al., 1985, 1989; clastic sediments produces a leachable component with Liewig et al., 1987; Girard et al., 1988; Hamilton et al, high Sm/Nd, in apparent isotopic equilibrium with .."' 1989; Barley and Flisch, 1988]. Laser probe ^Ar-^Ar nonleachable diagenetic illite with low Sm/Nd at the time dating of clastic diagenesis, as first illustrated by the work of diagenesis. In this respect, the commonly held assump of York and Hall [1986], has been surprisingly slow to tion that the rare earth elements are immobile in clastic 580 Halliday et al.: DATING ANCIENT CRUSTAL FLUID FLOW 29, 4 / REVIEWS OF GEOPHYSICS diagenesis is clearly incorrect. Research on Paleozoic mineralization. The results obtained so far are interesting low-grade metasediments from the Appalachians and the since the major MVT mineralization in the eastern United Welsh Basin indicate that it may be possible to date fluid States appears to have taken place at circa 380 Ma [Nakai equilibration in older clastic rocks using such a single et al., 1990] and therefore cannot be related to large-scale sample approach [Ohr and Halliday, 1990]. Again, the fluid flow during the Alleghanian Orogeny at 300 Ma questions of what the leachable component represents and [Oliver, 1986; Miller and Kent, 1988]. the mechanisms of Sm/Nd fractionation need to be A potentially very promising technique is the applica addressed. In this respect, it is important to determine the tion of Sm-Nd dating to hydrothermal assemblages that chemical composition of the leachates and examine the fractionate rare earth elements (REE) strongly [Mdller et mineral separates before and after leaching using scanning al., 1976; McLennan and Taylor, 1979; Alderton et al., transmission electron microscopy. There is, however, a 1980; Morgan and Wandless, 1980; Graf, 1984; clear advantage of single sample Sm-Nd leachate-residue Humphris, 1984]. The mechanisms of REE fractionation ages over the Rb-Sr isochron approach, namely that the appear to be variable and are in some instances poorly effect of provenance variations can be eliminated. understood. Complexing involving volatile phases such as In recent years the U-Pb and Pb-Pb methods have found CO2, Cl, and F could potentially play a role, as well as increasing application in the dating of marine carbonates middle REE substitutions into Ca minerals such as CaF2 and their metamorphosed equivalents [Moorbath et al., (fluorite). In addition, the precipitation of REE-enriched 1987; Ja/z/i, 1988; Smith and Farquhar, 198%; DeWolf and phases in hydrothermal systems can lead to marked Halliday, 1989; John et al., 1990]. The high U/Pb changes in Sm/Nd in the fluid. Sm-Nd dating has been commonly found in such rocks is partly a reflection of the applied to heavy REE enriched uraninites [Fryer and high U/Pb of seawater. However, high U/Pb has also been Taylor, 1984], scheelites [Bell et al., 1989], and fluorites found in secondary dolomites [Hoff and Jameson, 1989], [Chernyshev et al., 1986; Halliday et al, 1986, 1990; and U-Pb dating of secondary carbonates associated with Chesley et al., 1991]. Sm/Nd in fluorite can vary by as late fluid movements in limestones and hydrothermal vein much as an order of magnitude in an individual mineral systems may be possible. U-Pb dating of limestones vein, permitting precise (±1%) isochron ages [Chesley et appears to be a relatively robust technique that may record al., 1991]. This technique may be useful for determining the time of early diagenesis [DeWolfand Halliday, 1991] the ages of fluorite-bearing MVT deposits. even when the rocks have been disturbed. For example, the Another powerful approach has been to study fluid Paleozoic limestones of New York State acquired a inclusions in quartz with Rb-Sr, U-Pb, and ^Ar-^Ar secondary chemical magnetization supposedly caused by methods. Rb-Sr dating by total dissolution of quartz, in pervasive fluid flow during the Alleghanian Orogeny which it is assumed that the Rb and Sr are held in fluid [Wisniowiecke, 1983; Jackson et al., 1988; Van der Voo, inclusions, has been highly successful [Powers et al., 1989] yet display no sign of this disturbance in the U-Pb 1979; Shepherd and Darbyshire, 1981; Shepherd et al., systematics of the calcites [DeWolf and Halliday, 1989]. 1982; Shepherd, 1986; Darbyshire and Shepherd, 1987]. The mechanisms of U incorporation are not well under Similar approaches have been adopted by Hemming et al. stood, and it may be a late process [Hoff and Hanson, [1990] utilizing the U-Pb technique. All of these studies i990]. Chiing and Swan [1990] have suggested that are useful but suffer from the uncertainty in the location of variations in U concentration in carbonates may result the Rb, Sr, U, or Pb (fluid inclusion, solid inclusion, or from changes in the CO2 of the fluid, together with host mineral). This may not be a problem if the fluids and selective exclusion of U during precipitation of calcite. host are truly co-genetic, but if the fluid inclusions are U-Pb techniques have also been applied to hydrocarbons wholly or in part unrelated to the growth of the quartz (as themselves Parnell and Swainbank, 1990], and the direct is commonly thought to be the case), the isotopic ages may dating of oil formation or accumulation may be possible in date this later process. Relatively little work has been done the near future. on extracted fluids, and that which exists does not distinguish separate populations of fluid inclusions Dating Mineralization [Norman, 1978; Norman andLandis, 1983; Changkakoti et The Rb-Sr method has been successfully applied to al., 1988]. It may prove possible to separate individual hydrothermal phases such as low-temperature K-rich alkali generations of fluid inclusions, but this is not a trivial task. feldspar with high Rb/Sr, fine-grained muscovites, and For many kinds of fluid inclusions the difficulty of this sulfides [Halliday, 1980; Jackson et al., 1982; Nakai et al., extraction process is the limiting factor rather than blank or 1990; Brannon et al., 1991]. In the case of suifides it is machine sensitivity. unclear where the small amounts (<1 ppm) of Rb and Sr The 40 Ar-39 Ar dating of fluid inclusions has developed are located and what exact mechanism produces the range slowly over the past few years [Kelley et al., 1986; Bdhlke in Rb/Sr. Nonetheless, the method seems to permit the et al., 1987; Kirschbaum et al., 1987; Turner, 1988]. determining of ages of otherwise undateable hydrothermal Turner [1988] shows how, using correlation plots, the assemblages such as Mississippi Valley type (MVT) different Ar components (radiogenic, atmospheric, 29, 4 / REVIEWS OF GEOPHYSICS Halliday et al.: DATING ANCIENT CRUSTAL FLUID FLOW 581 extraneous) can be deciphered in such materials. As with methods complement traditional approaches, some of all of the fluid inclusion techniques, there is the limitation which are more appropriately used to define thermal of measuring unknown mixtures of different generations of histories or date the last significant thermal or tectonic . inclusion fluids, unless the inclusions are of sufficient size event The major developments needed include integrated and age that they can be analyzed on an individual basis isotopic, chemical, and mineralogical studies of the same with laser methods. geological problem. For example, dating clastic diagenesis Some of the most impressive geochronology of could involve combined Rb-Sr, Sm-Nd, and K-Ar dating hydrothermal ore deposits utilizes the power of the studies of authigenic illite and associated phases, in which 40Ar-39Ar dating technique for precise resolution of small the chemical compositions of leachates are fully deter age differences. Snee et al. [1988] report a resolution of mined, and mineral separates and leachate residues are 0.3% in 40Ar-39Ar ages of mica populations from characterized using scanning transmission electron Panasqueira, Portugal. The use of the laser probe ^Ar-^Ar microscopy. More exploratory work is needed and method for dating different phases in hydrothermal mineral anticipated, specifically with low-temperature applications assemblages has so far been barely explored [York et a/., of Re-Os, Sm-Nd dating of diagenesis, U-Pb dating of 1982; Sutler et al., 1983; Hall et al., 1989] but offers hydrocarbons, and ^Ar-^Ar and U-Pb dating of exciting possibilities for future research. hydrothermal and diagenetic phases. Major problems Some of the chronometers that have been developed for remain with our understanding of the location of radioac studying high-grade metamorphism may prove ideal for tive parents in some of the phases of interest, the factors the dating of other, more demonstrative products of controlling parent/daughter ratios, and the effects of acid crustal-scale fluid flow. These new chronometers include leaching. Finally, new techniques are needed for separating Sm-Nd, Rb-Sr, and U-Pb dating of garnet [Cohen et al, phases of interest at the microscopic and submicroscopic 1988; Christensen et al., 1989; Mezger et al., 1989a; scale, especially fluid inclusions from their host minerals. Vance and O'Nions, 1990] and U-Pb dating of sphene Further applications may involve broad-scale integrated [Tucker et al., 1987], monazite [Copeland et al., 1989], approaches using a variety of isotopic methods to study rutile [Mezger et al., 19896], and ilmenite/magnetite large crustal sections and determine the ages of fluid [Burton and O'Nions, 1990]. Corfu and Muir [1989] expulsion from sediments, mineral overgrowths in showed that Precambrian gold mineralization could be aquifers, hydrocarbon migration, and base metal dated using accessory phases that grew from the hydrother mineralization and hence assess the relationships between mal fluids. Similarly, Schandl et al. [1990] utilized these diverse products of crustal fluid flow. With such hydrothermal rutile to date sulflde deposition and associ information it should be possible to formulate dynamic ated alteration. Finally, Zeitler et al. [1990] have been able models of crustal fluid flow that are considerably more to deduce the timing of fluid flow in the formation of reliable than has hitherto been the case. quartz-graphite veins by U-Pb ion microprobe dating of zircon overgrowths. ACKNOWLEDGMENTS. Radiogenic isotopic studies of Accessory mineral U-Pb chronometers are in some crustal-scale fluid flow at the University of Michigan have been respects superior to all others, since they can give very supported from NSF grants EAR 86-16061, 88-04072, 88-05083, high precision (±0.1%) ages, and neither reset readily nor 90-04413, and 90-05516. We are grateful to Bob Bodnar, Paul suffer from the assumptions of isotopic equilibrium critical Dixon, Eric Essene, Lynton Land, Mack Kennedy, Steve Kesler, to the isochron approach. In addition, with the utilization Don Peacor, Rob Van der Voo, Peter Vrolijk, Lynn Walter, Bruce Wilkinson, and many others for discussion. of ion probe techniques they may be especially useful for H. Jay Melosh and Marcia Neugebauer were the editors placing the detailed mineral parageneses into a framework responsible for this paper. They thank Lynton Land and an of absolute time. anonymous referee for their help in evaluating this paper. CONCLUSION REFERENCES The new technique developments in isotope Alderton, D. H. M., J. S. Pearce, and P. J. Potts, Rare earth element geochemistry over the past 5 years have facilitated the mobility during granite alteration: Evidence from southwest England, Earth Planet. Sci. Lett.. 49, 149-165,1980. accurate dating of a wide range of fluid-related as Aronson, J. L., and C. B. Douthitt, K/Ar systematics of an semblages and have opened up new possibilities for acid-treated illite/smectite: Implications for evaluating age and constraining models of relevant geological processes such crystal structure, Clays Clay Miner., 34, 473-482,1986. as diagenesis, brine migration, mineralization, and Aronson, J. L., and J. 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Morgan1, R. I. Grauch2 Mj.S. Geological Survey, Reston VA 2U.S. Geological Survey, Denver, CO Rhenium, osmium and platinum abundances and 187Os/186Os ratios were determined in six Devonian black shales and associated Ni-Mo enriched sulfide layers from the Nick Property, Yukon Territory, Canada and in seven early Cambrian black shale-hosted Ni-Mo sulfide layers from mines at Tianeshan, Guizhou province, and at Ganziping, Daping and Sansha, Hunan province, China. Ni-Mo sulfides at the Nick mine are spectacularly enriched (up to 33,164 ppb) in Re, and enriched in Os to a lesser degree. The Ni-Mo sulfides have distinctly higher Re/192Os than associated black shales, but Pt/Re and Ft/common Os are similar in both black shales and sulfides. The two ore samples lie near a 375 Ma reference isochron with an initial 187Os/186Os between about 1 and 6, similar to the age of deposition of the associated shales. The ores appear to be approximately isochronous with the overlying shales (Figure 1). This suggests that the sulfide layer was enriched in Re, Os and probably the other PGE soon after deposition of the black shales. One black shale sampled immediately beneath the ore layer lies on the Re-rich side of the errorchron and, since deposition, may have gained Re (and Pt) from the overlying Re-rich sulfide. In the Chinese Ni-Mo sulfide samples, Re ranges from 900 to 15,000 ppb. All the sulfides lie near a 530 Ma reference line with an initial ratio between 1 and 6 (Figure 2). As for the Ni- Mo sulfide layer in the Yukon, Re and Os have seen only minor redistribution since soon after the time of deposition of the host shales. Five of the sulfides group closely in 187Os/186Os - 187Re/186Os space, and Re, common Os and Pt ratios are constant these sample five samples, although their locations are separated by as much as 400 km. Two other Ni-Mo sulfides have higher Re/common Os and Re/Pt, and therefore have more radiogenic Os. The Re and PGE enrichment in sulfide layers in both the Yukon and southern China probably have occurred soon after deposition of the host black shales when oxidizing fluids carrying high concentrations of Re and PGE were introduced into the reducing environment characterized by the black shales. Because the sulfide layers have a conglomeratic texture and were somewhat more permeable than the black shales, the fluids were channelled along the sulfide layers. Re and the PGE would have been easily precipitated in the anoxic environment. too 150 o 375 Ma reference line CD initial ratio = 6 co 100 00 o 0 CO 50 Ni-Mo sulfide O Black shale 0 0 10000 20000 18.7 ,186 Re/ 0s Figure i. Black shales and sulfides from Yukon, Canada. 100 80 OT o S 60 530 Ma reference line initial ratio = 6 OT O 40 CO 20 0 0 2000 4000 6000 8000 10000 187 ,186 Re/ Os Figure 2. Ni-Mo sulfides from southern China. 101 MODERN APPLICATIONS OF PRECISE U-PB GEOCHRONOLOGY by T. E. Krogh Precise U-Pb Dating Precise U-Pb geochronology is providing essential, new information to aid in the understanding of a wide variety of geological problems. Lead background levels have been reduced by six orders of magnitude over the past two decades leading to similar reduction in sample size and increase in sample selectivity. Methods that include abrading away geologically- leached or altered surfaces have been developed so that precise, closed-system results are obtained in most cases, (Krogh 1982). In ensimatic regimes zircon inheritance is'generally absent so ages for volcanism, intrusion and ophiolite formation with geologically-meaningful errors of ± 1 or 2 Ma are routinely achieved, (Dunning and Krogh 1985, Krogh et al., 1988 Davis et al 1985, Corfu and Ayres 1991). In Davis et al. (1985), we report 6 ages for two adjacent rhyolite horizons collected over a 15 km interval that have a range in age of 1.5 m.y. at 2735.5 Ma. Post-accretion Archean rocks, and young continental arcs can be more challenging since inherited zircons are common (Figs. 1-4). Selection of specific grain types and extremely small samples can aid in avoiding such problems but tests for inheritance must be made. Xenocrysts may be identical morphologically to cognate grains. A special case occurs when single visibly-cored grains provide an age for the granite protolith (Fig.5). In regions of rapid continental overthrusting such as the Grenville Front, where all Ar systems are reset (Haggart, et al. 1992 sub.), both the thrusting and the preceding metamorphic history can be determined by using partially to completely reset or newly- grown titanite, monazite and zircon (Figs.6-8). A special case occurs when coronitic gabbros are found to contain zircon forming at the expense of baddeleyite. These date the time of metamorphism (Fig.9, Davidson and van Breemen, 1988). In regions of more severe overthrusting and metamorphism, titanite and monazite are commonly completely reset while zircon U-Pb systems are preserved even under granulite conditions (Figs. 10, 11). Slow cooling may provide titanite ages younger than the zircon lower intercept. Results for the Kapuskasing granulite terrane indicate successive stages of horizontal laminations and post-accretion dehydration and rehydration suggestive of infra-crustal and crust-mantle delamination, (Figs. 12-16, T.Krogh submitted). Precise ages for these lower crustal processes and for gold deposits in nearby greenstone belts show that both are coeval and post-date magmatism by 20 to 95 Ma. (Fig. 17, Jemielita et al. 1990). Precise ages for diabase dyke emplacement utilizing baddeleyite, or perovskite provide a means of dating continental rifting. (Figs. 18, 19, LeCheminant and Heaman, 1989). These data demonstrate coeval dyke emplacement on 2,000 km scale. Continental plate interactions produce sediments which can be traced to their sources by using the chemically-inert, mechanically-resistant mineral zircon. For example, the Meguma zone of Nova Scotia shows affinity with North Africa, (Keppie and Krogh 1990) and the Torridonian sandstone of Scotland could be derived from Laurentia (Figs. 20-23). An exceptional example is provided by data for single zircons from the K-T boundary layer that exhibit varying degrees of shock and provide ages for both the K-T event and the impact site at 65.5±3 and 550±10 Ma, respectively. References 1. I.E. Krogh, Improved accuracy of U-Pb zircon ages by the creation of more concordant systems using an air abrasion technique, Geochimica et Cosmochimica Acta v. 46, 637-649, 1982. 2. G.R. Dunning and T.E. Krogh, Geochronology of ophiolites of the Newfoundland Appalachians, Can. J. Earth Sci., v. 22, #11, 1659-1670, 1985. 3. T.E. Krogh, D.F. Strong, S.J. O'Brien and V.S. Papezik, Precise U-Pb zircon dates from the Avalon Terrane in Newfoundland, Can. J. Earth Sci. 25, 442-453, 1988. 4. D.W. Davis, T.E. Krogh, J. Hinzer and E," Nakamura, Zircon dating of polycyclic volcanism at Sturgeon Lake and implications for base metal mineralization, Econ. Geol. v. 80, 1942-1952, 1985. 5. F. Corfu and LD. Ayres, Unscrambling the stratigraphy of an Archean greenstone belt: a U-Pb geochronological study of the Favourable Lake belt, northwestern Ontario, Canada, Precamb. Res. 50, 201-220, 1991. 6. M.J. Haggart, R.A. Jamieson, P.M. Reynolds, T.E. Krogh, C. Beaumont and N.G. Culshaw, Last gasp of the Grenville Orogen Thermochronology of the Grenville Front Tectonic Zone near Killarney, Ontario. Sub. Journ. of Geol., July, 1992. 7. A. Davidson and O. van Breemen, Baddeleyite-zircon relationships in coronitic metagabbro, Grenville Province,' Ontario: implications for geochronology. Contrib. Mineral Petrol., 100, 291-299, 1988. 8. T.E. Krogh, High precision U-Pb ages for granulite metamorphism and deformation in the Archean Kapuskasing Structural Zone, Ontario: implications for structure and development of the lower crust. Sub. Earth Planet. Sci. Lett. August 1992. 9. A.N. LeCheminant and LM. Heaman, Mackenzie igneous events, Canada: Middle Proterozoic hotspot magmatism associated with ocean opening, Earth Planet. Sci. Lett. 96, 38-48, 1989. 10. S. L Kamo, C.F. Gower and T.E. Krogh, A birthdate for the lapetus ocean? A precise U-Pb zircon and baddeleyite age for the Long Range dykes, S.E. Labrador, Geology, 17, 602-605, 1989. 11. T.E. Krogh and J.D. Keppie, Age of detrital zircon and titanite in the Meguma Group, southern Nova Scotia, Canada: Clues to the origin of the Meguma Terrane, Tectonophysics, 177, 307-323, 1990. 12. T.E. Krogh and S.L Kamo, U-Pb isotopic results for single shocked and polycrystalline zircons record 550 - 65.5 Ma ages for a K-T target site and 2700 - 1850 Ma ages for the Sudbury impact event. Sub. Int'l. Conf. on Large Meteorite Impacts and Planetary Evaluation, Sudbury, Ontario, August 1992. 13. R.D. Tucker, T.E. Krogh, R.J. Ross, Jr. and S.H. Williams, Time-scale calibration by high-precision U-Pb zircon dating of interstratified volcanic ashes in the Ordovician and Lower Silurian stratotypes of Britain, Earth and Planet. Sci. Lett., 100, 51-58, 1990. 14. R.A. Jemielita, D.W. Davis and T.E. Krogh, U-Pb evidence for Abitibi gold mineralization postdating greenstone magmatism and metamorphism, Nature, v.346, No.6287, 831-834, 1990. Figure Captions Fig. 1 U-Pb isotopic results for a single zircon tip and several microgram multigrain zircon fractions for an Archean rhyolite quartz porphyry flow. Fig. 2 U-Pb isotopic results for single and multigrain fractions for an intrusive granodiorite that cuts the volcanic pile dated in Fig.1. Fig. 3 Data for two samples from similar volcanic units, one from New Brunswick, the other from Maine, indicate identical ages and inheritance. Fig. 4 Data for a Nova Scotia granite that illustrate how inherited components can be avoided to provide a precise age of intrusion. Fig. 5 Large, visibly-cored grains from two Nova Scotia !Sf type granites indicate a common circa 630 Ma protolith. Data for other grains and circa 630 Ma, grain fragments plot between 372 Ma and about 2000 Ma. Fig. 6 Titanite U-Pb data from the Grenville Front Zone south of Sudbury, Ontario. Note that these "Grenville" gneisses are pre-Grenville. Fig. 7 U-Pb data for variably reset monazite, new titanite, and new zircon tips (the latter with ages of 987, 987 and 986 Ma) from the Grenville Front north of North Bay, Ontario. Fig. 8 U-Pb data for titanite, monazite and zircon from a 200 by 100 km zone in the Grenville Front of Labrador. The insert shows data for selected core- free new growth zircon from a Grenville-thrusting-induced melt pod in a 1650 Ma batholith. Fig. 9 U-Pb data for primary skeletal zircons and new microcrystalline zircon from the Grenville Front tectonic zone in Labrador. New grains define the time of coronite formation at 995±5 Ma. Fig. 10 U-Pb zircon results for a least-migmatized norite sample (sample 1A), and a highly-reconstituted, melted and deformed sample (sample 2). Note the correlation between degree of discordance and field appearance. Fig. 11 U-Pb zircon data for variably-discordant grains from an Archean granodiorite in a Proterozoic granulite terrane. The most and the least discordant grains were selected on the basis of lustre and have 50 and 500 ppm uranium, respectively. Fig. 12 Location map showing main structural elements of the Superior Province and the Kapuskasing structural zone. Fig. 13 Geological relationships in the study area. Fig. 14 U-Pb isotopic results for selected grains and grain fragments representing successive zircon growth stages. Fig. 15 U-Pb isotopic duplicate results for small and large grains from 200-600 g conglomerate clasts. Fig. 16 Schematic diagram illustrating how ages of ductile and brittle deformation young with depth. Fig. 17 Isotopic results for titanite and rutile from the Camflo gold deposit. Fig. 18 Map showing the extent of the MacKenzie dyke swarm. Fig. 19 U-Pb isotopic ages for baddeleyite from dykes in the MacKenzie dyke swarm. Fig. 20 Overview of U-Pb zircon data for detrital grains from the Goldenville Formation. Fig. 21 Detail of Lower part of Fig. 20. Fig. 22 Detail of Upper part of Fig. 20. Fig. 23 Results for detrital grains from the Torridonian sandstone, Scotland.. Fig. 24 U-Pb data for zircons used to date the Ordovician time scale (Tucker, et al. 1990). Fig. 25 Results for variably-shocked and reset zircons from the K-T boundary layer. 105 Pb isotopic composition of Paleozoic sediments derived from the Appalachian orogen. Eirik J. Krogstad, Dept. of Geology, University of Maryland, College Park, MD 20742. In Phanerozoic Earth history, the relatively depleted state of shorter-lived 235U relative to longer- lived 238U has resulted in a subdued growth rate of 207Pb relative to that of 206Pb. Thus, differences in 207Pb/204Pb at similar 206pb/204pb values must date from pre-Phanerozoic times, when the relative growth rate of 207Pb was greater. These differences in 207Pb/204Pb at similar 206pb/204pb are robust indicators of the earliest history of a crust or mantle reservoir, surviving later changes in U/Pb that may be due to melting, metamorphism, or sedimentary reworking. Distinct Pb isotopic compositions of discrete crustal blacks have been used as a tracer of magmas derived from those blocks. In the Appalachians, Ayuso (1986) and Ayuso and Bevier (1991) have used the 207Pb/204Pb differences between Devonian granites to trace their sources in either Laurentian ("Grenville") lithosphere, or allochthonous, docked ("Avalonian") lithosphere. If the Pb isotopic composition of Avalonian lithosphere is unique to that source, among all lithospheric reservoirs in the Appalachian orogeny, then the sediments shed off the orogen should record the first appearance of rocks with this extraneous Pb isotopic composition as they become accreted. Pb isotopic compositions of Paleozoic sediments in the Appalachians have been determined for a variety of sedimentary, metasedimentary, and basement rocks from three major areas in the orogen. These are N. Maine (colloboration with R. Hon, Boston College), W. New England (collaboration with G. N. Hanson, Stony Brook), and S. Virginia (samples from M. Norman, ANU, and K. Eriksson, VPI). Analysis of samples from Maryland has also been initiated. The high 207Pb/204Pb at similar 206pb/204pb that may ^ indicative of all "outboard" terranes, including Avalonia, occurs in all igneous, metaigneous and -sedimentary rocks in the Waterbury- Bridgeport CT area. It also occurs in rocks younger than middle Ordovician in New York and Maine, and younger than Ordovician in Virginia. Older sediments (Hadrynian, Cambrian), as well as autochthonous basement and paraautothonous basement slices, have lower 207Pb/204Pb at similar 206pb/204pb. The low 207Pb/204Pb at similar 206pb/204pb shown by these rocks may be a locally diagnostic signature of Late Proterozoic Laurentian lithosphere. The high 207Pb/2(^4Pb at similar 206pb/204pb may be a locally diagnostic signature of Late Proterozoic accreted terranes. Rocks with the "accreted terrane" Pb isotopic composition became dominant in the provenance of sediments along the strike of the Appalachian orogen by middle Ordovician time. Because sediments tend to mix materials from various parts of their provenance, "unmixing" of grain populations would seem a logical next step to determining various isotopic sources. Such unmixing studies, stressing highly stable accessory minerals (monazite, zircon), have been made by other workers. These minerals, while preserving U-Pb age information, do not preserve Pb isotopic initial ratios. However, single grain isotopic studies of major minerals (preserved feldspars, etc.) should more accurately represent the compositions of various source components. ALLEGHANIAN CLEAVAGE AND ACADIAN DIAGENESIS IN THE MARTINSBURG FORMATION, EASTERN PENNSYLVANIA: 40Ar/ 39Ar WHOLE-ROCK DATA AND GEOLOGICAL CONSTRAINTS Michael J. Kunk, Robert Wintsch and Jack Epstein 40Ar/ 39Ar age spectrum analysis of whole-rock samples from the Ordovician Martinsburg Formation at Lehigh Gap, eastern Pennsylvania, and structural and stratigraphic constraints support an Alleghanian age for the regional slaty cleavage and an Acadian age for initial diagenesis in these rocks. The 40Ar/ 39Ar age spectra from mudstone and slate samples from the Martinsburg climb from Tertiary to late Proterozoic ages and are'sigmoidal in shape. They are interpreted to reflect simultaneous degassing of a mixture of detrital late Proterozoic muscovite, late Devonian authigenic white mica, and early Permian cleavage-forming muscovite. The 280±10 Ma age of cleavage is calculated by subtracting the total gas ages of a parent mudstone from a daughter slate sample. A similar method is used to calculate the -360 Ma age of authigenic mica in the mudstone sample. These interpretations are supported by the calculated pressure-temperature-time path for these rocks, based on measured sections and inferred Permian tectonic loading. The calculations show that diagenetic conditions consistent with the illitization of smectite were first reached in the Middle Devonian, and that temperature >250°C were first reached in the Early Permian. No regional cleavage was produced in the Martinsburg Formation at Lehigh Gap during the Taconic orogeny--these rocks j were buried by no more than 2 km of overburden prior to deposition of the unconformably overlying Silurian Shawangunk Formation. J.D. Maccbugall References for "Radiogenic Isotopes in Seawater and Sedimentary Systems" Armstrong, R.L. (1971) Glacial erosion and the variable isotopic composition of strontium in sea water. Nature Phys. Sci. 230, 132-133. Brass, G.W. (1976) The variation in the marine 87 Sr/ 86Sr ratio during Phanerozoic time: interpretation using a flux model. Geochim. Cosmochim. Acta 40, 721-730. Burke, W.H., Denison, R.E., Hetherington, E.A., Koepnick, R.B., Nelson, H.F. and Otto, J.B. (1982) Variation of seawater 87 Sr/ 86 Sr throughout Phanerozoic time. Geology 10, 516-519. Capo, R.C. and DePaolo, D.J. (1990) Seawater strontium isotopic variations from 2.5 million years ago to the present. Science 249, 51-55. DePaolo, D.J. and Ingram B.L. (1985) High-resolution stratigraphy with strontium isotopes. Science 227, 938-941. Derry, L.A. and Jacobsen, S.B. (1988) The Nd and Sr isotopic evolution of Proterozoic seawater. Geophys. Res. Lett. 15, 397-400. Derry, L.A. and Jacobsen, S.B. (1990) The chemical evolution of Precambrian seawater: Evidence from REEs in banded iron formations. Geochim. Cosmochim. Acta 54, 2965-2977. Elderfield, H. (1986) Strontium isotope stratigraphy. Palaeogeogr. Palaeoclimatol. Palaeoecol. 57, 71-90. Goldstein, S.L. (1988) Decoupled evolution of Nd and Sr isotopes in the continental crust and the mantle. Nature 336, 733-738. Goldstein, S.L. and O'Nions, R.K. (1981) Nd and Sr isotopic relationships in pelagic clays and ferromanganese deposits. Nature 292, 324-327. Goldstein, S.L., O'Nions, R.K. and Hamilton, P.J. (1984) A Sm-Nd isotopic study of atmospheric dusts and particulates from major river systems. Earth Planet. Sci. Lett. 70, 221-236. Goldstein, S.J. and Jacobsen, S.B. (1988) Nd and Sr isotopic systematics of river water suspended material: Implications for crustal evolution. Earth Planet. Sci. Lett. 87, 249-265. Grandjean, P., Cappetta, H. and Albarede, F. (1988) The REE and 6Nd of 40-70 Ma old fish debris from the West-African Platform. Geophys. Res. Lett. 15, 389-392. Hess r J. r Bender, M.L. and Schilling, J.-G. (1986) Evolution of the ratio of Strontium-87 to Strontium-86 in seawater from Cretaceous to Present. Science 231, 979-984. Hodell, D.A. f Mead, G.A. and Mueller, P.A. (1990) Variation in the strontium isotopic composition of seawater (8 ma to present): Implications from chemical weathering rates and dissolved fluxes to the oceans. Chem. Geol. (Isotope Geoscience Sect.) 80, 291-307. Hooker, P.J., Hamilton, P.J. and O'Nions, R.K. (1981) An estimate of the Nd isotopic composition of lapetus seawater from ca. 490 Ma metalliferous sediments. Earth Planet. Sci. Lett. 56, 180-188. Jacobsen, S.B. and Pimentel-Klose, M.R. (1988a) A Nd isotopic study of the Hamersley and Michipicoten banded iron formations: the source of REE and Fe in Archean oceans. Earth Planet. Sci. Lett. 87, 29-44. Jacobsen, S.B. and Pimentel-Klose, M.R. (1988) Nd isotopic variations in Precambrian banded iron formations. Geophys. Res. Lett. 15, 393-396. m Keto, L.S. and Jacobsen, S.B. (1987) Nd and Sr isotopic variations of Early Paleozoic oceans. Earth Planet. Sci. Lett. 84, 27- 41. Keto, L.S. and Jacobsen, S.B. (1988) Nd isotopic variations of Phanerozoic paleoceans. Earth Planet. Sci. Lett. 90, 395-410. Krishnaswami, S., Trivedi, T.R., Sarin, M.M., Ramesh, R. and Sharma, K.K. (1992) Strontium isotopes and rubidium in the Ganga-Bramaputra river system: Weathering in the Himalaya, fluxes to the Bay of Bengal and contributions to the evolution of oceanic 87 Sr/"fe6 Sr. Earth Planet. Sci. Lett. 109, 243-253. Macdougall, J.D. (1991) Radiogenic isotopes in seawater and sedimentary systems. In Min. Assoc. Canada Short Course Handbook on Application of Radiogenic Isotope Systems to Problems in Geology (L. Heamon and J.N. Ludden, eds. ) , 337- 364. Martin, E.E. and Macdougall, J.D. (1991) Seawater Sr isotopes at the Cretaceous/Tertiary boundary. Earth Planet. Sci. Lett. 104, 166-180. McLennan, S.M., Taylor, S.R., McCulloch, M.T. and Maynard, J. B. (1990) Geochemical and Nd-Sr isotopic composition of deep-sea turbidites: Crustal evolution and plate tectonic associations. Geochim. Cosmochim. Acta 54, 2015-2050. O'Nions, R.K. , Hamilton, P.J. and Hooker, P.J. (1983) A Nd isotope investigation of sediments related to crustal development in the British Isles. Earth Planet. Sci. Lett. 63, 229-240. O'Nions, R.K., Carter, S.R., Cohen, R.S., Evensen, N.M. and Hamilton, P.J. (1978) Pb f Nd and Sr isotopes in oceanic ferromanganese deposits and ocean floor basalts. Nature 273, 435-438. Palmer, M.R. and Edmond, J.M. (1992) Controls over the strontium isotope composition of river water. Geochim. Cosmochim. Acta 56, 2099-2111. Palmer, M.R. and Edmond, J.M. (1989) The strontium isotope budget of the modern ocean. Earth Planet. Sci. Lett. 92 f 11-26. Palmer, M.R. and Elderfield, H. (1985) Sr isotope composition of sea water over the past 75 Myr. Nature 314, 526-528. Palmer, M.R. and Elderfield, H. (1986) Rare earth elements and neodymium isotopes in ferromanganese oxide coatings of Cenozoic foraminifera from .the Atlantic Ocean. Geochim. Cosmochim. Acta 50, 409-417. Peterman, Z.E., Hedge, C.E. and Tourtelot, H.A. (1970) Isotopic composition of strontium in sea water throughout Phanerozoic time. Geochim. Cosmochim. Acta 34, 105-120. Piepgras, D.J. and Wasserburg, G.J. (1982) Isotopic composition of neodymium in waters from the Drake Passage. Science 217, 207- 214. Piepgras, D.J. and Wasserburg, G.J. (1985) Strontium and neodymium isotopes in hot springs on the East Pacific Rise and Guaymas Basin. Earth Planet. Sci. Lett. 72, 341-356. Piepgras, D.J. and Wasserburg, G.J. (1987) Rare earth element transport in the western North Atlantic inferred from Nd isotopic observations. Geochim. Cosmochim. Acta 51, 1257- 1271. Piepgras, D.J., Wasserburg, G.J. and Dasch, E.J. (1979) The isotopic composition of Nd in different ocean masses. Earth Planet. Sci. Lett. 45, 223-236. Popp, B.N., Podosek, F.A., Brannon, J.C., Anderson, T.F. and Pier, J. (1986). 87 Sr/ 86 Sr ratios in Permo-Carboniferous sea water from the analyses of well-preserved brachiopod shells. Geochim. Cosmochim. Acta 50, 1321-1328. Raymo, M.E., Ruddiman, W.F. and Froelich, P.N. (1988) Influence of late Cenozoic mountain building on ocean geochemical cycles. Geology 16, 649-653. Richter, F.M. and DePaolo, D.J. (1987) Numerical models for diagenesis and the Neogene Sr isotopic evolution of seawater from DSDP Site 590B. Earth Planet. Sci. Lett. 83, 27-38. 110 Richter, F.M. and DePaolo, D.J. (1988) Diagenesis and Sr isotopic evolution of seawater using data from DSDP 590B and 575. Earth Planet. Sci. Lett. 90, 382-394. Shaw, H.F. and Wasserburg, G.J. (1985) Sm-Nd in marine carbonates and phosphates: Implications for Nd isotopes in seawater and crustal ages. Geochim. Cosmochim. Acta 49, 503-518. Shimizu, H. , Umemoto, N. , Masuda, A. and Appel, P.W.U. (1990) Sources of iron-formations in the Archean Isua and Malene supracrustals, West Greenland: Evidence from La-Ce and Sm-Nd isotopic data and REE abundances. Geochim. Cosmochim. Acta 54, 1147-1154. Spivack, A.J. and Wasserburg, G.J. (1988) Neodymium isotopic composition of the Mediterranean outflow and the eastern North Atlantic. Geochim. Cosmochim. Acta 52, 2767-2773. Staudigel, H. , Doyle, P. and Zindler, A. (1985) Sr and Nd systematics in fish teeth. Earth Planet. Sci. Lett. 76, 45- 56. Stille, P. (1992) Nd-Sr isotope evidence for dramatic changes of paleocurrents in the Atlantic Ocean during the past 80 m.y. Geology 20, 387-390. Stille, P. and Fischer, H. (1990) Secular variation in the isotopic composition of Nd in Tethys seawater. Geochim. Cosmochim. Acta 54, 3139-3145. Stille, P., Clauer, N. and Abrecht, J. (1989) Nd isotopic composition of Jurassic Tethys seawater and the genesis of Alpine Mn-deposits: Evidence from Sr-Nd isotope data. Geochim. Cosmochim. Acta 53, 1095-1099. Veizer, J. (1989) Strontium isotopes in seawater through time. Ann. Rev. Earth Planet. Sci. 17, 141-167. Veizer, J. and Compston, W. (1976) 87 Sr/ 86 Sr in Precambrian carbonates as an index of crustal evolution. Geochim. Cosmochim. Acta 40, 905-914. Veizer. J., Compston, W. , Clauer, N. and Schidlowski, M. (1983) 87 Sr/ 86 Sr in Late Proterozoic carbonates: evidence for a "mantle" event at ~900 Ma ago. Geochim. Cosmochim. Acta 47, 295-302. Wickman, F.W. (1948) Isotope ratios - a clue to the age of certain marine sediments. J. Geol. 56, 61-66. UPUFT HYDROTHERMAL SEA WATER CIRCULATION A representation of the geochemicai cycling of Sr, showing the important sources and sinks. This figure is modified after that in Palmer and Elderfield (1985). "Limestone" is used here to represent all types of marine sediment that carry Sr of seawater origin, i.e. carbonates in general, SUBDUCTJON evaporites, etc. .7100 .70«5- .7090 .7085- .7075 - .7070 .7005- .7000 TERTIARY CRETACEOUS I JURASSIC fTRIASSIC PERMIAN PENN. MISS. DEVONIAN ISlLURIANj OROOVICIAN CAMBRIAN PC. 100 200 300 500 MILLIONS OF YEARS Figure 1. Plot of 87 Sr/ 86Sr age (or 744 of 786 marine samples. 87 Sr/ 86 Sr values lor the 42 modern marine samples (Table 1) are not shown. Mod ern values, however, were accounted for in drawing band and line. For any given time, correct seawater ratio probably lies within band. Line represents our best estimate of seawater ratio versus lime. Pre-Cenozoic ages are based on van Eysinga (1975). Cenozoic ages are based on time scale provided by L. B. Gibson (1980. personal commun.). Pliocene-Pleistocene boundary is at 1.62 m.y. B.P., and Tertiary stage boundar ies are at 5.0, 23.5, 37.0. and 53.5 m.y. B.P. Fig. 1 from Burke et al., 1982. 112. - Holocene marina carbonete (HMC) ~ A Conlessa Quarry Pleistocene ^1 Pliocene O DSDP site 522 0.7090 ^^ Late Miocene -40 Middle Miocene 0.7088 \ \ ». Early Miocene -80 < \^ Late Oligocene >.» Early Oligocene * -120 *- ^^^"" PIPH i M, , 1 . O, .1 , E. , 1 , Pa, 1 Ma 0 to 20 30 40 SO 60 7 0 C6BH - 140 Age ( 10* years) | C13 | CI2 (C11| CIO f C9 I Cfl « » BarIMJBI Fig. I (left). Measured "Sr/^Sr ratios and A87Sr values oflate Eocene Oligocene Lale Eocene Early Miocene and Oligocene chalks and marls plotted as a function of stratigraphic position as determined by magnetic reversals (//. 20). Numbers on lower scale designate the paleomagnctic chrons (6). The A*7Sr parameter is ihc difference between a measured 87Sr/**Sr value and the value for modern carbonates, multiplied by 10s. Fig. 2 (righl). Measured "Sr/^Sr and A*7Sr values of Ccnozoic marine carbonate samples as a function of age. 0 70920 0 70915- 0.70910 v_ CO «J 0.70905 CO 0.70900 0.70895 0.70890 0 70885 00 05 10 15 20 25 30 35 40 45 Age (Ma } Fig. I. Three-point running average of Sr isotopicdata for the past 8 Ma. The error bars are ±14- 10~ 6 and represent 95% confidence limits. The 87Sr/ 86Sr scawatcr curve is marked by a scries of steep climbs and plateaus, with two slope changes at - 5.5 and - 2.5 Ma, which mark the beginning of steep rises in 87Sr/ 86Sr values. The 87Sr/86Sr record is quite well defined for the Tertiary, but shows much more scatter for earlier times, as is obvious from the Figure from Burke et al. on the previous page. But even hi the Tertiary, the record shows inflections at almost every level of resolution, as can be seen from the examples above. Figs. 1 and 2 (top) are from DePaolo and Ingram (1985); Fig. 1 (below) is from Hodell et aL (1990) 113 The Nd isotopic composition of present day seawater is not constant, unlike the case for ^Sr/^Sr. Fig. 5a (left) shows two Atlantic Ocean profiles from Piepgras and Wasserburg, 1987. --E FIG. 5. a) «Nd(0) as a function of depth for A-II109-1 Station 30 (solid squares). Note the large shift across the base of the thermocline (point D) and the very uniform -5 -10 Keto and Jacobssen (1988) have attempted to construct UJ -15 a "global average" Nd isotope curve for seawater over the past 800 Ma in Fig. 5 (left). Note the inter-oceanic variability. Except possibly for the high values of E Nd -20 near the Permian-Triassic boundary, where the Sr isotopic ratio plummets to low values, there is little correspondence between Sr and Nd isotopic records. -10 O = lndlonr«lhy» jompUj -15 V = North AtlonHc jomplt o =Soulh Allonllc lomplii O =0th*r octort samples -20 200 400 600 800 AGE(Ma) Fig. 5. The global average palcoccanic < Nd curve for the past 800 Ma. This curve (wilh crrorband) is estimated from the curves for individual oceans shown in Figs. 3 and 4. In (a) the t Nd data for the Pacific/Panlhalassa Ocean are piollcd. In (b) dala for all other oceans arc plotted. Note that the global average curve is significantly lower than the Pacific/ Panthalassa data only when the Pacific/Panthalassa was rela tively small in size. i.e.. during the Tertiary and Quaternary. O'Nions et al. (1983) showed that stratigraphic and calculated model ages for crustal sediments diverge for younger rocks (left), suggesting sedimentary recycling. At first glance, Sr isotopes do not support this hypothesis, but Goldstein (1988) proposed that the SU discrepancy is due to open system behavior, with 5,J possibly the addition of small amounts of high Sr content, low ^Sr/^Sr orogenic material to the sedimentary mass. In addition, weathering removes Sr Slrotiqrophic Age (Go) and adds Rb to the sediments. Figs, la, Ib and Ic Fig. 2. Comparison of stratigraphic ages and crustal residence below are from Goldstein (1988). age estimates (/DM) calculated relative to parameters for a model depleted mantle [19], /S=lsua metasediments [20|; FT Fig Tree shales [8]; M = Malene metasediments [20]; L Lewjsian metasedimenls (Table 1); T =* Torridonian sedi ments (Table 1); D - Dalradian (range indicated. Table 1); SU = Southern Uplands (range indicated. Table 1). Stratigraphic age of Fig Tree shales from Barton (personal communication). Fig. 1 Nd and Sr isotopes in Phanerozoic clastic sediments, a, Present-day c Nd plotted against depositional age in Phanerozoic Sr in Palaeozoic sediments (b) are a con -20 ^ sequence of in situ Rb decay, and Sr isotopes are bulfered by input of Sr from outside the sedimentary mass. Histogram and lines have - 2U the same significance as in b. Data are from refs 5-10, 12, 52-54, 0 100 200 300 iOO 500 600 K 61-66, and MPI unpublished data, e NJ = (/ / / ,. - 1) x 1<)4 . where Deoosuionai age (Myr) / is the 143 Nd/ 144 Nd, a refers to the sample and RF. 10 the hulk Earth. /HR = 0.512638 (ref. f.7). 3780 , - i - - _| 0.780 , , i i . i | p t i 0770 I | ~\ 0.770 r ^ 0760 ~ 0.760 -_ t a 0 750 "- 0.750 ~ * c I 0.71.0 n Q740i- ~ "* . ' > t 3 0730 0.730 L I .':': /5 J ... , i ^^i * * * 3 0720 0.720 0.710 t^! .-. ':fi»A ' ^ 0.710 ! \. ' ' ' j i "!'.. : : . . i , . | . i , i . .._! L_^ n inn n inn 1 , 1 , ! , 1 , 1 ! > .. ._ Oeoositwnal age iMyr) Oeposiional age \\5 <*OAr/39Ar STUDIES OF FLUID INCLUSIONS IN VEIN QUARTZ FROM BATTLE MOUNTAIN, NEVADA Edwin H. McKee Fluid inclusions in vein quartz from the radiometrically dated Late Cretaceous Buckingham stockwork molybdenum deposit and from quartz veins associated with radiometrically dated late Eocene to early Oligocene leucogranites near Buckingham yield isochron ages corresponding to these periods of igneous activity. The younger-period (late Eocene to early Oligocene) is clearly defined by three isochrons at about 38 Ma. The Late Cretaceous age is recognized by three isochrons, one well defined at 75.5 ± 1.1 Ma, one that is 55.1 ± 3.7 Ma and one that is 51.2 ± 16.3 Ma. All samples had inherited excess 40Ar in amounts of about 30 percent of the total argon. Because of the excess argon, individual age determinations are highly variable and cannot be interpreted isochrons based on several analysis are necessary to yield a meaningful age. Samples with small amounts of potassium proved unusable; sufficient potassium must be present to have produced enough radiogenic 40Ar to mask the excess 40Ar. CONCLUSIONS 40Ar/*'Ar dating of fluid inclusions in igneous minerals has promise as a means of dating the fluid and hence the age of mineralization assuming that the two are related and nearly synchronous. Several limiting factors are apparent form the quartz samples from the Battle Mountain mining district, Nevada. 1) Excess inherited 40Ar may be present, and should be expected, in the trapped fluid. Because of this a number of analysis are needed to provide points on a 40Ar/3*Ar versus 39Ar/36Ar diagram from which an isochron can be drawn. The slope of the isochron gives the age, the intercept on the ordinate (^Ar/^Ar axis) indicates the amount of excess argon if the value is above 295.5orthe 4°Ar/3«Arofair. 2) Samples with small amounts of potassium which yields proportionally small amounts of 39Aron irradiation are difficult to analyze with good precision and produce points on a ^Ar/^Ar versus 39Ar/*6Ar diagram that cluster near the 40Ar/36Ar axis and are of little value in describing an isochron. Low potassium samples proved nearly unusable in this study. 3) Areas with several periods of igneous activity such as Dattle Mountain (Late Cretaceous and late Eocene to early Oligocene) probably produce several populations of fluid inclusions. At Battle Mountain the youngest period of igneous activity (late Eocene to early Oligocene) proved datable with reasonable confidence. The Late Cretaceous event was evident but obscure. The mechanism for partial argon loss from fluid inclusions and of multiple periods of fluid entrapment in minerals is poorly understood but has a great effect on dating of mixed populations of fluid inclusions by the 40Ar/39Ar technique. K-Ar and 40Ar/39Ar ages of the Buckingham stockwork system and nearby intrusive rocks. Location shown on fig. 2. From McKee 1992. Rock type (host rock fig. 2) Mineral dated Apparent age Ma ± a Buckingham stockwork system Monzogranite porphyry Muscovite 61.3 ±1.5 11 ' " 61.7 ±1.5 Biotite and chlorite 65.1 ±1.6 Muscovite: 68.6 ±1.5 Aplite Whole rock 70.3 ±1.7 Monzogranite porphyry Muscovite 75.7 ±1.6 77.4 ±1.6 , fl " " 85.5 ±1.9 Biotite 85.7 ±0.4 v Muscovite 86.1 ±2.0 88.0 ±2.0 Intrusive rocks north and southwest of Buckingham stock work system Rhyolite Biotite 37.3 ±1.1 Leucotonalite Hornblende 37.7 ±1.4 Monzogranite Biotite 38.8 ±1.1 Hornblende 39.0 ±1.1 Rhyolite Biotite 39.1 ±1.0 Intrusive rock northeast and cutting Buckingham stockwork system Granodiorite porphyry Hornblende 35.4 ±1.1 17 Age from the two greatest release steps from an incremental heating ^Ar/^Ar experiment 3500 3000 2500 < 2000 1500 1000 1471-760 DB1TT121 500 079C77 H147M73 I 40 60 120 160 200 39Ar/36Ar versus ^Ar/^Ar diagram with isochron plots from all samples from the Battle Mountain district. \\c\ REFERENCES Dalrymple, G. B., and Lanphere, M.A., 1971, 40Arfl9Ar technique of K-Ar dating: A comparison with the conventional technique: Earth and Planetary Science Letters, v. 12, p. 300-308. ___1974, 4QArP9Ai age spectra of some undisturbed terrestrial samples: Geochiroica et Cosmochimica Acta, v. 38, p. 715-738. Damon, P.E., and Kulp, J.L., 1958, Excess helium and argon in beryl and other minerals: American Mineralogist, v. 43, p, 433-459. Kelley, S., Turner, G., Butterfield, A.W., and Shepherd, T.J., 1986, The source and significance of argon isotopes in fluid inclusions'from areas of mineralization: Earth and Planetary Science Letters, v. 79, p. 303-318. McKee, E.H., 1992, Potassium-argon and 40Ar/39Ar geochronology of selected plutons in the Buckingham area [in] Theodore and others, 1992, p. Nesmelova, Z.N., 1959, Gases in potassium salts of the Bereznikovsk mine: Transactions Vses. Nauchn.-Issled. Galurgii, no. 35, p. 206-243. Rama, S.N.I., Hart, S.R., and Roedder, Edwin, 1965, Excess radiogenic argon in fluid inclusions: Journal of Geophysical Research, v. 70, p. 509-511. Theodore, T.G., Silberman, M.L., and Blake, D.W., 1973, Geochemistry and potassium-argon ages of plutonic rocks in the Battle Mountain mining district, Lander County, Nevada: U.S. Geological Survey Professional Paper 798-A, 24 p. Theodore, T.G., and Hammarstrom, J.M., 1991, Petrochemistry and fluid inclusion study of skarns from the northern Battle Mountain mining district, Nevada, in Aksyuk, A.M., ed., "Application of Isotope Systems to Geological Problems" USGS Reston, Virginia, USA September 1992 Isotopic provinciality in the shallow mantle, on-craton & off-craton volcanism, and implications for lithospheric growth in the western USA. Martin Adrian Menzies, University of London, England INTRODUCTION Information regarding the temporal and spatial evolution of the continental lithosphere is forthcoming from the study of exposed crustal rocks and high pressure xenoliths. Basement crustal rocks [Zartman 1974] indicate that growth of the circum- cratonic lithosphere of the western USA, in post-Archaean times, occurred to the south and west of the ancient cratonic nucleus in Wyoming-Montana [Ernst, 1988; Hoffman, 1988]. Gradual accretion of oceanic/arc tenranes took place in the early Proterozoic and continued into the late Proterozoic and Phanerozoic when supra-subduction processes dominated. During the late Phanerozoic crustal thickening and extension led to recrystallisation and deformation of, crustal jocks. Intrusive crustal rocks (e.g. volcanic rocks) erupted in late Phanerozoic times [Armstrong 1970], provide a present-day probe of deep lithosphere composition and evolution. Pioneering studies noted lateral changes in the source region of volcanic rocks [Hedge 1966; Doe et al., 1969; Leeman 1970; Hedge and Noble 1971] and the presence of mantle heterogeneity in the deep lithosphere. Several decades later the presence can be demonstrated of unique on-craton reservoirs and "oceanic" off-craton reservoirs. Moreover the coincidence of these lithospheric domains with crustal age provinces is marked and their tectonic context similar to that of crustal rocks. High pressure xenoliths preserve a history of on-craton and off-craton isotopic provinciality that is consistent with deductions made from crustal rocks - (a) formation of a >2500 Ma cratonic nucleus in Montana-Wyoming stable to depths in excess of 150km; (b) modification of that cratonic keel by post-Archaean processes (subduction); (c) circum-cratonic accretion of oceanic lithosphere incorporating a recycled lithospheric component (eclogites), and (d) asthenospheric upwelling and the formation of young continental lithosphere in regions of Phanerozoic extension (Figure 1) Figure 1. Peridotite stability fields bencaih the continental crust. Note the predominance of garnet peridotites (GP) beneath the craton, spinel pcridotite (SP) beneath mobile belts and the overall paucity of ph'gioclase peridotites (PP) except in regions of considerable crustal extension. Lithospheric architecture changes in a similar fashion from the Basin and Range (oceanic) to the Wyoming-Montana craton (cratonic). \oL\ ON-CRATON & OFF-CRATON XENOLITHS Lithospheric mantle comprises a mechanical boundary layer (MBL), which provides an isolated repository for the development of aged isotopes. The thermal boundary layer, at the base of the MBL, acts as an important buffer between the rigid cold lithosphere and the hot convecting asthenosphere believed to have the characteristics of MORE (mid-ocean ridge basalt) or OIB (ocean island basalt). Heat flow and seismic data reveal that convecting asthenosphere occurs at a shallow depth beneath the Basin and Range and the southern Rio Grande rift thus insuring that the TBL has the characteristics of MORB/OIB. Consequently a thick, heterogeneous MBL has not survived in parts of California, Arizona and New Mexico but seismic tomographic data [Grand 1986] and the occurrence of diamondiferous kimberiites indicate that a thick MBL exists elsewhere in Montana, Wyoming and northern Colorado. ON-CRATON XENOLITHS Geochemical data on xenoliths from within the cratonic part of the western USA are restricted to the Crazy Mountains [Dudas et a/., 1987] and the Highwoods [Irving &. Carlson 1991]. The Crazy Mountain xenoliths have isotopic ratios similar to the Leucite Hills and Crazy Mountains magmas (EM1) and the Highwoods xenoliths much higher 87Sr/86Sr and lower 143Nd/144Nd ratios (EM2)(Figure 2). The approximate range of on-craton xenolith data is 87Sr/86Sr = 0.706-0.769 and 143Nd/144Nd = 0.5120- 0.5105, in part equivalent to EM1 and EM2 domains. Recent Re-Os data for the Highwoods reveal melt extraction in the late Archaean and melt migration in the late Archaean to early Proterozoic. Ancient metasomes with extremely low 143Nd/144Nd ratios may be important in the genesis of on-craton potassic and ultrapotassic volcanic rocks. OFF-CRATON XENOLITHS In contrast to the on-craton xenoliths, the off-craton xenoliths of the western USA are amongst the most intensively studied in the world [Eggier et ai., 1987; Wilshire et a/., 1988 for comprehensive review]. Basalt-borne xenoliths are characterised by 87Sr/86Sr = 0.7018-0.7065 and 143Nd/144Nd = 0.51345-0.51240 (Figure 2) similar to depleted oceanic domains (DMM and OIB) with a propensity toward an enriched arc component (EM2) in some xenoliths (e.g. Sierran Province, Colorado Plateau). This isotopic range is significantly different from that of on-craton xenoliths and to a large degree this difference reflects time and not necessarily the enrichment process. Overall off-craton xenoliths indicate that several enrichment processes have affected the liihosphere in post-Archaean times. An integration of peirological, geochemical [Kempton et al., 1987] and isoiopic [MenziesQl al., 1985] data reveal that the depleted mantle protolith (formed in the Proterozoic) was enriched by suprasubduction and intraplate processes in the Proterozoic to Phanerozoic (Memi.es, 1990]. The spatial relevance of such chronological information has been investigated beneath the Colorado Plateau where the lower lithosphere is chemically stratified [Roden et ai., 1990]. Immediately beneath the crust the liihosphere comprises a depleted spinel peridotite protolith (87Sr/86Sr = 0.703), most probably produced and stabilised in the Proterozoic, which has been enriched (87Sr/86Sr < 0.706) in the Proterozoic and Phanerozoic by upwelling melts from sub-lithospheric sources. 0.5135 KEY: OFF - CRATON O GERONIUO * KX.BOURNE HOLE 0.5130 X SAM CARLOS Q SIERRAN PROVINCE S THE THUMB O LUNAR CRATER ^ CRAZY MOUNTAINS 0 WEST POTRIULO (3 GRAND CANYON 0.5125 * HOOVER 0AM Figure 2 - Sr and Nd isotopic variability in xenoliihs from ihe western USA. Note that the on-craton lower liihosphere is enriched (EM1/EM2) and the off-craton lower liihosphere is primarily depleted with a EM2 propensity toward enriched (arc) 0.5120 compositions (EM2). ON - CRATON 0.5115 EM1 0.5110 0.702 0.704 0.706 0.708 0.710 "Sr/"Sr 0.5135 OFF -CRATON KEY: O GERONtttt + KUOURNE HOLE ECLOGrTES X SAN CARLOS 0.5130 O SCRRAN PAOVMCE * THE THUMB O LUNAR CRATER * CRAZY MOUNTAINS El WEST POTRUO O GRAND CANYON 0.5125 * HOOVER 0AM Figure 3. Sr and Nd isotopic variability in volcanic rocks and xcnoliths from the western USA. Off-craton volcanic rocks 0.5120 have mantle sources broadly similar to mid- ocean ridge basalts (Geronimo, Arizona), ON CRATON ocean island basalts (Lunar Crater, Nevada) or island arcs (Navajo, Sierran Province). On-craton volcanic rocks have a source component that appear to be unique to the lower lithosphere beneath the Archaean crust 0.5115 (after Menzies 1989). CRUSTAL THICKNESS 4 AGE {HII > SO km (> 2.7 b.y.) PH < 50 km (1.0-2.5 b.y.) EM1 0.5110 0.702 0.704 0.706 0.708 0.710 ON-CRATON AND OFF-CRATON VOLCANIC ROCKS In general, throughout the western United States elemental abundances and isotopic ratios in volcanic rocks (Figure 3) vary in accordance with the age of the basement and the thickness of the underlying crust [Leeman 1982, Menzies 1989]. ON-CRATON VOLCANIC ROCKS Alkaline/potassic/ultrapotassic volcanic rocks are found within the craton in the Highwood Mountains, Elkhead Mountains, Smoky Butte, Crazy Mountains, Independence, Leucite Hills and Bearpaw Mountains [Vollmer et aL, 1984; Fraser et aL, 1985; Meen and Eggler, 1987; Leat et aL, 1988; O'Brien et aL, 1991; MacDonald et aL, 1992] (Figure 3). On-craton alkaline volcanic rocks exhibit a range in 87Sr/86Sr=0.704-0.710 and 143Nd/144Nd=0.5126-0.5113 very different from that observed in oceanic volcanic rocks. While tholciitic volcanic rocks from the Yellowstone Plateau Volcanic Field and the Snake River Plain [Leeman 1982; Doe et aL, 1982; Menzies et aL, 1983] are also erupted within the craton they have less extreme isotopic ratios similar to ihe Sierran Province volcanic rocks (Figure 3). Although the origin of these "flood basalts" is debated [Carlson et aL, 1981; Carlson 1984] the alkaline to ultrapotassic magmas are believed to be wholly derived from within the Archaean lower lithosphere. This cratonic domain is preserved in a region of low heat flow and thick crust (50 km) similar to the Kaapvaal cralon of South Africa. It is apparent from Figures 3 & 4 that the cralonic lithosphere has a unique isotopic character and location, a result of both process and, more importantly, age. OFF-CRATON VOLCANIC ROCKS Off-craton alkaline and tholeiitic volcanic rocks have been intensively studied within the Great Basin, Colorado Plateau and the Rio Grande Rift [e.g. Hedge 1966; Doe et aL, 1969; Leeman 1970; Hedge and Noble 1971; Van Kooten 1980, 1981; Leeman 1982; Menzies et aL, 1983,1985,1991; Hart 1985; Perry et aL, 1987; Fitton et aL, 1988; Leat et aL, 1988; Ormerod et aL, 1988; Farmer et al 1989; Lum et aL, 1989; Fitton et aL, 1991; Kempton et ai.,. 1991]. The difference between on- and off-craton volcanic rocks is immediately apparent [Figure 3] and is similar to the differences observed between on-craton and off-craton kimberlites in South Africa [Smith 1983], In general off-craton volcanic rocks fall into two groups (a) those derived from sources similar to the source of oceanic magmas, or (b) those derived from an "arc" source with elevated LIL/LREE ratios. It can be inferred from these data that the cralonic nucleus in Wyoming-Montana is surrounded by accreted Proterozoic lithospheric domains with some of the attributes of oceanic lithosphere formed at active margins [Ernst 1988; Ormerod et aL, 1988]. These mantle domains are characterized by 87Sr/86Sr < 0.707 and 143Nd/144Nd > 0.51240 [Fitton et aL, 1988]. "Arc" like lower lithosphere is evident in recently enriched (<200 Ma) off-craton xenoliths from the western USA [Mattey et aL, 1989], In contrast regions of thinned continental crust and high heat flow are characterised by the presence of mantle identical to the source of mid-ocean ridge or ocean island basalts (Figure 4). This presumably replaced most of the pre-existent "arc" like lithosphere in the southern Basin and Range and the Great Basin [Menzies et aL. 1983]. Many Basin and Range xenoliths can be interpreted as fragments of 13,3 recently accreted (< 200 Ma) MORE or OIB mantle - the compositional antithesis of the on-craton source for potassic volcanic rocks. Figure 4 - Mantle source character for volcanic rocks in relation to crustal thickness. While the EM1 domain (filled circles) appears to be unique to the thick crust of the Wyoming-Montana craton. the sub-lithospheric DMM sources (open circles) are dominant in the areas of thin crust in California. Nevada, Arizona. & New Mexico. Accretion of lithosphere during destructive plate processes in the Proterozoic and Phanerozoic may account for the enriched ("arc") character (EM2) (half- filled circles) of the circum-cratonic lithosphere. Accretion of young intraplate lithosphere explains the presence of depleted (DMM/OIB) shallow mantle in the Basin and Range, a region where crustal extension has permitted upwclling of asthcnosphcre (after Memies 1989). CRUSTAL EXTENSION & SOURCE HETEROGENEITIES Localized isotopic provinciality has been recently reported in the Western Great Basin [Ormerod et al., 1988: Farmer et al., 19891 and the Rio Grandc rift [Perry et al^ 1987,1988: Menzies et al.. 1991). In the Western Great Basin, elemental and isotopic data for volcanic rocks indicates participation of depleted asihcnosphcric and enriched lithospheric mantle sources. These two sources correlate with depleted mid-ocean ridge mantle (i.e., DMM) and enriched mantle (i.e., EM2), respectively. In contrast, systematic temporal variations in the chemistry of magmatism close to the Rio Grande rift has been interpreted as the result of involvement of two isotopically depleted mantle sources (87Sr/86Sr < 0.7045) [Perry et al., 1987, 1988]. One of these source regions is similar to MORB and is believed to be located in the asthcnosphcre and the other, which has a slightly higher 87Sr/86Sr and slightly lower 143Nd/144Nd ratio lhan MORB, is believed to be located in the lithosphere (i.e., OIB). Depleted (5j7Sr/S6Sr < 0.7045) and enriched (87Sr/86Sr > 0.7045) sources arc reported from the Zuni-Bandcra volcanic field. New Mexico [Menzies et al.. 1991]. As in other models the depleted component is believed to be sub-lithospheric cither as pan of the MORB source or a plume OIB source. The enriched source has intraplate characteristics and is unlike the enriched "arc" like lower lithosphcre encountered elsewhere. It is suggested that this enriched source occurs within the lower lithosphere but may represent "plume" contaminated lithosphcre (Figure 5). In principle, the models proposed for the Rio Grande rift [Perry et al., 1987,1988; Menzies et al.. 1991] arc similar to that invoked for the Big Pine Volcanic field in the western Great Basin [Ormerod et al., 1988], but in all cases the enriched lithospheric mantle reservoirs are isotopically and genetically different. 200 km ZBVF CRUST SANCARLOS SPRINCERVHXE ZBVF ; Residual Iherzolite 100km ; protolith O m T3 '7Sr/ "Sr < 0.703 . 200km LITHOSPHERIC MANTLE Enriched Iherzolite "Sr/ "Sr < 0.706 ASTHENOSPHERE Figure 5. Stratified lithosphcrc proposed for the Zuni-Bandera Volcanic Field on the flanks of the Rio Grande Rift [after Menzies et al., 1991]. This is similar to that outlined for the Colorado Plateau on the basis of data from spinel (shallow) and garnet (deep) peridotite xenoliihs [Roden el al.. 1990]. Part of the problem in Zuni Bandera is that both the alkaline and tholeiitic magmas have an intraplate character and as such one cannot invoke extraction of one or other from "arc" like lithosphere. If one accepts that the asthenosphere beneath the Basin and Range is MORB like then it is a suitable source for the alkaline basalts. However for the tholeiitic basalts with more OIB like character one has to argtie for either (a) considerable sub-crustal mantle heterogeneity at the time of eruption (MORB-OIB mix) or (b) imposition of OIB intraplate chemistry on the lithosphere in the past such that it can be recently reactivated. Over the last thirty years ^oriels for the genesis of Tertiary to Quaternary volcanic rocks erupted throughout the western USA have been refined (Figure 6) such that u'-.c. identity of the enriched reservoirs (Hedge 1966; Doe et al 1969; Leeman 1970 & Hedge and Noble 1971]) can be resolved. Careful selection of volcanic rocks unaffected by shallow crustal processes (e.g. McMillan and Dungan 1988) indicates the presence of the following reservoirs in tiic upper mamle. Cratonic lithospheric sources Aged enriched lower lithosphere (87Sr/86Sr > 0.7055 & 143Nd/144Nd < 0.5120) stabilised in the Archaean (>2500Ma) and affected by early Proterozoic enrichments. This mantle source is similar to that encountered as inclusions in diamonds. Circum-cratonic lithospheric sources Subduction modified lower lithosphere (87Sr/86Sr < 0.7080 & 143Nd/144Nd < 0.5124; Ba/La > 31) accreted in the Proterozoic and Phanerozoic. This mantle source is similar to that encountered in arc environments and occurs beneath the Sierran province and the Colorado Plateau. Plume contaminated lower lithosphere (87 Sr/86Sr < 0.7060 & 143Nd/144Nd < 0.5124; Ba/La < 31) produced in Phanerozoic times. This mantle source is similar to that of enriched ocean island basalts but may reside in the lower lithosphere. Oceanic mantle sources Sub-lithospheric reservoirs that include an ocean island basalt/plume source (87Sr/86Sr < 0.7060 & 143Nd/144Nd > 0.5124) and a mid-ocean ridge source (87Sr/86Sr< 0.7034 & 143Nd/144Nd > 0.5130). The latter is important throughout the Basin and Range [Leeman, 1970; Menzies et al 1983] and the former is important within the "sphere of influence" of any active plumes (e.g. Yellowstone) MANTLE HETEROGENEITY ENRICHED CRATONIC UTHOSPHERIC LIMITED CRUSTAL CONTAMINATION KEEL RESERVOIRS EiuNotw ooe * iiie OAtM.Il *M»OLItt« ' ARCHAEAN CRUST /III 4r &U-I_L1I ENftCHEDl KEa 1 »MOOM«| ^ A ^ SUBOUCTION - MOOIREO ARCHAEAN ENMCHEO A3THEN03PMERC- LOWER UTHOSPHEHE MANTLE UTHOSPMERE PROCESSES ARCHAEAN CRUST .. 19MU1 EMVCMD ^ , IT < MULTIPLE SOURCES LITHOSPMER1C ACE ON 4 Off CRATON PROVINCES UTHOSPHERIC SOURCES ON CRATON ' OFF - CRATON SUIOUCHON MODIFIEO PROVINQAUTY LOWER UTHOSPHERE INTRAPLATE SOURCES MEROES (1MB MEMBE3 «« ( itti| 4 f- Figure 6. Representative crust-mantle sections depicting different mantle source regions inferred from the isotopic and elemental geochemistry of volcanic rocks from the western USA. Early investigations concluded that the high °'Sr/°°Sr ratios in continental basalts did not always indicate contamination with continental crust. Cratonic mantle sources were originally defined on the basis of volumetrically significant tholeiitic basalts from the Snake River Plain and Yellowstone National Park [Leeman, 1975; Doe et aL, 1983] and more recently on the basis of volumetrically insignificant potassicXultrapotassic magmas from Montana, Wyoming and Colorado [e.g.Vollmer et al., 1984; Fraser et al., 1985]. Clrcum-cratonic (arc-like) mantle sources were alluded to by Leeman (1970) and confirmed by Carlson (1984). on the basis of Sr-Nd-Pb isotopes, and Fitton et o/.[1988,1991] and Kempton et a/.[1991] on the basis of elemental data (e.g. LIL/LREE ratios). Oceanic mantle sources were originally noted by Hedge (1966) and have been subdivided into asthenosphere (MORB) (Menzies et a/.. 1983] and plume (OIB) (Leal et al.. 1988]. 7, K. MEZGER Department of Earth and Space Sciences State University of New York at Stony Brook Stony Brook, NY 11794 USA ABSTRACT. Techniques are now available to obtain high precision age information on a variety of metamorphic minerals such as zircon, garnet, monazite, sphene, rutile, hornblende, micas, apatite and feldspars. These ages provide valuable information on the timing of geologic events and duration of pro cesses. In order to provide a valid interpretation for these mineral ages it is essential to have some knowledge of the closure temperatures. By combining the ages with the closure temperatures and the maximum temperatures reached during metamorphism it is generally possible to decide whether the ages give information on the prograde or retrograde metamorphic path. Quantitative pressure-temperature-time paths of metamorphism can be constructed when age data are combined carefully with temperature, pres sure and lexturai data. In some cases it has been possible to use age information deduced from minerals that are involved in mineral reactions to constrain the timing of partial melting, intrusion of synmetamorphic magmas and the duration of prograde metamorphism even in granulite terranes. More commonly rates of cooling have been determined from ages deduced from minerals with different closure temperatures for various parent/daughter systems. 1. Introduction It is essential to understand the dynamic aspects of metamorphism in order to be able to relate metamorphism to tectonic processes (England and Thompson 1984, Thompson and England 1984). Most successful qualitative correlations of crustal dynamics and metamorphism have been made for amphibolite facies terranes. This is because in such terranes a wealth of information on the prograde metamorphism can be deduced from mineral textures and mineral zoning (Selver- stone et al. 1984, Spear and Rumble 1986). In granulite terranes, all prograde mineral zoning and most of the reaction textures are obliterated by the high temperatures and deformation associated with the formation of these high-grade rocks. As a result the construction of even qualitative pressure-temperature-time (P-T-t) paths for high grade terranes is difficult. In rocks up to and including grades of the middle amphibolite facies it is possible to obtain precise age information from a large variety of minerals (Table I). However, most mineral systems have closure tem peratures that are significantly lower than those achieved during granulite grade metamorphism. Therefore the determination of precise mineral ages that give reliable age information on processes that occurred prior and during high grade metamorphism is particularly challenging and requires new approaches. This articles discusses examples where it has been possible to obtain high precision mineral ages and relate them to the sequence of mineral reactions and duration of from various geologic processes in high grade terranes. The correlation of ages with geologic events and processes is a prerequisite for the construction of quantitative P-T-t paths for metamorphism and to correlate metamorphism with tectonic processes that are responsible for orogenesis. D. Vielzeufand Ph. Vidai (eds.), Granulites and Crustal Evolution, 451-470. © 1990 Kluwer Academic Publishers. Printed in the Netherlands. 452 K. MEZGER 2. Requirements for High Precision Geochronoiogy In ordento obtain precise information on rates of metamorphic processes and the absolute timing of certain geologic events (e.g., mineral reactions, partial melting, heating, cooling, deformation, magmatic intrusions), it is essential to have chronometers capable of high temporal resolution. This restricts one to minerals that incorporate only small amounts of the daughter isotopes during their growth or later re-equilibration. In such minerals, the uncertainties related to the corrections for these incorporated daughter isotopes can be minimized. If minerals incorporate significant amounts of daughter element, mineral-mineral or mineral-whole rock isochrons can be deter mined. Although it is possible to obtain very precise ages from such isochrons, it is generally difficult to interpret such ages with the same confidence as mineral ages where the correction for the daughter isotope is negligible. The precision of an isochron is a function of the analytical precision of each data point as well as the amount of data points and their scatter around the isochron. The requirements for an isochron are only strictly fulfilled, if the scatter of the data around the isochron is random and purely analytical. In slowly cooled terranes, it is likely that the individual phases cool below their respective closure temperatures at different times, and thus produce a systematic variation in the position of the data points with respect to the isochron. In this case each point may represent a different temperature and time during a prolonged cooling history (Giletti 1985). Therefore, an apparently precise mineral isochron can only be related to a specific geologic event with the same confidence as mineral ages if all phases closed to diffusion of parent and daughter elements at the same time, or have grown at the same time and the rock did not reach temperatures above the temperature of closure. In order to interpret isochrons, it is important to know the closure temperature for each phase and to evaluate with which other pha- se TTc =______EJR : O) where E. = activation energy; R = gas constant; A = geometry factor, i.e. sphere, infinite cylinder or mfiniic piatc; D0 = frequency factor; a = effective diffusion radius; Cr = cooling rate. GEOCIIRONOLOGY IN GRA.NTLITES 453 This equation takes into account that minerals gradually change over a finite temperature range from being open to diffusion to become closed (or vice versa). Thus during cooling the daughter products are not completely lost before Tc is reached, nor completely retained thereafter. A requirements of Dodson's statement is that the phase cooled from a temperature significantly higher than Tc. If a mineral grew significantly below Tc and is subsequently exposed to tem peratures only slightly above Tc, it may not reset completely and record an age that docs not correspond to Tc but is older. For a mineral that grew at a temperature only slightly higher than Tc, the age will be too young. Mineral Temperature Grain Size References (in°C) (in U-Ps SYSTEM Zircon >900 - Garnet >800 >1000 Mezger et aL 1988 Monazite 650-740 40-200 Pamsh 1988, Copeiand etaL 1988, Mezger et aL in prep. Sphene 500-670 500-30000 Cliff and Cohen 1980, Gascovne 1986, Mezger et aL in prep Rutiie 420-380 430-130 Mezger et aL 1989b Apatite 350-550(7} 200-1000 Matunson 1978, Ci5 and Cohen 1980, Watson et aL 1985 K.-AJL AM) AX/AJI SYSTEM Hornblende 500-450 160 Harrison 1981 Muscovite 350-400 Haoson and Cast 1967, Purdy and Jager 1976, Qiff and Cohen 1980 Biotite 300 Purdy and Jiger 1976, Harrison et aL 1985, Dodson and Mcdelland-Brown 1985 Microciine 150-250 125-250 Harrison and McDougail 1982 Muscovite 450-500 Hanson and Gast 1967, Jiger et aL 1967, Purdy and Jiger 1976, Wagner et aL 1977 Biotite 350 Jiger et aL 1967, Purdy and Jiger 1976, Wagner et aL 1977, Dodson 1979, Harrison and McDougail 1982 Onhociase 320 1000 Dodson 1979 Table I. Approximate closure temperature for selected minerals using a cooling rate of ca. l-10"C/Ma and common grain sizes. By comparing Tc with the maximum temperature achieved in a given rock sample (as deter mined by careful thermometry), it is possible to assess whether the ages record the time of mineral growth, and give information on prograde metamorphism, or whether they record cooling ages, and thus relate to the retrograde metamorphic history. 454 K. MEZGER There is insufficient knowledge to be able to predict the diffusion behavior for a given ion in a specific mineral from first ^principles. Therefore, closure temperatures have to be determined empirically. This is possible through experiments (Harrison 1981, Harrison et al. 1985) or in geologic settings where the thermal history may be evaluated such as contact aureoles (Hart 1964, Hanson and Cast 1967, Hanson et al. 1971) or regional metamorphic terranes (e.g., Purdy and Ja'ger 1976, Mezger et al. 1989b). Table I summarizes Tc's for minerals that can yield high precision ages using the U-Pb, ^Ar/^Ar - K-Ar, Rb-Sr and Sm-Nd systems and a brief discussion follows below. For the dis cussion cooling rates of ca. l-10*C/Ma will be assumed. Tc is strongly dependent on the effective diffusion radius. In cases, where no exsolutions or structural transformations occur, this might be approximated by the grain size (e.g., U-Pb in garnet, monazite, rutile) in other cases it is a func tion of the size of exsolution lamellae (e.g., ^Ar/^Ar in hornblende, alkali-feldspar). Tc may also show a,dependence on the composition of the mineral, the composition of the surrounding fluid and deformation after mineral growth. However, for most minerals there is very little known as to the importance of these parameters and in certain case they might lead to appreciable deviations from the values given in Table I. Therefore the values given in Table I should be used with the appropriate caution. 3.1. U-Pb SYSTEM The U-Pb system has a great advantage over other systems because two isotopes of U decay to two isotopes of Pb. By analyzing for U and Pb abundances and Pb isotopic compositions it is possible to obtain three ages" (^Pb/^U, 206Pb/23*U, ^Pb/20^; see Faure (1986) for a general reference). These ages give an internal check on the possible disturbance of the system after the last complete reequilibratiqn. By plotting the data on a U-Pb concordia diagram it is possible to obtain two additional ages in many cases. The age given by the upper intercept with concordia ideally corresponds to the time the mineral grew and the age given by the lower intercept on the concordia corresponds to the lime of disturbance or partial reequilibration. However, care must be taken to interpret ages derived from such discordance patterns. 3.1.1. Zircon The U-Pb systematics in zircon are generally considered to be the most difficult to reset com pletely, even by granulite grade metamorphism and partial melting (Pidgeon and Aftalion 1978, Schenk 1980, Kroner et al., 1987a, 1987b) and Tc is considered to be >900*C. It is likely thai only very small zircons can be reset during metamorphism in the continental crust. Larger zircons probably must be destroyed completely and reprecipitated in order to eradicate all memory of their previous isotopic composition. Zircons typically show some disturbance in their U-Pb systematics as a result of Pb-loss at low temperature. At higher grades of metamorphism new zircon overgrowths may form and therefore give discordant ages (e.g., Kroner et al. 1987a). This problem can be overcome by analyzing different batches from the same sample and treating the zircons, preferentially by air abrasion (Krogh 1982a, Krogh 1982b, Goldich and Fischer 1986). In some studies, zircons are leached with acids to yield more concordant ages. This method may complicate, however, the discordance patterns by superimposing an artificial discordance on already discordant populations. Therefore leaching of zircons is strongly discouraged in favor of air abrasion techniques to obtain more concordant populations. Particular care must be taken in interpreting the lower intercept ages, because they may not have any obvious geologic signifi cance (e.g. Tilton 1960, Goldich and Mudrey, 1972). In situ spot analysis by ion microprobe (although associated with comparatively large analytical errors e.g.. Kroner et al., 1987b), or conventional analysis of single zircon cores (Krogstad et al., 1986) should be able to resolve mosi of these ambiguities in interpreting discordant U-Pb zircon ages. 132, GEOCIIRONOLOGY EN GRANUUTES 3.1.2. Garnet Garnet is an important mineral in isogradic reactions, geothermometers and gcobaromcters (Es- scnc 1982, Bohlen and Lindsley 1987, Essene 1989. Powell and Holland 1988) and is one of the most widely used minerals for determining metamorphic P-T paths (Spear and Selverstone 1983. Bohlen 1987, Spear and Rumble 1986). U-Pb ages for garnet are particularly useful for dating times of mineral reactions or the development of equilibrium mineral assemblages in meta- morphic terranes. Such ages are essential to construct quantitative P-T-t paths. Since Ca and U have identical ionic radii, it can be expected that U is incorporated to a limited extent in the M2*-site in garnet. Except for andradite-rich garnets in skams, aimandine-pyropc- grossular-spessanine garnets typically have U concentrations of less than 1 ppm (Haack and Gramse 1972). Garnet has been successfully used for fission track dating for which it has a closure tem perature of about 280*C (Haack, 1976). The garnets used for fission track dating have come from a large selection of geological sites and have a broad range in compositions. Haack (1976) found that garnets show a regular distribution of the fission tracks. The fission tracks and thus U, are more evenly distributed throughout individual garnets than almost any other common mineral used for fission track dating. However, garnets may also host U-rich phases within the matrix or along grain boundaries and fractures (Haack 1976. Mezger et al. 1989a). Special care has to be taken to remove or leach these extraneous U-rich phases that could overwhelm the structurally bound U in garnet. Relatively large, and thus visible inclusions, will preserve information that might be unrelated to garnet-growth. These larger inclusions can be easily detected using a petrographic microscope or with back scattered electron imaging on the electron microprobe. Hand picking of small, clear grains under a microscope should reduce the possibility of incor porating the larger inclusions. Acid washing of the garnet before analysis should eliminate the U-rich phases along^grain surfaces. If inclusions are only micron-sized, possibly as a result of exsolution, they will have a low Tc. The rate at which the U and Pb associated with these samll inclusions will diffuse into or out of the garnet, will be controlled by the garnet structure and the Tc for garnet will apply. The age obtained from garnets with such small inclusions will record the time garnet, rather than the inclusion, became closed to U-Pb diffusion. Many garnets contain significant amounts of common Pb. Using Pb isotope ratios for the common Pb correction based on a Pb-evolution model such as that of Stacey and Kramers (1975), as is done routinely for zircons, can introduce a significant error in the U-Pb ages for garnet. In order to obtain precise ages it is therefore recommended that a common Pb correction be applied using the isotopic ratios obtained from the whole rock or from a coexisting phase with high Pb to U ratios such as K-feldspar. The accuracy of the gamet-K-feldspar age is dependent on the time elapsed between the closure for garnet and that of the K-feldspar. If this time is long, the age can be biased significantly towards younger values. Therefore, feldspar should only be used if it reequilibrated at approximately the same time as the garnet, or if U/^Pb for the whole rocks was low and the Pb-isotopic ratios did not evolve very much over time. Some garnet populations show variable discordance with a lower intercept age of 0 Ma, suggesting that the discordance is a result of analytical procedures. Improvement of analytical techniques might solve this problem (Mezger et al. 1989a). U-Pb systematics in almandine-pyrope rich garnets are not reset by granulite facies meta- morphism at temperatures of at least 800'C (Mezger et al. 1989a). Sofar only a small number of garnets have been dated by the U-Pb method (Mattinson 1986, Mezger et al. 1989a), so it is not known whether there is a significant compositional dependence of Tc in garnet. 133 456 K. MEZGER 3.7.3. Monazite Recent studies have shown that U-Pb systematics in monazite are only paru'ally disturbed during partial melting at temperatures of ca. 700"C (Parrish 1988, Copeland et al. 1988), and are not disturbed by contact metamorphism at temperatures of ca. 650"C but completely reset by regional metamorphism reaching 740*C (Mezger et al., in prep.). This high Tc for monazite is in contrast to the earlier suggestion by Wagner et al. (1977) that Tc may be as low as 550'C, but is consistent with the study by Kb'ppel and Griinenfelder (1975) who favored a Tc significantly higher than 550*C. Such high closure temperatures indicate that, in granulite grade terrenes, monazites (0.04-02 mm grains) record information following the maximum thermal conditions. In terranes that have undergone at most upper amphibolite grade metamorphism they may record growth ages. 3.1 A. Sphene Sphenes give concordant U-Pb ages in most terranes. However, some sphene populations show discordance patterns similar to those observed in zircons (Tucker et al. 1987). In such cases, sphenes seem to record two different events. The discordance patterns can be the result of a short thermal disturbance (Tucker 1988) but may also be a result of a second episode of sphene growth with new material overgrowing older cores. In the latter case, the discordance cannot be used to infer a .short thermal disturbance, but may indicate that the terrane did not reach conditions sig nificantly above lower amphibolite facies at any time bracketed by the two ages. To distinguish the two different discordance patterns it is necessary to evaluate the Th/U/Pb ratios as well as their concentrations, as a function of location within the sphene grains (core vs. rim). It also helps to be able to constrain the highest temperatures achieved during the period of the disturbance or new growth of the rim material. Tc's for sphenes are commonly considered to be about 500-550"C (e.g., Mattinson 1978, Gascoyne 1986, Cliff and Cohen 1980), for typical igneous and metamorphic sphenes which are commonly smaller than 1 mm in their longest dimension. In some pegmatites and high grade marbles, sphenes can reach several cm in their longest dimension. For a sphene 30 mm in maximum dimension Tc is about 670"C at a cooling rate of ca. 2"C/Ma (Mezger et al. in prep). Thus by selecting sphenes of different sizes from the same area, it is possible to obtain informa tion on rates of cooling following high grade metamorphism. 3.7.5. Rutile Only a few rutiles from metamorphic rocks have been analyzed for their U-Pb systematics. Rutiles typically give concordant or only slightly discordant U-Pb ages (Scharer el al. 1986. Mezger et al. 1989b). U-Pb ages deduced from rutile are typically vounger than those determined for sphene ages and are equivalent or slightly younger than ^Arr'Ar ages obtained from meta morphic amphiboles. Tc for 0.2-0.4 mm grains is about 420"C (Mezger et al. 1989b). 3.1.6. Apatite Tc for the U-Pb system in apatite is still poorly known. Experimental studies by Watson et al. (1985) suggest a f c for Pb in fluorapatite (grain size of 0.2-0.1 mm) of 530-590*C at a cooling rate of l-10*C/Ma. Mattinson (1978) found that igneous apatite and sphene give similar U-Pb ages and suggested a Tc of ca. 500"C. Cliff and Cohen (19801) found that metamorphic apatite has a Tc similar to the K-Ar system in muscovite i.e., ca. 350*C Only a small pan of this dis crepancy may be the result of different cooling histories, the major pan may be related to different composition (particular OH, F, G) of apatite or the fluid phase present in the rocks during GEOCIIRONOLOGY IN GRANUUTES cooling. Apatite is isostructural with pyromorphite and thus incorporates large amounts of com mon Pb into its structure during growth. High precision ages can therefore be obtained only if the uncertainty in the common Pb correction can be minimized (see discussion at 3.1.2.X proper interpretation of the ages must await better knowledge of Tc. 3.2. "Ar/^AT AND K-Ar SYSTEM 32.1. Hornblende The most widely used mineral dated by the ^°Ar/39Ar method is hornblende. It seems that among the major rock forming minerals hornblende has the highest Tc for the ^°Ar/39Ar system. Tc is typically around 500*C (Harrison 1981), but can be quite variable. Variations in Tc may be a function of the composition of the hornblendes and the cooling rate. It has not been shown conclusively whether there is a direct correlation between hornblende composition, particularly Fe/Mg ratio and Tc, but it is evident that the composition has an effect on the possible exsolution and alteration of hornblendes during cooling (Robinson et al. 1982). Exsolution and alteration reduce the effective grain size of the hornblendes and if they occur at high enough temperatures, can lead to substantially lower Tc (Harrison and Fitz Gerald 1986, Onstott and Peacock 1987). Due to these complexities it is advisable to determine the composition and structural state of hornblendes used for geochronology (e.g., Onstott and Peacock 1987). An additional problem is that some hornblendes can contain extraneous argon and thus can yield old ages of no geologic significance. However, using the "^Ar/^Ar technique and step-wise degassing it is possible to detect the presence of extraneous Ar and ideally make the required corrections (e.g., Harrison and McDougail 1981). 322. Micas Micas can yield precise *°Ar/39Ar and K-Ar ages but biotites can also be prone to the incorpor ation of extraneous argon (e.g., Phillips and Onstott 1988). Tc for the K-Ar system in muscovite is about 350-400'C (Hanson and Cast 1967, Purdy and Ja'ger 1976, Cliff and Cohen, 1980). Experimental studies indicate that Tc for ^Ar in biotite is a function of composition and has a significant pressure dependence (Harrison et al. 1985). For most biotites Tc is around 300*C (Purdy and Ja'ger 1976, Dodson and McClelleand- Brown 1985) but increases with the Mg/Fe ratio (Harrison et al. 1985) and can be as high as 450'C in phlogopite (Dodson 1979). Hart (1964) studied the K-Ar and Rb-Sr systematics of biotite flakes with a diameter of ca. 8 mm, by separating different zones from individual flakes. The result show a significant decrease in ages from core to rim. Harrison et al. (1985) suggest that biotite has an effective diffusion radius of 0.15-0.2 mm and flakes that are larger yield the same ages independently of grain size. A decrease in ages with decreasing grain size was only observed for smaller flakes. These results are consistent with the findings of Hanson and Cast (1967). 32.3. Feldspars Microclines have a Tc for the ^Ar/^Ar system of about 150-250"C (Harrison and McDougail 1982). They give information on the very late stages of cooling, close to the time the rocks are exposed to the surface. Orthoclase has Tc's that are significantly higher than those for micro- dine (Heizler et al. 1988). 135 458 }1. MEZGER 3.3. Rb-SF SYSTEM &- .^- ";-> 3J.7. Miow According to the study by Hanson and Cast (1967) the Rb-Sr system has only a slightly higher Tc than the K-Ar system for the same mica, and Tc for the Rb-Sr and K-Ar system in muscovite is significantly higher than in bionte. Tc for Rb-Sr in muscovite is ca. 450-500*C and in biotite ca. 350'C (Hanson and Cast 1967, Ja'ger et al. 1967, Purdy and Jager, 1976 Dodson 1979). Compared to the ^Ar/^Ar system, the Rb-Sr system is only rarely used for obtaining mineral ages, although it can yield very precises ages particularly for micas (see also Peterman and Sims 1988). 3.4. sm-Nd Sm and Nd have similar ionic radii, the same charge and therefore similar geochemical prop erties. As a consequence they are not fractionated sufficiently in any rock-forming mineral to allow to obtain a mineral age without significant correction for inherited Nd. The Sm-Nd system can thus be used only if an isochron is constructed. This requires that at least two components (i.e. two minerals or one mineral and the corresponding whole rock) are analyzed. If two minerals are used, ideally both of them should have the same Tc for the Sm-Nd system. In order to avoid ambiguities mineral-whole rock isochrons should be obtained rather than miner al-mineral isochrons. The precision obtainable for a two point isochron is a function of the spread in the Sm/Nd ratio of the two points. A common rock-forming mineral that discriminates strongly between Sm and Nd is garnet. Thus garnet-whole rock isochrons hold promise for dating metamorphic rocks on which age information is difficult to obtain by other methods. Tc for the Sm-Nd system in garnets is not well established. Humphries and Cliff (1982) concluded in their study Tc is ca. 480-600"C. However, a recent study by Cohen et al. (1988) indicates that garnets preserve their Sm-Nd systematics up to temperatures of 900*C. This high temperature is consistent with the proposed Tc of ca. 850*C for the system gamet-clinopyroxene from an eclogite xenolith studied in detail by Jagoutz (1988). If these high vales for Tc are cor rect, then Sm-Nd mineral isochrons involving garnet can yield absolute age information on pro cesses in the upper mantle and lower crust. Since zircon is extremely rare in mafic rocks and absent in ultramafic rocks, and because these garnets may have low concentrations of U, Sm-Nd geochronology on gamei-bearing samples may the system of choice to obtain age information on these types of rocks. 4. Dating Metamorphic Processes The above discussion of Tc's indicates that ii is comparatively easy to obtain information on the cooling history of granulite terranes, but it is more difficult to obtain reliable information on the timing of prograde metamorphic processes and events (sec also summary in Cliff 1985). The only systems that seem to be able to provide precise age information on prograde events in high grade terranes are U-Pb in zircon and garnet and possibly Sm-Nd in garnets. In the following discussion we will give examples where geochronology provides important age constraints on the evolution of high grade metamorphic terranes. The data are taken from our studies in the Pikwitonei granulite domain (Manitoba, Canada), the Adirondack Mountains (New York, USA) as well as from the literature. For a further discussion the reader is referred to ref erences given in the text. GEOCIIRONOLOGY IN GRANUUTES 459 4.1. DURATION OF METAMORPHISM First order questions one faces in attempting to understand the evolution of metamorphic terranes concern the duration of metamorphism and whether metamorphism was caused by a single con tinuous change in P and T or whether there were several distinct metamorphic episodes. In some cases structural studies combined with petrographic observations may provide clues regarding the poly-metamorphic history of a tcrrane. The ultimate test, however, is dating meiamorphic min erals with high Tc's. The most promising systems are U-Pb in zircon and garnet. Figure 1 gives an example from the Pikwitonei granulite domain in Manitoba, where meiamorphic garnets indicate four distinct episodes of garnet growth that we interpret as distinct thermal peaks in the metamorphic history. The garnet ages are similar to zircon ages from the same area and support the episodic character of metamorphism. Metamorphism lasted for about 150 Ma, but during this time, new minerals (gamet and zircon) grew only during short intervals from 2744-2734 Ma, 2700-2687 Ma, 2660-2637 Ma and 2629-2591 Ma (Mezger et al. 1989a, 1989c). Caucnon Laxe 300 - 600 - 500- 2750 2700 2650 2600 2550 age/Ma Figure 1. This diagram shows the temperature history of a small area within the Pikwitonei granulite domain. Temperatures were estimated from the location of garnet forming reactions identified by mineral textures. The temperatures are then combined with the ages obtained from such garnets. The crosses give the age and temperature uncertainties (assuming a(HzO)-l) for the different points. This diagram indicates that high grade metamorphism lasted for at least 150 Ma within this area and there were several thermal "peaks" (modified after Mezger et al. 1989a). 42. MINERAL REACTIONS The construction of truly quantitative P-T-t paths for metamorphic terranes requires precise knowledge of the time at which certain pressures and temperatures were achieved in a rock. In most granulite grade rocks, prograde zoning in gamet is obliterated by the high temperatures achieved during metamorphism. In such rocks information on P-T and time can only be inferred if the garnet-forming reaction can be observed in the sample. For example: in metapelitic gneisses from the Pikwitonei domain, it is possible to observe textures that give an indication of which reaction lead to the formation of gamet. Several samples show textures that indicate that gamet formed by the breakdown of staurolite according to the reactions given in Table II. These 13*7 460 K. MEZGER 2659 Mo (b) Go-Bt-PI- 2697 Ma (a) Ksp-Sil-Qz Go- Ksp 2641 Mo (c) Figure 2a. Sketch of migmatite sample from the Pikwitonei granuiite domain. From this sample three batches of petrographically distinct garnets were extracted for dating by the U-Pb method (Mezger ei al. 1989a). The three types of garnet yielded the distinct ages of 2697 Ma (a), 2659 Ma (b) and 2641 Ma (c). r- Figure 2b. This photomicrograph (plane light, 3x4.2 mm) shows an area of the migmatite sample along the leucosome-melanosome inteface where all three petrographically distinct garnets are present: a = corroded garnet surrounded by biptite in the meianosome; b = large garnet at the leucosome-melanosome border; and c = small garnet in the leucosome surrounded by K-feldspar. 1*58 GEOCHRONOLOGY IN GRAMJUTES 461 garnets were dated by the U-Pb method and the ages are given in the same table. According to experimental studies and the assumption that a^ is ca. 1 the formation of garnet by the reactions in Table II require temperatures of 680'C and 795'C (Richardson 1968)(Fig. 4). 4.3. PARTIAL MELTING High grade metamorphism commonly results in in-situ partial melting. In the Pikwitonei granu lite domain, garnets formed by partial melting reactions such as those given in Table II. Determination of the growth ages of garnets in the leucosome yields the time of formation of the partial melts. Care must be taken to separate newly formed garnets from those accidently incorporated into the melt from the melanosome or those that formed on the melanosome/leuco- some interface. The garnets in the melanosome may have formed by a completely different reaction than those in the leucosome and may give significantly older ages (Mezger et al. 1989a). Those on the melanosome leucosome interface may give an intermediate mixed age (Figure 2). At higher crustal levels it might be possible to determine the origin and time of intrusion of S-type granites, by dating the garnets in these intrusions. One example where the garnets can give information on the time of intrusion as well as the timing of earlier metamorphic episodes in the source is a late-kinematic S-type granite from the Pikwitonei granulite domain. Four garnets from the same granitic intrusion were dated and yielded ages of 2984, 2744, 2605 and 2591 Ma (Mezger et al. 1989a). The two older ages most likely represent metamorphic episodes in the source of the granite whereas the two younger ages may date the time of intrusion of the granite (Mezger et al. 1989c). The ages indicate, that restite and melt did not separate completely and that some of the garnets formed directly from the granitic melL Reaction Age NATAWAHUNAN LAKE: (A) stauroiite + quartz = garnet + sillimanite + vapor 2744 Ma (B) stauroiite = garnet + sillimanite + spinel + vapor 2738 Ma CAUCHON LAKE: (C) biotite + cordierite -f- quartz -h vapor = garnet -h raeit 2700 Ma (B) stauroiite = garnet -h sillimanite + spinel -f- vapor 2687 Ma (D) biotite + plagiociase + sillimanite + quartz = garnet + K-feldspar 4- melt 2641 Ma Table II. Ages of mineral and partial melting reactions in the Pikwitonei granulite domain (from Mezger et al. 1989a). 4.4. SYNMETAMORPfflC INTRUSIONS Synmetamorphic intrusions play a significant role in the overall heat-budget during high grade metamorphism (e.g., Wells 1980). Table III gives two examples from the Adirondack Mountains where the intrusion of a now metamorphosed igneous body was dated by the U-Pb method on zircon. The time of the syn-regional contact metamorpnism of the surrounding metapelitic gneisses was determined by dating metamorphic garnets (Table III). (39 462 K. MEZCER One of the intrusions is the Diana Complex located along the amphibolite granulke facies transition, the other, a hornblende granite from Piseco Dome within the granulite lerrane (for a location map see McLelland et al. 1988). The Diana syenite shows igneous fabrics but is also strongly deformed in many places and has preserved a contact aureole as indicated by meta- morphic temperatures >850*C in a terrane that regionally experienced temperatures of ca. 650"C (Powers and Bohlen 1985). The hornblende granite from the core of Piseco Dome has a strong gneissic fabric and has no obvious unusually high temperature mineralogy preserved adjacent to the intrusion that could indicate the presence of a syn-regional metamorphic contact aureole. Dating of zircons from metaigneous rocks (Grant et al. 1986, McLelland et al. 1988) and garnets from adjacent country rocks (Mezger et al. 1988, Mezger et al. in prep.) shows that garnet growth was contemporaneous with the intrusion. Combining ages obtained on zircon, garnet and monazite throughout the Adirondacks it can be shown that these magmatic bodies intruded during a time of regional metamorphism lasting from ca. 1170-1130 Ma (Mezger et al. 1988). Such a relationship of magmatism and metamorphism was predicted by Powers and Bohlen (1985) for the area surrounding the Diana Complex and the age information deduced from zircons and garnets corroborates this important relationship. These data support the broader conclusion that synmetamorphic intrusions can play an important role in the heat budget for a metamorphic ter rane. Due to their strong deformation, some synmetamorphic intrusions may be recognized as such only with difficulty, and may be interpreted instead as pre-metamorphic. Comparison of the ages detained for the intrusions and minerals in the immediate contact aureole with ages obtained from metamorphic minerals taken further away from the contact zone should allow determination of relative timing of igneous intrusion and metamorphism. Intrusion Temperature Age of intrusion garnet zircon Diana Complex: Svenite >1000°C 1154+3 Ma 1155+4 Ma Piseco Dome: Hornblende Granite 1154+11 Ma 1150+5 Ma Table III. Evidence for synmetamorphic intrusions in the Adirondacks. Comparison of zircon ages from igneous rocks with garnet ages from the surrounding metapelitic gneisses. The mctamorphic episode lasted from ca. 1170-1130 Ma (Mezger et al. in prep.). * Mezger ei al. 1988, Mezger et al. in prep. ** Grant et al. 1985. *** McLelland etai. 1988. 4.5. RATES OF DEFORMATION Garnets strongly prefer Sr over Rb and will record the Sr-isotope composition of the matrix at the time of mineral growth. By analyzing different garnet zones for their Sr-isotopc composition and the assumption that the Rb/Sr ratio of the matrix changes only by incorporation of Sr into the gamet and no other processes, it is possible to obtain growth rates. Christcnscn et al. (1988) GEOCIIRONOLOGY IN GRANULATES -63 studied large (3 cm) snowball garnets from the amphibolite facics Ottauqueche Formation (Ver mont) and combined the growth rates with the amount of rotation contained in the garnet. The shear strain rate obtained is on the order of 10"u s"1 . Depending on Tc for Sr in gamet and the availability of snowball garnets this technique might have some promise to yield also valuable information on the deformation history of granulite facies rocks. 4.6. RATES OF HEATING In order to determine rates of heating it is important to be able to determine the ages of tem perature sensitive mineral reactions. In theory it should be possible to obtain values for the rate of heating form the two reactions given in Table II and the prograde parts of the temperature-time diagram shown in Figure 1. Although the ages for mineral growth are quite precise, the recon struction of the P-T conditions of gamet growth by the dehydration reactions is hampered by the extreme difficulty to reconstruct the fluid activity for the time of gamet formation. This uncertainty introduces a large error in any estimate of the heating rates based on the reaction given in Table II. Thus in order to obtain reliable heating rates it will be necessary to select areas where the fluid activiues are well constrained or where gamet forms by solid-solid reactions with a significant temperature dependence. 4.7. RATES OF COOLING By combining various mineral ages with their closure Tc's it is possible to describe the rate of cooling of a granulite terrane following high grade metamorphism. Table IV gives the mineral ages determined on gamet, monazite and rutile from a single sample taken from the Adirondacks. If the gamet grew during peak metamorphism as given by the metamorphic temperatures (Bohlcn et al. 1985) and the monazite and male Tc's are correct, this yields a cooling rate of 2.0±0.5"C/Ma. Using a single sample to determine cooling rates by dating several minerals with different Tc's avoids the ambiguities thai can be introduced by comparing ages from different minerals over a large area where cooling might be quite variable. Mineral Age Temperature Garnet 1064±3 Ma 750±30°C Monazite 1033±l Ma 670±30°C Rutile 911±lMa 420±30°C > time integrated cooling rate 2.0+0.5°C/Ma Table IV. Cooling history of sample SP-1 from the Adirondack Highlands (from Mezger et al. in prep.). Figure 3 gives the ages from various minerals plotted as a function of their closure tempera tures for the southern part of the Adirondack Highlands (Mezger et al., 1989b). The diagram yields a cooling rate of ca. 3*C/Ma immediately following high grade metamorphism and ca l*C/Ma in the time period around 800 Ma, ^Ar/^Ar ages in K-feldspar are consistent with a 464 K. MEZGER cooling rate of 0.5*C/Ma at around 700 Ma (Heizler and Harrison 1986). The slow and gradually decreasing cooling rate may indicate that the terrane was not uplifted very fast, if at all, and cooling is mostly the result of the decay of the perturbed geotherm following high grade meta- morphism. For minerals that have a well defined Tc or where Tc can be calculated, it is possible to contour a terrane with the ages obtained for these minerals. These contours have been termed thermochrons (Harper 1967) or chrontours (Armstrong 1966). They describe the time a specific area passed below the Tc for a single mineral. In some ways, these chrontours are similar to isograds but give information of the retrograde rather than the prograde history (see examples in Easton 1986). Thermochrons can be used to describe late stage, large scale deformations and uplift histories (e.g., Peterman and Sims 1988, Harrison et al. 1989). T(oQ Garnet Cooling History 700 Adirondack Highlands Monazite 600 500 Hornblende 400 Rutile Biotite 300 200 h 1050 1000 950 900 850 800 time (Ma) Figure 3. in this diagram mineral ages obiamed on garnet, monaziie, sphcnc and ruu'ic with ihc U-Pb method and hornblende and bioutc with the ^Ar/^Ar method arc plotted against the Tc from Table I; garnet is assumed to have grown at peak temperatures. Based on this diagram the Adirondacks cooled initially at a rate of ca. 3VMa and at a rate of ca. IVMa at 800 Ma. 4.8. CONSTRUCTION OF P-T-t PATHS FOR HIGH GRADE TERRANES By combining mineral ages with mineral reactions for which the temperature can be estimated, it is possible to derive a temperaiure-iimc path. Figure 1 describes the possible temperature history of a small area at Cauchon Lake within the Pikwitonci granulitc domain. This diagram indicates that high grade metamorphism lasted for at least 150 Ma within this area and there were several thermal "peaks". These peaks correspond to periods of abundant mineral growth (i.e., gamct and zircon growth) separated by times of no observed mineral growth. Thus it seems that the tcrranc was not metamorphosed by a single heating and cooling event, but there were at least three periods of increasing temperature possibly separated by times of cooling. Following the las: metamorphism, the terrane cooled initially at a rate of only 2*C/Ma. In Figure 4 all petrographic information is combined with the geochronology and thermomciry GEOCHRONOLOGY IN GRAiNULTTES ^65 and barometry to describe a P-T-t path for the Pikwitonei granuiite domain at Cauchon Lake \ Mezger ct ai. 1989c). Based on pseudomorphs of andalusite after sillimamte, ihe prograde path must have passed below the aiuminosilicate triple point The first observable reaction that can be dated is the formation of garnets around 2700 Ma by the partial melting reaction (C) (Table ID. Around 2687 Ma new garnets formed by reaction (A). Between 2687 Ma and 2660 Ma no new garnets formed and it is possible that the terrane cooled somewhat before the next thermal puisc. From 2660-2637 Ma a second set of migmatites formed. In one peiitic sample garnets formed via the melt producing reaction (D) at 2641 Ma. Peak metamorphic conditions as given by thermo- barometry most likely coincide with the last formation of metamorphic garnets at 2637 Ma. Following the last metamorphic pulse, garnet- and sillimanite-bearing granites and pegmatites intruded around 2600 Ma as dated with garnet, zircon and allanite. The stable occurrence of sillimanite in the late felsic intrusives indicates that at the time of intrusion the pressure was below the sillimanite-kyanite transition. The retrograde dP/dT is also deduced from retrograde reactions and retrograde zoning in garnet (Mezger et ai. 1989c). P-T-t path 8- Cauchon Lake P(kb) GRANITE MINIMUM 400 500 600 700 800 T(°C) Figure 4. The P-T-t path for the Cauchon Lake area in the Pikwiionei granuiile domain is based on the combination of reaction textures, mineral zoning, geothermometry, geobarometry and U-Pb geochronology on zircon, garnet and ruule. Although it is possible to draw a continuous path, the geochronologic data indicates that mineral growth was episodic. During the intervals with no new mineral growth (dotted parts) there may have been excursions towards lower temperatures (see also Figure 1). (circles indicate ages, numbers give ages in Ma, the contoured boxes represent P-T estimates; the location of the garnet-forming dehydration reactions is approximate) (after Mezger et al. 1989c). K. .VEZGER The youngest age is given by b'-Pb ages from mtile. This age corresconds 10 a temperature of ca. 42CTC (Mezger el al. 19895). Thus from 2630 Ma to 2430 Ma tne tcrrane cooiec oniy 350"C. This corresponds to a time integrated cooling rate of 1.6'C/Ma. 5. Error Assessments In many cases it may not possible to take full advantage of the high precision of many of the mineral ages particularly for determining heating and cooling rates. A special problem is dating of continuous reactions. By dating individual minerals* the age obtained represents an average for the growth episode. To improve on this it will 5e necessary to date individual zones within single crystals. An additional uncertainty is introduced, because the mineral compositions found in the rocks now may be significantly different from the composition at the time the dated mineral grew. Although the mineral texture may be diagnostic for a specific reaction, the individual phases may have reequilibrated with respect to their major element compositions at significantly higher tem peratures and pressures. The trace elements used for geochronology, particularly U-Pb and Sm-Ndt may not have reequilibrated due to their lower diffusiviry as a result of their large ionic radii. In other cases one or more phases involved in the reaction are depleted or are only pre served as relic inclusions. In these situations subsequent reactions may have changed the com positions of some of the phases as well. Since almost all geothermomcters and geobarometcrs use the major element compositions of the minerals, the temperatures and pressures may reflect conditions that were attained after the minerals formed. Many garnet-producing reactions arc dehydration reactions. In granulite terranes a^o can be quite variable and is difficult to estimate its value at the time of garnet growth. These petrologic uncenainues may contribute significantly to the uncertainty in a proper geologic interpretation of the ages. It will always be very difficult to get precise information about the rate of rapid processes. For example, consider a heating rate of 10"C/Ma. With such a heating rate, it would take 10 Ma to increase the temperature by 100'C. If it were possible to find reactions in a rock that docum ented this temperature increase and the reactions could be dated with a precision of ±2 Ma. the rate of heating would be uncertain by at least 35%. For a heating rate of re/Ma the uncertainty would be only 3%. In many cases there is a substantial uncertainty in the temperature estimates for a specific reaction. This is the result of the uncertainty in the composition of the phases at the time of reaction and the uncertainty in the activities of the fluid species. For each case it is necessary to consider separately which factor causes the major uncertainty in the correlation of the petrologic information with geochronology, and where it is most important to improve on the precision of the data. 6. Concluding Remarks In order to improve our understanding of metamorphic processes it will be necessary to select phases for geochronoiogy that give information on at least one other parameter (i.e., pressure, temperature, melting, deformation) in addition to the age. Some examples for such an approach are given above and they lead to important conclusions concerning mciamorphic processes. Figures 1 and 4 show, that at least in the Pikwitonei granulitc domain (Manitoba, Canada), the mineral assemblages observed are not the result of a single metamorphic pulse, but rather of prolonged metamorphism with punctuated temperature, pressure and fluid activities. This suggests that in other terranes even if a smooth, continuous P-T-t path can be drawn based on observed mineral reactions or textures, it may not reflect the actual complete metamorphic history of the tcrranc. GEOCIIRONOLOGY IN GRANULTTES -67 Acknowledgments S.R. Bohlcn. G.N. Hanson and EJ. 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Wagner GA, Rcimer GM, Jagcr E (1977) Cooling ages derived by apautc fission track, mica Rb-Sr and K-Ar datinc: the uplift and cooling history of the Central Alps. Mem Isi geoi Petrol Univ Paaova 30: 1-28. Wells PRA (1980) Thermal models for the magmauc accreuon and subsequent mciamorphism of conti nental crust. Earth Planet Sci Lett 46: 253-265. The nature of the crust in western Alaska as inferred from the chemical and isotopic composition of Late Cretaceous to early Tertiary magmatic rocks in western Alaska by Elizabeth Moll-Stalcup and Tom Frost The remnants of an usually wide continental margin arc discontinuously cover much of western Alaska, overlapping a number of exotic basement terranes. The basement terranes are all pre-Cretaceous and the overlying arc rocks are latest Cretaceous and early Tertiary (73-56 Ma). Some of'the pre-Cretaceous basement terranes have continental affinities but most are thought to be pieces of oceanic crust or island arcs that were accreted to the north American continent in mid-Cretaceous time. We studied the chemical and isotopic composition of the 73 to 56 m.y. old arc rocks to see if there are correlations between the composition of the arc rocks and the type and age of the underlying basement. We have studied numerous volcanic fields and plutons over a 250 x 1000 km along-strike segment of the continental margin arc. Our data set for 10 volcanic fields and 6 plutons indicate that the most common rock type is andesite or its plutonic equivalent. Basalt is uncommon and rocks having less than 56% SiO2 and more than 6% MgO are rare. Chondrite-normalized Rb, Ba, Th, and K contents are elevated and Nb and Ta contents are depleted relative to the LREE in all the andesites and dacites and in their plutonic equivalents. Almost all the rocks fall into one of three groups: (1) Moderately LREE-enriched andesites, (2) strongly LREE- enriched andesites and dacites, and (3) highly variable felsic rocks. We describe the salient features of each group below. The first group, moderately LREE-enriched andesites and their plutonic equivalents, comprises the most common rock type in the 250 x 1000 km study area. The andesites are surprisingly uniform in major and trace-element composition over a broad region. LREEs within a given pluton or volcanic field generally increase slightly with increasing SiO2 from a low value of 40-60 x chondrites to a high value of 90-120 x chondrites. HREE remain anchored at about 8-20 x chondrites. Andesites and intermediate composition plutonic rocks that intrude island arc terranes have Sr and Nd isotopic compositions plot between the field for MORE and bulk earth on 87 Sr/86Sr vs. 143Nd/ 144Nd diagrams (Fig. 1). Andesites that were erupted through Paleozoic and Precambrian continental terranes have 143 Nd/ 144Nd near bulk earth and 87 Sr/86sr from 0.704-0.708. We only have Pb isotopic data for the rock within the island arc terranes; all of these data plot within the MORE field. We believe the parent magmas of the moderately LREE-enriched intermediate rocks originated in a subduction modified mantle-wedge and arrived at present compositions by crystal fractionation and assimilation as they rose to the surface. Their final isotopic composition is a mixture between the starting composition of the magma and the composition of the crust. Shifts in isotopic composition may occur in this group but are only apparent when the isotopic contrast between the magma and the crust is large. The only clear case of crustal contamination is found in rocks of the Nowitna and Sischu volcanic field which were erupted through the Precambrian Nixon Fork terrane and have relatively low initial 143Nd/* 44Nd (0.51257-0.51244). The second group consists of strongly LREE-enriched andesites and dacites that are much less abundant within the study area than the first group, although they are the dominant rock type within individual volcanic fields and plutons. These rocks are characterized by steep REE pattern that have LREE 80-200 and HREE 3-5 x chondrites. They generally have higher SiO2 contents than the moderately LREE-enriched andesites though the two groups have considerable overlap. Sr and Nb isotopic compositions generally plot in a broad area near bulk earth on ^Si/^Si vs. 143Nd/ 144Nd diagrams (Fig. 1). The strongly LREE-enriched andesites and dacites originated by partial melting of garnet or hornblende-bearing lower crust in areas underlain by accreted terranes having arc affinities. The third group consists of dacites and rhyolites within the study area. These felsic rocks have highly variable trace-element and isotopic compositions and were generated by a variety of processes (Fig. 2). Most of the rhyolites have Nd isotopic compositions that are similar to at least some of the nearby andesites and plutonic rocks, but Sr isotopic compositions that vary significantly, probably because their 87 Sr/86Sr ratios are much more easily modified by assimilation of basement rocks than their 143Nd/ 144Nd ratios due to their low Sr contents. Rhyolites and dacites with moderately LREE-enriched patterns like nearby andesites (Blackburn Hills) were generated by fractionation of the andesites. Those with extremely low HREE patterns (Sischu volcanic field) are highly evolved rocks that have fractionated at least some garnet. Others that high very high trace-element concentrations appear to have assimilated significant amounts of crust. Some of the rhyolites from areas underlain by known Paleozoic or Precambrian continental crust have anomalously high Th, Sn, W, U, and F values, whereas none of the rhyolites from areas underlain by arc or oceanic crust have anomalously high contents of these elements. In general the highly evolved felsic rocks appear to be most sensitive to crustal type but they are also most difficult to interpret because they are so ISO highly evolved and because their low Sr contents make them more susceptible to secondary alteration as well as more sensitive to assimilation. 151 FIGURE 1. Data for mafic and intermediate 0.5130 Moderately LREE- enrlched group 0.5129 Oceanic terranes o Kipchik-Tulip vf Crooked Pluton 0.5128 a A Plummer and Canyon plutons Z Yukon river vf 0.5127 BBH vf, group 1 Continental terranes 0.5126 Nowitna vf M Sischu vf Strongly LREE- 0.5125 enrlched group + Kanuti vf 0.5124 B BBH vf, group 2 U.703 0.704 0.705 0.706 0.707 0.708 87Sr/86Sr Figure 2. Data for rhyolites 0.5130 0.5128 a Z « BBH rhyoiites a Sischu rhyolites Kanuti rhyoiite Yukon River 0.5126 0.5124 U.703 0.704 0.705 0.706 0.707 0.708 87Sr/86Sr RHENIUM AND OSMIUM ISOTOPE SYSTEMATICS IN METEORITES John W . Morgan USGS Reston Rhenium and osmium are highly siderophile elements. They are amongst the least abundant elements in the Earth's crust and mantle because most of the complement of these elements resides in the Earth's core. The low terrestrial abundances of Re and Os have been a major difficulty in the application of Re-Os isotope systematics to terrestrial systems. The Re-Os isotopic system is uniquely suited to the geochronology of iron meteorites, however. The highly siderophile nature of these elements contrasts with the largely lithophile character of other elements with useful long-lived radio-isotopes; K, Rb, Sm, Lu, Th and U. Many iron meteorites are fragments of the cores of aster oids. These meteorites are called magmatic irons and divide into groups, each of which samples a small planetary core that has undergone fractional crystallization. The two most populous of these are the IIAB and IIIAB groups. An isochron through six IIA irons yields an intercept of 0.8007 4-/-0.0029 that is not signif icantly different from the ca'rbonaceous chondrite initial of 0.302 +/- 0.049. Uncertainty in the slope (0.07S24 +/- 0.00053) corresponds to an error of + '-- 31 Ma for an 4500 Ga age. A clo sure age of 4,596 +/- 152 Ma is derived if errors in decay con stant- are included. Accepting the canonical chondrite age as an upper limit, the IIA irons crystallized between 4,560 and 4,444 Ma ago. The IIB iron, Mount Joy, lies 3 per mil. above the IIA isochron. The IIB irons crystallized from a highly evolved IIA melt with 187Re/ 186Os possibly as high as 20. Thus Mount Joy could have a closure age <5 Ma younger than the IIA irons. Three IIIA meteorites plot significantly above (7 to 10 per mil) the IIA isochron. The slope of 0.0775 +/- 0.0018 is similar to that of the IIA irons but the intercept of 0.8120 + /- 0.0075 appears significantly higher. Thus, there may be isotopic hetero geneities between the IIAB and IIAB parent bodies. Alternatively, the IIIAB irons may have evolved somewhat later than the IIA irons . Not all iron meteorites are of magmatic origin. Group IAB irons, for example, possibly originated as pockets of impact melt near the surface of their parent body. In the Canyon Diablo IA iron, the bulk metal datum lies about 5 per mil above the IIA isochron, and forms a linear array with data for "swathing" kamacite and adjacent schriebersite from the rim of a large troilite nodule. The steep slope and low intercept of this array suggest isotopic disequilibrium or recent Re distribution (per haps due to shock on impact ?) Chondrites are essentially collections of space junk and whole rock samples do not yield Re-Os isochrons in the same sense as the magmatic irons. An enstatite chondrite (Pillistfer, EL6) and an ordinary chondrite (Chainpur LL3) are almost identical in isotopic composition and plot 7 per mil below the IIA isochron. A carbonaceous chondrite (Mighei CM2) is even less radiogenic and plots 11 per mil below the IIA line. 153 1.5 D IA O IIA O IIB m 1.3 A IDA O Carbonaceous CO 00 Enstatite Ordinary + 12 in 1.1 a +6 1> OQ AQs o 0.9 -8 '4596±31 Ma f 1=0.800710.0029 ~ 120 4 8 8 10 0.7 0 ,4 6 8 10 107Re/186 0s Nd and Pb isotopic evolution of basalts of the 1.1 Ga Midcontinent rift: Evidence for a region-wide model for plume-lithosphere- asthenosphere interaction Suzanne W. Nicholson, USGS, National Center MS-954, Reston, VA 22092 and Steven B. Shirey, Carnegie Institution of Washington, 5241 Broad Branch Rd., NW, Washington, D.C. 20015 The more than 1 x 106 km3 of dominantly tholeiitic basalt erupted during the Midcontinent rifting event has been attributed to the upwelling of a mantle plume beneath North America at about 1.1 Ga (Paces and Bell, 1989; Hutchinson et al., 1990; Nicholson and Shirey, 1990). Volcanism associated with the Midcontinent rift lasted less than 25 m.y. from about 1109 Ma to 1086 Ma (Davis and Sutcliffe, 1985; Palmer and Davis, 1987). Basalts exposed around Lake Superior span the entire age range, thus providing an ideal suite in which the chemical and isotopic composition can be used to deduce the evolution of basaltic magmatism as continental rifting progressed. In the western Lake Superior region, the basal flows are slightly alkalic to transitional tholeiites that fall into two compositional groups (Nicholson et al., 1991). One group has clinopyroxene phenocrysts, a rarity in younger high- alumina flows, and is characterized by low A12O3 contents, steep REE patterns (Fig. 1A) and average La/Yb * 23, Th/Ta = 1.45, and Zr/Y = 11. For this group, model initial fi ranges from 7.7 to 8.3 and initial e^d = -0-7 to +0.7. In contrast, the second group is either aphyric or contains olivine and plagioclase phenocrysts rather than clinopyroxene phenocrysts. Additionally this group has higher AhOs contents, lower light REE enrichment and average La/Yb * 11.2, Th/Ta = 2.6, and Zr/Y = 6.1. Model initial fi range from 8.2 to 8.7 and initial £N 155 model initial (i = 8.2 (Brannon, 1984; Dosso, 1984; Paces and Bell, 1989; Nicholson and Shirey, 1990). The very youngest rift basalts are exposed in the North Shore Volcanic Group and as dikes cutting older rift basalts in the Powder Mill Group. Compared to the main stage basalts, the youngest basalts are more depleted in incompatible trace elements (Figs. IA, IB). These basalts have La/Yb=4.1, Th/Ta = 1.78, and Zr/Y= 4.4. Initial E^d ranges from -2.4 to 3.6 ±2; and model initial fi = 8.0-8.2. Klewin and coworkers (Klewin and Berg, 1991; Klewin et al., 1991; Klewin and Shirey, in press) had first proposed a model of time-dependent plume- lithosphere-asthenosphere interaction based on the continuous basaltic section exposed at Mamainse Point in eastern Lake Superior. The new data presented here from widespread exposures in western Lake Superior fit this model and allow it to be extended to the entire rift that is exposed in the Lake Superior basin. In addition, basalts that erupted earlier than basal picrites at Mamainse Point allow a clear look at what appear to be first melts from the plume. The clinopyroxene-bearing basal basalt flows were the first lavas to be erupted in the western Lake Superior region and are hypothesized to be the products of low degrees of partial melting of the plume that would have had an initial e^d = 0±2 and model initial (i = 8.2 (Fig. 2). If this were true, then in northwestern Lake Superior there appears to have been local crustal contamination by rocks of the Superior Province that resulted in a lowering of initial Pb isotope compositions towards model initial (i = 7.7 but little change in initial e^d (Fig. 3). The non clinopyroxene-bearing early basalts are slightly younger than the clinopyroxene- bearing basalts based on stratigraphic relations at Pigeon Point, Minnesota. In some areas of northwestern, southwestern and eastern Lake Superior these rocks are the basal basalts. This magma type is widespread around Lake Superior and can be explained by mixing of melts derived by higher degrees of partial melting of the plume and melts from some other source, which may have been crust or mantle lithosphere. The main stage basalts are remarkable for their great volume (Hutchinson et al., 1990), apparent high extrusion rate (Davis and Paces, 1990), and their apparent isotopic homogeneity (Figs. 2,3). Although a subcontinental lithospheric source can not be ruled out on isotopic grounds, the most likely source that could account for these characteristics is an upwelling, enriched mantle plume that underwent decompression melting in a region of lithosphere thinned by extension. isfc The youngest basalts are more strongly depleted than the older rift basalts. As indicated by their trend towards more depleted initial e^d (up to +3.5) (Figs. 2, 3), they most likely resulted from mixtures of melts formed by higher degrees of partial melting of the plume and melts from a MORB-type asthenosphere. Thus, the progression in sources through time began with localized small degree plume melts which were the first magmas to erupt, followed by widespread flood basalts derived from mixtures of small degree plume melts+lithospheric melts as the lithosphere began to thin substantially. Volumious high-alumina tholeiitic basalts followed, most of which were deposited in the rapidly subsiding central graben. These basalts were derived from plume melts that represented large degrees of partial melting. Most of the early and mainstage lavas were erupted through fissures; thus, there was little fractionation of magmas. Towards the end of the mainstage of volcanism, crustal magma chambers were established (for example, beneath the Porcupine Mountains in Michigan and in some intrusions in the Duluth Complex) in which extensive assimilation and fractional crystallization took place. Finally the last fissure basalts to erupt occurred as the plume had begun to wane, allowing mixtures to develop of plume melts and MORB asthenosphere. 157 References Brannon, J.C., 1984, Geochemistry of successive lava flows of the Keweenawan North Shore Volcanic Group: Ph.D. dissertation, Washington University, St. Louis, Missouri, 312 pp. Davis, D.W., and Paces, J.B., 1990, Time resolution of geologic events on the Keweenaw Peninsula and implications for development of the Midcontinent Rift system: Earth and Planetary Science Letters, v. 97, p. 54-64. Davis, D.W., and Sutcliffe, R.H., 1985, U-Pb ages from the Nipigon plate and northern Lake Superior: Geological Society of America Bulletin, v. 96, p. 1572-1579. Dosso, L., 1984, The nature of the Precambrian subcontinental mantle: Isotopic study (Sr, Pb, Nd) of the Keweenawan volcanism of the North Shore of Lake Superior: Ph.D. dissertation, University of Minnesota, Minneapolis, 221 pp. Hutchinson, D.R., White, R.S., Cannon, W.F., and Schulz, K.J., 1990, Keweenaw hot spot: geophysical evidence for a 1.1 Ga mantle plume beneath the Midcontinent rift system: Journal of Geophysical Research, v. 95, p. 10869-10884. Klewin, K.W., and Berg, J.H., 1991, Petrology of the Keweenawan Mamainse Point lavas, Ontario: Petrogenesis and continental rift evolution: Journal of Geophysical Research, v. 96, p. 457-474. Klewin, K.W., and Shirey, S.B., in press, The igneous petrology and mamgatic evolution of the Midcontinent rift system: Tectonophysics Klewin, K.W., Berg, J.H., Shirey, S.B., and Carlson, R.W., 1991, Isotopic and trace element evidence for time progressive changes in the source region of flood basalts: EOS, v. 72, no. 17, p. 280. Nicholson, S.W., and Shirey, S.B., 1990, Midcontinent rift volcanism in the Lake Superior region: Sr, Nd and Pb isotopic evidence for a mantle plume origin: Journal of Geophysical Research, v. 95, p. 10851-10868. Nicholson, S.W., Shirey, S.B., and Green, J.C., 1991, Regional Nd and Pb isotopic variations among the earliest Midcontinent rift basalts in western Lake Superior: Geological Association of Canada, Program with Abstracts, v. 16, p. A90. Paces, J.B., and K. Bell, 1989, Non-depleted sub-continental mantle beneath the Superior Province of the Canadian Shield: Nd-Sr isotopic and trace element evidence from Midcontinent Rift basalts: Geochimica et Cosmochimica Acta, v. 53, p. 2023-2035. Palmer, H.C., and Davis, D.W., 1987, Paleomagnetism and U-Pb geochronology of Michipicoten Island: precise calibration of the Keweenawan polar wander track: Precambrian Research, v. 37, p. 157-171. , Taylor, S.R., and McClennan, S.M., 1985, The Continental Crust: Its composition and evolution, Blackwell Scientific Publications, London, 312 pp. A. 1000 2 100- ^ 'C *-^ o o o Q. CO 10 -\ La Ce Nd Sm Eu Tb Yb Lu A Late basalts a High Ti02 main stage basalts Low-Ti02 main stage Dasalts Early non-cpx-bearing Dasalts Early cpx-bearing Dasalts B. lOOOq 100- CO E r!""13 a 10- Q. CO CO Cs RbBa Th K Ta Nb La CeSr Nd P Hf ZrSm Ti Tb Y Fig. 1: A. Rare earth element patterns for early, main stage, and late basalts of the Midcontinent rift. B. Spidergram shows trace element abundances for average early, main stage, and late basalts normalized to primitive mantle abundances. Elemental abundances for primitive mantle are from Taylor and McClennan (1985). FIG. 2: SOURCE RESERVOIRS FOR MRS MAGMATISM Western Lake Superior* Eastern Lake Superior2 £Nd SOURCES £Nd ____ J, Plume " -1 {GroupS} ^« 0 to +3 J__Plume + asthenosphere -1 to +3 {Groups 6,7} -9 to -17 ' w Plume + local -2 to -9 {Groups 3,4,5} 5 U crustal assimilation about 0 I Plume (main stage) -1 {Group 2} -2 to -7 > Plume + lithosphere -4 to -5 {Group 1} about 0 u Plume ____ 1 Data for the western Lake Superior region indude published analyses for main stage basalts (Nicholson and Shirey, 1990) and the authors' unpublished data for the early (in the North Shore Volcanic Group and the Powdermill Group) and late basalts (basalt flows in the North Shore Group and a dike that intrudes the Powdermill Group). 2 Data for the eastern Lake Superior region from Mamainse Point, Ontario (Klewin and Shirey, in press). Western Lake Superior 1 6- DM 4- ®» 2- $ $ B\A D l A 0- * I r [ \ 03 i \ 2 -2- A o $\ 'D 4v AA o «2t ^t -4- A A A ^/j - A Cfo1 A c -8- _g'in ^b E 10- m Q. m 381 LU ufe L 12- 4 O ALC I AUC ALC II 14- WMT 16- 18- Q I r ., , ., 1 T ' 1 f\j T 7A 7.6 7.8 8.0 8.2 8.4 (3.6 8.8 9 .0 model initial jl & Late basalts £3 Porcupine Volcanics basalts and andesites D PLV basalts (Mainstage) A Early non cpx-bearing basalts A Early cpx-bearing basalts Fig. 3: Diagram of initial e^a vs. m illustrating estimated reservoirs available at about 1100 Ma. Reservoir symbols as follows: CM=Central Minnesota, DM= depleted mantle, EM= enriched mantle, ALC 1= Archean lower crust, low-u. composition, ALC 11= Archean lower crust, high-u. composition, AUC= Archean upper crust, and WMT= Wisconsin Magmatic terrane. The Rb-Sr, Sm-Nd and Re-Os Isotopic Systems and the Cosmochronology and Geochronology of Igneous Rocks Steven B. Shirey, Carnegie Institution of Washington, Department of Terrestrial Magnetism, 5241 Broad Branch Road, NW, Washington, DC 20015 *Note: These short course notes have been excerpted from a longer review article (Shirey, 1991) which ap peared in Heaman, LM. andLudden, J., eds., Application of Radiogenic Isotope Systems to Problems in Geology. Mineralogical Association of Canada, Short Course 19,103-166. Introduction The detailed understanding of igneous systems and the role they play in the Earth's crustal and mantle evolution has been greatly advanced by the application of the naturally occurring long-lived radioactive de cay schemes of Rb-Sr, Sm-Nd and Re-Os. The long half-life of these decays (40 to 100 Ga) makes these isotopic systems suited to problems in the cosmochronology of lunar rocks and meteorites and in the geochronology of terrestrial rocks ranging in age from the Archean through to the Paleozoic. Together with the U-Pb system, these decay schemes form the backbone of our understanding of the age relations of early Solar System materials and of Precambrian and younger igneous rocks. It is now quite common for data from several of these isotopic systems to be obtained on one suite of rocks. Each isotopic system has a different geochemical response to geological disturbances, therefore the independent chronometers can serve as checks on closed-system behavior --an important part of any study of absolute age. A more involved, but equally fundamental approach has been to use these decay schemes to trace the long-term changes that occur in their parent to daughter ratios as rocks are melted or remelted. These different sys tems are useful because they display wide differences in sensitivity to typical igneous processes. The mul tiple isotope system approach is and will continue to be an important direction in isotope geoscience. The three isotopic systems covered, the Rb-Sr, Sm-Nd and Re-Os systems, are in widely different states of maturity and degree of application in isotope laboratories around the world. The Rb-Sr system has been actively applied to geochronology for more than 35 years resulting in more than 5000 references dealing with isochron-determined ages. The Sm-Nd system has been applied only over the last 16 years in a much smaller number of laboratories and has resulted in more than 400 references dealing with isochron ages. The Re-Os system has been applied for the last 11 years, and for terrestrial geochronology really only the last 4 years in a handful of laboratories. This has resulted in less than 20 references using the Re- Os system for geochronology. Historical development of parent-daughter isochrons The discovery of radioactivity early in the twentieth century and the application of natural radionuclides to absolute age determination has had a profound impact on the earth sciences. Major advances such as the correct-assessment of the age of the Earth and the Solar System and the theory of plate tectonics hinge on the correct analysis and application of radioactive decay schemes. The historical development of the Rb-Sr system has been chronicled in Hamilton (1965) and Faure and Powell (1972). According to these authors, the beta decay of 87Rb to 87Sr was conclusively proven when Sr separated from an old lepidolite by Hahn and coworkers in 1937 was shown by Mattauch in the same year to be composed of 99.7% 87Sr. Goldschmidt was the first to suggest that old Rb-rich minerals could be dated by this decay and the first age of 530 Ma was obtained by Hahn and coworkers in 1943 on pollucite. Early on, only extremely Rb-rich minerals could be dated and the application of the Rb-Sr scheme in its present form had to await techniques for the efficient chemical separation of Rb and Sr from rocks and improvements in mass spectrometer precision, accuracy and sensitivity. These advances oc curred through the application of cation exchange chromatography and isotope dilution to the chemical procedures and through the addition of the vibrating reed electrometer, the digital voltmeter, the magnetic field controller and the microcomputer for on-line data reduction and instrument control (e.g. Wasserburg et al. 1969). The graphical representation of the Rb-Sr, Sm-Nd and Re-Os systems for cosmochronology and geochronology is the parent-daughter isochron diagram. In this diagram, the numerator isotope in the isotopic ratio of the abscissa (e.g/°7Rb in 87Rb/86Sr) decays to the numerator isotope in the isotopic ratio of the ordinate (e.g. 87Sr in &7Sr/86Sr) and the denominator isotopes are the same stable isotope (e.g. 86Sr), having no component derived from radioactive decay. All rocks and minerals that are part of the same closed system, having the same initial 87Sr/86Sr and age, will fall on a straight line, the slope of which corresponds to the age of the system. The mechanics of this diagram can be found in numerous texts (e.g. Faure and Powell, 1972; Hamilton, 1965; Faure, 1986 and DePaolo, 1988). According to Hamilton (1965), the use of this diagram for the graphical analysis of the age of a suite 163. S.B. Shirey ~ Rb-Sr, Sm-Nd and Re-Os Cosmo- and Geo-chronology 2 of rocks and minerals was first applied to the Rb-Sr system by Allsopp and Nicolaysen at the Bernard Price Institute in South Africa and was referred to at the time as a "Nicolaysen" or a "B.PJ." diagram. After its utility had beerTclearly demonstrated for the Rb-Sr system, it was subsequently applied to the K- Ar, U-Pb, Th-Pb, Sm-Nd and Re-Os isotopic systems, among others. In general, the advantage of the isochron method is in the statistical treatment that can be applied to the analyzed rocks and minerals to evaluate the uncertainty of the age, to discover any geological basis for this uncertainty and to investigate multiple disturbances to the system. These advantages are important in studies that combine the Rb-Sr, Sm-Nd and Re-Os isotopic systems because of their differing behavior during post-crystallization pro cesses such as metamorphism in the Earth's crust and shock metamorphism in the Solar System. Compared to the Rb-Sr system, the historical development of the Sm-Nd system (see, O'Nions et al. 1979-for brief discussion) proceeded exceedingly rapidly primarily because the theoretical basis for such isochrons was well understood and because mass spectrometers capable of high-precision isotope ratio measurements were already being applied to Rb-Sr studies on lunar materials and the Allende carbona ceous chondrite. Also, chemical procedures for the effective separation of Sm from Nd had been fully es tablished. In a pioneering study, Notsu et al. (1973) tried to determine whether a 142Nd/144Nd anomaly existed in the achondrite Juvinas that would imply the existence of the extinct radionuclide 146Sm in the early Solar System and that might put age constraints on the formation interval of the Solar System. They pointed out that 143Nd, the decay product of the the long-lived radionuclide 147Sm, could be used to date the crystallization age of the meteorite at the same time the product of the extinct radionuclide was being studied. While the analytical uncertainties on the 142Nd/144Nd and 143Nd/144Nd ratios were too large to provide meaningful results, they showed that a sufficient range was present to answer both the age and isotopic anomaly questions if higher precision Nd isotopic determinations could be made. Shortly there after Lugmair et al. (1975) published the first high precision Sm-Nd isochron which was obtained on a mare basalt from Apollo 17 (sample 75075). The development of the Re-Os isotope system (discussed briefly by Faure, 1986) has proceeded in stages since the pioneering work in the early 1960's of Herr and coworkers on meteorites and Hirt and coworkers on molybdenites. This early work provided the most accurate age estimates at the time for iron meteorites and showed that, within 800 Ma age uncertainties, they probably had early Solar System ages. The application of the Re-Os system was severely limited by the low sensitivity of the thermal-ionization mass spectrometers (TDvIS) of the day and the low abundances of Re and Os (sub-ppb) in terrestrial crustal rocks. Sixteen years later, using the much more sensitive secondary ion mass spectrometry (known as SIMS or the ion-probe), Luck and Allegre (Luck et al. 1980) initiated a new era in the application of the Re-Os isotopic system to cosmochronology with a study of iron meteorites and the metallic phase from one chondrite. Their results were an order of magnitude more precise analytically than the previous studies and gave an age of 4580 ±210 Ma. This age is in surprisingly good agreement with the early data and gave further support to the early Solar System age for iron meteorites. More importantly, this work spurred the application of the newest high-sensitivity mass spectrometric techniques to Re-Os isotopic analysis and to apply the Re-Os isotopic system to new geological problems. Rb-Sr system The Rb-Sr system is based on the beta decay of 87Rb to 87Sr (Table 1). Faure (1986), Steiger and Ja'ger (1977), Faure and Powell (1972) and Hamilton (1965) review the history of measurements of the 87Rb decay constant. The currently used decay constant of 1.42 ±0.01 x lO'^yr1 is that adopted by the IUGS subcommission on geochronology (Steiger and Jager, 1977) which was based on the best mea surements at that time of the growth of 87Sr in a pure Rb salt (Davis et al. 1977) and samples of well known age. Up to this time, much previous work had used a 87Rb decay constant of 1.37 x 10'11 yr1. Subsequent work on lunar samples and chondrites that have been dated very precisely with the U-Th-Pb systems have shown better agreement with Rb-Sr ages if a decay constant between these two values is used (e.g. 1.402 x lO'Uyr1; Minster et al. 1982). In reading the literature, it is important to be aware of which decay constants have been used to calculate Rb-Sr ages. The accuracy of the Rb decay constant still is one of the major absolute uncertainties in employing the Rb-Sr system. All ages in this paper have been calculated with the 1.42 x lO-Hyr1 decay constant The potential of the Rb-Sr system for geochronology and as an isotopic tracer was recognized early because there is a large range in Rb/Sr ratios present in common rock forming minerals and in some ig neous rocks and sediments (Table 2, Fig. 1). The accuracy of Rb-Sr isochrons is largely dependent on whether or not the system has remained closed since crystallization. Unfortunately, the parent radionu clide, 87Rb, is a volatile and mobile alkali element, characteristics which lead to open-system behavior and S.B. Shirey - Rb-Sr, Sm-Nd and Re-Os Cosmo- and Geo-chronology 3 anomalous ages. The current practice is not to rely on the Rb-Sr system to give the only absolute age in formation on the crystallization age of a suite of rocks but to use it in concert with other decay schemes. Summaries of the Rb-Sr system and its applications in geochronology can be found in Faure and Powell (1972), Jager (1979), Faure,(1986) and Potts (1987). An 8sr notation to represent 8 'Sr/86Sr in the Rb-Sr system in a manner analogous to the Sm-Nd sys tem (see below) has been defined and is sometimes used. It has not gained widespread acceptance proba bly because of the difficulty in defining a bulk earth reference reservoir for Sr and because the often radio- fenic initial Sr isotopic compositions found in crustal rocks leads to exceedingly large 8$r values. Initial 7Sr/86Sr compositions in this paper are given directly without the e$r notation. In the chemistry laboratory, Rb and Sr abundances typically are analyzed by the isotope dilution method using enriched 8^Rb and ^Sr spikes. If the ^Sr spike is pure enough, the Sr isotopic composi tion can be measured on the same aliquot used for isotope dilution. Separation of Rb from Sr and from the rock is by a one-step procedure using cation-exchange chromatography. The separated Rb and Sr typically are loaded on Ta or W filaments, respectively and analyzed by positive thermal ionization mass spectrometry. Potts (1987) gives a recent summary of the chemical and mass spectrometry procedures. Sm-Nd system The Sm-Nd isotope system is based on the alpha decay of 147Sm to 143Nd (Table 1). DePaolo (1988) presents a review of the half-life determinations of 147Sm. The current decay constant value of 6.54 x 10' i2yr * (Table 1) is based on an average of the last 4 precise measurements from 1960 to 1970, which are in good agreement. An important use of the Sm-Nd isotopic system, in conjunction with absolute age determinations, is to trace the history of light REE enrichment or depletion that accompanies the evolution of an igneous sys tem. This history is recorded in initial 143Nd/144Nd variations of the igneous system. Because these variations are small, generally they are expressed in Ejsrd units which are defined as deviations in parts in 104 of the Nd isotopic composition of the sample at the time of interest compared to the Nd isotopic com position of a refererence reservoir at the same time. A popular reference reservoir for the Nd system is the Ohpndritic uniform reservoir or CHUR. DePaoio (1988) and Patchett (1989) give the appropriate equa tions and CHUR parameters. Positive values of ejsrd at a given time indicate a long-term history of light REE depletion (higher Sm/Nd) of a rock or its source relative to the chondritic reference reservok (CHUR) whereas negative 8^ indicates a history of long-term light REE enrichment (lower Sm/Nd) of a rock or its source relative to the chondritic reference reservoir. In general, the Earth's upper mantle or juvenile continental crust displays positive 8Nd values during and subsequent to the Archean whereas older, recycled continental crust displays lower positive or negative 8Nd values. It is important to remember that one CNd unit corresponds to a difference in 143Nd/144Nd of only 0.000050! This is only about 2 - 3.5 times the state-of-the-art for mass spectrometer precision between different runs of the same standard. The utility of the Sm-Nd system for dating ancient rocks is enhanced by the ability of the REE to reside in some common rock-forming minerals (e.g. clinopyroxene in komatiite and basalt) and common acces sory minerals (e.g. monazite, allanite, sphene and zircon in granitoids) that are resistant to alteration. This makes the isotope system relatively unsusceptible to parent and/or daughter redistribution on the whole- rock scale during metamorphism, a feature which has been highly touted in Archean geochronology. However, as shown below, this characteristic can be a disadvantage because the system can be to difficult to reset during crustal melting and it often displays only a narrow range in Sm/Nd (Table 2, Fig. 1) which limits the absolute age precision possible from a Sm-Nd isochron. Introductions to the behavior of the Sm-Nd isotopic system in geochronology are given in O'Nions et al. (1979), Faure (1986), DePaolo (1988) and Patchett (1989). The common practise in the chemistry laboratory is to determine Sm and Nd concentrations by isotope dilution using spikes of 149Sm and 150Nd. Typically, Sm is separated from Nd after the light rare-earth elements (REE) have been separated as a group from the rock using cation-exchange chromatography. An excellent overview of this procedure can be found in Potts (1987). An efficient time to carry out the light REE group separation is at the end of the primary column separation of Rb from Sr. Two methods to sep arate Sm from Nd are in widespread use with equally good results: 1) ion-exchange chromatography using 0.25 molar methyllactic acid on a cation column and 2) ion-exchange chromatography using di-(2- ethylhexyl)-orthophosphoric acid mixed with teflon powder. Typically, the purified salts of Sm and Nd are loaded separately on Ta and Re filaments (respectively) and analyzed by positive thermal ionization mass spectrometry (e.g. Potts, 1987). Two different schemes for normalization of Sm-Nd isotopic data for instrumental fractionation com- S.B. Shirey ~ Rb-Sr, Sm-Nd and Re-Os Cosmo- and Geo-chronology 4 monly appear in the literature. In one scheme, 146Nd/144Nd is taken to be 0.72190 and present day £Nd of zero equals a 143Nd/144Nd of 0.512638. In the other scheme, 146Nd/142Nd is taken to be 0.636151 and a present day £Nd df zero equals a 143Nd/144Nd of 0.511847. The different normalization schemes used have been discussed in detail by DePaolo (1988), Faure (1986) and Wasserburg et al. (1981). Note that in going from the latter to the former, 143Nd/144Nd is multiplied by 1.00154. The different normal ization schemes will produce slightly different atomic weights for Nd which will result in slightly different 147Sm/144Nd depending the the normalization scheme. Note that in going from the latter to the former, 147Sm/144Nd is multiplied by 1.0015. When working with literature data it is especially important to be aware how these normalization schemes affect 143Nd/144Nd since the raw ratios are 30 £Nd units differ ent. The differences in 147Sm/144Nd have a lesser effect on the differences between age-corrected initial 143Nd/144Nd but they are significant and will be important for example, when comparing data from each scheme on an isochron diagram. Each normalization uses reference reservoir values that are appropriate for that normalization, so initial £Nd values quoted in any paper and model ages generally are equivalent regardless of normalization used. Re-Os system The Re-Os isotopic system is based on the beta decay of 187Re to 187Os (Table 1). Lindner et al. (1989) have recently measured the decay constant of 187Re at 1.64 ± 0.05 x lO'^yr 1 and have reviewed previous determinations of the decay constant. Their value is higher outside of experimental uncertainties of the best geological estimate of the decay constant (1.52 ± 0.04 x 10'11 yr1) from the iron meteorite isochron of Luck and Allegre (1983) and slightly higher than their earlier estimate of 1.59 ± 0.05 x 10^ ^yr 1 (Lindner et al. 1986). Re-Os isochron ages in this paper have been calculated using the earlier Lindner et al. (1986) 187Re decay constant because it is intermediate between the extremes of the experi mental and geological determinations and gives the best agreement between the precise U-Pb zircon age for the Stillwater Complex and its Re-Os isochron age. Obviously, continued use of this geochronometer will require determining the decay constant of 187Re to higher accuracy and precision. The Re-Os system has great potential as a tracer of geological processes and for geochronology in ig neous systems because initial 18 /Os/186Os can vary by more than several tens of percent and 187Re/186Os can vary by more than several orders of magnitude (Table 2, Fig. 1). Because it is uncertain just how sus ceptible the Re-Os system is to alteration during metamorphism, it is not clear yet whether the Re-Os system will be routinely useful in Proterozoic and Archean rocks. Re and Os abundances are analyzed by isotope dilution using spikes of l85Re and 190Os. Since Re and Os occur at such low concentrations in igneous rocks, large samples (1 to 50 g) are used. Typically, these have typically been dissolved by silicate digestion or by flux-fusion. Os can be separated from sili- cate^digestions by distillation into HC1, from peroxide fusions by distillation into HBr or from Na2CO3- borax fusions by concentration into an immiscible sulfide liquid (nickel-sulfide fire-assay). After Os dis tillation, Re can be separated from the rock by solvent extraction or by anion-exchange chromatography Until recently all of the modern Re-Os isotopic analyses were determined by secondary-ion mass spectrometry (SIMS). Currently, four techniques other than SIMS can produce Re-Os isotopic data: res onance ionization mass spectrometry (RIMS), inductively-coupled plasma mass spectrometry (ICP-MS), accelerator mass spectrometry (AMS) and negative thermal ionization mass spectrometry (NTIMS). At present, NTIMS has superseded all other techniques because of its superior sensitivity which leads to an order of magnitude more precise data. . Geochronology and cosmochronologv with the Rb-Sr. Sm -Nd and the Re-Os systems The concerted co-application of the Rb-Sr and Sm-Nd systems to terrestrial and extraterrestrial chronology has been extremely valuable in spite of the fact that the most precise ages are derived from the U-Th-Pb system. The Sm-Nd system has made the major contribution to the chronology of the moon by providing a reliable time-scale for lunar highlands formation, mare basalt eruption and KREEP evolution. It also has been a major source of reliable ages for differentiated and cumulate meteorites (Patchett, 1989). The Rb-Sr system has only been useful as a cosmochronometer in lunar basalts, chondrites and some achondrites. However, it has been valuable as an indicator of disturbance and as a tracer of planetary evo lution. In studies of Archean and Proterozoic crust on Earth, the Rb-Sr and the Sm-Nd systems have been pivotal in highlighting the differences among cratons. One endmember of craton formation, typified by the Superior Province, that formed by the relatively rapid extraction of crust from the mantle and its stabi lization on 50 to 200 Ma timescale. If significant reprocessing of existing crust occured, it often happened within the uncertainties of Sm-Nd and Rb-Sr isochrons. Therefore these systems themselves can not be S.B. Shirey Rb-Sr, Sm-Nd and Re-Os Cosmo- and Geo-chronology 5 used to quantify the reprocessing except to put an upper limit on it and petrogenetic constraints derived from trace and major elements must be used. The other endmember of craton formation, typified by the North Atlantic Craton, the Yilgarn Block or the Antarctic Craton, is protracted tectonothermal evolution and significant crustal reprocessing which may be coincident with crustal extraction from the mantle. This may have occurred over the 1000 Ma timescale. In this case, Rb-Sr and Sm-Nd isochrons and their initial Sr and Nd isotopic compositions provide vital information on the protoliths, allow an evaluation of the relative proportion of juvenile crust to reprocessed crust and help unravel the deformational and metamor- phic history of the craton. The application of the Sm-Nd isotopic system to cosmochronology and geochronology can be divided conveniently into five major groups of igneous rocks: lunar samples and meteorites, volcanic rocks (ultramafic and mafic to felsic), gabbros and anorthosites, lower crustal granulites, and ophiolites. For the purposes of these short course notes, the discussion of the combined application of the Rb-Sr Sm-Nd and the Re-Os isotopic systems will follow these basic groups. Space limitations here prohibit most of the discussion of the geochronologic application of these isotopic systems which is found in Shirey (1991). The entire list of these isochron studies has been included as Table 3 for completeness. Except for felsic volcanic rocks, feldspathic granulites, and sialic gneisses, these five groups of ig neous rocks are largely basic in bulk composition. For the Sm-Nd system in particular, rocks of basaltic chemistry are the chief ones to have sufficient variation in 147Sm/144Nd for a geochronologic study, either using mineral separates, different lava flows, or layers of contrasting mineralogy in layered intrusions. However, the generally limited spread in 147Sm/144Nd and the current analytical precision on 143Nd/144Nd determinations of 0.003% translates to an optimum age uncertainty of ± 20 Ma regardless of the age of the rock under study (e.g. DePaolo, 1988). It is only in older rocks where a 20 Ma absolute age uncertainty will produce an acceptably low uncertainty as a percentage of the absolute age. This has lim ited the practical application of the Sm-Nd system for geochronology to extraterrestrial samples and Precarrjbrian to Phanerozoic rocks older than several hundred million years. Since there are large varia tions the parent daughter ratios in the Rb-Sr and the Re-Os systems this severe a limitation for them does not exist The Rb-Sr system has other features which limit its utility in basic systems, namely the mobility of Rb and to a lesser extent Sr during alteration and metamorphism under a wide variety of conditions. One example of the mobility of Re and Os during amphibolite grade metamorphism of ultramafic-maiic, Archean schists has been discovered; it remains to be seen whether the Re-Os system will show more widespread open-system behavior. Thex Sm-Nd system is less useful for internal and whole-rock isochrons on granitic rocks because granitic magmas usually have a rather restricted and low Sm/Nd which imparts a low Sm/Nd to all their crystallizing major and trace phases. Indeed, apart from the applications of the Sm-Nd system to the dat ing of Archean trondhjemite-tonalite-granodiorite gneisses, there have been fewer applications to granitic systems than there have been to mafic-ultramafic systems. Because of this low Sm/Nd, the main use of the Sm-Nd isotopic system in granitoids is to obtain model ages for the time at which the granitoid or its precursor was extracted from the depleted mantle. The Rb-Sr system can yield good isochron systematics in granitic systems when the constituent min erals are fresh. However, in a granite, the phases with the most radiogenic Sr isotopic compositions which will control the isochron age (e.g. biotite, K-feldspar), commonly reflect the last hydrothermal, metamorphic or uplift event to which the granite was subjected. Since nearly all granites contain zircon, the U-Pb system is often the most successful technique for determining the emplacement age of granites. The Re-Os isotopic system has yet to be used to obtain isochrons on granites. In many igneous suites, the Rb-Sr system has fallen into disfavor for providing absolute crystallization ages because it is too easily reset. This is not true for all igneous suites, especially those that are young, involve large fractionations between Rb and Sr and have high abundances of Rb and Sr. Some notable examples are the following: carbonatites, kimberlites, and evolved rhyolites. The ability of the Rb-Sr system to be reset has created a valuable niche for its use in the study of post-crystallization processes such as hydrothermal circulation, regional metamorphism, crustal uplift and brittle deformation. Lunar samples and meteorites The Rb-Sr and Sm-Nd isotopic systems have formed an invaluable pair of decay schemes for investi gation of the age, pre-Solar System history and shock metamorphism of extraterrestrial samples. The most precise Sm-Nd cosmochronology on extraterrestrial materials has been carried out on single samples using internal Sm-Nd isochrons between mineral separates and their whole rock. Wherever possible, the use of these internal isochrons has been preferred because differences in the individual isochron age of meteorites in the same class can exist as can differences in age between different meteorite classes. In S.B. Shirey -- Rb-Sr, Sm-Nd and Re-Os Cosmo- and Geo-chronology 6 addition, since the exact relationship between the sources of extraterrestrial samples is unknown, there is the possibility of radiogenic isotopic source heterogeneity even though work to date has shown it to be small and difficult to demonstrate. Chondrites and some achondrites show significant variations in 87Rb/86Sr and for these meteorite classes good ages can be obtained with the Rb-Sr system. Since many stony meteorites have low 87Rb/86Sr or contain phases with low 87Rb/86Sr, the Rb-Sr system has been very useful for examining initial 87Sr/^6Sr in the early Solar System. This has been facilitated by the volatility of Rb which has resulted in a large range in S'Rb/^Sr between the solar nebula, basaltic mete orites, the moon and the earth and hence a large degree of isotopic divergence in Sr in a rather short time. The Re-Os system is just beginning to be applied to iron meteorites and metals in stony meteorites. At present, the analytical precision on 187Os/18&Os has improved so substantially that the isotopic system is showing great promise as a cosmochronometer. Some research groups have found systematic differences in initial 187Os/186Os between iron meteorites and chondrites. An example of Rb-Sr and Sm-Nd isochrons on the achondrite Angra dos Reis are shown in Fig. 2. In Lunar rocks, the Sm-Nd system gives the most reliable ages because of favorable partitioning into the major silicate phases which produces a large variation in 1^7Sm/144Nd. Some of the Lunar Sm-Nd isochrons are among the most precise yet produced. The Rb-Sr system is less reliable for lunar chronol ogy. Rb was volatilized during lunar impacts, many Lunar rocks have low ^Rb/^Sr and much of the variation in 87Rb/86Sr in Rb-Sr mineral isochrons is evident in individual olivine splits perhaps due to the presence of small amounts of an exotic, high 87Rb/86Sr component. Rb-Sr and Sm-Nd isochrons on lu nar troctolite 76535 are shown in Fig. 3. Ultramafic tofelsic volcanic rocks The initial applications of the Sm-Nd system to terrestrial geochronology were for absolute age de terminations in Archean mafic to ultramafic volcanic rocks. Historically, these initial Sm-Nd results for each,terrane were quite exciting for geochronology because they demonstrated that on the scale of individ ual whole-rocks and relative to the Rb-Sr and Pb-Pb systems, the Sm-Nd system is resistant to being reset by metamorphism. By the time that the Srn/Nd system was first being applied to terrestrial rocks it was recognized widely from the general disagreement between whole-rock and internal Rb-Sr isochrons and U-Pb zircon ages, that Rb-Sr isochron ages accurately reflecting crystallization were difficult to obtain in mafic to ultramafic Archean rocks. This is a consequence of the limited range in 87Rb/^6Sr in these rocks, the low Rb and Sr content of primary minerals such as olivine, orthopyroxene and clinopyroxene and the susceptibility of these primary minerals to alteration. In current studies of Archean mafic to ultramafic rocks, there are relatively few researchers that combine Sm-Nd with Rb-Sr data for primary crystallization ages. Rb-Sr is sometimes included for completeness in a study or to show the degree to which subsequent metamorphism may have affected the rocks. The Sm-Nd isotopic system now has been applied successfully to the geochronology of Archean supracmstal rocks on every Archean craton. The main limitation to getting good Sm-Nd isochron sys- tematics is the limited spread in parent-daughter ratio that is displayed by rocks related to the same source. This spread can be maximized by careful collecting of geologically related flows in the field to sample their natural variations in modal mineralogy or by carrying out mineral separations on well preserved samples. The best Sm-Nd ages are obtained with internal isochrons on fresh mafic to ultramafic rocks. Such fresh samples are exceedingly rare in the Archean, however. The next best alternative is to analyze related volcanic rocks that, because of field relations, are suspected to have a common source. In the push to maximize the Sm-Nd isochron systematics, caution must be exercised in putting rocks that, because of major or trace element compositional differences, are clearly petrogenetically unrelated on the same isochron. They may have had isotopically distinct sources which can lead to large scatter about the isochron or worse yet can give anomalously old or young ages A good example of this can be seen in Fig. 4. In general, the limited spread in 147Sm/144Nd for whole rocks prevents the Sm-Nd isotopic system from being able to reach practical precisions of less than ± 50 Ma on average. Although this age uncer tainty is not small enough to permit stratigraphic correlations such as those possible with the U-Pb system in zircon, it is sufficient to resolve major age discrepancies in the ages of the supracrustal rocks. Further, initial 143Nd/144Nd ratios, determined from isochrons, accurately reflect the time-averaged light REE pat terns of the mantle sources for the supracrustal rocks. This is important in understanding the geochemical evolution of the mantle, especially as the ultimate source of continental crust, throughout the Precambrian. It also can lead to an understanding of Precambrian tectonic and petrogenetic processes. The Re-Os system shows great promise for geochronology in mafic-ultramafic rocks because of the large range in l87Re/18§Os that occurs in whole-rocks. Under greenschist-grade, burial metamorphism the S.B. Shjrey ~ Rb-Sr, Sm-Nd and Re-Os Cosmo- and Geo-chronology 7 Re-Os isotopic system has remained closed even when the Rb-Sr system has been severely disturbed (Fig. 5). It can be, however, severely disturbed under the tectonic conditions that might involve shear in the amphibolite fades, high degrees of fluid flow and the remobilization of other platinum group elements. High-grade gneisses and granulites Sm- Table 1: Comparison of Rb-Sr, Sm-Nd and Re-Os isoiopic systems and reference reservoirs. Rb-Sr Sm-Nd Re-Os Elemental Characierisiics and Decay Schemes cr oo BJ2 Si Sm m Efi Qs p Element type alkali alkaline earth middle REE light REE platinum group oo Valence (Vl-fold coordination) + 1 +2 +3 +3 +4,+5,-f6,+7 +4,+5,+6,+7,+8 3 Ionic Radius (A) 1.52 1.18 0.96 0.98 0.63,0.58, 0.63,0.58,0.55, a 0.55,0.53 0.53,0.39 p P. Decay Scheme 147Sm-» 144Nd a 187Re_>1870s p- Decay Constants 1.4210.01 x 10' lla 6.5410.05 x lO' 12^ 1.5210.04 xlO- llc c/> 1. 40210.008 xlO' 11 * 1.5910.05 x 10' lld n o 1. 6410.05 x 10' 11/ c^ 3 o Reference Reservoirs 87Rb/86Sr 147Sm/l44Nd 187Re/186Os Chondritic Reference Reservoir "3.3' 0.0827* 0.1966* aO o 87Sr/86Sr 143Nd/144Nd 1870s/186os r. Chondritic Reference Reservoir 1.06' f 0.70450* 0.5 12638* 3 Depleted Mantle (MORE) 0.702715/ 0.5132il> 1 .0414* O Enriched Mantle (OIB) 0.703417, 0.705317/ 0.513012, 0.51 2612/ 1.1013* Convergent Margin (IAB) 0.703911 (V 0.513012, 0.51 2612/' Continental Crust (granite, sediment) 0.7058130/ 0.512112"1 14" The term "chondritic reference reservoir" is only applicable to the Sm-Nd system (CHUR) and the Re-Os system. For the Rb-Sr system, this term is not directly applicable because the parameters are derived from the Sr-Nd mantle array for oceanic basalts and are distinctly different from the growth curve for chondrites. Data sources for this table are as follows: ^Steiger and JSger (1977), ^Lugmair and Marti (1978), cLuck and Allegre (1983), ^Lindner et al. (1986), ^Minster and Allegre (1982), Nyquist et al.(1986) Aindner et al. (1989), SDePaolo (1988), ''Jacobsen and Wasserburg (1984), Patchett (1989) (Values for fractionation correction to 146Nd/144Nd = 0.72190), 'Morgan and Walker (1989), ^Morris and Hart (1983), *Martin (1991), 'Faure (1986), mTaylor et al. (1983) and "Esser and Turekian (1990). oo ba cr co CO 3 Table 2: Comparative abundances of Rb, Sr, Sm, Nd, Re and Os and their ratios in rocks Earth reservoirs and rocks Rb Sr Rb/Sr Sm Nd Sm/Nd Re Os Re/Os sp. Primitive mantle 0.48a 15.5fl 0.03 0.3 14a 0.%7a 0.32 0.26^ 3.1^ 0.08 CD Oceanic crust 2.2C \W 0.02 3.3C K)c 0.33 0.33 -\.5d 0.001 - Q.3d 1 -1500 i Continental crust 32C 260^ 0.12 3.5C 16C 0.22 0.40^ 0.04 \d 10 O 0n 11. 4" 0.7 lla 35.8^ snb 0.07 01 C-l chondrite 3.45a 0.30 0.23 \ a 0.32 3 Komatiitee 0.8 - 3.6 7-36 0.10 0.4 - 0.86 0.86-1.9 0.47 0.5- 1.3 1 -2.2 0.5 oi MORB l.26f 113/" 0.01 3.75/" \\.lf 0.33 0.33 -\.5d 0.001 - 0.09^ 3.6- 1500 OIB 9.368 363# 0.03 5.78$ 2238 0.26 0.4 - 0.8d 0.03:0.30^ 1.1 -27 P. Granite \59h 163*1 0.98 5.61h 28.7^ 0.20 0.04 - 0.34' 0.01 -0.02' 4-17 O o o Rb, Sr, Sm and Nd analyses are in ppm, Re and Os are in ppb. Data sources areas follows: ^Taylor and McLennan (1981), ^Morgan (1986), cjaylor and McLennan (1985), ^Martin (1991), ^Walker et al. (1988),/Hofmann (1988), ^Newsom et al. (1986), ''McCullocri and Chappell (1982) and 'Walker et 1 al. (1991). 2. Table 3: Compilation of Sm-Nd, Rb-Sr and Rc-Os .iron ages for terrestrial and ertralerrcstrial rocks. Type 87Sr/86Sr(I) S ample Name Sample Type Sm-Nd Age Type ENdO) Ref Rb-Sr Age Ref Other age Ret 00 1 UNAR ROCKS IT, 76535 lunar troctolite 4260160 int. 0.010.5 1 4510170 int. 0.69909 2 60025 ferroan anorthosite 4440120 int. 0.510.6 3 4470 to 4520 4 75075 A-17 mare basalt 3700170 int. 5 10072 A- llhigh-K basalt 3570130 int. 6 3560150 10062 A- 11 low-K basalt 3880160 int. 6 39201110 6 12039, 12031 A-12 pigeon ite basalt 3200150 int. 7 3162170 int. 0.69957 7 14304, 127 A-14 high-K aluminous mare basalt 40401110 int. 0.312.6 8 3870140 int. 0.69938 8 cr 14304, 128 A-14 high-K aluminous mare basalt 3910120 int. 0.69938 8 j-ioo 15386 KREEP basalt 3850180 int. -1.6 9 3860110 int. 0.70038 10 0.69903 28 00 LUNI (best Lunar initial 87Sr/86Sr ) 3 METEORITES 2 Angra dos Re is achondrite (angrite) 4550140 int. 2.4 11 0.69892 12 455112 23 Angra dos Reis achondrite (angrite) 4564137 int. 0.110.2 13 Juvinas monomict eucrite 4560180 int. 14,15 4500170 int. 0.69898 18 453914 24 Pasamonte monomict eucrite 4600140 int. 16 disturbed 4573111 25 ? Bereba,Nv. Laredo$ouvante monomict eucrites 4510-4530 22 6 Yamato(Y750ll) polymict eucrite 45501140 int. 34 4460160 int. 0.69896 34 C/5 n Moore County cumulate eucrite 45801120 int. 17 o Moore County cumulate eucrite 4457125 int. 19 V3 3 Moama cumulate eucrite 4460130 int. 13 4430140 21 o Serra de Mage cumulate eucrite 4410120 int. 20 439717 21 BAB1 basaltic achondrite initial 87Sr/86Sr 0.69907 12 455914 27 CL Allende chondrite 0.69885 '2926 H.E.LL chondrites 4498115 w-r 0.69885 455213 30 O 0} a Nakhla non-eucritic basaltic achondrite (SNC) 1260170 int. 16 31 1340120 int. 0.70241 32 oi Zagami.Shergotty,AH77005 non-eucritic basaltic achondrites (SNC) 1340160 w-r 33 circa 180 int. 33 o MAFIC TO FELSIC VOLCANIC ROCKS I Zimbabwian Craton Beliqwe, Que Que, Fort Victoria grn. 26401140 w-r -1.0 58 o*o_ w-r North Atlantic Craton Isua supracrustal sequence 3770142 2.110.9 59 rrq Kaapvaal Craton, S Africa Barberton gm., Onverwacht volcanics 3540130 w-r 1.210.8 35 >3489134 116 Barberton gm., Onverwacht volcanics 35601240 w-r 1.914.5 36 disturbed w-r 36 >343816 117 Barberton gm., Onverwacht volcanics 3269184 w-r 115 348215 118 Commondale gm., Matshempondo pdt 3334118 w-r 2.010.7 37 Nondweni greenstone belt 3120-3210 w-r 37 3170115 37 Pongola Supergroup 29341114 w-r -2.6 38 2883169 w-r 0.70240 38 2940122 38 Usushwana pyroxenite 2871130 int -2.9 38 Usushwana gabbros 31241123 w-r -2.4 38 Pilbara Block, W Australia Talga-Talga Spgrp, N. Star basalt 3540130 w-r 1.310.7 40 >3542116 42 Talga-Talga Spgrp, N. Star basalt 3712198 w-r 1.610.4 41 Yilgam Block, W Australia Warriedar belt, Murchison Province 29801120 w-r 0.711.2 43 Southern Cross Province 30501100 w-r 0.910.7 43 Kanowna area, E Goldfields Province 31301250 w-r 715 44 -f- Kanowna area, E Goldfields Province 2780170 w-r 2.310.5 43 Kambalda area, E Goldfields Province 2790130 w-r 3.410.6 44 27201105 45 Kambalda area, E Goldfields Province 3262144 w-r 46 Kambalda area, E Goldfields Province 32301120 w-r 47 2730130 Kambalda area, E Goldfields Province 269214 48 on Superior Prov. Abitibi Belt, Munro Tnshp komatiites 26221120 w-r 1.9 49 Abitibi Belt, Munro Tnshp komatiites circa 2700 w-r 2.6 65 [1200] 2726193 65 w-r 00 Abitibi Belt, Alexo komatiites 2752187 2.410.5 50 sr Abitibi Belt, Tamiskaming volcanics 27011105 w-r 1.911.6 51 Abitibi Belt, Kidd Creek volcanics 2674140 w-r 52 2576126 w-r 0.70470 52 I Abitibi Belt, Newton Twshp Form. 2826164 w-r 2.610.3 53 269711.1 53 Wabigoon Belt, Rainy Lake area 2737142 w-r 1.910.7 54 Kamataka Craton Holenarsipur greenstone belt 26201110 w-r 55 Kolar Schist Belt 2700 w-r 1.8-8.5 57 China Hiebei Province 3500180 w-r 3.310.3 56 cr in northern Sweden Kiruna greenstone belt 1932145 int 3.611.0 60 1909117 60 J1 Churchill Province Trans-Hudson belt, Flin Flon area 1875138 w-r 4.010.2 61 w-r 00 Trans-Hudson belt,Cape Smith 1871175 3.4 62 15861150 inl 62 3 Arabian Shield Wadi Shwas area 7571256 w-r 63 721155 w-r 63 "k Washington (state) Windmere Spgrp, Huckleberry Fm 7951115 w-r 64 Colombia Gorgona Island komatiites 155143 66 CJ 8814 66 p. HIGH-GRADE GNEISSES AND GRANULITES CD North Atlantic Craton Lew i si an Complex 2920150 w-r 2.311.0 67 6 26001150 w-r -2.4 68 00 Lewisian Complex, tonalitic gn n Lewisian Complex, Scourian gn 2490130 int. 69 O S. Harris Igneous Complex 2100-2200 w-r 70 C/l 3 S. Harris Igneous Complex 1870130 int. 70 o Islay gneisses 18801350 w-r 2.0 71 1782 71 -4 Isukasia area, Amitsoq grey gneisses 36621198 w-r 1.5 72 36721135 w-r 0.7006 72 3700 72 (T Isukasia area, Amitsoq white gn 35811220 w-r 1.0 72 3585156 w-r 0.7016 .72 3600 72 Isukasia area, Amitsoq pegmatitic gn 3362162 w-r 0.0 72 3383181 w-r 0.8248 72 3450 72 O Labrador, Uivak gneisses 36651104 w-r 2.5 73 35841250 w-r 0.7006 73 CD w-r O China Shadong Province, Wangfushan gn 2700135 3.3 74 2767-2690 w-r 0.70050 74 o3- Shadong Province, Aloishan granites 2395160 w-r 0.2 74 2490150 w-r 0.70280 74 >-! w-r O Hebei Province, Quinan enclaves 3450195 2.7 75 disturbed 75 3 Hebei Province, Qianxi granulites 24801125 w-r 2.7 76 2480170 w-r 76 o"O 3680170 w-r -0.2 77 373016 78 Vilgarn Block, W Australia W. Gneiss Terrane, Manfred Complex era W. Gneiss Terrane, Ringa gneiss 32101190 w-r 0 79 W. Gneiss Terrane, Jimperding gneiss 30301135 w-r 0 79 Eastern Goldfields, Pioneer dome 28001150 w-r 3.5 79 2870160 w-r 0.70070 79 Arunta Block, C Australia Strangways Range granulites 20701125 w-r 1.5 90 1690-1740 w-r 90 Antarctic Craton Napier Complex, Ml Sones 35001700 w-r 80 3927110 81 Napier Complex, Fyfe Hills 30601160 w-r -2 82 31201200 w-r 82 27901270 w-r 82 Kaapvaal Craton, S Africa Ancient Gneiss Complex 3417134 w-r 1.110.6 39 Kamaiaka Craton, India Madras granulites 25551140 w-r 1 83 Hal i ic Shield Tjottamanselka tonalite gneisses 30601123 w-r -3.7 84 2640 84 Suomussalmi-Kuhmo granodioritic gn 2650-2850 w-r 85 2620-2860 w-r 0.70240 85 Wyoming Craton Big Horn Moutains 2950140 int. 1.1 86 Snake R. Plain crustal xenolilhs 27601220 w-r -3.9 87 Colorado Front Range granulites 1800190 w-r 3.7 88 L/i Kae Province, Canada Mountain Rapids area 2436144 w-r -2.6 89 189815 w-r 0.70714 Sweden Caledonian eclogites 503118 int 5.3 91 New Zealand Fiordland granulites 100-160 w-r 1.9-4.1 92 100-160 w-r r.ABBKUS. ANORTHOSITES AND LAYERED INTRUSIONS North Atlantic Craton Fiskenaesset Anorthosite Complex 2860150 inl 2.9 Pilbara Block Millidinna Complex 2830120 w-r -1 93 Superior Province Mulcahy Lake Intrusion 2744155 int 2.6 94 2740120 ini 0.70082 94 273311 94 GO Bad Vermilion Anorthosiie Complex 2747158 int 2 102 26901100 int 0.70079 102 Sudbury Igneous Complex 1800 106 185011 114 Wyoming Craton Slillwaier Complex 270118 inl -2.8 95 2743176 96 270514 97 Trans-Hudson orogen gabbroic pi u tons 1710-1840 inl 99 Shabogamo Intrusive suite 1379165 int -5.6 98 13661171 int 0.70407 98 cr drenville Province Adirondacks, Marcy Massif 1290 w-r 102 1290 w-r 102 1288136 int 102 973119 int 102 C/J Adirondacks, Snowy Mountain Dome 109517 int 103 3 Mealy Mountains Complex 1400 w-r 0.6 - 3.6 104 1380150 w-r 0.7028 104 Nain Province Kiglapait layered intrusion 1305122 int -A.I 101 Harp Lake Anorthosite Complex 1450 w-r -5 104 disturbed w-r 0.704- 0.707 w-r -5.6 Flowers River anorthosiles 1411148 105 P- Appalachians Baltimore Mafic Complex 490120 int 100 386129 inl 100 CD OPHIOLITES 6 C/3 Saudi Arabia Jabal Wask ophiolite 743124 int 5 107 o Jabal Ess ophiolite 782138 int 9 107 o Newfoundland Appalachians Bay of Islands ophiolite 501-508 int 7.6 108 disturbed c/; 3 Variscan basement Chamrousse ophiolite 497124 w-r 5.1 109 o Southern Urals Kempersai Massif 397120 int 8.7 110 disturbed Oman Semail ophiolite, Ibra locality 130112 int 7.7 111 Semail ophiolite, Wadi Fizh locality 100120 int 7.7 111 California King's River ophiolite 483121 int 10.7 112 1 O Feather River Belt disturbed 113 315 113 a oi Fiddle Creek Complex 206143 w-r 113 o, w-r? 3- Smartville Complex 178121 9.2 113 M O 3 * Lugmair et al., 1976; 2Papanassasliou and Wasserburg (1976); ^Carlson and Lugmair (1988), (note that this is one of many pristine lunar highlands rocks that have been studied in detail, see ref. 3 for summary); 4U-Pb and Pb-Pb ages from literature, (uncertainty due to assumptions in initial Pb isotopic composition, see discussion in Ref. 3); ^Lugmair et al. (1975); 6Papanastassiou et al. (1977); 7Nyquist et al. (1979); 8Shih et al. (1987); 9Carlson and Lugmair (1979), 10Nyquist et al. (1975); n Lugmair and Marti (1977); 12Wasserburg et al. (1977), (Angrados Reis.Allende and BABI initial 87Sr/86Sr corrected for inter laboratory bias as given in ref. 3); ^Jacobsen and Wasserburg (1984); "Lugmair (1974); "Lugmair et al. (1976); 16Unruh et al. (1977); 17Nakamura et al. (1977); 18Allegre et al. (1975); 19Tera et al. (1987); 20Lugmair et al. (1977); 21Pb-Pb isochron age (Tera et al., 1989); 22 Pb-Pb isochron ages on other monomict eucrites Bereba, Nuevo Laredo and Bouvante (Carlson et al., 1988 and ref 21); 2^Average of Pb-Pb model ages from literature as given in Tilton (1988); 24U-Pb concordia (Manhes et al., 1984); 25Pb-Pb age (ref. 16); 26Gray et al. (1973) (corrected for interlab bias as given in ref. 3); 27Pb-Pb age (Chen and Wasserburg, 1981) (this aye is fur Ca-Al rich inclusions); 28Nyquist et al. (1974); 29Minster et al. (1982); ^Summary of best Pb-Pb model ages for chondrites as given in Tilton (1988); ^Nakaniura et al. (1982); ^Papanastassiou and Wasserburg (1974), (corrected for interlaboratory bias as given in ref. 3); "Shih et al. (1982), (note that the Sm-Nd internal isochronsfor these meteorites were disturbed at 116-620 Ma and that no w-r Rb-Sr was obtained); ^4Nyquist et al. (1986), (Sm-Nd isochron combines matrix, clasts and minerals from each, Rb-Sr isochron is that given fur matrix); ^Hamilton et al. (1979); 36jahn et al. (1982); 37pb-Pb whole-rock isochron on least contaminated samples (Wilson and Carlson, 1988), (Note that the Nondweni greenstone belt displays three subparallel Sm-Nd isochrons with different initial ratios); -"Hegner et al. (1984), ("other age" listed is U-Pb zircon age on interbedded rhyolite); -"Carlson et al. (1983); 40Hamilton et al. (1981); 41Gruau et al. (1987); 42Minimum age for Talga-Talga based on U-Pb zircon age of overlying Duffer Fm (Pigeon et al. (1978); 43Fletcher et al. (1984); 44McCulloch and Compston (1981); 45Pb-Pb isochron age (Roddick, 1984); 46Cloue-Long et al. (1984); 47Chauvel et al. (1984), ("Other age" listed is Pb-Pb w-r a^e, in cluding sulfldes); 48Claoue-Long et al. (1988), (U-Pb zircon age on correlative chert horizon, accepted Katnbalda age); 49Zindler (1982); 50Dupre et al. (1984); 5l Basu et al. (1984); al. (1986); 53Cattell et al. (1984); 54Shirey and Hanson (1986); 55Xuan et , 86); 56Drury et al. (1987); 57Balakrishnan et al. (in press); 58Hamilton c J977); 59Hamilton et al. (1978); 60Skiold and Cliff (1984); 61 Chauvel et al. (1986); 62Zindler (1982); 63Bokhari and Kramers (1981); 64Devlin el al. (1988); 65Walker et al. (1988), (Note y. that the "other age" is a Re-Os isochron age which agrees well with a 2720±20 Ma Pb-Pb age on nearby flows. See text.); ^"Two Re-Os isochron ages obtained on eastern komatiitus and CO iholeiites respectively (Walker et al. (in press); 67Hamilton et al. (1979); 68Whitehouse (1988); 69Humphries and Cliff (1982); 70Cliff et al. (1983); 71Marcantonio et al. (1988), 00 ("Other age" listed is U-Pb zircon age); 72Baadsgaard et al. (1986), ("Other ages" listed are the means of large number of conventional U-Pb zircon analyses); 73Collerson el al. (1 989); ^ 73Jahn et al. (1987b); 75Jahn et al. (1987a); 76Jahn and Zhang (1984); 77Fletcher et al. (1988); 78Ion-microprobe U-Pb zircon age, (Kinny et al. 1988); 79McCulloch el al. (1983); .^ 80Black and McCulloch (1987), Black (1988); 81U-Pb zircon ion-microprobe age (Black el al. 1986b); 82McCulloch and Black (1984); ^Bernard-Griffiths et al. (1983); 84Jahn et al. ( 1 984), ("Other age" listed is Pb-Pb whole-rock age); ^Martin el al. (1 983), (Only agreement with Sm-Nd reference isochrons was obtained); 8"Carlson and Diez de Medina; 87Leeman ! et al. (1985); 88DePaolo (1981); 89Burwash et al. (1985); 90Windrim and McCulloch (1986); 91Mork et al. (1988); 92McCulloch et al. (1987); 93Korsch and Gulson (1986); 94Morrison et al. (1985), ("Other age" listed is U-Pb zircon age); 95DePaolo and Wasserburg (1979); 96Re-Os whole-rock, mineral isochron (Lambert et al. 1989); 97U-Pb zircon agu cr (Premo et al. (1990); 98Zindler et al. (1981); 99Hegner el al. (1989); 100Shaw and Wasserburg (1984); 101 DePaolo (1985); 102Ashwal et al. (1985); 103Basu and Petlingill (1983); %> 104Ashwal et al. (1986); l^Hill (1988); ^Walker et aj (1991), ("Other ages" listed are three separate Re-Os isochrons with distinctly different initial Os isotopic compositions); '^ 107Claesson et al.(1984); 108Jacobsen and Wasserburg (1979); 109Pin and Carme (1987); 110Edwards and Wasserburg; in McCulloch el al. (1980); 112Shaw et al. (1987); 3 I13Saleeby et al. (1989), ("Other age" listed is U-Pb zircon age), 114U-Pb zircon age (Krogh et al. 1984); 115Gruau et al. (1990); 116Ar 40/39 age (Lopez-Martinez ei al. 1984); ^ 1 ^Evaporation single zircon Pb-Pb age (Kroner and Todt, 1988); ^ 8Ion microprobe U-Pb zircon age (Armstrong et al. 1990). (T) c/i6 n c/>o 3 o CO O CD O oI o 3 crO (fQ S.B. Shirey - Rb-Sr, Sm-iNd and Re-Os Cosmo- and Geo-chronoiogy 18 10 MANTLE Rb/St M * ? @ G E 2 Q. 10 ^^fvKX a. 1 CD o C1 ^ * ^V* M 10 0 _; 03 TJ c /'* ' \ C1 -2 10 PM /N. MANTLE Sm/Nd -3 j£ % K MANTLE Re/os oCO -4 / , ReJ vs Os 10 o > M © Rt) vs Sr TJ Xr ° f- Snn vs Nd ^i_5 - CRUSTAL Re/Os ' 10 -6 : C/D OOcDOOo 0000 Rb, Sm or Re Abundance (ppm) Fig. 1: Abundances of parent vs daughter element (in ppm) for the Rb-Sr, Sm-Nd and Re-Os systems plotted on the same axes. Data and sources are given in Table 2. Dashed lines represent constant parent- daughter ratio. Cl=carbonaceous chondrites, PM=primitive mantle, K=komatiite, M=mid-ocean ridge tholeiite, O=ocean island tholeiite, G=granite. rtf S.B. Shirey -- Rb-Sr, Sm-Nd and Re-Os Cosmo- and Geo-chronoiogy 19 0.5135 ACHONDRITE ANGRA DOS REIS 0.5130- 4550 ± 40 Ma INITIAL 143Nd/ 144W= 0.50682±5 0.5125- PYROXENES 0.5120- 0.5115- 0.5110- -PHOSPHATES 0.5105 0.12 0.14 0.16 0.18 0.20 0.22 147 Sm/'^Nd144, 0.6992 ACHONDRITE ANGRA DOS REIS 0.6991- BASALTIC ACHONDRITES 0.6990- 4380±240 Ma co 0.6989- ANGRA DOS REIS C/) 0.6988- oo \ ALLENDE 0.6987- 0.6986 0.000 0.001 0.002 0.003 87 Rb/ 86 Sr Fig. 2 Comparison of internal Rb-Sr and Sm-Nd isochrons on the achondrite Angra dos Reis. The Sm-Nd isochron is essentially a two-point isochron that gives an age equal to the formation of the solar system. The fractions analyzed for Rb-Sr work include whole-rock splits, pyroxene and the phosphate, whitlockite. They are extremely unradiogenic and do not regress to a precise age. They are consistent with an initial 87Sr/86Sr that is clearly resolved as lower than the basaltic achondrite isochron but higher than the initial 87Sr/^6Sr on Ca-Al rich chondrules from the Allende meteorite. Figure 2a is redrawn from Lugmair and Marti (1977). Figure 2b is redrawn from Wasserburg et al. (1977) and The Sm-Nd isotope systematics of Angra dos Reis have been reanalyzed by Jacobsen and Wasserburg (1984) with similar age results. S.B. Shirey - Rb-Sr. Sm-Nd and Re-Os Cosmo- and Geo-chronoiogy 20 0.714 LUNAR TROCTQLITE 76535 4510±70 Ma 0.710- INITIAL 87Sr/ 86Sr = 0.69909±3 CD CO 0.706- CO 0.702- PYFOXENE -PLAG & TOTAL ROCK (4 POINTS) 0.698 0.04 0.08 0.12 0.16 0.20 87 Rb/ 86 Sr 0.522 LUNAR TROCTOLITE 76535 0.520- 4260±60 Ma INITIAL £...= 0.0±0.5 Na 0.518- PYROXENE 0.516- T3 z OLIVINE CO 0.514- ii MAGNETIC FRACTION SYMPLECTITE 0.512- -TOTAL ROCK PLAGOCLASE 0.510 0.10 0.20 0.30 0.40 0.50 147 Sm/144Nd Fig. 3 Internal Rb-Sr and Sm-Nd isochrons for lunar troctolite 76535, a typical early cumulate from the lunar highlands. The Rb-Sr and Sm-Nd isochron ages are not in agreement. The current interpretation of the Sm-Nd age is as the age of crystallization, whereas the Rb-Sr age currently is interpreted as anomalously old (Carlson and Lugmair, 1988). All phases on the Rb-Sr isochron are unradiogenic and the slope appears to be controlled by olivine mixing with some old radiogenic component. In contrast, note the large range in 147Sm/144Nd of the magmatic phases on the Sm-Nd isochron. Fig. 3a is redrawn from Papanastassiou and Wasserburg (1976) and Fig. 3b is redrawn from Lugmair et al. (1976). 181 S.B. Shirey - Rb-Sr, Sm-Nd and Re-Os Cosmo- and Geo-chronology 21 0.5131 NQNDWENI GREENSTONE BELT 0.5129- 3123±337 Ma 0.5127 X KOMATIITES t KOMATIITIC BASALTS 0.5125 O BASALTS >20a±87 Ma 0.5123 0.5121 NONDWENI GREENSTONE BELT 0.5119 3122±93 Ma 0.5117 0.14 0.16 0.18 0.20 0.22 147 Sm/l44Nd 0.5130- NONDWENI GREENSTONE BELT 0.5125- MAFC ROCKS AND MINERALS 8 12 16 20 24 FELSIC ROCKS MgO (wt%) 0.5120' 0.5115 CO "tf 3429±32 Ma 0.5110 0.5105 0.11 0.13 0.15 0.17 0.19 0.21 147 Sm/144Nd Fig. 4: Sm-Nd isochrons and £Nd vs MgO relationships for volcanic rocks of the Nondweni greenstone belt, Kaapvaal Craton, South Africa. When grouped by composition (Fig. 4a), three isochrons with similar ages but different initial 143Nd/144Nd are apparent. Adding felsic volcanic rocks to this group isochron produces an artificially old age (Fig. 4b). The initial End of the samples varies directly with their MgO content (Fig. 4c), suggesting the lower £Nd are produced by crustal contamination as shown by the assimilation-fractional crystallization curves. Tick marks indicate percentage of crustal input. Figs. 5a-c redrawn from Wilson and Carlson (1989). IU S.B. Shirey -- Rb-Sr, Sm-Nd and Re-Os Cosmo- and Geo-chronoiogy 22 0.5145 PYKE HILL KQMATIITES 0.5144- 0.5143- 4.0 co PYKE HILL KQMATIITES 3.5 - 0.51421 2720 Ma FB&&CE ISOCHRON 3.0 J ' INITIAL 8 = +2.6 3 0.5141 "^ 2-5 0.270 0.275 0.280 0.285 0.290 147 Sm/' 44Nd O 2.0- >» 2726±93 Ma 0.7160 1.0 INITIAL [8 os/ ' a 0.7000 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 87 Rb/ 86 Sr Fig. 5: Sm-Nd, Rb-Sr and Re-Os whole-rock isochrons for komatiites from the Pyke Hill locality, Munro Township, Ontario. The komatiites show an extremely limited spread in 147Sm/144Nd that does not regress to an isochron. The Rb-Sr systematics have clearly been reset at some time after crystallization. The Re-Os isochron shows substantial spread in 187Re/186Os and gives the accepted crystallization age. Figures redrawn from Walker et al. (1988). 185 S.B. Shirey -- Rb-Sr. Sm-Nd and Re-6s Cosmo- and Geo-chronoiogy 23 0.78' AMITSOQ GREY GNEISSES 0.90- AMITSOQ WHFTE GNEISSES 0.76H 0.86- CO CO CO oo 0.82- oo 0.74-1 CO r>. 0.78- CO oo 3672±135 Ma 3585±56 Ma °-72 87 86 INITIAL Sr/\r/ 86Sr=0.7006±1Sr=0. 0.74- INITIAL 8 !Sr/r/ 86Sr=0Sr=0.7016±1 MSWD=19 MSWD=20 0.70 0.70- 0.0 0.4 0.8 1.2 1.6 i 2 3 87 Rb/86Sr 87 Rb/ 86 Sr 24 0.5140' AMITSOQ PEGMATITIC 0.5130- GFEY O WHITE CO 0.5120- ^PEGMATITIC 16H oo 0.5110- CO r>. T3 0.5100- co 3 z 3383±81 Ma CO 0.5090- 877 86 INITIAL Sr/ Sr=CSr=0.8248±3 Pegm. gneisses: 3362±62 Ma 0.5080- MSWD=114 White gneisses: 3581 ±220 Ma 'Grey gneisses: 3662±198 Ma 0.5070 100 200 300 400 500 0.00 0.04 0.08 0.12 0.16 0.20 0.24 0.28 87 Rb/86Sr 147l44Sm/Nd Fig. 6: Rb-Sr and Sm-Nd whole-rock isochrons for Amitsoq gneisses from the Isukasia area, southern West Greenland. The white and grey gneisses show such a limited spread in 147Sm/144Nd that their Sm-Nd isochron ages are indistinguishable outside of errors. The mean age for the regressions, however, agree quite well with the individual Rb-Sr isochrons for each of the gneiss groups. Note the changes in scale for the Rb-Sr isochrons. Figures redrawn from Baadsgaard et al. (1986a). I8 1/ S.B. Shirey -- Rb-Sr. Sm-Nd and Re-Os Cosmo- and Geo-chronoiogy ST1LLWATER COMPLEX 50 2734±38 Ma 3 A-TYPE CUMULATES 40 INIT 1 U-TVPE CUMULATES co MASSIVE 03 30 - 1 2707 Ma ISOCHRON SULFIDES OJ I 20 -3 r A-SEAM CHROMnTTES 10 -BRONZfTE PEGMATTTE -5 UMS SULFIDES -KCHROMITITE 0 1.0 2.0 3.0 4.0 200 400 600 800 1000 (Nd/Sm) n 187 186 Re/ Os A-TYPE REFERENCE ISOCHRON 2.0 INITIAL RATIO=1.13 co 00 1.6 5 1.2 U-TYPE ISOCHRON H INITIAL RATIO=0.87 -G CHROMnTTE 0.8 4 8 12 16 20 187 186 Re/ Os Fig. 7: Initial £Nd vs Nd/Sm and Re-Os whole-rock isochrons for whole-rocks from the Stillwater Igneous Complex, Montana. Differences are apparent in the initial £Nd of the magmas (Fig. 7a). A large and apparently magmatic 187Re/l86Os is displayed by ultramafic series sulfides, silicates and chromitites (Fig. 7b) allowing a precise age for the intrusion to be calculated. A significant difference exists, however, between anorthositic type magmas and ultramafic-type magmas (Fig. 7c) with substantial evidence for magma mixing. These figures are redrawn from Lambert et al. (1989). 85 S.B. Shirey - Rb-Sr, Sm-Nd and Re-Os Cosmo- and Geo-chronology 25 -10 D SUPRACRUSTAL ROCKS INTRUSIVE ROCKS O FLOOD BASALTS -10 1000 1500 2000 2500 3000 3500 4000 4500 AGE (Ma) no £ CO -5 -10 - D = juvenile granitoids A = recycled granitoids DM = depleted mantle -15 = banded iron formation CS = clastic sediment 1000 1500 2000 2500 3000 3500 HC = hypothetical crust AGE (Ma) Fig. 8: Initial £Nd vs time for a majority of the mantle-derived rocks and crustally derived rocks from the literature that are discussed in the text. The data are plotted as individual samples from Sm-Nd isochron regressions with the age taken from the Sm-Nd isochron if it is the accepted age of crystallization. Supracrustal rocks in Fig 8a include both mafic and felsic major element compositions but are dominated by the former. Intrusive rocks include anorthosites, gabbros and mafic layered intrusions. High-grade gneisses are included with granitoids on Fig. 8b. Additional data on initial e^ in flood basalts has been added. Note the positive £Nd growth curve for the mantle in the Archean. It is not clear from the data whether the mantle has evolved in continuous or a stepwise fashion. Note also the occurrence of various types of rocks during certain periods of Earth history. The granitoids are divided into two types. Juvenile granitoids clearly have a much higher initial £Nd- Note the time-scale change for Fig. 8b compared to 8a. S.B. Shirey - Rb-Sr, Sm-Nd and Re-Os Cosmo- and Geo-chronoiogy 26 OSMIUM ISOTOPIC EVOLUTION 2.0 3.0 Age (Ma) Fig. 9: Initial 187Os/ I86Os vs time for Re-Os isotopic data from the literature. Three possible terrestrial growth curves are plotted: 1) a curve through osmiridiums (Allegre and Luck, 1980), 2) a curve calculated from the analyses for chondrites (Walker et al. 1989) and 3) a curve passing through primitive ocean island basalts (Martin, 1991). See text for details. Lithospheric peridotites have the lowest initial 187Os/186Os, whereas upwelling plumes and enriched portions of layered intrusions have the highest (87 CHARACTERISTICS OF "GOOD" ISOCHRONS THE THREE PRIMARY ASSUMPTIONS FOR VALID ISOCHRONS: All samples on an isochron formed at the same time. All samples had same initial isotopic composition at time of crystallization. System remained closed to parent-daughter diffusion. ADDITIONAL CHARACTERISTICS TO HELP JUDGE ISQCHRON QUALITY: Clear geological relationship among samples on isochron. High degree of linearity on parent-daughter plot. Age agreement with precise data from another system. "Sensible" age that agrees with stratigraphy. Accurately and precisely date a real geological event (i.e. crystallization, high-T metamorphism, uplift). Isochron initial derivable from reasonable reservoirs. PRACTICAL COMPARISON OF ISOTOPE SYSTEMS (CONT.) RB-SR SM- ND RE-os chondrites meteorites iron meteorites sialic gneisses lunar samples peridotites granites Pre-C volcanics komatiites AMENABLE TO pegmatites Pre-C gneisses picrites ISOCHRONS rhyolites ophiolites ophiolites hydrothermal ores layered intrusions layered intrusions anorthosites oo diff. meteorites NOT AMENABLE low vol. meteorites granites lunar samples TO ISOCHRONS lunar samples young rocks (basalts) Pre-C vole, rocks (andesites) __(granites) granites peridotites AMENABLE TO granites alkalic rocks molybdenites MODEL AGES gneisses eclogites (basalts) (granites) NOT AMENABLE Pre-C vole, rocks komatiites komatiites TO MODEL AGES basalts chromitites PRACTICAL COMPARISON OF ISOTOPE SYSTEMS RB-SR SM- No RE-os HOST MINERALS major major and trace ultratrace PAR./DAUGH. RANGE large limited profound METAMORPH. EFFECTS large very limited limited hydrothermal uplift crystallization crystallization MAIN USES metamorphism mixing hydrothermal PGE -D fault movement \ high Rb systems LESSER USES crystallization post-crystallization post-crystallization INTERNAL VS WHOLE-ROCK ISOCHRONS THE INTERNAL ISQCHRON: : COMPRISED OF MINERALS SEPARATED FROM ONE SAMPLE. ADVANTAGES: -All components of isochron formed at same time. -All components of isochron will have same initial. DISADVANTAGES: -Minerals are more susceptible to parent-daughter interdiffusion (more easily reset). INTERNAL VS WHOLE-ROCK ISOCHRONS (CONT.) THE WHOLE-ROCK ISOCHRON: COMPRISED OF DIFFERENT WHOLE-ROCK SAMPLES. ADVANTAGES: -Components are too far apart for interdiffusion even on geologic time scales (more difficult to reset). DISADVANTAGES: -Components of may not have formed at same time. -Components may not have had the same initial ratio. ISOCHRON AGES VS MODEL AGES ISOCHRQN AGES: Based on multi-sample least-squares regression line fit. Statistical treatment of systematics of fit possible. Validity of age uncertainty can be estimated. Disturbances to system can be discerned. Requires a large amount of data for each isochron. ISOCHRON AGES VS MODEL AGES (CONT.) MODEL AGES: Based on isotopic growth curve-reservoir intersection. No check of data with systematics possible. Age uncertainty is large and has no geological significance. Disturbances to system are not evident directly. Can be used on just one sample (this may be enough to decide between various petrogenetic processes. v.c e~ - o-ods -nows a pr.orirusr :»5 «n^rKS (Jnrniinira el Cuimnenmica ACia Vol. }6. 00. 000-000 ;'IS^ ?£hor The hvdrothermal stability of zircon: Preliminary experimental and isotopic studies A. FCRISHNA SINHA. DAVID M. WAYNE.' and DAVID A. HEWTTT Depanment of Geological Sciences. Virginia Polytechnic Institute and State University. Blacksburg. Virginia 24061. USA (Received Ocwotr 8. 1991: accepted in reused form June 16. 1992) Abstract Experimental investigations of the stability of the U-Pb isotopic system in nonmetamict zircons show that appreciable losses of Pb and U can be induced at amphiboliie grade conditions (400*C to 600*C. 4 to 6 kb) in 2 M NaCl and 2% HNO, solutions. The severity of U loss and, to a lesser extent Pb loss, varies with solution composition: in this case the 2 M NaO solution induced more Pb and U loss than the 1% HNO? solution at the same P-T conditions. Scanning electron microscopy of the run products also revealed a range of corrosion-reiated surface features, which suggest that some of the observed trends in Pb and U loss must be attributed to zircon dissolution. Backscattered electron (BSE) imaging of the run products further suggests that partial homogenization of chemical zoning patterns occurred during the experiments. Microprobe analyses of treated and untreated grains show that both populations have a similar range of Hf contents. Thus, the apparent loss of sharp, well-denned zoning features is most likely due to small-scale "smearing out" of formerly sharp chemical gradients and is perhaps related to the annealing of lattice defects caused by alpha-recoil damage. Thus, experimentally induced U-Pb isotopic discordance in zircon is a complex function of zircon stability and annealing effects. INTRODUCTION con-hosted U, Th, and Pb may undergo a considerable degree of redistribution atsubsolidus conditions. In some instances, THE CHEMICAL AND ISOTOPIC response of zircons to changes the zircon U-Th-Pb system remains undisturbed regardless in P and T may be complicated by primary intracrystalline of P~Tconditions or kinematic regime ( PSUCAT et al., 1985: chemical, structural, and isotopic inhomogeneities (e.g_ TlLTON et aL. 1958). It is likdy that variations in the degree STEIGER and WASSERBURG. 1966; SOMMERAUER, 1974, of metamorphically induced U-Th-Pb discordance may be 1976: and others). STEIGER and WASSERBURG (1966) first attributed to a number of factors: (I) growth of rims on pre suggested that the anisotropic response of zircon crystals to existing zircon crystals implying either residual enrichment, thermal events was due to the presence of discrete isotopic or solution and transport of Zr during metamorphic or hy- and physiochemical microdomains within each grain. SOM- drothermal events (GASTU. et aL. 1967: DA vis et al.. 1968: MERAUER ( 1974. 1976) demonstrated that zircons rich in HART et aL. 1968: GULSON and KROGH. 1975: SINHA and trace elements (>2 mol% total) consist of two phases: a ther GLOVER. 1978: PEUCATW al.. 1985: GEBAUER et ai., 1981: mally stable structure with low trace element concentration VAN BREEMAN et aL. 1987: WAYNEetaL. 1992): (2) radiation and an amorphous, microheterogeneous mixture of SiO? and damage, hydroxyiization. and subsequent structural anneal ZrO; which is enriched in trace components: an observation ing incurred prior to or during metamorphism (GAST1L et now more fully documented by the transmission electron ai.. 1967: GEBAUER and GRONENFELDER. 1976: CORFU et microscopy studies of MCLAREN et al. (1991). Low tem ai., 1985: SILVER and DEUTSCH. 1963); (3) discontinuities perature (ca_ 350°C) annealing and loss or gain of radiogenic in the bulk composition of the enclosing rocks or minerals Pb, U, Th and other trace elements is likely to occur more (GEBAUER and GRONENFELDER, 1979: ALEINIKOFF. 1983: readily in the latter phase (SOMMERAUER. 1976). IR and WAYNE et aL. 1992): (4) high fluid pressure and activity NIR spectroscopy of metamict and nonmetamict zircons during metamorphism (GESAUER and GRCNENFELDER. ( AINES and ROSSMAN, 1986) indicates that molecular water 1976: SINHA and GLOVER. 1978: SCHARER. 1980): (5) direct may enter radiation-damaged zircon crystals and dissociate U adsorption without new crystal growth (GRAUERT et ai.. to form (OH)~ groups. The hydroxyl groups may actually 1974); (6) decrease in structural integrity of zircon crystal stabilize the metamict state by satisfying local charge imbal structure through radiation damage ( HOLLAND and GOTT- ances. Heating of these samples showed that (OH)'and (H)~ FRIED, 1955: OZXAN. 1976: YADA et aL, 1981) in association reconstitutes to H?O and escapes prior to recrystallization. with volume changes may cause brittle failure (CHAtcou- Conceivably, this "water of metamictization" could carry ra MAKOS et aL, 1987) and enhanced leachability of U-Pb by diogenic daughter products (e.g^ Pb°) and trace elements fluids ( EWING et aL. 1982:1CROGH and DA vis, 1975). From out of the zircon as it escapes (GOLORICH and MUOREY. 1972). these studies, it is apparent that the significance of a particular discordance-generating circumstance or mechanism may A number of geochronologic studies of metamorphic rocks vary, and that no single factor can be correlated to consistent (GEBAUER and GRCNENFELDER. 1976, 1979: SiNHA and trends of isotopic discordance. However, the importance of GLOVER. 1978: WILLIAMS et al., 1984) have shown that zir- fluid/rock ratios during metamorphism and the ability of hydrothermai and metamorphic fluids to dissolve and trans Present address: Department of Eartn Sciences. The University, port Zr. Hf, U. Th, Pb. REEs. and other elements is undeni Leeds LS2 9JT England. able (GEBAUER and GRONENFELDER- :976: CUNEY. 197S: SINHA and GLOVER. 1978: PAGEL. 1982: WAYNE and SINHA, 1988: ZsrrLER et aL. 1990: WAYNE st at. 1992). Ouhng a metamorphic episode involving fluids, the ra diation-damaged portion of a zircon may be subject to a number of processes leading to isotopic discordancy. These processes tndude (1) preferential teaching of mctamicr zones due to the penetration of Quids along microfractures (cf. WAYNE and SJNHA, 1988). (2) annealing of metamic: zones, or entire crystals during metamorphtsm (GULSON and KXOGH. (975). and (3) volume or grain boundary diffusion of ?b {or U) out of the zircon (TiLTON. i960: WA5S£RauRC. 1963). The factors controlling the rate and extent of these processes must indude (1) the physical and chemical nature of the zircons involved. (2) the intensity and duration of the P'T conditions of the metamorphic/hydrothennal episode, and (3) the composition and amount of Quid present. SELECT REFERENCES ON ZIRCONS, MYLONTTES AND DICORDANCY 1. Wayne, D.M. and Sinha, A.K., 1988, Physical and chemical response of zircons to deformation. Contrib. Mineral. Petrol., 98,109-121. 2. Wayne, D.M. and Sinha, A.K., 1992, Stability of zircon U-Pb systematics in a greenschist-grade mylonite: An example from the Rockfish Valley Fault Zone, Central Virginia, USA. J. Geol. (in press). 3. Sinha, A.K. and Glover, Lynn m, 1978, U/Pb systematics of zircons during dynamic metamorphism. Contrib. Mineral. Petrol., 66, 305-310. 4. Wayne, D.M., Sinha, A.K. and Hewitt, DA., 1992, Differential response of zircon U- Pb isotopic systematics to metamorphism across a lithoiogic boundary: An example from the Hope Valley Shear Zone, southeastern Massachusetts, USA. Contrib. Mineral. Petrol., 109, 408-420. 5. Sinha, A.K., Wayne, D.M. and Hewitt, D.A., 1992, The hydrpthermal stability of zircon: Preliminary experimental and isotopic studies. Geochim. Cosmochim. Acta, 56, 000-000. 6. Pettingill, H.S., Sinha, A.K. and Tatsumoto, M., 1984, Age and origin of anorthosites, charnockites, and granulites in the Central Virginia Blue Ridge: Nd and Sr isotopic evidence. Contrib. Mineral. Petrol., 85, 279-291. 7. Sinha, A.K., Hund, EA. and Hogan, J.P., 1989, Paleozoic accretionary history of the North American plate margin (Central and Southern Appalachians): Constraints from the age, origin, and distribution of granitic rocks. In J.W. Hillhouse, ed., Deep Structure and Past Kinematics of Accreted Terranes, Am. Geophys. U. Geophys. Monograph 50, IUGG v. 5, 219-238. ABSTRACT FORM FOR ALL GSA MEETINGS IN 1992 Complete all sections a) through J) below D TYPE ABSTRACT COMPLETELY WITHIN THE BLUE LINES BELOW. CHECK ONE. DISCIPLINE '.category) oeiow in wnicn re N2 33438 viewers will oe oest Qualified c evaluate your aDstrao. CRUSTAL EVOLUTION OF GRENVTLLE TERRANES IN THE CENTRAL AND SOUTHERN 1 archaeoiogicai geology APPALACHIANS: THE Pb ISOTOPE PERSPECTIVE FOR GRENVILLE TECTONICS 2 coaigeotogy PARKS, Jane E.. JENKS, Patrick J..SINHA. A.Krishiuu Department of Geological 3 computers Sciences. Virginia Polytechnic Institute and State University, 4 economic geotagy Blacksburg. VA 24061 5 engreenng geology Q 6 envvonmentai geology Grenville (1.0 b.y.) age rocics are recognized in eastern North America from Newfoundland to Georgia Q 7 geocnemean/. aqueous (approximately 2700 km) and are pan of a globe encircling belt As the majority of these rocks are of Q 8 geocnemissry. other granuiite grade, accretionary tectonics and pre-Grenville terranes are difficult to evaluate. However, Q 9 geotagy eaucaaon whole rock Pb-U-Th isotope systematics permit recognition of distinct lead isotopic reservoirs that Q >0 geomorpnotogy may reflect juxtaposition of different crustal blocks. Qn geopnysics/ Pb isotopic analyses of over 80 samples of basement rocks from PA to GA define at least teapnopnyscs two distinct groups. Group I includes rocks from VA, MD, and PA, while Group II includes rocks Q12 geosaence nfexmaoon from GA and NC. Initial Pb isotopic compositions of the basement rocks of the Virginia Blue Ridge Q:3 gtooai change (of Group I) are used as a reference for comparing all other isotopic ratios. These reference isotopic Q u hisoy of geology values (the average of 25 whole rocks) are 206pb/204Pb: 16.63-18.64 (average 1727). 207Pb/204Pb: Q15 hyarogeotogy Q 16 rnanne geology 1538-15,58(average=15.48), ^Pb/^Pb: 33.52-39.51 (average=36_50). The isotopic deviation in Qt7 merooaJeornoiogy percent (A207/204, A208/204) show a remarkable separation of the basement massifs into separate U- Q18 mneraJogy/ Th-Pb provinces. For example, A207/204 and A208/204 values for other Group I rocks (such as the crystatiograpny State Farm Gneiss of Virginia) range from -4.4 to 3.6 and -30.9 to 11.1 respectively. Rocks of Q '9 paieoceanograorjy/ Group II have a higher percent deviation from the reference. For example, the Carvers Gap Gneiss of paJeocumatoiogy North Carolina has a A207/204 range of 4.63-13.25 and a A208/204 range of 91.78-414.78 and Q 20 paleontology/ defines a clearly distinct reservoir for A208/204 values.. pajeoootany Limited published lead isotopic data for other Grenville age basement massifs from Q21 petroleum geology Newfoundland to Texas have similarities and differences in terms of their time-integrated Th/U and Q 22 petrology, experimental U/Pb relative to the reference values presented here. For example, data from Texas have higher time- Q 23 petrology, igneous integrated Th/U and similar U/Pb while basement massifs from the Adirondacks have similar time- Q 24 petrology, rnetamorDnic integrated Th/U but higher U/Pb. Q 25 petrology, sedimentary Q 26 planetary geology The use of Pb isotopes to determine source region characteristics for crustal provinces has far Q 27 Precamonan geowgy reaching implications. Differences between juvenile crust and reworked older crust leading to Q 23 Quaternary geology similarities or differences in reservoirs can be used as a method for determining the accretionary Q29 remote sensing history of distinct terranes during the Grenville Orogeny. OX seaimentotogy Q 31 straograony O 22 structural geology "5^23 teoonics Q 24 voteanottgy Q3S otner SELECT ONE FORMAT ..._ ..._.._. ...._...._....._._. __ . . . __ .-.__ 05; ___ INVITED FOR SYMPOSIUM NUMBER: WHERE? WHEN? {first tme wofas y trt/e at symposium) VOLUNTEERED FOR DISCIPLINE SESSION CHECK IF YOU ARE WILLING TO BE A SESSION CHAIR VOLUNTEERED FOR THEME SESSION NUMBER: Your Name ______. ______Office Phone Home Phone (first rtve wonjs c: title at Them* Session i SPEAKER'S IDENTITY AND MAILING ADDRESS Name JOT.£ 5 for*-^ . 'A> SELECT ONE MODE (Be aware mat some sessions may have Address 2t0C(f~}jT:£^_/" ^^" &"^,iC~. £'<-/ ~ ^<>". C«2j seen designated soecncaily as either 'poster' or *oraO Address V.» J i n i <*- / Cc." A. ___ ORAL Vernai assentation oetore a seared audience. C4ty»SV21P &(t(£.tS]y±ri}t ' > <"jl /'u. ^ ^X^* POSTER Graorjc oisoiay on ooster ooams suoo»emented by Country U J ^ soeaxer comments. OfRce Phon Selected References: Lund, K., Snee, L.W., and Evans, K.V., 1986, Age and genesis of precious metals deposits, Buffalo Hump district, central Idaho: implications for depth of emplacement of quartz veins: Economic Geology, V.81, p.990-996. Snee, L.W., Lund, K., Evans, K.V., Gammons, C.H., and Kunk, M.J., 1991, 40Ar/3eAr thermochronology of fracture-controlled mineral deposits of the Idaho batholith - age, thermal history, and origin: U.S.G.S. Circular 1062, p. 74-76. Goldfarb, R.J., Snee, L.W., Miller, L.D., and Newberry, R.J., 1991, Rapid dewatering of the crust deduced from ages of mesothermal gold deposits: Nature, v.354, p.296-298. Snee, L.W., Sutter, J.F., and Kelly, W.C., 1988, Thermochronology of mineral deposits: dating the stages of mineralization at Panasqueira, Portugal, by high-precision 40Ar/39Arage spectrum techniques on muscovite: Economic Geology, v.83, p.335-354. Snee, L.W., and Wang, Z., 1989, Geology, geochemistry, and age of the Geiju batholith and associated polymetallic deposits, southern China: U.S.G.S. Circular 1035, p.69-70. Chesley, J.T. , Halliday, A.N., Snee, L.W. , Mezger, K. , Shepherd, T.J., and Scrivener, R.C. , in press, Thermochronology of the Cornubian Batholith: implications for pluton emplacement and protracted hydrothermal mineralization: Geochimica et Cosmochimica Acta. Geissman, J.W., Snee, L.W. , Graaskamp, G.W. , Carten,R.B. , and Geraghty, E.P. , 1992, Deformation and age of the Red Mountain intrusive system (Urad-Henderson molybdenum deposits), Colorado: evidence from paleomagnetic and data: G.S.A. Bulletin, v.104, p. 1031-1047. Snee, L.W. , and Hayes, T.S., 1992, 4QAr/3SAr geochronology of intrusive rocks and Mississippi-valley-type mineralization and alteration from the Illinois-Kentucky fluorspar district; U.S.G.S. Open-File Report 92-1, p. 59-60. Snee-2 II. 1986. pp AGE AND GENESIS OF PRECIOUS METALS DEPOSITS, BUFFALO HUMP DISTRICT CENTRAL IDAHO: IMPLICATIONS FOR DEPTH OF EMPLACEMENT OF QUARTZ VEINS KAREN LUND,* LAWRENCE W. SNEE/ AND KARL V. EVANS U. S. Geological Survey, Boi 25046, Mail Stop 922. Denver Federal Center, Denver, Colorado 80225 1 40* 2 (MUSCOVITE) j 3 {MUSCOVITE} 1 I / 300r- :**1: :1. M/ . : : ' '. /1 tooTTE) 200J- 2 (MICROCLINE} ; ? ^-^ OOr- C B A 60 TO 80 m.y. FlC. 3. Cooling curve for the Buffalo Hump district. 1 - am- phibolite; 2 = muscovite-biotite granite; 3 = quartz vein: A = rapid cooling (about 95°C/m.y.) of amphibolite at about 9 km; B « em placement of muscovite-biotite granite at 4 to 9 km; C = fracturing and gold mineralization at >4 km; D = slow coding (about 3.5°C/ m.y.) of region at about 4 km. 4O USGS Circular 1035, p.69-70 Ar/^Ar Thermochronology of Fracture- Controlled Mineral Deposits of the Idaho Batholith-Age, Thermal History, and Origin provides information about the distribution of argon in the analyzed mineral or whole rock and can indicate whether By L.W. Snee, Karen Lund, K.V. Evans, C.H. the dated material formed before, during, or after alteration. Gammons, and M.J. Kunlc Duration of mineralization and number of episodes can be evaluated by comparing mineral data from veins that formed during multiple stages with data from associated age-spectrum dating is a highly precise wall rocks. "Ar/^Ar age-spectrum dates are unique (<0.15 percent absolute anaJytical uncertainty) and accu because the time when various minerals close to diffusion of rate isotopic technique that is a powerful tool for solving argon can be related to temperature; thus, the dates provide some long-standing problems in economic geology, includ a thermochronology. These time-temperature data are use ing the age, duration, number of stages and (or) episodes, ful for understanding details of ore-forming processes and and temperance of mineralization. This method offers the temporal resolution necessary for dating different stages of for planning mineral exploration. ^Ar/^Ar thermochrono- mineralization and alteration in hydrothennaj systems. An logic data have been used to provide valuable constraints on the age, thermal history, and origin of fracture-controlled age-spectrum or isochron analysis of the data from a sample mineral deposits of the Idaho batbolith. than cooling ages of the peraluminous granites in most The age and origin of gold-bearing quartz veins districts. Therefore, the vein deposits are Cretaceous or, hosted in Cretaceous rocks of the Idaho batholith or older less commonly. Paleocene and were not formed by hydro- rocks in centra] Idaho were the subject of debate prior to thermal activity associated with Eocene plutons. Further detailed isotopic dating. Eocene plutonic and dike rocks more, the *Ar/*Ar age spectra for minerals from the crop out in many of the mining districts, and, locally, deposits and (he cooling history of the region after emplace disseminated gold deposits are present in Eocene volcanic rocks such as in the Thunder Mountain district. It has been ! ment of Cretaceous granites quantify the thermal and spatial long argued that the numerous gold-bearing quartz veins effects of younger events. In particular, age spectra of distributed throughout the Idaho batholith were genetically quartz-vein muscovites commonly show ^Ar loss that related to the Eocene plutonic and volcanic event. occurred during younger Cretaceous and Paleocene miner Many quartz veins in the southern part of the Idaho alization; only those samples collected within a few meters batholith (within the Elk City, Chillis, Hailey. and Twin of Eocene dikes, plutons. and volcanic centers display Falls 1° x 2* quadrangles) are near the roof zones of Late partial "Ar loss incurred during Eocene events. In addition, Cretaceous (78-70 Ma), marginally peraluminous, granite- microcline from nearby Cretaceous plutons yields Late granodiorite (primarily biodte granodiorite and muscovite- Cretaceous to Paleocene ^Ar/^Ar dates which indicate that biotite granite) plutons: other quartz veins are in older the ambient temperature of host rocks and mineral deposits metaluminous granodiorite-tonaliie plutons (93-87 Ma) and was already below about 150 *C (the argon closure temper metamorphic rocks that were intruded by the younger ature of mkrociiDe) before Eocene magmatic events. Thus, plutons. The deposits are both in discrete quartz-filled only Cretaceous or Paleocene mineral deposits that were cut fissure veins and in disseminated deposits along silkified by Eocene plutons or dike swarms show the effects of shear zones. All the deposits are characterized by quartz temperatures exceeding 150 *C. Mixed-layer illite/musco- flooding, episodic brecciation. and open-space filling. vite, which has an estimated argon closure temperature of Wall-rock alteration is minor. The fissure-vein and shear- less than 150 "C, was collected from two alteration zones zone deposits contain sulfides and have produced gold, adjacent to Eocene dikes and yielded ^Ar/^Ar ages of 52 silver, copper, lead, zinc, molybdenum, tungsten, anti Ma. Therefore, metals were remobilized locally during mony, and mercury. Sulfide minerals of the veins vary from Eocene magmatic activity, but the importance of such an district to district, perhaps because of the depth of formation event has not been evaluated. of the vein systems and possibly because of different In summary, most of the studied mineral deposits sources of the metals. Although parallel Eocene dikes are were episodically formed in fractures at or near the roof of common in several districts, the dikes cut mineralized rock marginally peraluminous. Cretaceous granite plutons, either and are neither silicifted nor mineralized; thus, the Eocene in extension*! fissures that opened during postemplacement dikes formed after the mineralization. cooling and uplift of the plutons or in preexisting and High-precision ^Ar/^Ar age-spectrum dates of mus- long-lived shear zones near the roof of the plutons. The covite and potassium feldspar from quartz veins and altered Paleocene metaltogenic activity may have been related to host rock from 15 districts range from 78 to 57 Ma. Ages of local slow cooling after the Cretaceous magmatic event or the deposits within any district tend to form clusters; to undocumented Paleocene magmatism. Subsequently, locally, multiple mineralization events occurred in some most of these same fracture systems served as avenues for districts (for example, Edwardsburg, Profile Gap, Yellow the emplacement of Eocene dikes and local remobilization Pine, Atlanta). Ages of the deposits are slightly younger of metals. Snee-4 3,00 Economic Cfoiogy Vol S3. 19«8. pp. 335-334 Thermochronology of Economic Mineral Deposits: Dating the Stages of Mineralization at Panasqueira, Portugal, by High-Precision 40Ar/39Ar Age Spectrum Techniques on Muscovite LAWRENCE W. SNEE,' Department of Geology, Oregon State University. Coroaliu. Oregon 97331 JOHN F. SUTTER, U. S. Geological Survey. 981 National Center, Reston, Virgin* 22092 AND WILLIAM C. KELLY Department of Geological Sciences. University of Michigan, Ann Arbor, Michigan 48109 Abstract 40Ar/39AT age spectrum dates for 13 muscovites have been used to reconstruct the ther mal history (thermochronology) of the Panasqueira, Portugal, tin-tungsten deposit, a de posit spatially associated with a belt of Hercynian plutons. Muscovite samples with an age difference as small as 2.2 m.y. (0.7% of the age) are statistically distinct. Statistics are even better for comparison of multiple samples from separate events; that is, a difference of 0.9 m.y. (0.3%) can be resolved in this 300-m.y.-old deposit. The major tin and tungsten ore-forming stages, which are the oxide-silicate stage, the main sulfide stage, and greiseni- zatiom occurred between 296.3 ± 0.8 (1 a) and 291.6 ± 0.8 m.y. (1 cr). The first substage of the oxide-silicate stage was a short-lived thermal pulse at 296.3 ± 0.6 m.y.; the fluids responsible may have emanated from the known granite cupola. The main sulfide stage was active at 294.5 ± 0.9 m.y. as a slightly longer lived pulse with oldest evidence for this stage (295.8 ± 0.6 m.y.) coming from areas farthest away from the known cupola and youngest evidence (293.5 ± 0.8 m.y.) closest to the cupola. A second substage of the oxide-silicate stage occurred as a short-lived thermal pulse at 292.9 ± 0.7 m.y., synchronous with grei- senization of the cupola and alteration of the silica cap at 292.1 ± 0.4 m.y. The duration of activity of the oxide-silicate stage, the main sulfide stage, greisenization. and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4.2 ± 0.5 m.y. (1 a). Minor argon loss from all dated muscovites occurred during later reheating, probably during the longer lived pyrrhotite alteration stage. A single center, the known cupola, had a prolonged role and was the source for main sulfide stage, oxide-silicate stage II, greiseniza tion, and alteration of the silica cap and possibly oxide-silicate stage I and the pyrrhotite alteration stage; however, a separate source for these latter two stages cannot be ruled out. This study is an example of a new and powerful application of 40Ar/3'Ar age spectrum dating of muscovite. Because of the high precision demonstrated in this study, it is now possible to establish time constraints necessary for solving some of the long-standing prob lems in economic geology. Beyond this, the unique geologic situation of Panasqueira has allowed us to quantify the thermal characteristics of muscovite. Published fluid inclusion data have been used to estimate a muscovite argon closure temperature of -325°C during rapid cooling or short reheating and a temperature of 270°C during slow cooling or extended reheating. Argon-loss patterns displayed by all dated muscovites resulted from reheating after original closure; the mechanism for this argon loss appears to have been argon transport by volume diffusion. Thus. 40Ar/wAr age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age. duration, and number of episodes of mineralization. Snee-5 2.01 Stage of Sample no. mineralization 92.5 296.3 ± 0.8 PCL 503 OSS 21.67 ±0.05 296.3 ± 0.8 21.67 ±0.05 76.3 PGL 207A OSS 71.0 293.3 ± 1 -0 PGL 207B OSS 21.43 ±0.07 292.4 ± 0.8 21.36 ±0.05 58.7 PGL 2791 OSS 71.4 295.8 ± 0.6 PCL 119 MSS 21.63 ±0.03 294.8 ± 0.8 21.55 ±0.05 78.1 PGL 294 MSS 97.4 294.3 ± 0.6 PGL 381 MSS 21.51 ±0.03 293.9 ± 0.8 21.48 ±0.05" 89.6 PGL 33 MSS 83.3 293.5 ± 0.8 PCL 75 MSS 21.45 ±0.05 291.6 ±0.8 21.30 ±0.06 85.6 PGL 354 Creisen 70.9 292.3 ± 0.9 Creisen 21.35 ±0.06 292.0 ±0.9 PCL 83 21.33 ±0.06 63.9 PGL 86 Creisen 100 292.4 ± 0.8 PCL 318 Silica cap 21.36 ±0.05 OSS - oxide-silicale stage, MSS - main sulfide slage; F = eq (3) in text MAIN SULFIOE STAGE OXIDE SILICATE STAGE CUMULATIVE % MAr flEUASED FlC. 7. ArAr age spectrum diagramsiagrams foror oxide-silicateoxe-scae stage I (PCL 503 and PGL 207 A) and oxide-silicate stage II (PCL FlC. 8. ^Ar/^Ar age spectrum diagrams for main sulfide stage 207B and PGL 2791) muscovites. muscovites. OXIDE- m.l±0.l SILICATE , O-H STAGE <« RAMGC MAIN SULFIDE STAGE 2W.1 ± 0.4 GREISEN * LATE KM MUSCOVITES <«» GKEISEN ft SILICA CAP IN SILICA CAP ARGON LOSS PYRHMOTm ALTEHATIOH EVENT STAOE (FAS) CUMULATIVE % MAr RELEASED FlC. 9. ^Ar^'Ar age spectrum diagrams for greisen and al tered silica cap muscovites. FIG 10. Revised paragenesis of Panasqueira deposit showing results of detailed *°Ar/wAr geochronology. Snee-o LETTERS TO NATURE shear zones that formed between 65-55 Myr and 50-48 Myr as a result of rapid differential npiift of the Coast orogen2. Gold-bearing quartz veins of the Juneau gold belt are wide spread along the northern 200 km of the megalineament. These veins record a high fluid flux along this structure. Stable isotope data from silicate minerals in the veins can be used6 to calculate 6"O values for the ore fluid of 7.2- 12.83d and 6D values of -35 to -15*. 5 IiO = [( l*0/"0)Mmpte/( ItO/ l60)«.n<1-nJ]-l and 5D = [(2D/ l H)MmpJe/(2D/ l HUmurd]-l- Fluid inclusion data7 indicate that the hydrothermal fluids were rich in H 2O, CO}, CH4 , N2 and H2S, and that the veins were formed at depths of at least 5 km and at temperatures of at least 250 °C. These deposits are typical of mesothermal gold-bearing vein systems found throughout the Earth's orogenic belts. Many different sources for the vein-forming fluids can be postulated, but existing data are only consistent with a metamor phic fluid. Interstitial pore flmids in the subducted, sedimentary rock-dominant terranes would have been expelled at shallow depths, long before the host rocks of the veins reached their maximum burial depths of perhaps 30-35 km (ref. 8). The lack of temporal and spatial association of the veins with specific igneous activity, and the consistently low salinity of the fluids7, rule out the possibility of a magmatic fluid source. Calculated Rapid dewatering of the crust 6D values for the fluid are incompatible with a meteoric water source with any feasible water/rock regime6. The stable-isotope deduced from ages of and fluid-volatile chemistry, as well as the fact that the vein swarms are restricted to greenschist fades rocks, suggest that mesothermal gold deposits the fluid was generated during metamorphic reactions of green- schist and amphibolite fades*-7. R. J. GoWfarb*. L W. Snee*. L D. MBert The ^Ar/^Ar dates of hydrothermal muscovite from the five & R. J. Newberry* largest vein swarms in the goM belt show a remarkably narrow range, 55.0-56.1 Myr, for samples collected along 200 km (Fig. ' US Geological Survey. Box 25046. KC 973. Denver Federal Center. 1 ). Well-denned plateaus characterize ail spectra of 39Ar release. Denver. Colorado 80225. USA The concordance of apparent ages might indicate that the dates t Echo Bay Mines. 3100 Channel Drive. Juneau. Alaska 99801. Canada of micas had been reset by a single thermotectonic episode or $ Department of Geology. University of Alaska Fairbanks. cooling of all veins through the 325 °C isotherm at ~56-55 Myr. Alaska 99775. Canada ___ It could, however, indicate actual fluid ascension and vein deposition at geologically rapid rates; that is, extensive meta THE large-scale migration of fluids through the continental crust morphic dewatering and gold vein formation may be a relatively has been well documented, but there is no consensus regarding the brief and late event during a much more prolonged period of timing of fluid migration relative to orogenic episodes, or rates of orogenesis. crustal dewatering 1 . Here we present "Ar/^Ar dates for mns- The resetting of ail *°Ar/39Ar dates to 56-55 Myr from covites from quartz veins along a major shear zone in southeast originally older dates is unlikely. Exposed igneous rocks in the Alaska, which show that the veins were enplaced in the early immediate vicinity of the Juneau gold belt are clearly older than Eocene, during the late stages of orogenic deformation. Hydrotber- quartz veins. Veins cut through 105-Myr monzodiorite9 at mal activity took place for only about 1 Myr and along a distance Kensington and Jualin, Cretaceous monzodiorite at Treadwell of at least 200 km. The fluids were generated by metamorphic and Mesozoic mctagabbro at Alaska-Juneau. A belt of tonalitic reactions in subducted crust along the North American plate plutons. generally 5 km east of the megalineament, was episodi margin, and were apparently trapped in the crust by the low cally emplaced from 68.2 = 2.0 to 61 = 1.5 Myr (refs 10-12). permeabilities accompanying a convergent tectonic regime until Granite and granodiorite of the Coast batholith were intruded 56 Myr ago. The rapid dewatering event coincided with a change between 54 ±2 and 48 = 2 Myr within a belt 20-50 km east of, in plate motion at $6-55 Myr, which caused a shift from con>ergent and parallel with, the megalineament 1 '. This belt of plutons to partly transcurrent tectonics. We suggest that this change in could in theory have reset the hydrothermal micas to 56-55 Myr, tectonic regime led to increased crustal permeabilities and hence but the thermal effects of the magmatism apparently did not the possibility of large-scale fluid migration. extend as far west as the megalineament (fig. 1). Hornblende Terrene accretion and subdnction, thrusting, deformation, and biotite K/Ar data for schist and amphibolite 5 km east regional metamorphism and magmatic thickening of the Coast of the structure at the latitude of Juneau show no evidence of orogcn characterized the northern North American Cordillera thermal overprinting 14. Farther south, near the Sumdum Chief between 110 and 50 Myr (ref. 2). Rapid uplift of the orogen mine, Ar-Ar studies'* indicate that the western margin of the core occurred during the last 15 million years of this period3. belt of tonalite bodies has cooled below the 280±40°C biotite The 700-km-long, northwest-trending Coast Range megalinea- ment cuts medium- and high-grade metamorphic rocks 15-20 km blocking temperature by 59x1 Myr. It is unlikely that the micas were reset by circulation of west of the core of the orogen and of the Coast batholith in meteoric water during uplift Silicate AD values for country southeast Alaska and British Columbia. The megalineament has rocks near the megalineament attest to the lack of significant been defined in Alaska and British Columbia. The megalinea meteoric water circulation west of the Coast batholith6. Further ment has been defined in Alaska as a prominent topographic more, even if such circulation did occur, the undisturbed shape zone, up to 10 km wide, formed by selective erosion along closely of the wAr spectra (Fig. 1) is evidence against resetting. spaced joints, foliation, com positional layering and small faults'*. It is also doubtful that the 56-55 Myr concordance reflects Farther south in British Columbia, this structure is recognized uplift of previously formed veins across the 325 ± 25 °C isotherm, as a steep to vertical ductile shear zone3. There the megalinea which is the approximate blocking temperature for sericite15. ment is interpreted to be the westernmost of several ductile NATURE VOL 354 . : 28 NOVEMBER 1991 296 Snee-7 LETTERS TO NATURE , - a Dates from ^Ar/^Ar data for hydrothermal Muscovite from gold-bearing veins at the five largest mines of the Juneau gold belt, ranging from 56.1 to 55.0 Myr. Ages obtained from the U/Pb ratio are 68-61 Myr (refs 8-10) for a tonatite sill belt to the east of the gold belt, indicating that it pre-dates the gold veining. U/Pb ages for the Coast bathdith11 provide evidence that some magmat ism may have been coeval with ore deposition. But K/Ar dates of metamorphic rocks to the east of Juneau14 and ^Ar/^Ar dates from the southern part of the sill belt12 suggest that (1) the thermal effects of Eocene igneous activity were not felt as far west as the gold belt and (2) rocks near the gold belt had already cooled below the biotite blocking temperature of 280 °C before gold was formed. Dates labelled 'hod' are from hornblende; bt biotite. Fluid inclusion studies7 suggest that vein formation tem fluid volumes. The cause of this metamorphic event is uncertain. peratures were probably less than or dose to 325 °C. Lower Re-equilibration of perturbed isotherms during uplift and/or greenschist facies rocks 16 that host the veins at the Treadwell^ during a declining rate of convergence20'21 is one possibility. mine on the west side of the megalineament never reached Alternatively, thermal input from intrusion of the tonalites has temperatures above -325 °C. The uplift histories were probably been suggested1. notably different for rocks on opposite sides of the megalinea Rather than migrating upwards along the megalineament at ment2-17, and there is no evidence that the sampled veins on various times, fluids might have ponded at depth below imper ' ->th sides of the structure cooled through the 325 °C isotherm meable units. The mainly compressional environment kept per :xactly the same time. meabilities low along the western edge of the Coast orogen, The most logical explanation for the exceptional concordance even along any existing principal shear zones, including the of calculated dates is that massive fluid circulation and vein formation occurred over a very brief tine span in the early Eocene. This event took place over a length of at least 200 km along the Coast Range megalineament. Whether such an event affected other parts of the megalineament is uncertain. The lack of extensive gold-bearing quartz vein networks along the southern part of the structure might be explained by the fact that deeper crustal exposures of the megalineament and sur rounding rocks occur to the south. If such veining did occur to the south, the evidence has long since been eroded away. The widespread fluid event at 56-55 Myr might reflect an important change in crustal stress regime, as considerable changes in plate motion occurred at roughly that time (Fig. 2). Plate trajectory models18 show a counterclockwise swerve of the Kula plate concentrated in the 56-55 Myr interval, causing a shift from orthogonal subduction to a more oblique direction and the initiation of strike-slip motion. Structural and uplift studies 19 along the southern part of the megalineament indicate that compressional tectonic events ceased between 60 Myr and 55 Myr. An abrupt change in the type and location of magmatism occurred near the megalineament between 54 and 48 Myr. The locus of magmatism shifted 20-50 km farther to the east-north east, and plutons became more siliceous in composition and Coast range characterized by lower initial ''Sr/^Sr ratios, pointing to megaiineament changes in magma source13. It was suggested13 that these charac teristics correlated with the change to a moreextensional tectonic regime. The emplacement of the siliceous plutons in response to changing crustal stresses may be a more gradual process than fluid migration and quartz vein emplacement. Our favoured scheme (Fig. 2) is one in which the vein-forming FIG. 2 Vein-forming fluids were released through devoiatilization of subduc : aids may have formed over millions of y,eais during devolatiliz- ted sedimentary and volcanic rocks during plate convergence before 56- ation of subducted crust. A period of progressive Harrovian 55 Myr. Compressional tectonics maintained low crustal permeabilities, and metamorphism from 70 Myr to 60-55 Myr, superimposed on therefore the released fluids probably collected below relatively impermeable deeply buried, high-pressure, low-temperature prehnite- units. A shift to a more oblique plate margin regime at 56-55 Myr (ref. 18) pumpellyite facies and lower greenschist facies rocks east of the initiated considerable strike-slip motion and allowed hydrothermal fluids to megalineament8, is the event likely to have produced the laree ascend rapicty. NATURE - VOL 354 28 NOVEMBER 1991 Snee-8 LETTERS TO NATURE Coast Range megalineament (if it then existed). Seismic reflec 15. SHM. L W. Suttw. JL f. ft Ka«y. W. C. Eton Gtot 83. 335-354 (1988). 16. Dustf-Bacon C. BfM. 0. A. ft Dotajacs. & L US Gaol Surv. Open-Oe fep. 81-88. 46P (1991). tion data from present-day convergent margins provide evidence 17. Stowei. K H ft Hoceer. R I rectories 8. 391-407 (1990). lat large fluid volume may be trapped at mid-crustal levels 18. tonsdtfe. P G*at Sac. Am. But. 188. 733-754 (1988). 19. Crawtord. M. U ft Oawford. W. A. GeoL As*ac Can Profr. Aastr. it, A28 (1990). .-curing compressional events22. Hydrologic modelling23 of meta- 20. England. P C ft Ttampson. B, J Artrat 28. 894-955 (1984). morphic fluids supports the seismic observations and indicates 21. Kemch. R ft Wymart. 0. G«*w 18.882-886 (1990). 22. Hynanm. R. 0. Yorath. C. J.. Oowe*. R M. ft D***. E. E. Cm i Eartn Sa 27. 313-329 (1990). significant crustal porosities even long after peak metamorph- 23 Thompson. A. a ft Connolly. J. A. 0. Tactonopfirs** 182. 47-55 (1990). ism. The hydrology of deep crustal fluids is complex, however, 24 MHer. L 0 ft Redman. E. C. Geor. Sac Austr. ADstr. 23. 374 (19881 25 Sfcson. R. K. Robert, f. ft PoUsea K. K Geotogy 18. 551-555 (1988). and needs further study. 26 Henley. R W, Norm. R. J. ft Psterson. C. J. Mner* Oeposrt* 11, 180-196 (1976) The trapped fluids were rapidly discharged along the mega- 27 Bames. I.. Irmn. W. P ft White. 0. E. US Get* Strv Mac Hvest Map H528 (1984). lineament over a period of <106 yr. Failure along the structure 28. Doer, 0. R. ft Casnman. S. M. G»ot Soc Am. AOstr. Prof. Cora. Sect. 23. 21 (1991). 29 Bor*e J. K. ft KisOer. R W. £0*1 GeoL 81. 296-322 (1986). during some degree of relaxation of compression at 56-55 Myr X Engebretson. 0. C, Cox. A. ft Gordon. R G. Geof Soc. Spec. Pm 208, 45P (1985). reduced confining pressures and created pockets of fluid over 31 Schweickert. R A. Boeen. N. L ft Merguenan C. Metamorpn»am and Crust* £votuton of the pressure, especially in zones of maximum dilation. Swarms of Western uma Sate* vol. VH (ed. Ernst W G.) 789-822 (1989). brittle-ductile shear veins24 formed in dilational sites within a ACKNOWLEDGEMENTS We thar* Fred Barker. Bob Burruss. Unc Farmer and 0 Lamar Leadt for few kilometres of the megalineament during large-scale crustal reviews. Rfcfc Freotouen and Retard Krtham for mme access, and Barren Cieutat jnd J. Carter failure, probably according to the fault valve model of Sibson BorOen for laboratory assistance. and others25. Mesothermal gold-bearing quartz vein^ networks may delineate zones of metamorphic dewatering26 and are often spatially associated with principal crustal lineaments. Dating of gold-bearing, metamorphic quartz veins located along large- scale structures allow precise determination of the time of changes in crustal stresses and possibly in relative plate move ment. Dewatering of the middle crust is a relatively instan taneous consequence of seismic failure, perhaps marking the start of a more transpressive type of plate margin regime. The discharge of non-meteoric fluids immediately following seismic events has been documented along many shear zones2 . The isotope dates of 56-55 Myr from the Juneau gold belt are believed to define the onset of failure along the northern pan of the Coast Range megalineament. The formation of other Phanerozoic gold systems in western North America may also correlate with periods of considerable shift in plate motion. A marked change in the relative motion of the Farallon and North American plates at 133 Myr may be recorded by gold veining in the KJamath mountains23. Along the Melones fault zone of central California, K/Ar and Rb/Sr data from some of the mines in the Alleghany district, near the north end of the Melones fault zone, and from the Mother Lode district, ~200 km farther south on what may be the same struc ture, are statistically identical at 110-116 Myr (ref. 25). Plate reconstruction models30 for the southern Cordillera often include a shift from left-oblique to right-oblique convergence beginning at -115 Myr. Although there is little evidence for Cretaceous strike-slip motion along the southern Melones fault zone31 , the change in plate slip direction still may have been the driving force for localized opening of dilational jogs along the fault zone. Our gcochronological results from southeast Alaska clearly show that an episode of considerable fluid flow occurred rela tively rapidly over great crustal lengths. We believe that the remarkable correlation between the time of this episode and that of significant shifts in plate motions is not coincidental. Rather, catastrophic crustal fluid flow and gold genesis along the outboard flank of an erogenic belt seem to be inherent tectonic processes, ultimately related to changing plate stresses in Cordilleran-type environments. D Received 19 June: accepted 23 September 1991. 1. Torcersen. T. fOS 7Z 18-19 (1991). 2. Crawfora M. U Holhster. L S ft Woodsworttt G. J. Tectoncs «. 343-36111987). a HoHister. L S. CM Mneral. 20. 319-332 (1982). 4. Brew. 0. A. ft Ford. A R C»i J. Eartfr Sa 18.1763-1772 (1978). S Crawfortt M. L ft rWlister. L S. J *eo0r*s. Res. 87, 3849-3860 (1982J. 6. GoMfaro. R. i. Newoeny. R X Pickthom. W. i ft Gent C. A. Eton. Get* 8ft. 66-80 (1991). T. GoMtarb. R i. Leach. 0. U teses. S. C. ft Lano*. G. P. £con Geot Uonofr *. 363-375 (1989). a rfcnmetterfc G. R. Brew. 0. A. ft Brew. 0. A. J. meumcrprtc Geot. 9. 165-180 (1991). 9. Gehrels. G. E. ft Mtter. L 0. Conf Juneau-91. Abstr. Prof. Pta. 23-24 (1981). 10. Gehrels. G. E_ Brew. 0. A. ft SaieeOy. J. a US Geot. St*v. Oc 93». 100-1O2 (1984L 11. Barker. F. Arth. i G ft Stem. T. W. Am. Mherat 71. 632-643 (1986). 12. Wooa 0. J. StowelL KH.OnstoaT.C- ft Ho»ster. L S. Geor. Sot Am. 8uO.UO, 849-860 (1991). 13. Barker. F. ft Ann. J. & GeoL Soc. Am. Mem. 174. 395-40511990). 14. Fbrbes. R B ft Engels. J. C. Geot Soc. Am. Butt. 81. 579-584 (1970). 298 NATiiRF vni Compositional and isotopic data are available for approximately 200 samples of plutonic rocks, altered and Geology, Geochemistry, and Age of the Gejiu unaltered country rocks, and minerals from the Gejiu area. Batholith and Associated Polymetallic Deposits, The majority of the granitic rocks are weakly to moderately , jouthern China peraluminous; gabbro, diorite, and syenite are metalumi- nous. Mafic, intermediate, and syenitic plutons east of the Lawrence W. Snee and Wang Zhifen Gejiu fault are not related by simple magmatic processes to granites east and west of the fault. Relative to other Gejiu The 320-km2 Gejiu batholith, composed of more than plutons, granites are variably enriched in rubidium, cesium, 10 mafic and felsic intrusions, is well known for its large tantalum, and uranium and depleted in barium, strontium, granite-hosted tin deposits but also is mined for Cu, Pb, Zn, and hafnium. Concentrations of Rb. Cs, Ta, U, Hf, and Th W, Bi, Be, F, and S. The batholith is divided into eastern are uniform in nongranitic plutons, but strontium and and western parts by the post mineralization, north-trending barium decrease with increasing SiO2. Granites are depleted Gejiu normal fault. Intrusion compositions and mineral in light rare-earth elements (LREE) (<200 times chondrite deposit types are distinctly different on opposite sides of the abundance) and enriched in heavy rare-earth elements fault. Plutons in the west, grouped by age from oldest to (HREE) (>20 times chondrite abundance) relative to non- youngest, include (1) gabbro. diorite, and monzonite; (2) granitic rocks (LREE=200-800 and HREE=5-20 times granodiorite, granite porphyry, and granite; and (3) syenite chondrite abundance). Large europium anomalies are char and nepheline syenite. Lead and zinc are disseminated as acteristic of granites. Strontium initial ratios for all Gejiu galena and sphalerite in many western plutons; tin occurs as plutons are elevated, but the ratios for western phitons are disseminated cassiterite in granite porphyry. East of the less than 0.712, whereas the ratios of eastern plutons are Gejiu fault, minor exposures of a large, subsurface granite greater than 0.716. The strontium isotopic signature and the body crop out within Triassic sedimentary rocks. Core major and trace element compositions of all plutons were drilling indicates that these outcrops represent parts of a probably derived from a heterogeneous, chemically continuous, 20-km-long granite pluton of relatively uniform evolved, continental source. composition but variable texture. Major tin deposits are Granitic plutons associated with Gejiu tin deposits are associated with the numerous cupolas of this pluton and compositionally distinct from nonproductive granites. Pro- > occur in skam, greisen, and open-space veins. ductive granites are characterized by 69 to 75 weight percent SiO2; Na2O/K2O of 0.59 to 0.74; enrichment in Rb Preliminary 40Ar/39Ar age spectra constrain the age (300-1,000 ppm), Cs (10-70 ppm), Ta (3-17 ppm), U and the duration of tin mineralization and intrusive activity. (10-60 ppm). F (1,000-4,000 ppm), and Sn (10-30 ppm); Diorite in the west is 84.1 ±0.2 Ma. Granite emplacement and depletion in Ba (<300 ppm). Sr (<300 ppm), and Hf and tin mineralization in the east took place between (<7 ppm). Rare-earth-element (REE) patterns of productive 82.6±0.2 and 80.6±0.1 Ma. Nepheline syenite was granites show relative depletion in LREE (35-110 times intrude^ in the west at 79.9±0.5 Ma. The age spectra show chondrite abundance), large europium anomalies, and that tinV mineralization and emplacement of associated enrichment in HREE (20-^40 times chondrite abundance). granites occurred over at least 2 million years and that REE patterns for biotite from these granites are similar to temporal-spatial relations among the tin-mineralized gran the REE patterns of the whole rock except that biotite, ites are resolvable. Relative age relations and isotopic data which forms about 10 modal percent of the rock, is enriched indicate that emplacement of nepheline syenite and forma 10 times in total REE; thus, biotite is the principal REE tion of associated disseminated galena and sphalerite took rarrier. In contrast, biotite from nonproductive plutons is place near the end of, or subsequent to, tin mineralization. not the primary REE carrier. The tin content of biotite from Thus, because lead-bearing mineral deposits, associated plutons that have less than 69 weight percent SiO2 is less with plutons that are older than the tin-mineralized granites, .nan 32 ppm. In contrast, the tin content of biotite from are also found west of the Gejiu fault, formation of lead iranites that have more than 69 weight percent SiO; is deposits was either a multicycle phenomenon or occurred ireater than 100 ppm to nearly 700 ppm. However, plutons over a longer time period than formation of tin deposits. hat have significant tin deposits contain biotite having .ower tin contents (that is, nearer 100 ppm). A possible mechanism for tin mineralization that USGS Circular 1062, p.74-76 vould account for these chemical characteristics might nclude (1) a plutonic source region relatively enriched in n, (2) an evolved granitic magma that concentrated tin, (3) pisodic thermal activity that occurred over at least 2 million years, and (4) either a late-stage fluid phase into hich tin from the granitic magma was partitioned or a te-stage fluid phase that leached tin from biotite and ^posited tin in the altered host rock. Snee-10 Deformation and age of the Red Mountain intrusive system (Urad-Henderson molybdenum deposits), Colorado: Evidence from paleomagnetic and ^Ar/^Ar data Unmnay of New Mexico. Albuquerque. New Mexico 8713 1-1116 JOHN W GEBSMAN Department o c '/^ GARRETT W. GRAASKAMP Dun* Geoscience Co*. 5 Norihway *"**»* If*** Nf» 7ork 12UO RICHARD B. CARTEN US. Geological Survey. APO New York, New York 09697-7002 ENN1S P. GERAGHTY StiBwater Mining Company. Box 365. Nye, Moiuam 59061 spectra from orthodase and biotite, were ABSTRACT blocked between 28.7 and V* Ma. Magnet- Pafeomagnetic and ^Ar/^Ar age-spec- he and magbemste are the major carriers of tram data from most stocks of the Red Moun magnetization in these rocks. On the basis of an *Ar/*Ar tbermocfarono- tain mtrusive system, in the northwest Colo rado mineral belt, provide an improved logk study of the Red Mountain intrusive understanding of me structural and cooling system, thermal activity started at or just be history of the sole of intrusions host to a fore 29.9 ± 03 Ma and ended at 26.95 ± 0.08 worid-dass molybdenum deposit Pafeomag- Ma. The age-spectrum data are interpreted to netk data from five stocks at the surface and indicate that the porphyry of Red Mountain, eight younger stocks exposed in the subsur- one of the oldest stocks, was unplaced before nce Hendenoo Mine support field observa 29.9 ± 03 Ma (possUy befere 3038 ± 0.09 tions (for example, dike and vein orientations, Ma). Nearby bunprophyre dues were em- stock geometries, and distribution of zones of placed at 29.8 ± 0.1 Ma; rayoite dikes in mmenization) that imply moderate tilting truded at 29.4 ± t~2 Ma. The Urad and (15°-25° down to the east-southeast) since Seriate stocks intruded after 29.8 Ma but be attest OBgocene time after cooing and miner- fore rmpltrrmfnt of me Vasojnez stock at aization. Surface stocks contain magnetiza- 28.71 ± 0.08 Ma. The system core cooled tiom carried by both magaetite and hematite. below 280 ± 40 °C (the argon closure temper The Red Mountam stock is the youngest sur ature of biotite) at 27.59 ± U3 Ma. The bst face intrusion and contains mostly normal po period of thermal activity involved pulses of larity magnetizations (for example, D = 321°, uiaguetite-seriche alteration around the Se- I = 59°, 095 = 19°, k = 9, N = 6 samples, she riate stock between 27.51 ± fJB and 26.95 ± RM9), whereas okier East Knob and Rubble 0.08 Ma; this activity did not thermaBy over Rock breccia intrusions contain a nearly an print unaltered parts of me intrusive system. tipodal, well-characterized magnetization TiHmg of the Red Mountain area is implied (East Knob stock: declination = 161°, tncKna- by a comparison between a grand mean (on tion = -47°, aw = 13°, * = 23, average of five the basis of 10 stock means, D = 333°, I = 49°, she means). Polarity chanced from reverse to 095 = 5°, k = 78) and a mid-Tertiary reference normal during emplacement and coofing of field. The Red Mountain ntnstve system and the Red Mountain intrusions exposed at the host Precambrian rocks probably were de surface. ^Ar/3*Ar age-spectrum data on bio- formed along a nearly north-south horizontal tite and ortbodase from the Red Mountain axis in response to northwest-side down, stock and stocks of the Heoderson Mme indi strike-sip faulting with displacement hugely cate the reversal to be older than 30 Ma. Afl along the Woods Creek bull zone. Late Ter- i Henderson Mine stocks have normal polarity tiary deformation of Precamhrian-cored parts j magnetizations (Primes stock: D = 333°, I = of the Front Range, host to mmif i ous mineral i 51°, aM = 5°, k = 44, average of six she deposits, was more complicated than simple,! means) which, on the basis of ^Ar/^Ar age near-vertical uplift of me crust, i Geokvol Society of America BuDerin, v. 104, p. 1031 -1047,15 figs, 5 table, August 1992. Snee-11 TA*LE 4. SUMMARY OF K-Ar BOTOOC -At^*Af BOTOnC AGE AMD nSSIQH-THAC*. (f-Tt ACE DATA FKOM BED MOUNTAIN KTXUSVE SYSTEM EM bah. F.T 213*2-2 34.4 t 1.7 217 t 2.9 a. ±3 2»»iOJ 2UI t OilO 2f.4 t*2 11 317 1 15 12 UntfMte. 13 14 UntfMae. ZUtU P*?*j»y 15 UntfUae, P^f^TT H UntfMae. 2U*«l3 17 aJi 1.4 Ar/'Ar II BBAI.IOB 211MB 19 20 27.1 i*2 21 274 till 22 2t2 t«L2 23 774i 02 24 274t 07 23 2171 tOOI at 274 tO3 27 2«J9iO« 21 2* 274 ±0.1 30 2713 t 010 31 214103 32 274i«i2 (l«n. L W SMC «d H I. Cam. «pA 40 Figure II Composite *Ar/*Ar age-spectrum diagram for ortbo- Porphyry of Red Mountain dase! muscovite, and biotite from tbe Red Mountain mtrusm system. 30h -Rhyolttedike ^^ . ____W-^H errors for data for oxrf stoostfcafly sign-Van! > between QM and 0.10 Ma.) (A) Age- 20 for orthodase from potpbyry of Red Mountain and 40 Urad, Seriate, Henderson, Ute, and Vasquez stocks] from a Ayoile dike enpbced fato Precambnan « & B tn for biotites from Hendersoo, Ute, asquez, and Senate slocks c20 within tbe central part of the Red Mountain intrusive S40 System core, cooling below 280°C zone around the Seriate stock. 20 40 Magnetite-serlctte alteration AV*-?AM API 20 50 100 Percent "Ar, released Snee-X2 TMU V SUMMA4Y Of IHTtWMTlD *»»/**» THEJtMOOmONOLOGV. Rtd Mountain MAtiMETiZATlON ACOUSmON AND STltCTV«AL EVENTS. IED MOUNTAIN MTtUSIVC SYSTEM EHaofi ESEi JT3I tOuU rOO*C -an *a« > JOJI t OuO» contacts between tarastons. Stippled region represents approzsaatdy the part of the sys tem thai cooled below -280 °C at 2759 ± Figure 12. Scb : block diagram of the 0.03 Ma on the basis of six biotite ^Ar/^Ar Red Mountain intrasive system showing rela "***r Pattencd t*ffw represents area of tive ages of stocks and roofing of fnnpiacr- oia^netite-sericite ahentkM Conned between ment (see Table 5); al ages in wSKom of 2751 ± 0.03 and 26.95 ± 0.08 Ma at the end years. Dashed fines represent of system coofine, -23 - -24 - -25 - 26 -27 CO s -28 -29 -30 -31 -32 -33 T^ure 15. Geoma^netk ooiarity time states for ble Eocene and OtH;oc« tin* co^ and -\r/-»A, a^e^pecJnnn determinatioos for the Red Mountain intrusive system. Numbers a«w«ni to tesK« ° detennuiauons correspond to sample numbers in Table 4. Vertical lines indicate * <~ ** ^» ^ refer to onhociase, btotite, and muscovite (seriate), respectivery. Q nee- 13 Geochronology of Intrusive Rocks and Mississippi-Valley- type Mineralization and Alteration from the Illinois-Kentucky Fluorspar District Lawrence W. Snee and Timothy S. Hayes (USGS) Determining the isotopic age of Mississippi-Valley-type (MVT) mineral deposits is difficult because datable phases with suitable isotopic integrity are generally absent from MVT ore. In the Illinois-Kentucky fluorspar district, numerous small igneous intrusions are exposed or have been intersected by drill core. Goldhabcr and others (1991) presented new evidence supporting a thermal relationship between MVT deposits and igneous activity, their evidence includes the thermal zonation revealed by fluid inclusion homogenization temperatures in fluorites around Hick's Dome, Illinois. Biotiie/phlogopitc of lamprophyre and mica peridotite dikes and plugs of the district were visibly altered to sericite by the MVT mineralization. Many of the igneous rocks and two alteration phases in this area have been dated in the past but the isotopic dates range from 100 to nearly 400 Ma. Although many of these dates cluster in the mid-Permian, the analytical precisions generally span about 30 million years. We are using the 4°Ar/"Ar age-spectrum technique to date primary and alteration phases from the Grants intrusive breccia (Illinois), the Hamp mine intrusive breccia (Illinois), a dike at the Hutson mine (Kentucky) and alteration phases from the West Monison and Annabelle Lee mines (Illinois). 40Ar/59AT plateau dates for hornblende and biotite from unaltered Grants intrusive breccia, which is loccicd about 2.5 miles south-southwest from the crest of Hick's Dome, are concordant at 27I.7±0.7 and 272.7±0.7 Ma, respectively (fig. 1). Slightly altered biotite from the Hamp mine intrusive breccia yields a disturbed age spectrum but is approximately the same age or slightly older, less altered biotite from the Hamp mine breccia will soon be analyzed in an attempt to improve the age determination. Sericite mat formed from alteration of biotite in the Hamp breccia during MVT mineralization yields equivocal *Ar/*Ar results and is also being re-analyzed. 300 )9Ai Age Spectrum DtU for the Grants Intrusive Breccia co 200 50 100 % 39Arr Released Hgure 1. Compa^ArrAr age specmun Illinois-Kentucky fluorspar district Ard-1-^ Ma. Be ,...... ^ wiihin a regional Mississippi Valley Type system-fflino.s-Kenw ^ <*n _ S *' Kentucky districts: Geological Society of America Abstracts w,0i Programs, v. 23. no .5. p. Snee"14 2,10 RHENIUM-OSMIUM DATA FOR SULFIDES AND OXIDES FROM CLIMAX- TYPE GRANITE-MOLYBDENUM SYSTEMS: MT. EMMONS, COLORADO STEIN, Holly J. and MORGAN, John W., U.S. Geological Survey, M.S. 981, Reston, VA 22092; WALKER, Richard J., Dept. of Geology, Univ. of Maryland, College Park, MD 20742; HORAN, Mary F., USGS as above. The successful application of the Re-Os isotopic method (using negative ion thermal mass spectrometry) to evolved Climax-type magmatic systems shows that Re-Os has great potential for ore and magma petrogenesis studies related to economic geology. A carefully collected sample suite from the 17 Ma Climax-type deposit at Mount Emmons includes specimens containing pyrite and magnetite from the higher temperature molybdenite ore shell and specimens containing pyrite, chalcopyrite, and sphalerite from the lower temperature, cross-cutting but presumably related, base metal halo peripheral to molybdenum ore. Concentrations of Re (-130 ppb) and Os (-50 ppt) for pyrite and chalcopyrite from the base metal halo are similar, and both yield 187Re/186Os around 100,000 and measured I87Os/186Os of 10-20. Pyrite associated with the molybdenite ore shell, on the other hand, has much lower Re (-10 ppb), indicating that Re is partitioned into molybdenite. In sharp contrast, sphalerite and magnetite provide a direct measure of initial 187Os/186Os because they have Os concentrations of 100-200 ppt (well above the 2-10 ppt Os blank) and Re concentrations <20 ppt; their 187Re/186Os is <10. Although Pb, Nd, and Sr isotopic data affirm a lower crustal origin for Climax-type melts in Colorado (Stein, 1985), the low initial 187Os/186Os for Mount Emmons magnetite and sphalerite (1.4 - 1.7) are consistent with accepted mantle compositions and preclude any upper crustal contribution. Alternatively, these low initial 187Os/186Os values may reflect granulitic lower crust in Colorado. Limited Re-Os abundance data for granulites have comparably low 187Re/186Os values (Morgan and Lovering, 1967). No other radiometric dating method offers such a wide range of isotopic values as demonstrated by the Re-Os measurements in this study. These results show that the Re-Os method is no longer limited to mafic magmatic systems and ores enriched in Re and PGE, but that Re-Os can be used to unravel the origin of ore deposits formed from silicic-felsic systems containing Re and PGE in the ppb and ppt range. °Arr ;Ar Thermocnronoiogy: Applications to Stratigraphy, Tectonics, and Mineralization by John Sutler Since its inception in the mid-1960's, the 40Ar/j9Ar variant of the K-Ar method of geochronoiogy has fostered an explosion of innovative applications to a wide variety of geologic problems. Applications run the gamut of most subdiscipiines in geology. The purpose of this presentation is to briefly describe the 40Ar/39Ar method and its variations, to show why its inception has fostered this explosion of possible applications, and finally to outline three applications that illustrate some of the major strengths and weaknesses of the method. 40Ar/39Ar dating technique The 40Ar/39Ar dating technique is a variant of the conventional K-Ar method. To obtain an age by this technique, the sample of unknown age and a standard of known age are irradiated together in a nuclear reactor to produce 39Ar from 39K by fast neutron bombardment. After irradiation, the 40Ar/39Ar ratios of sample and standard are measured. The age of a sample can be calculated from its 4 Ar/39Ar ratio when compared to the Ar/39Ar ratio of the standard. Most importantly, only the isotopic composition of argon need be measured and this is done by gas-source mass spectrometry, potentially a very precise analytical technique. In contrast, for a conventional K-Ar date, both K and 40Ar must be measured quantitatively. To do this, argon in one aliquant of the sample is measured by isotope-dilution, gas-source mass spectrometry. Potassium in a different aliquant of sample is determined by some other analytical method such as flame photometry, X-ray fluorescence, or isotope-dilution solid-source mass spectrometry. Thus, one inherent problem of the conventional K-Ar technique is the necessity of measuring isotopic abundances for separate aliquants of the same sample. This poses the danger that, because of sample inhomogeneity, different potassium and/or argon contents may exist in each aliquant. Two major advantages of the ^Ar/^Ar dating method are: only isotopic ratios of argon need be determined, and all measurements are made on the same sample aliquant, thus avoiding the question of homogeneity. In addition, by the 40Ar/39Ar method, it is possible to obtain a series of dates on a single sample when the argon is extracted by step heating. The combination of these advantages potentially increases the precision of the 40Ar/ AT method over the conventional K-Ar technique. However, the Ar/39Ar technique will suffer if proper corrections are not made for interfering radiation-induced isotopes. 40Ar/39Ar age spectra The 40Ar/39Ar method was first used in total fusion experiments in which an irradiated sample was completely melted and all isotopes of argon measured in a single analysis to calculate an age for the sample. This total fusion age is roughly analogous to a conventional K-Ar age of the sample except that no isotopic concentration measurements are required. Very soon after the first uses of the ^Ar/^Ar method, it was realized that a sample could be progressively degassed in temperature increments. An age could be calculated for each increment of gas released and the ages of all temperature increments of a sample were plotted against percent of released argon to form an age spectrum. The character of the spectrum can be evaluated within a theoretical framework to interpret the apparent distribution of potassium and argon within the sample. Early studies showed that some spectra of meteorites display characteristics that would be expected if volume diffusion were the dominant mechanism controlling the loss or argon from a sample in the geologic environment. Since that time, many studies have shown that meaningful ages of samples could be determined by the age spectrum technique even though some loss of 40ArR had occurred during the sample's geologic history. It should be noted here that loss or gain of ^A^ by a sample is generally thermailv controlled, samples from thermally complex regions should be analyzed by 40Ar/ Ar age spectrum techniques. Ar/Ar Isotope Correlation (Isochron) Diagrams In recent years workers have demonstrated that samples from thermally complex geologic settings can incorporate extraneous ^Ar during heating, cooling, alteration, and/or recrystallization. If the 40Ar released from the sample in the laboratory by step- heating is a simple two-component mixture (inherited and radiogenic), it is possible that the argon isotopic data from the heating steps will define a straight line on a ^Ar/^Ar vs 39Ar/40Ar correlation diagram. This straight line can be interpreted as either a mixing line or an isochron. It is not yet clear why some minerals, especially hornblende, exhibit this type of behavior. Applications: Stratigraphy - Mogollon - Datil Volcanic Field Tectonics - Southeastern New England Mineralization - Panasquiera, Portugal Calibration of the latest Eocene-Oligocene geomagnetic polarity time scale using 40Ar/39Ar dated ignimbrites W. C. Mclntosh New Mexico Bureau of Mines and Mineral Resources. Socorro. New Mexico 87801 J. W. Geissman Deoanment of Geological Sciences. University of New Mexico. Albuquerque. New Mexico 87131 C. E. Chapin New Mexico Bureau of Mines and Mineral Resources. Socorro, New Mexico 87801 M.J. Kunk U.S. Geological Survey. Resfon. Virginia 22092 C. D. Henry Texas Bureau of Economic Geology, Austin. Texas 78713 ABSTRACT the ^Ar/^Ar method, particularly for dating A discontinuous record of late Eocene-Otigocene geomagnetic polarity has been deter sanidine (e.g., Hess and Lippolt, 1986; Dalrym mined using high-precision (±<0.15 m.y.) ^Ar/^Ar sanidine dating and a pateomagnetic ple and Duffield, 1988: Mclntosh et al.. 1990). study of 37-27 Ma ignimbrites in New Mexico. Colorado, and Texas. This record provides age control for several geomagnetic polarity reversals that occurred during three periods of intense STUDY AREA ignirabrite voicanisnu 36.8-33.5 Ma. 32.7-31.4 Ma. 29.1-26.9 Ma. The relative timing of these This study has focused on four late Eocene- polarity reversals permits four possible correlations with the geomagnetic polarity time scale Oligocene silicic volcanic fields: the Mogolion- (GPTS). The preferred correlation yields calibration ages for Chron C10R (28.0-29.0 Ma) and Datil and Boot Heel fields in New Mexico. Chron COR (34.4-33.1 Ma) that indicate an Eocene-Oligocene boundary age near 33.4 Ma. Thirtynine Mile field in Colorado, and Trans some 03-0.6 m.y. younger than boundary ages indicated by other recently proposed GPTS Pecos field in Texas (Fig. 1). The sequences at calibrations based on terrestrial and marine sedimentary sequences. each of these volcanic fields include several (10-35) widespread (50-10,000 km2), volumi INTRODUCTION (Berggren et al. 1985; Prothero, 1985; Prothero nous (50-1300 km3), generally rhyoiitic ignim Radioisotopic calibration of the mid-Ceno- and Armentrout, 1985). A revised Eocene- brites (ash-flow tuffs). The composite ignimbrite zoic geomagnetic polarity time scale (GPTS) has Oligocene boundary age of 34 Ma has recently stratigraphy at each field has been established by been the focus of much work during the past been proposed following redating of the same detailed mapping, in some cases augmented by two decades. The number and relative lengths of ash deposits using the 40Ar/ 39Ar single-crystal long-range correlations supported by ^Ar/^Ar Cenozoic geomagnetic polarity chrons have laser-fusion method (S wisher and Prothero, and paleomagnetic data (see references in Table been well established using marine magnetic 1990). This value is in general agreement with 1). The Trans Pecos sequence includes several anomaly data (Manktnen and Dalrymple, 1979: GPTS calibrations based on K-Ar. Rb-Sr, and enigmatic widespread rhyolites that were prob Ness et al.. 1980: Berggren el aL 1985: Harland "^Ar/^Ar dating of biotites from bentonites ably emplaced as unusually fluid and volumi- et al.. 1989V ana these chrons have been reliably wuhin much-studied pelagic limestone se correlated with marine biostratigraphy (Lowne quences in Italy (boundary age = 33.7 Ma; et al.. 1982: Berggren et al.. 1985). However. Montanan. 1988: MontananetaL 1988. 1991; precise radioisotopic calibration points for the Premoli Silva et aL 1988; Odin et al.. 1991) GPTS have proven elusive. Direct calibration of and with ^Ar/^Ar studies of microtektites in the GPTS by dating of sea-floor basalts is se upper Eocene marine deposits in Barbados verely limited by problems of alteration and ex (boundary age = 34.4 Ma; Glass et aL 1986). cess Ar retention (Berggren et al.. 1985). Herein we present a terrestrial volcanic cali Instead, terrestrial and marine straugraphic se bration of the late Eocene-OHgocene GPTS quences have been used to provide calibration using ^Ar/^'Ar dated ignimbrite sequences points. from the southwestern United States. This A particularly problematic period for radio purely volcanic approach is analogous to the isotopic calibration of the GPTS has been late widely accepted calibration of the late Neogene Eocene to Oligocene time. Published estimates GPTS using K-Ar ages and polarity determina of the age of the Eocene-Oligocene boundary tions from terrestrial lava sequences (Cox and have ranged from 32-to 38 Ma (Ness et al.. Dalrymple, 1967; McDougail et al.. 1976; Har- 1980: Harland et al.. 1989); this 20% variation rison et aL 1979). It was previously impossible considerably exceeds the precision and accuracy to extend this purely volcanic-based calibration of available dating methods. method beyond 10-15 Ma. because errors in The widely cited 36.5 Ma Eocene-Oligocene conventional K-Ar determinations become large Figure 1. Map showing locations of selected boundary age of Berggren et al. (1985) was relative to the lengths of individual polarity in mid-Cenozoic silicic volcanic fields in New based largely on K-Ar data from volcanic ash tervals (Berggren et aL 1985). Extension of this Mexico and adjacent areas. Darker stipple within magnetostratigraphically studied terres approach into mid-Cenozoic time is now made patterns show volcanic fields examined in this trial sedimentarv sequences in North America possible by the increased precision afforded by study. GEOLOGY, v :0. p. 459-463. May 1992 459 Sawmill-Mag da l«na ARIZONA NEW MEXICO cauldron Plains of San Augusiin MtWlthlngton Chuoaaera Mts cauldron MagaaJena Mts San /Wareo A^rs -29.0-28.1 : MarnyoHte^; ' EXPLANATION Truth or Conseauences Silver City Emory SchooihouM cauldron Mountain cauldron NEW MEXICO Big Burro Mts Doha Ana Mts Mogollon Datil volcanic field Method Mineral Unit Age (Ma) n Or crX Ref. Ma % Ma % Plateau Sanidine South Canyon 27.36 3 ±0.07 ±0 .26 ±0.04 ±0.15 Plateau Sanidine Bloodgood Canyon 28.06 8 ±0.04 ±0 .14 ±0.01 ±0.05 Plateau Sanidine Vicks Peak 28.56 3 ±0.06 ±0 19 ±0.03 ± 0. 1 1 Plateau Sanidine Caballo Blanco 31.65 5 ± 0.06 ±0 17 ±0.03 ±0.09 Plateau Sanidine Hells Mesa 32 06 5 ±0.10 ±0 30 ±0.06 ±0.17 Plateau Sanidine Box Canyon 33 51 7 ±0.13 ±0 40 ±0.05 ±0.15 Plateau Sanidine Kneeling Nun 34 89 4 ±0.05 ±0 15 ±0.03 ±0.08 Plateau Sanidine Bell Top # 4 34 96 3 ±0.04 ±0 11 ±0.02 ±0.07 K-Ar Sanidine Bloodgood 26 9 28 ± 1.3 ±4 8 ±0.2 ±0.9 2 K-Ar Biotite Bloodgood 28 8 8 ±1.4 ±4 9 ±0.5 ±1.7 2 Fission-track Sphene Bloodgood 28 1 4 ±2.2 ±7 8 ±1.1 ±3.9 2 Fission-track Zircon Bloodgood 28 2 10 ±2.1 ±7 4 ±0.7 ±2.4 2 Plateau Biotite Rat Creek 26 47 2'1 ±0.08 ±0 32 ±0.06 ±0.22 3 Plateau Biotite Showshoe Mtn. 26 78 2'1 ±0.10 ±0 38 ±0.07 ±0.27 3 Laser Sanidine Taylor Cr. Lava 28. 21 7 ±0.04 ±0 13 ±0.01 ±0.05 4 Laser Sanidine Bloodgood Canyon 28. 19 2'1 ±0.01 ±0 05 ±0.01 ±0.04 4 Laser Sanidine Pahranagat Lakes 22.65 5 ±0.02 ±0.08 ±0.01 ±0.04 5 Laser Sanidine Nine Hill 25. 11 5 ±0.02 ±0.07 ±0.01 ±0.03 6 Laser Sanidine New Pass 25.07 3 ±0.04 ±0. 15 ±0.02 ±0.09 6 n, number of samples/unit; n too few for meaningful a. I, this study; 2, data compiled in Marvin et al. (1987); 3, Lanphere (1988); 4, Dalrymple and Duffield (1988); 5, Demo and Best (1988); 6, Deino (1989) * Q 10 34 plateau 34 nml58 sanidine ^ 26 26 - b) 25 ->f. percent 39 Ar 100 percent 39 Ar 100 oo oo 10 10 1 nm505 sanidine 39 nm90 sanidine Box Canyon Tuff i- McCauley Rancn - Oatil Well Tuff 1550 38 ~m Horse Springs plateau age = 33.65 ±.12 Ma 45 37 ' 90.8% of 39Ar no plateau 36 plateau "*^ ^* 1400 3.35 - 1550 3,40 V 1310 r ^34 j^° 1150 '250 '250 '150 35 F c a) 30 percent 39 Ar 100 percent .39 Ar 100 Fly,. 5a-h. Representative age spectra from Mogoilon-Datil sanid- age spectrum: both d and e indicate contamination by older K- ines. a Concordant plateau age spectrum and flat K./Ca spectrum feldspar. f Irregular discordant age spectrum of an altered sanid typical of 80% of analyzed samdines. b Concordant plateau age ine. g Concordant plateau age spectrum 01 an apparently contam spectrum accompanied by a somewhat discordant K./Ca spec inated sample, h Somewhat discordant age spectrum, still meeting trum, c Age spectrum that climbs in age slightly with increasing plateau criteria, of an apparently contaminated sample temperature, d Steeply climbing age spectrum, e Steeply climbing fusion ages (Dalrympie and Duffield 1988: Deino and agreement with Stratigraphic order is also shown by less Best 1988: Deino 1989). well-constrained units in this study. The best examples But how does crX translate to actual resolution of are from a sequence of nine ignimbrites erupted over a ignimbrite correlation problems? Stratigraphic se 1.6-Ma period from calderas near the northern and quences offer the most rigorous tests of this question. western margins of the volcanic field (Fig. 7). The Stra In this study, the mean ages of better studied units tigraphic order of these units has been unequivocally (n>3) all agree with independently established strati- demonstrated by detailed mapping (Osburn and graphic order, although the most closely erupted pair of Chapin 1983b: Ratte et al. 1984), augmented by paleo- well-constrained units (Kneeling Nun and Bell Top no. magnetic correlations (Mclntosh 1989: Mclntosh et al. -i Tuffs. Table 3) differ in mean aee bv 0.09 Ma. Good 1986. in press). Except tor one apparently contami- NEW MEXICO map area Mogollon i: Datll ?T" volcanic n-s«^::-.t: field .) NJ^a^; V CONTRASTING P-T-t PATHS: INTRODUCTION THERMOCHRONOLOGIC EVIDENCE FOR A LATE PALEOZOIC FINAL ASSEMBLY One of the more persistent questions relating to the tectonic evolution of the New England Appalachians concerns the OF THE AVALON COMPOSITE TERRANE arrival time of the late Proterozotc Avaion terrane to the EN THE NEW ENGLAND APPALACHIANS lithotectonic zones (of Zaranan (19881) to the west that now overlie it: the Putnam-Nashoba. Memmack Trougn. Central R. P. Wintscn.1 J. F. Sutter.: NL J. Kunk.2 Maine, and Bronson Hill (Figure 1). Some (e.g.. Robinson and J. N. Aleinikoff,3 and M. J. Doiaia1 Halt 1980; Skehan and Rast 19901 have argued that the Middle Ordovician arrival of the Avaion terrane was responsible for the laconic orogeny. Osbcrg (19781 and Williams and Hatcher (19831 argue that the accretion of Abstract. Strongly contrasting pressure-temperature-ume Avaion occurred in the Early Devonian, when its arrival was pains for the Avaion composite terrane and the structurally responsible for the Acadian orogeny. Zen (19831. Wintsch and overlying Putnam-Nashoba zone in eastern New England Sutler (19861. and Gromet (19891 have argued that at least the obtained from thermochronologic and thennobarometnc data last stages of assembly were in the late Paleozoic. More are best explained by a lace Paleozoic underthrusung of cover recently. Stockmai et ai. (19901 and van der Pluijm et al. rocks by the Avaion composite terrane. We present new AT [1990] proposed that initial collision occurred in the Silurian and U-Pb thermochronologic data that show that in toe but conunued in a protracted way to the late Paleozoic. southern Hope Valley zone. Permian (280 Ma) anatecuc Discrimination among these hypotheses has been stymied bv metamorphic conditions ot 700°C and 6 kbar were quencned the high grades of metamorphism of rocks of all zones, by the by relatively rapid cooling (.12°C/m.y.) and exhumation (0.5 lack of temporal control of metamorphism of Avaloman ana km/m.y.) for -40 m.y. In contrast peak metamorphic adjacent rocks, and by the scarcity of fossils. conditions in the Putnam-Nashoba zone predate Silurian One approach to constraining the time of final juxtaposmon intrusions, and slower cooling (3.5°C/m.y.) began at about 400 of the Avaion terrane to the lithotectonic zones to the west is Ma. One-dimensional thermal modeling suggests that these to establish the extent of Alleghanian metamorphism in eastern two belts were not in thermal equilibrium during the Penman New England. If this metamorphism were Later than important metamorphism of the Avaion composite terrane. Because of motion on terrane boundaries, then Permian isograds would cut the absence of high-grade AUeghanian metamorphism in rocks across zone boundaries (as proposed by O'Hara (19861). and overlying the Avaion icrrane. we conclude that high-grade the cooling histories of the rocks would be continuous across Alleghanian metamorphism in the Avaion terrane occurred east terrane boundaries. If. however. Alleghanian metamorphism in of rocks now overlying it and that significant motion between the Avaion terrane were earlier than final assembly, then major Avaion and this cover occurred after peak Alleghanian differences in cooling histories would exist, and the final metamorphism. Similarly contrasting metamorphic histories juxtaposition of Avaion to the rocks now above it would between Avaion iniiers (Willimanuc window. Massabesic postdate peak Alleghanian metamorphism. complex cneiss. Pelham dome) and their cover rocks reveals In this paper we present thermochronologic data trom trie the regional significance ot this boundary. The core rocks all Avaion composite terrane and the adjacent Putnam-Nashoba show Permian cootme. but the cover rocks show post-Acadian zone showing that these two zones had distinct metamoronic coolinc aces dccreasine trom cast to west to the Pelham area, and cooling histories trom the Silurian to the Eariv Friassic. .vhere nombiende aces in Avaion and cover differ by only 35 The slow cooling of the Putnam-Nashoba zone trom high- rauier tnan 80 m.v. Model calculations show that thermal grade Silunan metamorpnism contrasts strongly with the pea* equilibrium between instantaneously thrusted blocks of rocks Permian metamorphism and relatively fast Permian and is generally obtained in tens of millions of years. Triassic cooling of the Avaion terrane. Similar discrepancies Consequently, undenhrusung of Avaion is constrained to be between the cooling histories of Avaloman iniiers and their middle Mississippian or younger. Because the leading edge ot overlying rocks in east central New England constrain the tune the undenhrusung block would have been heated the longest of final assembly of the Avaion terrane to the New England and would have most closely approached thermal equilibrium Appalachians to be late Paleozoic. We follow Zaranan s (19881 widi its cover, core rocks of the Pelham dome must have been suggesuon of using the neutral term 'zone' to refer to the relatively close to this leading edge. Thus Carboniferous to various belts of rocks with common sedimentary, metamorphic. Permian underpiaung trom a generally eastward direction best and/or plutonic histories. We break the Avaion composite explains these thermocnronoloeic relationships. terrane into the Esmond-Dedham. Hope Valley. Massabesic. and Pelham 'zones.' with Avaloman rocks exposed in the Willimanuc window correlated with the Hope Valley zone. We refer to the parts of the Putnam-Nashoba zone as the Pumam Department of Geology, Indiana University. Bloomington. 'U.S. Geological Survey. Reston. Virginia. belt (Connecucut) and the Nashoba belt (Massacnusctts). JU.S. Geological Survey, Denver. Colorado. GEOLOGIC SETTING Copyngnt 1992 by the American Geophyncai Union. The Avaion and Putnam-Nashoba zones lie on the eastern Paper numMr 4ITC029O4. margin of New England (Figure 1). The Putnam-Nashoba zone DT78-7407/9?y9lTC-02904S10.00 contains late Proterozoici ?) pelitic metasedimentarv and matic 1.00=* CO O 0.10 0.01 88-313a 450 Hornblende CO < TJ 400 CD O) Plateau Age = 339 + 2 Ma 350 CO 300 I I I I I 100 39 Ar K Released (%) PRESTON GABBRO . MONAZITE WILL1MANT1C \ HOPE VALLEY DOME \ 600 TITANITE ? V SHARPNERS *r POND ' * "^"iHORNBLENBi^ \ DIORITE IL O 400 Rb/Sr B10T 200 1 This study 2 Zartman & Nayior, 1984 3 Getty & Gromet, 1989 K-FELDSPAR 4 Hepburn et ai., 1987b 0 450 400 350 300 250 Ma Economic Ceoinev Vnl S3. liJhN. op. jJS-354 Thermochronology of Economic Mineral Deposits: Dating the Stages of Mineralization at Panasqueira, Portugal, by High-Precision 40Ar/39Ar Age Spectrum Techniques on Muscovite LAWRENCE W. SNEE,° « Department of Geology. Oregon State University, Corvallis, Oregon 97331 JOHN F. SUTTEE. U. S. Geological Survey, 981 National Center. Reston. Virginia 22092 AND WILLIAM C. KELLY Department of Geological Sciences. University o/Michigan. Ann Arbor, Michigan 48109 Abstract 40Ar/39Ar age spectrum dates for 13 muscovites have been used to reconstruct the ther mal history ^thermochronoloey; of the Panasqueira. Portugal, tin-tungsten deposit, a de posit spatially associated with a belt of Hercynian plutons. Muscovite samples with an age difference as small as 2.2 m.y. (0.7% of the age; are statistically distinct. Statistics are even better for comparison of multiple samples from separate events; that is. a difference of 0.9 m.y. (0.3%) can be resolved in this ~ 300-m.y.-old deposit. The major tin and tungsten ore-forming stages, which are the oxide-silicate stage, the main sulfide stage, and greiseni- zation. occurred between 296.3 ± 0.8 (1 a) and 291.6 ± 0.8 m.y. (1 a). The first substage of the oxide-silicate stage was a short-lived thermal pulse at 296.3 ± 0.6 m.y.; the fluids responsible may have emanated from the known granite cupola. The main sulfide stage was active at 294.5 ± 0.9 m.y. as a slightly longer lived pulse with oldest evidence for this stage (295.8 ± 0.6 m.y.) coming from areas farthest away from the known cupola and youngest evidence (293.5 ± 0.8 m.y.) closest to the cupola. A second substage of the oxide-silicate stage occurred as a short-lived thermal pulse at 292.9 ± 0.7 m.y., synchronous with grei- senization of the cupola and alteration of the silica cap at 292.1 ± 0.4 m.y. The duration of activity of the oxide-silicate stage, the main sulfide stage, greisenization, and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4.2 ± 0.5 m.y. (1 a). Minor argon loss from all dated muscovites occurred during later reheating, probably during the longer lived pyrrhotite alteration staee. A single center, the known cupola, had a prolonged role and was the source for mam sulfide staee, oxide-silicate staee II. greiseniza tion. and alteration of the silica cap and possibly oxide-silicate staee I and the pyrrhotite alteration stage; however, a separate source for these latter two stages cannot be ruled out. This study is an example of a new and powerful application of 40Ar/3sAr age spectrum dating of muscovite. Because of the high precision demonstrated in this study, it is now possible to establish time constraints necessary for solving some of the long-standing prob lems in economic geology. Beyond this, the unique geologic situation of Panasqueira has allowed us to quantify the thermal characteristics of muscovite. Published fluid inclusion data have been used to estimate a muscovite argon closure temperature of 325°C during rapid cooling or short reheating and a temperature of ~270°C during slow cooling or extended reheating. Argon-loss patterns displayed by all dated muscovites resulted from reheating after original closure; the mechanism for this argon loss appears to have been argon transport by volume diffusion. Thus. 40Ar/JSAr age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age, duration, and number of episodes of mineralization. Introduction studies of ore-forming processes. Until recently, ALTHOUGH there have been numerous eeochrono- isotopic techniques have been used only to date ore logic studies of economic mineral deposits, there deposits, but they lacked the precision necessary have been few high-resolution thermochronoloeic for measurement of the total duration of mineraliza tion or dating or the separate thermal pulses within an episode of mineralization. Moreover, the effects * Present address: U. S. Geological Survey. Denver Federal of chemical and/or thermal alteration on most iso- Center. Mail Stop 90S. Denver. Colorado 80225. topic systems were so poorly understood that criti- i):J61 -U 128/88/787/335-20S2.50 335 a a. a- (4) Mscu II (3) Apatite (207B) b) »l*'|V//**»'l\«/ Is \ ^/n < v ~M I 1 i Tr\r\n ? -th/lt?o*iT*' *" ll"l I'/ \ \\* "/ O 'i \ /» / ii, ' . \ / t '/ II J lOpGZ T IVlSCV 1 K / \ ' / , ' ') «. , / , i » , , \ - x I207A) I SCHIST FOOTWALL Illllllillllllllllllllllllllllill FlC. 6. Diagrammatic cross section of a vein showing the paragenetic relation of samples PGL 207 A and PGL 207B. ui bo = unuii - RIC' 80 T »- S6S 001 SO 0 T9C IS (IlTD l'.\H!$ «M 98' (i 0 + 0 SOS 6 C9 90 0 TCC IS nnspi') Dd C8 r B 0 T c *6S 6 OL 90 0 T SC IS U3SI3IJ) Del 80 T 9 IRS 9 S8 90 0 T OC IS MOSIOJ'J f SC' Da SL r 80 T S COS C C8 SO 0 TSI \z SSI^ Dd CC' 80 T 6 C6S 9 68 SO 0 T 8h IS SSN Dei I8C r 90 T C frRS V £6 CO 0 T IS IS SSH Del 80 T 8 frGS \ 91 SO 0 TSS IS ssn ^G3 r «.)ej 90 T 8 S6S \ \L CO 0 TC9 IS SSW 6ir Del 80 T 1 SOS I 9S SO 0 T9C IS SSO 16AS' Del 0 t + C CfiS 0 U to 0 T C^ IS SSO BIOS' Del 80T C 96S C 9L SO 0 T19 IS SSO V/.OS ' Dd HO T C ('< III) uciijrjd uo ^.iy & urnts iini|R7i|rJaiiiHi ou ;)J(hurc; ofl « |ii; Ml ckI V I'-joi jo |M;>.).i.)t| jo ;>"rj§ uio.i J Vr,t-/J V 0|. J° ISOTOPIC REFERENCE MATERIALS - ABSOLUTE OR OTHERWISE Robert D. Vocke, Jr., Inorganic Analytical Research Division, National Institute of Standards and Technology, A23/221, Gaithcrsburg, MD 20899 Isotopic standards have always played an important role in isotope ratio mass spectrometry. They allow results from different laboratories to be nonnalized so that data may be compared and combined. They provide a basis for correcting instrument measurement biases arising, for example, from non-linearities in the detection system. This can be especially important for elements which have isotopic abundances which span a large dynamic range. Isotopic standards provide a means of checking the validity of corrections for mass fractionation and mass discrimination during ion generation. They also play a role in chemistry, by allowing a researcher to evaluate isotope effects during separation chemistry. With the advent of the new generation of mass spectrometers capable of collecting multiple ion beams simul taneously, the need for calibrated or absolute isotopic standards for gain calibration, cup efficiency determinations, etc. is even more pronounced. Standards can be divided into three types. The least stringently specified isotopic reference materials are the working standards. They are generally produced by a laboratory from material at hand for daily calibration and quality control. Values for a working standard are derived from a cross calibration with a primary standard which may be a reference material (RM) or a certified reference material (CRM). Another kind of standard are the RMs. These are materials that have a wide distribution. They do not have certified isotopic values but instead have values set by a consensus survey of top laboratories. These samples are often measured concomitantly with unknowns, with the value of the unknowns expressed not in absolute units, but rather as relative deviations from a given standard. Excellent examples of this type of standard are the light stable isotopes of hydrogen, oxygen, nitrogen, carbon, sulfur and silicon distributed by the IAEA and MIST. These are listed in Table I. Isotope ratios of these elements, when measured on a gas isotope ratio mass spectrometer, are determined by switching back and forth between standard and unknown. The results of the unknown are then expressed as a relative deviation from a standard value. With this approach, highly precise data can be collected without the need for conversion to absolute values as long as everyone corrects to the same value for the standard. This kind of standard has also been important for solid source mass spectrometry. The former La Jolla and CIT neodymium standards and the Eimer and Amend strontium carbonate standard are examples of isotopic solutions prepared and distributed on a limited basis by early researchers in these fields. The current use of BCR-1 as a Nd isotopic interlab comparison standard is another example of an RM. The last type of standard is the absolute isotopic reference material, designated Standard Reference Materials (SRM) by NIST and Certified Reference Materials (CRM) or Isotope Reference Materials (IRMs) by national standards labs in Europe such as CBNM. These standards differ from the previous two in that all known sources of measurement bias have been eliminated or corrected for. This means that the "true" value of the isotopic ratios lies To: Or. Robert Ayuso From: Division 834.00 9-4-92 13:49am :. 3 of 7 within the error of the absolute determination. The production of an absolute isotopic reference material requires considerable effort and is, in tact, an atomic weight determination. After a pure, stoichiometrically definable form of the element being considered has been selected, pure separated isotopes of known assay of the same element must be found. Accurately known isotopic mixtures of the separated isotopes must be gravimetrically or volumethcally prepared. The principal factor limiting the overall accuracy of the absolute ratios is generally the quantiiation during this step of the chemistry. At present, isotopic mixtures can be prepared on an absolute basis with an accuracy of a part in 10,000 or slightly better. Synthetic mixtures of the enriched isotopes are thus made that bracket the range of rados in the candidate isotope reference material and are used to correct the measured ratios to an absolute basis. A ngidly defined mass spectrometric protocol specifying the sample form, amount, hearing parameters, etc. is then followed from which simple correction factors for the measured isotope ratios are obtained. The absolute isotopic rados and their uncertainties are derived from the corrected ratio data and a consideration of all the contributing sources of error or bias occurring during the certification process. Table II is a list of all the non-nuclear absolute isotopic standards currently available. .2.2,6 Tabie I. Light Stable Isotopic Reference Materials* Normalized Isotopic Compositions in parts per thousand (permit)" Reference ZE1. Material Type «W*, S'Ovwaw a^Cvro. &NM . i^Scirr ^ww 1 H VSMOW Water 0* 0* GISP Water 189.8 -24.85 SLAP Water -428* -55.5* NBS30 Bintke 6*.7 -+51 NBS22 OU -118.5 -29.73 PEF1 Polyethylene Film -100.3 -31.77 6 C NBS18 CartxMUtile +7.16 -5.04 NBS19 TS Limestone +28.65 + 1.95* NBS22 OU -118.5 -29.73 LSVEC Li Carbonate 46.1. PEF1 Polyethylene Film -100.3 -31.77 USCS24 Graphite -15.9 Sucrose ANU Sucrose -10.47 7 N NSVEC Gaseous N} 2.81 IAEA-MI Ammonium Sulfate +0.4 1AEA-N2 Ammonium Sulfate +20.3 IAEA-N3 PotexBtum Sulfate +2 Ui +4 USGS25 Ammonium Sulfate -30.4 USGS26 Ammonium Sulfate +53.5 8 O VSMOW Water 0* 0- GISP Water -189.8 -24.85 SLAP Water -428* -55.5* NBS18 Carbonatitc + 7.16 -5.04 NBSI9 TS Limestone +28.65 + 1.95* NBS2I Silka Sand +9.58 0 NBS30 Biotite -66.7 -+5.1 NBS127 Ba Sulfalc +94 +20.32 14 Si NBS-28 Silica Sand +9.58 0 16 S Soufre de Lacq Elemental S + 16 NZ1 Silver Sulfide -0.3 NZ2 Stiver Sulftdc + 21.0 NBS123 Sphalerite - + 17 NBS127 Ba Sulfate *9.4 +20.32 'o: Or. Robert Avuso From: Division 834.00 3-4-92 10:49am ;. 5 of 1 Note: These materials are available through either: I.A.E.A. N.I.S.T. Section of Isotope Hydrology Standard Reference Materials Program P.O. Box 100 Room 204, Building 202 A-1400 Vienna Gaithersburg, MD 20899 AUSTRIA USA With the exception of the WH ratio of VSMOW, none of these materials are certified on the basis of absolute isotopic ratios. However, they provide samples whose isotopic compositions are expressed as pan per thousand (permil) deviations from various light stable isotope standards. Thus, Vienna Standard Mean Ocean Water (VSMOW) is the reference standard for WH and "0/"0 ratios and is exactly defined as 0 for the two isotopic systems. Standard Light Antarctic Precipitation (SLAP) is also exactly defined as -428 for 6DVSMOW and -55.5 for ^"OVSMOW- The Vienna PeeDec Belemite (VPDB) is the reference standard for 13C/12C ratios and is exactly defined as 4-1.95 for NBS19. Atmospheric N} (AIR) is the reference standard for "N/WN ratios, while the Canyon Diablo Troilite (CDT) is the reference standard for ^S/^S ratios and NBS28 is the reference standard for MSi/*Si ratios. Exactly defined ratios. 2.2,8 Table 11. Absolute Isotopic Standards Z El. SRMName Type Source* Isotope Ratio Certified Ratio 1 H SMOW Natural Water IAEA WH 0.00015576 3 Li LSVEC Li Carbonate N1ST 'um 0.0832 IRM-015 Li Carbonate CBNM Li/I,! 21.78 IRM-016 Li Carbonate CBNM 'Li/Li 0.08137 MIRF-03 Li Hydroxide CETAMA 'Li/'Li 0.86926 5 B SRM951 Boric Acid NIST WB/UB 0.2473 SRM952 Boric Acid NIST IOB/UB 18.80 IRM-011 Boric Acid CBNM >°B/IIB 0.24726 IRM-610 Boric Acid CBNM Atom % IOB 0.949 IRM-611 Boric Acid CBNM Atom % "B 0.802 12 Mg SRM980 Mg Metal NIST "Mg/^Mg 0.12663 *Mg/*Mg 0.13932 14 Si SRM 990 Silicon NIST "sra 29.74320 "SiPSi 1.50598 IRM-017 Silicon CBNM aSi/»Si 29.82956 ^SiPSi 1.51197 1RM-018 Silicon Dioxide CBNM ^i/^Si 29.76566 ' Si/^Si 1.51323 17 Cl SRM 975 Na Chloride NIST Mcirci 3.1272 " 19 K SRM 985 K Chloride NIST *K/4IK 13.85662 "K/^K 0.0017343 24 Cr SRM 979 Cr Nitrate NIST »Cr/52Cr 0.05186 S)Cr/S2Cr 0.11339 wCr/3JCr 0.02822 28 Ni SRM 986 Ni Metal NIST slNi/*Ni 2.596061 4>Ni/*°Ni 0.043469 "Ni/^Ni 0.138600 "Ni/^Ni 0.035295 29 Cu SRM 976 Cu Metal NIST "Cu/^Cu 2.2440 31 Ga SRM 994 Ga Metal NIST "Ga/^Ga 1.50676 35 Br SRM 977 Na Bromide NIST ''Br^'Br 1.02784 37 Rb SRM 984 Rb Chloride NIST "Rb/'Tlb 2.593 "o: Dr. Robert Avuso From: Division 634.00 9-4-92 10:50am p. 7 of 7 Table II. Absolute Lsotopic Standards (continued) Z El. SRM Name Type Source* Isotope Ratio Certified Ratio 38 Sr SRM987 Sr Carbonate NIST wSr/*Sr 8.37861 "Sr/MSr 0.71034 MSr/*Sr 0.05655 47 Ag SRM 978a Ag Nitrate N1ST ""Ag/^Ag 1.07638 75 Re SRM 989 Re Metal NIST ltsRe/irRe 0.59738 81 Tl SRM 997 Tl Chloride NIST 3tnTl/aosTl 2.38714 82 Pb SRM 981 Pb Metal NIST ^Pb/^Pb 0.059042 ^b/^Pb 0.91464 " Pb/^Pb 2.1681 SRM 982 Pb Metal NIST "Pb/^Pb 0.027219 ^Pb/^Pb 0.46707 "Pb/^Pb 1.00016 SRM 983 Pb Metal . NIST ^Pb/^Pb 0.000371 3D7pb/»pb 0.071201 "Pb/^Pb 0.013619 SRM 991 Pb Nitrate NIST Atom % MPb 0.99979 Note; These materials are available from: CBNM Central Bureau for Nuclear Measurements Commission of the European Communitees Joint Research Centre Gael, BELGIUM CETAMA Centre d* Etudes Nucldaires 60-68 Avenue du G&ie'ral Leclerc BP 6 - 92265 Fontenay aux Roses FRANCE IAEA International Atomic Energy Agency P.O. Box 100 A-1400 Vienna AUSTRIA NIST National Institute of Standards and Technology Standard Reference Materials Program Room 204, Building 202 Gaithersburg, MD 20899 USA 23® ISOTOPIC REFERENCE MATERIALS ABSOLUTE OR OTHERWISE Workshop on the "Application of Isotope Systems to Geological Problems" USGS Reston VA Sept. 14-16, 1992 Robert D. Vocke, Jr., Inorganic Analytical Research Division, National Institute of Standards and Technology, A23/221, Gaithersburg, MD 20899 INTRODUCTION Isotopic standards have always played an important role in isotope ratio mass spectrometry. They allow results .from different laboratories to be normalized so that data may be compared and combined. They provide a basis for correcting instrument measurement biases arising, for example, from non-linearities in the detection system. This can be especially important for elements which have isotopic abundances spanning a large dynamic range. Isotopic standards provide a means of checking the validity of corrections for mass fractionation and mass discrimination during ion generation. They can also play a role in chemistry, by allowing a researcher to evaluate isotope effects during separation chemistry. Moreover, with the advent of the new generation of mass spectrometers capable of collecting multiple ion beams simultaneously, the need for additional and better calibrated or absolute isotopic standards is even more pronounced. Isotopic standards can be divided into three types. The least stringently specified isotopic reference materials are the working standards. They are generally produced by a laboratory from material at hand for daily calibration and quality control. Values for a working standard are derived from a cross calibration with a primary standard which may be a reference material (RM) or a certified reference material (CRM). Another kind of standard are the RMs. These are materials that have a wide distribution. Typical of RMs are the stable isotopes of the light elements distributed by IAEA and NIST. They do not have certified isotopic values but instead have values set by a consensus survey of selected laboratories. These samples are often measured concomitantly with unknowns, with the value of the unknowns expressed not in absolute units, but rather as relative deviations from a given reference standard. The third type of standard is the absolute isotopic reference material, designated Standard Reference Materials (SRM) by NIST and Certified Reference Materials (CRM) or Isotope Reference Materials (IRMs) by national standards labs in Europe such as CBNM and CEA. These standards differ from the previous two in that all known sources of measurement bias have been eliminated or corrected for. This means that the "true" values of the isotopic ratios lie within the error of the absolute determinations. The periodic table shown below characterizes the stable isotopic RMs and CRMs that are currentl available worldwide. rcnouic uwie 01 isr^pic xciciviico muwnais CRM, RM Shading highlights CRM - Certified Reference Material - absolute values CRM elements not suitable RM - Reference Material - no absolute values H ^ He for stable IRMs CRM, RM Note: CRM is equivalent to SRM & IRM 2 nit 2 air CRM X CRM RM CRM, RM RM CRM. RM 3 air, nit . rut - natural isotopic composition ' Li He, -""""^^^ B c N o F ArV Number of isotopes ^x^ spk - enriched isotopic composition 2 nil, spk monoiio 2 nit, ipk 2 nat 2 air, nat 3 Mt monoiso 3 air, Ml CRM CRM, RM RM CRM CRM, RM radio - radioactive element Na Mg monoiso - monoisotopic element Al Si P s Cl AT monoiso 3 Ml monoiso 3 nat monoiso 4 nat 2 nat 3 air, nat CRM, RM CRM CRM CRM CRM CRM CRM CRM, RM K Ca Sc Ti V Cr Mn Fe ftW|V Ni Cu Zfl Ga Ge As Se Br Kr 3 nit 6 monoiio 5 2 4 Ml monoiso 4 Ml monoiso 5 nat 2 nat 5 2 Ml 5 monoiso 6 2 nat 6 air, nat CRM CRM CRM CRM.RM Rb Sr Y Zr Nb Mo Ru IB, Pd Ag Cd In Sn Sb Te / Xe 2 Ml 4 Ml monoiso 5 monoiso 7 radio 7 monoiio 6 2 nat 8 monoito 10 2 8 monoiso 9 air. nal CRM CRM CRM Cs Ba La-Lu Hf Ta W Re 05 h Pi Au ng Tl Pb Bi Po At Rn monoiso 7 6 2 5 2 nil 7 2 6 monoiso 7 2 Ml 4 nat. ipk monoiso radio radio radio Fr RB Ac-Lr radio radio RM RM La Ce Pr AW Pm Sm Eu Gd Tfc Dy Ho Er Tm Yb Lu 2 4 monoiso 7 nil radio 7 Ml 2 7 monoiso 7 monoiso 6 monoiso 7 2 CRM CRM CRM Ac Th Pa tf Np Pu /1/n Cm l?Ar Cf Es Fm Md No Lr radio 1 ipk I radio 3 nit, «pk radio radio, ipk radio radio radio radio radio radio radio radio radio METHODOLOGY Unlike CRMs, RMs can be homogeneous natural materials with complex matrices, as well as pure elemental separates. One important difference between RMs and CRMs is that RM values are generally consensus values and not absolute values and are thus subject to revision as more data becomes available. Despite this limitation, RMs are often able to fulfil the same objectives as CRMs by simply providing a universally available basis for normalization. The procedure for preparing a RM is schematically depicted below. Excellent examples of RMs are the stable isotopes of hydrogen, oxygen, nitrogen, carbon, sulfur and silicon distributed by the IAEA and NIST. Isotope ratios of these elements, when measured on a gas isotope ratio mass spectrometer, are determined by switching back and forth between standard and unknown. The results of the unknown are then expressed as a relative deviation from a standard reference. With this approach, highly precise data can be collected without the need for conversion to absolute values. RMs are also important in solid source mass spectrometry. The La Jolla and CIT neodvmium standards and the former Eimer and Amend strontium carbonate standard are examples of isotopic RMs prepared and distributed by early researchers in these fields. Monitor standards for 40Ar/39Ar and other noble gas measurements also fit this category. The production of an absolute isotopic reference material requires considerable effort and is, in fact, an atomic weight determination. While many aspects of producing a CRM are similar to the protocol for producing a RM, a CRM must be based on measurements of fundamental units of matter, such as mass, and must be traceable to those units. A pure, stoichiometrically definable form of the element for the candidate isotope reference material must be selected, and pure separated isotopes of known assay of the same element must be found. Accurately known isotopic mixtures of the separated isotopes must be gravimetrically or volumetrically prepared and become the accuracy basis for the mass spectrometry. The principal limit to the overall accuracy of the absolute ratios is generally the quantitation during this step of the certification. At present, isotopic mixtures can be prepared on an absolute basis with an accuracy of a part in 10,000 or slightly better. Synthetic mixtures of the enriched isotopes are made that bracket the range of ratios in the candidate isotope reference material and are used to correct the measured ratios to an absolute basis. A rigidly defined mass spectrometric protocol specifying the sample form, amount, heating parameters, etc. is then followed from which simple correction factors for the measured isotope ratios are obtained. The absolute isotopic ratios and their uncertainties are derived from the corrected ratio data and a consideration of all the contributing sources of error or bias occurring during the certification process. This procedure is schematically outlined in the diagram below. Generalized Isotopic RM Generalized Isotopic SRM Production Scheme Certification Scheme MASS SPECTROMETRY STANDARD PREPARATION MASS SPECTROMETRY CLASSICAL CHEMISTRY . VI up mass sped ro Obtain iiialeii.tl Set up mass spectro- Develop accurate md no procedure for for1 st aiulai d mel ric procedure for assay procedure isotope ratio measure? isolope ratio measure Ill' Ills | ments i T Process 1standard Obtain enriched lih'iilify sources of material (eg grind, Identify sources of isotopes - Verify error and bias. purity, d( ) error- and bias purity and assay l)e\e|op a high precision t Develop a high precision Disl ribnteI st andard Produce calibration mass spectrometric technique mass spectrometric technique to participating lh,it minimizes error and that minimizes error and mixes bracketing the laboratories controls bias controls bias isotope ratios of interest 01 Determine values of interest Determine mass spedrometric using mass sped roiud ric calibration factors using the measurements from selected synthetically produced mixes laboratories ! I 1 1 Compute "Consensus Value" Determine accurate isotopic ratios for the SRM SUMMARY In order to further their utility to the geochemical and environmental community, the currently available isotopic RMs and CRMs have been grouped into general categories below. TIMS & ICP-MS Isotopic Reference Materials TIMS & ICP-MS Isotopic Reference Materials Z lil. SRM i CRM/RM Form Source III. SRM I CRM/RM Type Form Soim 3 Li IRM-016 CRM Natural Li Carbonate CBNM 90 Th IRM-060 CRM Spike Th Solution CBNM IRM-015 CRM Spike Li Carbonate CBNM 92 U U-0002 CRM Synthetic Mixture V Oxide NRl LSVEC CRM Natural [ i Carbonate NIST-RS U-005 CRM S)nthelic Mixture U Oxide NIH MtRF-03 CRM Spike Li Hydroxide CETAMA I) -010 CRM Synthetic Mixture U Oxide NUl 5 B SRM 951 CRM Natural Boric Acid NIST U-015 CRM S)nthetic Mixture U Oxide NISI SRM 952 CRM Spike Boric Acid NIST U-020 CRM'CRM S)nlhelic Mixture U Oxide NUl IRM-011 CRM Natural Boric Acid CBNM U-030" Synthetic Mixture U Oxide NIU IRM-610 CRM Spike Boric Acid CBNM U-050 CRM Synthetic Mixture U Oxide NUl IRM-6I1 CRM Spike Boric Acid CBNM U-IOO CRM Synthetic Mixture U Oxide NIH 12 Mg SRM 980 CRM Natural MH Metal NIST tl-150 CRM Sjnlhelic Mixture U Oxide NIH J4 Si SRM 990 CRM Natural Silicon NJST " U-200 CRM S)nlhelic Mixture U Oxide NUl IRM-017 CRM Natural Siluon CB'NM lJ-350 CRM S)nihelic Mixture U Oxide NUl IRM-018 CRM Natural Silicon Dioxide CBNM U-500 CRM Synthetic Mixture U Oxide NIH 17 Cl SRM 975 CRM Natural Na Chloride NIST U-750 CRM Synthetic Mixture U Oxide NUl 19 K SRM 985 CRM Natural K Chloride NIST U-800 CRM Synthetic Mixture U Oxide NIH 24 Cr SRM 979 CRM Natural Cr Nitrate NIST U-850 CRM Synthetic Mixture U Oxide NIH 26 Fe IRM-014 CRM Natural Fe Metal CBNM U-900 CRM S)nthetic Mixture U Oxide NIH 28 Ni SRM 986 CRM Natural Ni Meial NIST U-930 CRM Synthetic Mixture U Oxide NUl 29 Cu SRM 976 CRM Natural Cu Meul NIST U-960 CRM Natural U Meial NUl 31 Ga SRM 994 CRM Natural Ga Mcul NIST U-970 CRM S)nihetic Mitiure U Oxide NUl 35 Br SRM 977 CRM Natural Na Bromide NIST SRM 993 CRM Spike U Solution NUl CO 37 Rb SRM 984 CRM Natural Rb Chloride NIST IRM-040-1 CRM Spike U Solution CUNM IRM 018 CRM Spike Rh Solution CBNM IRM-050 CRM Spike U Solution CUNM 38 Sr SRM 987 CRM Natural Sr Carbonate NIST IRM-183 CRM Synthetic Mixture U Nitrate Soln. CUNM 47 Ag SRM 978 CRM Natural Ag Nilrate NIST IRM-184 CRM Synthetic Mixture U Nitrate Soln. CUNM 60 Nd La Julia RM Natural Nd Solution UCSD IRM-185 CRM Synthetic Mixture U Nitrate Soln CUNM CIT RM Natural Nd Solution CIT IRM-186 CRM Synthetic Mixture U Nitrate Soln CUNM 62 Sm err RM Natural Sm Solution CIT IRM-187 CRM Synthetic Mixture U Nitrate Soln. CUNM 75 Re SRM 989 CRM Natural Re Metal NIST IRM-199 CRM Synthetic Mixture U Nitrate Soln. CUNM 81 TI SRM 997 CRM Natural TI Chloride NIST 94 Pu SRM 946 CRM Synthetic Mixture Pu Sulfale NUl 82 Pb SRM 981 CRM Common Pb Pb Meial NIST SRM 947 CRM S)nthetic Mixture Pu Sulfate NUI SRM 982 CRM Equal Atom Pb Pb Metal NIST SRM 948 CRM Synthetic Mixture Pu Sulfale NUl. SRM 983 CRM Radiogenic Pb Pb Meul NIST IRM~042a CRM Spike Pu Solution CUNM SRM 991 CRM Spike Pb Solution NIST IRM-043 CRM Spike Pu Solution CUNM IRM-044 CRM Spike Pu Solution CUNM 1RM-049 CRM Spike Pu Solution CUNM Gas IRMS Reference Materials Noble Gas Isotopic Reference Materials / lil. SUM tf CRM/RM Type l :orm Source Z lil. SRM ff CRM/RM Type I;orm SDIII 1 H VSMOW CRM Synthetic Waier IAEA-NIST 2 He AIR RM Natural Air SLAP RM Natural Water IAEA-NIST 10 Ne AIR CRM Natural Air (MSP RM'RM Naluial Uaier IAEA-NIST BRUDERHEIM RM Natura Rock Powder IK Ikik NBS30 Natural Bi.mie !AEA : NiST 18 Ar AIR CRM Natura Air NBS22 RM Natural Oil lAEA-Nlsi MMhb-l RM"RM Nalura Rock Powder PF.FI RM Synthetic Pol) irili) Icne Film IAEA-NIST BCR-2 Natura Rock Powder IK IKik 6 C NBS18 RM Natural Carbonaliie IAEA-NIST BRUDHRHEIM RM Natura R Z El. SRM # CRM/RM Type Form Source 92 U IRM-072 ' CRM 1 Syntheuc Mixture i IS Soluuons CBNM IRM-199 1 CRM 1 Syntheuc Mixture | Uranyi Nitrate I CBNM U-0002 CRM Syntheuc Mixture I U Oxide NBL U-005 CRM Syntheuc Mixture 1 U Oxide NBL U-010 CRM Syntheuc Mixture i U Oxide NBL U-015 CRM Syntheuc Mixture i U Oxide NBL U-020 CRM Syntheuc Mixture i U Oxide NBL U-030 CRM Syntheuc Mixture I U Oxide NBL U-050 i CRM Syntheuc Mixture I U Oxide NBL U-100 CRM Syntheuc Mixture I U Oxide NBL U-150 , CRM Syntheuc Mixture i U Oxide NBL U-200 CRM Syntheuc Mixture I U Oxide NBL U-350 CRM Syntheuc Mixture i U Oxide NBL U-500 : CRM Syntheuc Mixture i U Oxide NBL U-750 CRM Syntheuc Mixture I U Oxide NBL U-800 CRM Syntheuc Mixture i U Oxide NBL U-850 CRM Syntheuc Mixture i U Oxide NBL U-900 CRM Syntheuc Mixture i U Oxide NBL U-930 CRM Syntheuc Mixture i U Oxide NBL ! U-960 { CRM i Natural ; U Metal NBL U-970 CRM Synthetic Mixture i U Oxide NBL Sources CBNM Central Bureau for Nuclear Measurements NBL U.S. Department of Energy Joint Research Centre. New Brunswick Laboratory. BIdg. 350 S teen wee naar Retie 9800 South Cass Avenue B-2440 Geel Argonne, 1L 60439-4899 BELGIUM USA Tel: (014)571 211 ATTN: Reference Materials Sales Tel: (708) 972-2767 CIT Dr. D. Papanastassiou California Institute of Technology MIST National Institute of Standards and Technology Division of Geological & Planetary Science Standard Reference Materials Program Pasadena. CA 91125 Room 204. Building 202 USA Gaithersburg, MD 20899 Tel: (818) 356-6123 USA Tel: (301) 975-6776 CETMA Centre d'Etudes Nucleaires 60-68 Avenue du General Leclerc UGBerk Dr. J. Reynolds BP 6 - 92265 Fontenay aux Roses University of California. Berkeley FRANCE Department of Physics Tel: 33-146-54-71-17 Berkeley, CA 94720 USA IAEA International Atomic Energy Agency UCSD Dr. G. Lugmair Section of Isotope Hydrology Scripps institution PO Box 100 University of California. San Diego A-1400 Vienna La Jolla. CA 92093 AUSTRIA USA Tel: 43-2254-3361-226 2.39 This section has copies of the certificates for the currently available Certified Isotope Reference Materials. ^" "S. Isotope Abundances RM 8535 (VSMOW) is the isoiopic standard to which RM 8536 (GISP). RM 8537 (SLAP), and most other oxygen bearing suhsiances are compared |4|. The hydrogen isotope abundance of VSMOW is |5|: *'*>m 5. Hagemann. R., Nief. G., and Roih. E, Absolute isotopic scale for deuterium analysis of natural waters. It is recommended that these RMs be used to calibrate internal laboratory standards immediately upon Absolute D/H ratio for SMOW. Tellus. vol. 22. 712-715 (1970). opening. After opening glass ampoules, RMs can be stored in small, dry. glass vials with conical plastic insert caps to prevent evaporation. 6 Baenschi, P . Absolute 18O content of standard mean ocean water. Earth and Planetary Science Letters, vol 31. 341 344 (1976). NOTE: Because very limited quantities of these materials exist, distribution is limned 10 one unit of each per three-year period of lime. Users arc strongly advised to prepare their own internal standards for daily use and 7. Li. W., Ni. IJ. Jin. D., and Chang. T.L. Measurement of the absolute abundance of oxygen-17 in V- / calibrate those standards against these RMs. SMOW. Kcxuc Tongbao, vol. 33, 1610-1613 (1988). Gaithersburg. MD 20899 William P Reed. Chief 8. Gonfiantini, R., The <5-notaiion and the mass-spectrometric measurement techniques, in Stable Isotope June 22. 1992 Standard Reference Materials Program Hydrology, Deuterium and Oxygen-18 in the Water Cycle, scientific editors J. R. Gat and R. Gonfiantini, (over) 35-S4, International Atomic Energy Agency. Vienna. (1991). It is recommended ihai these RMs be stored in I he containers in which they arc supplied to the user. NOT!:: Because very limited quantities of these materials exist, distribution is limited to one unit of each per National Institute pf ^tanfcarba & three-year period of lime. Users are strongly advised to prepare their own internal standards for daily use and lalibratc those standards against these RMs. Report of Investigation Isotope Abundances Reference Materials 8538-8542 The hydrogen isotopic abundance of these RMs relative to VSMOW (RM 8535) is |l|: RM <>DvsMOW' ***> 8538: NBS30 (hiotile) 8539. NBS22 (nil) 8540: PEFI (polyethylene foil) 8541: USGS24 (graphite) RM 8538 (NBS30) -66.7 ± 0.3 RM 8539 (NBS22) -118.5 ± 28 8542: Sucrose ANU (sucrose) RM 8540 (PEFI) -100.3 ± 20 'Ilicse Reference Materials (RMs) arc intended to provide samples of known isotopic composition with D/l I. The carbon isoiopic composition of these RMs relative to VPDB using a 41JCvpr)B value of + l.9S%ofor RM 1 'C/|2C and 18O/'*O Isotope ratios staled in parts per thousand difference (%o) from the Vienna Standard Mean 8544 (NBSI9) is |l|: Ocean Water (VSMOW (RM 8S3S)| or Vienna Pee Dee belemnitc (VPDB, |l.2|) isotope-ratio standards. These RMs are not certified, hut their use allows comparability of stable hydrogen, carbon, and oxygen RM isotope-ratio data obtained by investigators in different laboratories RM 853H (NBS30) is intended for stable hydrogen and oxygen isotope-ratio calibration of silicates and is issued in units of 2 g. Hydrogen isotope ratios should be determined on the water fraction (3.5%). RM 8539 (NBS22). RM 8540 (PEFI). and RM 85-12 50 (Sucrose ANU)are intended for stable hydrogen and carbon isotope-ratio calibration of organic materials and RM 8539 (NBS22) -29.73 ± 0.09 [l| -F- are issued in units of I mL, a few mg. and I g, respectively. RM 8541 (USGS24) is intended for stable caibon RM 8540 (PEFI) -31.77 ± 0.08 |1| isotope-ratio analysis and is issued in units of 0.8 g. RM854I(USGS24) -159 ±0.25(5) RM 8542 (Sucrose ANU) -10.47 ± 0.13 |l] These RMs are distributed on behalf of the International Atomic Energy Agency (IAEA). Vienna. Austria. The overall coordination of preparation for N 1ST distribution was carried oui hyT. B. Coplcn, U S Geological The oxygen isoiopic composition of NBS30 is: Surrey and R. D. Vockc, Jr., NIST Inorganic Analytical Research Division. RM <»' The supporting aspects concerning the distribution by NIST of these RMs were uxirilmaicd through the Standard Reference Materials Program by J. S. Kane. RM 8538 (NBS30) -5.10 ± 002(4] Maicnal preparation -5.24 ± 0.24 jlj NHS30 was prepared by I. Friedman, J.R. O'Neil, and G. Ccbula of the US. Geological Survey from a sample of Uikcview tonalite (Southern California batholith) provided by L Silver, California Institute of Technology, REFERENCES Pasadena. RM 8539 (NBS22) was prepared by S. Silverman, Chevron Oil Company. La llabra. California. RM 8540 (PEFI) was prepared by H. Gcrstcnberger and M. Herrmann, Zentralinstiiut filr Isotopen-und 1. Hut. G., Consultants' group meeting on stable isotope reference samples for geochemica! and hydrological Strahlcnfonchung, Leipzig. Germany |2|. RM 8S4I (USGS24) was prepared by T.B. Coplen. US Geological investigations. Report to the Director General, International Atomic Energy Agency. April 1987. Survey from Baker* technical grade graphite (96%, <44 urn). Prior to splitting with a sample splitter, six spatially separated l-mg samples were analyzed to ensure isotopic homogeneity of the material. Pcak-io- 2. Coplen. T B . Normalization of oxygen and hydrogen data. Chemical Geology (Isotope Gcoscicnce Section), pcak variation was 0 ll%o. RM 8542 (Sucrose AND) was supplied to the IAEA by H Polach, Australian vol. 72. 293 297 (1988). National University, Canberra, and was originally intended to repl.icc NBS oxalic .iud used for I4C standardization (I] } Gcmcnbcrger, H.,and (lerrmann.M.. Report on the intercomparison for the isotope standards Limestone KH2 and Polyethylene Foil PEF I. ZFl-Mitteilungen. vol. 66. 67-«3 (1983). Gaiilicrshurg. MD 2IHW William P Reed. Chief June 22. 1992 Standard Reference Materials Program 4. Coplen. T.B.. Kcndall. C., and Hopple. J.. Comparison of stable isotope reference samples. Nature, vol. 302.236-238(1983). (over) 5 Coplen. T B., unpublished data. It is recommended that these RMs be stored in the containers in which they are supplied to the user. To minimize the potential for oxygen isotope exchange of carbonate RMs with atmospheric water vapor. RM K541 (NBS18) and RM K544 (NBSI9) can be stored in a desiccator. *~m*' NOTE: Because very limited quantities of these materials exist, distribution is limited to one unit of each per ihiec-veur pent> Report of Investigation jsoiope Abundances The carbon isoioptc abundance of NBSI8 and NBSI9 have been measured as |5|: Reference Materials 8543-8546 RM 8543 (NBSI8) RM 8544 (NBS19) 8543: NBSl8(carbonaiiie) 8544: NBS19 (limestone) 8545: LSVEC (lithium carbonate) 98KWK ± 0.0028 atom percent I2C 98.8922 ± 0.0028 atom percent I2C 8546: NBS28 (silica sand-optical) 1.1002 ± 00028 atom percent I3C 1.1078 ± 0.0028 atom percent ' 'C The carbon isoiopic composition of these carbonate RMs relative to VPDB. using the defined d 1 JCvpl)|| value These Reference Materials (RMs) are intended to provide samples of known isotopic composition for isotope- of +1 95%ofor NBSI9. is |l.2|: ratio analysis of lithium, carbon, oxygen, and silicon. RM 8543 (NBS 18) is intended for C7i:C and I8O/'*O isotope-ratio analysis of carbonates wilh isotope ratios stated in parts per thousand difference (%o) from Vienna RM H-%0 Pee Dee Bclemnite (VPDB) or Vienna Standard Mean Ocean Water |VSMOW (RM 8535)|. respectively. RM 854-4 (NUSI9) is intended for I3C/ I2C and I8O/"O isotope-ratio analysis of carbonates and is used to define I he 50 VPDB scale 11.2). RM8S4S (LSVEC) is intended for lithium and carbon isotopic abundance calibrations. RM 8546 (NBS28) is the silicon isotope reference for reporting silicon isotope-ratio data, and it is also intended RM 8543 (NBS18) -504 ± 0.06 for oxygen isotope-ratio calibration of silicates. These RMs are issued in units of approximately 0.4 g each. RM8544(NBSI9) + 1.95 RM 8545 (LSVEC) -46.7 ± 0.3 These RMs are distributed on behalf of the International Atomic Energy Agency (IAEA), Vienna. Austria. The oxygen isoiopic composition of these RMs relative to VPDB using the defined d'8O value of -2.20 %o for The overall coordination of preparation for N 1ST distribution was performed by T. B. Coplcn. U S Geological NBS 19, is listed below ||,2|. Also listed is the (J I8O value relative to VSMOW using the relationship |6| that Survey and R.D. Vocke. Jr., NIST Inorganic Analytical Research Division. The supporting aspects concerning Ihe distribution by NIST of these RMs were coordinated through (he = 1.030924 180upnil + 30.92 Standard Reference Materials Program by J.S. Kane. RM - %0 Material Preparation RM 8S43 (NBS18) and RM 8544 (NBS19) were prepared by I. Fricdman. J.R. O'Neil and G. Cebula |3| of (he US. Geological Survey. RM 8543 (NBS 18), a carbonatite from Fen, Norway, was collected by B. Taylor, RM 8543 (NBSI8) -23.05 ± 0.19 + 7.16 ± 0.19 University of California, Davis, and crushed by H. Fricdrichsen, University of Tubingen, Federal Republic of RM 8544 (NBSI9) -2.20 + 28.65 Germany. The fraction between 88 (im and 440 |im was slorcd and bottled as NBS 18. RM 8544 (NBS19), also RM 8546 (NBS28) +9.58 ±0.10 known in the literature as TS-Ltmestone, was obtained from a single slab of white marble of unknown origin. After crushing, the fraction between 177 |im and 325 urn was bottled. RM 8545 (LSVEC) was prepared by H. Svec, Iowa Stale University |4|. RM 8546 (NBS28) was obtained by I. Friedman, U.S. Geological Survey from The lithium isotope abundance ratio of LSVEC is |4|: Corning Glass Company. It was washed with acid to remove impurities and the fraction between 100 um and 177 um was separated and packaged. 6Li / 7Li = 0.0832 ± 0.0002 Although no absolute isotope abundance measurement of RM 8546 (NBS28) has been performed, this material Gaiihersburg. MD 20899 William P Reed. Chief has served as the reference for relative ^Si^Si measurements for more than a decade; thus, J^Si of June 22. 1992 Standard Reference Materials Program RM 8546 = 0 %o. (mer) REFERENCES 1 Hut. G , Consultants' group meeting on stable isotope reference samples for gciKhcmicul and hyifrological investigations. Report to the Director General. International Atomic Energy Agency. April 1987 2 Coplcn.T B., Normalization of oxygen and hydrogen isotope data. Chunka! Geology (Isoiopc Gcosuence Section), vol. 72. 29.V297 (1988). \ 1 riedman, I., O'Neil. J R.. and Ccbula. G.. Two new carbonate stable isotope si.imi.irds. Geostandards Newsletter, vol. 6. 11-12 (1982). 4 Mesch, G.D., Anderson. A.R.. and Svec. 11.J.. A secondary isotopic standard for ''I i/ 7 l.i determinations. Im J. Mass Spcctrom. Ion Phyv. vol. 12. 265-272 (1973). 5 ('hang, T.L. and Li. W, A calibrated measurement of the atomic weight of oirbon. Chinese Science Bulletin, vol. 35. no. 4. 290-2% (1990). 6 Coplen. T.B., Kendall. C., and Hopple, J.. Comparison of stable isotope reference samples. Nature, vol. 302.236-238(1983). Storage It is recommended ihai these RMs be stored in Ihc containers in which Ihey arc supplied 10 the user. When RM 8552 (NSVEC. gaseous nitrogen) is opened, ii should be used immediately for calibration. It can be National Ilnatttute nf £>tanbar&H & (Eecljnulngu; stored in a glass container fabricated with an all-glass stopcock coated with Apiezon N* hydrocarbon-based stopcock grease. Because the salts are hygroscopic, they should be stored in a desiccator. Report of Investigation NOTE: Because very limited quantities of these materials exist, distribution is limited to one unit of each per three-year period of lime. Users are strongly advised 10 prepare their own internal standards for daily use and to calibrate those standards against these RMs. Reference Materials 8547-8552 8547: IAEA-N1 (ammonium sullale) Isotope Abundances 8548: IAEA-N2 (ammonium sulfaie) The absolute isotope ratio of nitrogen in air. reported by Junk and Svec is |1|: 8549: IAEA-N3 (potassium nitrate) 8550: USGS25 (ammonium sullale) ' These Reference Materials (RMs) are intended lo provide samples ol known isotopic composition wuh ISN/I4N isotope ratios stated in parts per thousand difference (%o) from atmospheric nitrogen in air (AIR). These RMs are not certified, but their use allows comparability of stable nitrogen isotope-ratio data obtained by investigators in different laboratories. RM 8552 (NSVEC) is issued in units of 3(X) nmol and the other RMs are issued in units ranging from 0.4 to 2 g. RM 8547 (IAEA-NI) +0.4 ± 0.2 |3| 0\ RM 854S (IAEA-N2) +20.3 ± 0.2 |3| These RMs are distributed on behalf of the International Atomic Energy Agency (IAbA). Vienna. Austria RM 8549 (IAEA N3) +2 10 +4 |4| RM 8550 (USGS25) -304 ± 0.5 |5| The overall coordination of preparation for NIST distribution was carried out by T B Coplcn. U S. Geological RM 8551 (USGS26) +53.5 ± 0.5 J5| Survey and R.D. Vocke, Jr., NIST Inorganic Analytical Research Division. RM 8552 (NSVEC) -2.81 |6| The supporting aspects concerning the distribution by NIST of these RMs were uxudmaitil through ihc Slumlord Reference Materials Program by J S. Kanc REFERENCES 1. Junk, G.. and Svcc, H.J., The absolute abundance of nitrogen isotopes in the atmosphere and compressed gas from various sources, Geochimica el Cosmochimica Acia, vol. 14. 234-243 (1958). RM 8547 (IAEA-NI) and RM 8548 (1AEA-N2) were prepared by E. Salaii, Centra de Encrgia Nuclear na 2. Hut, G., Consultants' group meeting on stable isotope reference samples for geochemical and hydrological Agricultura, Brazil. RM 8549 (IAEA-N3) was prepared by A. Mariotti, Universal P. and M. Curie. Tour. investigations. Report to the Director General, International Atomic Energy Agency, April 1987. Paris, Fiance. RM 8550(USGS25) was prepared in 1991 by J K_ Boh Ike. U.S. Geological Survey from Fisher* ammonium sulfaie (A938-500, lot #915021) and Cambridge Isotopes* ammonium sulfalc ('ft «« percent MN; 3. Bohlke. J K., U S. Geological Survey, written communication. 1992. lot Bl 1328). RM 85S1 (USGS26) was prepared in 1991 by J.K. Bohlke, U.S. Geological Survey from Fisher* ammonium sulfale (A938-500, lot 4*915(121) and Cambridge Isotopes* ammonium sulfaie (10 percent 15N; 4 Siichlcr, W. International Atomic Energy Agency, Vienna, oral communication, 1991. lot Bl-1050). RM 8SS2 (NSVEC) was originally prepared by G. Junk and H.J. Svcc, Iowa Stale University 111; C. Keudall, U.S. Geological Survey (hen split the sample into several hundred aliquot*. 5. Bohlkc, J.K., U.S. Geological Survey, unpublished data. 6. Kendall. C. and Grim, E., Combustion lube method for measurement of nitrogen isotope ratios using Ciaiiheishurg. MD 208<» William P. Reed. Chief calcium oxide lor total removal of carbon dioxide and water, Analytical Chemistry, vol. 62,526-529 (1990). June 22. 19-12 Standard Reference Materials Program (over) Commission of In* European Communities 4. Certified values are based on thermionic mass spectrometric measurements G«i!l Lstabhshmunt JOINT Central Bureau lor Nuclear Measurements on sdjuples converted to Lll. The measurements were calibrated with the did RESEARCH Sletnwfg op flrtl*. 2'?40 Geel. Halgium lei (OHI 571 211 - Telrx 33M9 tUllAT B of synthetic mixtures of isotopically enriched Li isotopes. CENTRE Telefax OH/5842 71 i The preparation and characterisation of the synthetic Isotope mixtures were performed by Jean Pauwels. The isotnpic measurements and their calibration with synthetic Isotope ISOTOPIC REFERENCE MATERIAL CBNM - IRM - 015 mixtures, as well as the chemical preparation of samples for isotopic measurements, leading to this IRM. were performed by Andre*e I .imberty. T|IK IftM fs supplied with an atomic Isotope ratio certified as 6-2440 Gee I PAUL DE BIEVRE 6Li/ 7Lf - 21 .78 t °- 12 1 February 1986 Head CBNM Mass Specr.rometry corresponds to an isotopfc composition with following isotope abundances' Isotopic Atom X Isotopic Mass X So SLl 95.610 94.916 >/- 0.025 7Li 4.390 5.084 * /- 0.025 The atomic weight of the lithium Is 6.059 06 + 0.000 22 The IRM is intended for use in calibrating Li isotope ratio measurements. NOTtS i 1. All uncertainties indicated are accuracies, computed on a 2s basis. 2. Ihe Reference Material consists of LlgCOj and is supplied in about 0.05 g units. 3. The atomic masses used in the calculation of mass X .ihundances and of the , atomic weight, are : \\ : 6.015 121 4 +/- 0.000 001 4 7LI : 7.016 003 0 \l- 0.000 001 6. Commission ol Ihc European Coinmuiiilies JOINT Git'1 Establishment 4. Certified values are based on thermionic mass spectrometrlc measurements RESEARCH Caniral Bureau lor Nuclear Measurements Slaanwcg ge Hf>>'* ' 14° ft**' Brlyium on s.imples converted to Lil. The measurements were calibrated with the iid CENTRE " leV OH7 571 211 T"" 335M eu"* T B of synthetic mixture;; of isotopically enriched Li isotopes. Full details ISOTOPIC REFERENCE MAIERIAL CBNM - IRM - 016 of this procedure can be found in : ' E. Michlels, P. Oe Bievre : International Journal of Mass Spectrometry and Ion Physics. 49, pp. 265-274 (1983) ' Thfi IRM is supplied with an atomic isotope ratio certified as The preparation and characterisation of the synthetic isotope mixtures were ' performed by Jean Pauwels. 6Li/ 7Li 0.081 37 f/- 0.000 34 The devplopment of a precise isotopic measurement procedure for LI, the isotopic measurements and their calibration with synthetic Isotope mixtures, This corresponds to an isotopic composition with following isotope Abundances as well B-2440 Geel PAUL DE BIEVRE . i I he atomic weight of the lithium is 6.940 69 +/- 0.000 29 50 1 September 1984 Head CBNM Mass Spectrometry I The 1RM is Intended for.use in calibrating Li isotope ratio measurements. NOTES ' 1. AH uncertainties Indicated are accuracies, computed on a 2s basis. 2. ihe Reference Material consists of L1 ?CO, and is supplied in .ibout 1 g units. 3. The atomic masses used in the calculation of mass X abundances and of the' atomic weight, are : 6I I : 6.015 123 2 »-/- 0.000 001 6 7LI : 7.016 004 5 +/- 0.000 001 8 Commission of lh« European Communities JOINT MOTPS RESEARCH fli lit J'.:c Gt'fl itdijiufn CENTRE Tel IflUI S7I ii - I*iei ].':£<' IUII4T n 1. All uncertainties indicated are accuracies, computed on a 2s basis, taking Into account both measurement reproduclhllItles and uncertainties of CERrrricAH systematic nature estimated on a 2s basis. ISOTOPFC REFERENCE MATERIAL CRNM IRM-61!> 2. Ihe IRM solution has a molality of 0.5 m IIC1 (i.e. 0.5 mol HCl-kg-l'of solvent ur a molarlty of 0.5 M HC1 (I.e. 0.5 mol HCl-1-1 of solution) 3. The Avogadro constant used is (6.022 131 i 0.000 01?) 1023 mol-1. the IRM Is supplied with a molar concentration of 6li certified to hp 4. The atomic masses, used in the calculations, are (3.825 t 0.027)-lO-3 mo I 6Li-kg-l of solution! 6L1 : (6.015 121 4 ± 0.000 000 7) u Other Lithium Isotopes present are related to the 6l I concentration through the 7L1 : (7.016 003 0 t 0.000 000 8) u following certified molar ratio : 5. Using this Spike IRM, 7Li and LI concentrations in unknown samples can'be 6L1/7LI : 21. 78 t 0.12 [ determined by Isotope Dilution Mass Spectrometry, through a measurement of the molar isotope dilution ratio RB - 6Li/7 M in the blend. They should 1 be computed with the aid of the following equations which allow an easy P- Ihis corresponds to an isotopic composition with following abundances : identification of the sources of the uncertainties In the procedure : 00 Hole X Mass X Uncertainty c(7l(L 95.610 94.916 i 0.025 4.390 5.084 t 0.025 R,-R a I I R, c(LO,= X R.-R, 1+R, The atomic weight of the Lithium is 6.059 06 1 0.000 22 where molar Isotope ratio 6L1/7 L1 1n the unknown sample material From the certified values, the following concentrations are derived : Rr Rr molar Isotope ratio 6L1/7L1 in the spike material mx mass of the unknown sample (2.301 i 0.016)-10-5 kg 6l.1-kg-l of solution mass of the sample of spike solution used (4.001 1 0.02B)-10-3 mol Ll-kg-l of solution mr number of noles 7LI*kg~^ of sample material (2.425't 0.017)-10-5 kq Li-kg-1 of solution number of noles ^l-kg"1 of spike solution number of moles L1>kg-l of sample material e(Li)r number of moles Li-kg-1 of spike solution. Isotoplc measurements by Ihermal lonisatlon Mass Spectrometry were carried out by Andree I amberty. Hetrologlcal aspects Involved In the preparation and certification were performed by frans Hendrickx. t The antpouldtlon nf this IRM was accomplished by Aridre Vcrhruggcn and Adulfo Alonso-Muno?. ! (he coordination of the preparation of this IRH was accomplished hy Andre Verbruggen. Ihe overall coordination of the establishment leading to the certification 'and issuance of this IKM was performed by Andree Laraberty. B 2410 Geel Paul DE BlfVRE April 1991 Head CBNH Mass Spectrometry -O U. S. Depart flranf of Commerce MauriceVH Stana J Nillui.al II lHTWa st.nd.rd, (Hedificate of Analysis A V irtctor (_ ty Standard Reference Material 951 Boric Acid lljllMj. a. idhnclric assay, weight percent ...... 100.00 i 0 01 Absolute AluiiiilaiiiT Iliilin, IO I(/'' II ...... 0.2m ± 0 0002 lioron 10. atom percent ...... I').1(27 ±001.1 lloron I I. atom percent ...... 110 17.1 iOOI.I Tin atomic uciglil of llir boron, calculated from I In: absolute al>iiiul.uu r r.ihn n.iing the inn-hilic masses 10.0129 anil 11.0093, is 10.1112. This lot of boric nciil was prepared lu ensure material of high purity and homogeneity. \s rcccitcd. it way slight!) ilrfiriciil (approximately 0.01 percent) in moisture, lull adjusts to a sli'ichiiunclric composition in about 'M minutes exposure to a normal room hiniiiilily (approxi mately it.*) pern-ill relative hiiiniilil}). One.e adjusted ID composition, the nialrii.il is relatively iii.scnsilikc (<().()I permit) |o iiioislnre eliaiigcs between 0 and dO percent relative hnmidit) , and absorb* only about (1.02 percent excess moisture in room temperature hnniidiliea as high as 'Ml |x-rcceil The material eaiinol lie healed as it decomposes with the loss of considerable water. \ss.iy was liy eonloinelrie tilralioii of samples larying in size from 0.2 to I.Og of horir aenl. di.-.solted in 10(1 ml of a prencnlraliicil solution I.I/ in KCI and II.75A/ m inannilol. Hi.: inflection IMIJII) of (he poleiiliiniielrie curve obtained from iiieasiiriMiieiils ivilh a glass calomel electrode Msti-in i\a> taken iia the end point. The pll of the maximum inflection point uas taken as the end 01 point The pll of the maximum inflection point v\i|| var\ from approximately 79 to 11.5 for the range of sample M/e- given above, and the lilralioii must, therefore. l>e conducted in the absence of G tarhoii dioxide or carbonates. The indicated tolerance is ill least as large as the ')5 percent confidence level for a single determination of any sample in the lot of material, and the average essential!} indicate!- a horon hydrogen ion ratio of 1.0000 since separate examination show* the material contains les.- than 0.001 percent of free strong acid. Tbr .ilxinilance ratio ivas determined by single-filament solid-sample mass bpTlroinclry using the ion Na } IK Ij. Mixtures of known "Ml/ 1 ' It ratio (at a 1:4, 1:1, anil 4:1 ratio) were prepared from higli |)iiril\ separated isotope solutions ami used a- comparison standards. Correction was deter mined f,.r the I6 ()/"O ratio ("U/'°H ratio. -00007')) b) measuring mass "0 using the high pncilv horiin-l I separated isotope. The indiealed lolerancrs are at least as large as the *)5 percent i iiiilnli-in-e limit* for a single determination ulnrli include.-, terms for inhoinogeneilK-s in the mate rial a- uell a> anulv lical error. The material ua- prepared h) the j. T. Maker (!oinpan> of I'hillipsbnrg. New Jerse) , for the .\rgonne National l.alioralory. Separated isotopes were purified and solutions prepared by K. M. Sappenfield and T. j. Murphy, coulomelric lilralions were made by (' . Marinenko and ('.. I-., ('liampion. mas.- speetromelric measiiremrnls were made b) E. j. Calanzaro and L L. Garner. Analv lical Chcinisln Mivision. The various procedures developed have been puhli-hcd and are av.ulalile ni Special I'nldicalion 2(>0-I7. The overall direi-lion and coordination of (he technical measurements leading to certification ku-fc performed under the chairmanship of \\. K. Shields. The technical and support aspects involved in the preparation, certification, and issuance of this Standard Itcferrinc Material uere coordinated through the Office of Standard Itcferencr Materials b) j. I.. Hague. Washington. I). C. 202III \\.\VayiieMeinke.Chief Felirnur) 211, !%<> Office of Standard Keference Materials (lU-vis.'dOi-lolwr 12. 1!>7I) (Tliu irrlifkalr luprnrdu crrtifirair o( Au«uil 9 !9hH) U. S. Depui trtumt' of Commerce Maurice/-}) Slans secrttfliry j>.- : ?J Nalmna) lltiNftA ol SUndanls A. V. Aklll). Duertor (flrrttftrutc nf Atutlpia Sr.incl.ird Reference Material 952 Enriched Boric Acid Ali.-olute Abundance Ratio. "H/"H . . . 18 80 ; 002 l»»ron 10. atom percent ...... 94949-' 0005 Horon II. atom |iercunt ...... 5(151 t 0 005 II HO , acidimetric assay, weight percent...... 99 07 s 002 I In: |)|-c'|iiinitiiiu furnished in nil enriched IHHOII III boric acid It is slightlx con- laminated liy occluded niot|ier-li(|uor lint the as.sax. \;ilnc should make it useful Ity diicct xveiithinn f°r u "spiking" materiiil fur horon as.sax. s, as well as a useful rnateri.il for the c.ililn .il inn of ni;iss -ipccti onicter.s 'I'liu atoniic weight <>f the tinrnii. c;ilciilnlrd finni Hie iil>.sidiit:( Tlie nlxindaiici- ratio was determined by .sintrlc fdanient soiid-siiinple rna.s.s spectrom- elry. ii.^ini; the inn Na HO'.. Mixtures uf known "I1/"B ratio were prepared from high- pni il\ separated isotopes and used an comparison standards. Correction wits determined for ihu "O/' :O ratio ("It '"B ratio 0.00070) lix measurinft mass 0(1 nsintf the liigh- piuity l>ornn II separated isotope The indicated tolerance is at le;ust as lar^e as the 05 percent confidence limits for a single determination which includes terms for inhomo- Kuni'iiii'.s in the materiiil as xvell as analytical error. Details of the. preparation!! and measurements are avuilahle in Special Publication 2(>0 17. The material xva* prepared liy the Oak Hi(lt,re National Laboratory. 'I'he mat..>rial and Hie separated i.Mi|o|ie.s were purified and solutions prepared hy K M. Sappcnfield and T. I. Murphy, conlometric tilratious \xere made liy (I Marinenko and (' F.. Champion, mass-spi etromelric measurements xveri' made by K .1. Catanzaro and K I. (iarner. Analytical Chemistry Division. The overall direction and coordination of the technical ineaMiiremenls lo.idiiiK to iiTlilication were performed under the chairmanship of \V. K Shields. The technical and support aspects involxed in (he preparation, certification, and ixtiiaiire of this Standard Reference Material xven: coordinated through the Ollicu of Standard Reference Materials hy .1. I, lla^ne \Va>hiiiKMon. I). C. \iir2lll XV. XVayne Meinke, Chief Fehrnary 28. 106!) Oilier of Standard Reference M.ilenah (XfMsolO. l(d>cr I- I'l7ll Commission ul Hie Europr>in Communities NOTES JOINT Sleenweq on Hcnc 2UO Gftt, Belijium RESEARCH lei (OM) 571 211 - I'-lei 3-T.fll FlIlAf B CENTRE ineitt nu/;a 4? 73 i. All uncertainties Indicated are accuracies, computed on a 2^ bdsis. CERTIFICATL ?.. Ttiu [RM is a solution of HjDOj In subboiled water and is supplied in cjudrtz ampoules containing about 5 g of solution. I ISOTOPIC RITC-UNCC MATERIAL CRNM IKM-610 3. Tlie Avogddro Constant used is (6.022 134 i 0.000 012) 10?3 . I 4. Ihe atomic masses, used In the calculation;;, are ihe IKM Is supplied with an 1°0 atomic isotope concentration certified as I 10B 10.012 936 9 t 0.000 000 3 u J (2.?18 02 i 0.000 S3)-1Q21 n (ato«s lOB)-kg-l (solution) 11B 11.009 305 4 t 0.000 000 4 U from the certified isotope concentration, the following concentrations am derived : 5. Usiny this Spike 1RH, B concentrations in unknown samples can bn determined (3.683 11 t 0.000 88)-tO-3 mole (lOu)-kg-l (solution) by Isotope Dilution Mass Spectrometry, through a measurement of the molar (3.687 78 t 0.000 BR)-10-5 kg (lOfl) -kg-1 (solution) ' Isotope dilution ratio RB = '°B/1'B in the blend. Tliuy should be computed with the aid uf the following formula which allows dn easy identification of Other Boron isotopes present are related to the JOB isotope concentration through the sources of the uncertainties in the procedure : , the following molar ratio : i W. ! CJ\ : 18.80 ± 0.02 Ihis corresponds to an i so topic composition with following Isotope abundances : where molH % mass % Uncertainty RX molar Isotope ratio B in the unknown sample material Ry molar Isotope ratio ^°B in the spike material 10Q 94.949 S 94.474 7 ± O.OOb 1 MX mass of the unknown sample llB 5.050 5 5.525 3 t 0.005 1 MY mass of the sample of spike solution used CIO number of atoms '° B kg"* spike material Cll numher of atoms kg" 1 sample solution. Ihe atomic weight of the Boron is 10.063 259 ± 0.000 051 From the certified atomic isotope concentration, the following element concentrations are derived : (3.B79 02 ± 0.000 93)-lfl-3 mole (B)-kg-l of solution (3.903 56 t 0.000 94)-JO 5 kg (B) -kg-1 of solution - Coniinlssmn ol the Euiopcan Communities JOINT (ii:cl Establishment 4. Certified values are based on thermionic mass spectromelric measurements 1 RESEARCH Onltal Biircju \ Iliis corresponds to an isotuplc composition with following isutope abundances: B-2440 Gccl PAUL OF 8IEVRF Isotopic Atom X Isoropic Mass X 1 June 1984 Heat) 19.fl?4 10.359 »/- 0.070 C8NM Mass Spectrometry flO.176 81.641 /- 0.0?0 en The .ilomlc weight of the boron is 10.811 8 +/- 0.002 0 Ilia IRM Is intended for USP In calibrating B isotope ratio medburcmonts. NOIfcS 1. All uncertainties indicated arc accuracies, computed on a 2s basis. ?. The Reference Material consists of ll-jB03 and is supplied in about I g units. 3. Ihc atomic masses used in the calculation of mass X abundances and of the ,itnmlc weight, are : 100 : 10.01? 938 0 i/- 0.000 001 0 1 0 : 11.009 305 3 «/- 0.000 001 0 un nl the European Communities NOTES JOINT Ccni-al 9urccu lit Nuclear Measurement! RESEARCH Steenv/^g np Htilt 1' to Geel. Belgium 1=1. |OI<| S7I2II - lel^i 33!B9 Fl/fAT B 1. All uncertainties indicated are accuracies, computed on a 2s basis, taking CENTRE T«lelai 014/SHi'.! T3 into account both measurement reproducibilities and uncertainties of CFRTIHCAIE systematic nature estimated on a 2s basis. [SOIOPIC REFtRENCE MATtRIAL C8NM [RM-611 2. The IRH is a solution of 83003 in sub boiled water and is supplied in quartz ampoules each containing about 5y of solution. 3. The Avnqadro Constant used Is (6.0Z2 134 t 0.000 012) 1023 mol~ l . 7h« IRH Is supplied with a molar concentration of H« certified to be i 4. The atomic masses, used in the calculations, are (4.02S » 0.040)-10-3 mol llfl-kg-1 of solution) i 10B : (10-012 936 9 t 0.000 000 3)u Other Boron Isotopes present are related to the concentration through the 11B : (11.009 305 4 t 0.000 000 4)u i following certified molar Isotope ratio : 5. Using this Spike IRH, 10B and B concentrations in unknown samples can be determined by Isotope Dilution Mass Spectrometry, through a measurement of I JOB/llR : 0.247 26 t 0.000 32 | the molar Isotope dilution ratio RQ " ^B/^B In the blend. They should be This corresponds to an isotopic composition with the following Abundances : computed with the aid of the following equations for bl-lsotopic elements 01 which allow an easy identification of the sources of the uncertainties in the Hole < Mass X Uncertainty procedure : 10u 19.024 10.359 1 0.020 e w - R r~ Ra !"r u 118 60.176 B1.64I » 0.030 B ~ "x mjf R,-R 1 f Ri cCB), = -= - c(B)y I he atomic weight of the Boron is 10.811 7B i 0.000 20 I +R. From the certified values, the following concentrations are derived : where (4.431 J 0.044)-lO-5 kg Ufl-kg-1 of solution molar isotope ratio in the unknown sample material (5.020 t 0.050)-lO-3 mol B-kg-1 of solution molar Isotope ratio In the spike material (5.4?B ± 0.054)-10-5 kg B-kg-1 nf solution mass of the unknown sample mass of the sample of spike solution used number of moles '°B kg"1 of sample material c("B>r number of moles ^B kg" 1 of spike solution number of moles B-kg-1 of sample material number oF moles B-kg-1 of spiko solution. Isotopic measurements by thermal lonisation Mass Spcctrometry were carried out by Veronica Holland. Melro1oglc.il aspects involved in the preparation and certification were performed hy Frans llendrickx. ' The purity of H3003 was determined by Spark Source Mass Spectrometry by Hilly lyckc. ' The ampoulation of this IRH was accomplished by Andre Vei hruggen and Adolfo Alonso Mufioz. i The coordination of the preparation of this IRM was accomplished by Andre Verhruggen. I The overall coordination of the establishment leading to the certification and Issuance of this IRH was performed hy Andree Lamberty. I B-2440 Geel Paul OE BIEVRE January 1990 Head CBNM Mass Spactrometry cn U. S. Depart John T. Certificate of Standard Reference Material 980 Isotopic Standard for Magnesium Absolute Abundance Ratio, Mg-25 MK -I 0.12663 « 0.00013 Absolute Abundance Ratio, MK-2C> MK 21 0.13932 000026 Magnesium-21, Atom Percent 78.992 < 0.025 Magnesium-25, Atuin Percent 10.003 0.009 Magnesium 2(1, Atom Percent 11.005 0019 The preparation furnished is » commercial sample of high-purity mag nesium metal. Measurements ure bv triple fihinient (rhenium) IIIH.HH .spec- tromelry, usiiiK mixtures of known cnuipoHition prepared from high-purity separated isotopes of magnesium as comparison standards. Overall limits of error are bused on 1)5 percent confidence limits for the mean of the ratio measurements, and on allowances for the known sources of |n>ssible sys tematic errors. Details of the preparation and measurements ure published by E. J. Catanzaro, T. J. Murphy, E. L. (Jarner and W. R. Shields. J. Re- aeiirch NItS 70A, No. (i. 453-158 (It)fi(i) WasliinKtnn, I). I'. 20231 \V. Wayne Meinke, Chief Jnnnury III, 19(17 Ollice of Standard Reference Materials I > I), ll.llllllfhl I.I I .III (Up ^ I . K. Mi.rln Rational ^Bureau of j&tandards Certificate Standard Reference Material 990 Assay-Isotopic Standard for Silicon Irrrm e Material I- -M|>|ili Silirim _'H. .iliiin jierri nl 'IJ 2_").l Silieiui 2'), aliilll |MTi enl » f.f) The imln.ilril iinriTlaiiilirs an- ovrr.ill limits of error fur a -in»lr an. il\ -.i--. II.IM il mi '>"/' i (inficlriirr liinil^ nl l lie in ran anil knoun MHIFI i> nf M, sli-in.ilii lna-~. ni.i.-,- |HI Irniiirlrir llli'.l-iirrDirnl-- urn- mailr livIi I I., ll.irnr.- anil I. I Mtmrr mi -.inijilr^ |irr|iarnl Ii) I.. \, M.nlilai) inul T. j. Miiipliv. Tin' DM'i.ill ilirrrlioii anil roimliiialimi "f tin lrcliiiir.il inr.i-nn nirnl- Iradin^ In < i ililn .ilnm urrr iinili i llir rli.litnian.- Tlic lrrliinr.il anil -ii|i|mrl ,I-|K i N ronrrriiili^ llir |irr|i,iralioii, rrrlifii .ilnm. .mil i>-uaiur of this Slamlalil Hrftirnrr Material urrr eiiorilinalril lliri.i^li (lie (H'lirr <>l Slanilaiil Itclrmuc Materials I.V W.I', ll.e.l. \Va.s|iiii;:li.n. D.C. 2ILML I I'aulCaliClnrl (Illirr nl Sl.iliilanl Itrli reiirr Mali-rials It II. Kl Jl. tlrlrriiiiiiJluiiMirilir \.i«.nlio i:.m«Uiil. I'ln-I. .il It. ol Urn Europoan Communities JOINT i;pel Establishment I enlral Burca lo. Nuclear M«i«iAeuienif RESEARCH 3. The relative atomic masses used In the calculation of mass abundances and CENTRE Tc! 101') 5;i 2ii - lelcx ]]f.Rl E'JHAT B rcle'ai nu/ss 1373 atomic weight, are CERTIFICATE 2BS1 : 27.976 927 1 t 0.000 001 4 29$i : 28.976 494 9 i 0.000 001 4 ISOTOPIC REFERENCE MATERIAL CBNM IRM-017 30$i : 29.973 770 I ± 0.000 001 4 4. Certified values are based on gas isotope miss spectrometric measurements on The IRM is supplied with atomic Isotope abundance ratios certified as Si samples converted to SiF^ gas. 29si/28S1 - 0.050 69 * 0,000 12 The chemical work on the IRM (I.e. the conversions of Si to SiF^j) was carried out by G. Lenaers and S. Valklers. 30S1/28SJ « 0.033 52 ± 0.000 10 } The development of a precise procedure for Silicon Isotopic measurements was carried out by S. Valkiers. Q. lenaars and W. Oe Dolle. This corresponds to an Isotopic composition with following isotope abundances : i The measurements were calibrated with the aid of synthetic Isotope 'mixtures Isotopic atom % Isotopic mass 1 Uncertainty prepared from three enriched S1 Isotopes. 28S J 92.233 (J\ 91.877 i 0.014 The chemical development work and the preparation of the synthetic Isotope 29S 1 4.675 4.823 t 0.011 mixtures were performed by 6. Lenaers* and T. J. Murphy**. oO 30S I 3.092 3.300 ± 0.008 The Isotopic measurements (characterization of the synthetic mixtures and homogeneity verification of the IRM) and calibration of the IRM against the The atomic weight of silicon Is 28.085 40 ± 0.000 19 synthetic mixtures were performed by S. Valkiers. Flic IRM Is Intended for use In calibrating measurements of SI Isotope abundance Full details about the characterization of the IRH can be found In CBNM Internal ratios. Report GE/R/MS/1I/89 : i Characterization of two Silicon Isotope Reference Materials : CBNM IRM-017 (Si) and CBNH IRH-01B (SiOz) ; NO IES S. Valkiers, G. Lenaers and P. De Bievre 1. All uncertainties Indicated are computed on a 2s basis, plus bounds to possible systematic errors due to the Instrument and modelling. B-24-10 Geel Paul OE BIEVRE 1 May 1989 Head 2. The Reference Material consists of Si and 1$ supplied In units of about CBNM Mass Spectrometry SO mg * University of Antwerpen ** National Bureau of Standards, Gaithersburg MO, USA - Visiting Scientist at CBNM 1986-1987 HIT t ii van Ci}T.mi."Mit» JOINT 3. The relative atomic masses used In the calculation of mass X abundances and RESEARCH of the atomic weight are CENTRE 28S1 27.976 927 1 t 0.000 001 4 CERTIFICATE Z9SI 28.976 494 9 t 0.000 001 4 30$i 29.973 770 1 ± 0.000 001 4 ISOTOPIC REFERENCE MATERIAL CBNM IRM-018 4. Certified values are based on gas Isotope mass jpectrometrlc measurements on S1Q2 samples converted to SIFd. gas. The (RH Is supplied with atomic Isotope ratios certified as 29SI/2BSJ . 0.050 83 t 0.000 12 The chemical work on the IRH (I.e. conversions of SIOz to SiF-O was carried out by S. Valkiers and G. Lenders. , The development of a precise procedure for silicon Isotopic measurements was [3051/2851 - Q.Q33 60 ± 0.000 10 [ carried out by S. Valkiers, G. Lenaers and W. De Bolli. The measurements were calibrated with the aid of synthetic isotope mixtures prepared from three enriched Si Isotopes. This corresponds to an 1 sotopic composition with following abundances : The chemical development work and the preparation of the synthetic Isotope mixtures were performed by 6. Lenaers* and T.J. Murphy**. Isotopic atom X I so topic mass X Uncertainty The isotopic measurements (characterization of the synthetic mixtures and homogeneity verification of the IRM) and calibration of the IRM against the 2851 92.214 91.857 t 0.014 synthetic mixtures were performed by S. Valklers. 29S1 4.688 4.836 i 0.011 30SI 3.098 3.307 * 0.008 Full details about the characterization of the IRH can be found in CBNM Internal Report GE/R/HS/11/89 : Characterization of two Silicon Isotopa Reference Materials : CBNM IRM-017 (51) and CBNM IRH-018 (5102) Ibe atomic weight of the silicon Is 28.085 65 0.000 S. Valkiers. G. Lenaers and P. De Bievre The IRM 1s intended for use In calibrating measurements of SI Isotope abundanqe rut ios. B-2440 Gcel Paul DE BIEVRE NOTES 1 May 1989 Head CBNM Mass Spectrometry 1. All uncertainties Indicated are computed on a 2s basis, plus bounds to possible systematic errors due to the Instrument and modelling. ' University of Antwsrpen National Bureau of Standards, Galtharsburg HO, USA, - Visiting Scientist at 2. The Reference Material consists of 5102 and Is supplied In units of about CBNM 1986-1987 . 5 g Storage «*.* ' li is recommended dial these RMs be stored m the coniaincrs in which they arc supplied to the user. NOTE: Because very limited quantities of these materials exist, distribution is limned to one unit of each per ihrcc-vear period of time. Users are strongly advised 10 prepare their own internal standards for daily use and National Dnatitute of >tanaarbB calibrate i hose standards against these RMs. Report of Investigation Isoiope Abundances According to reference 2 the sulfur isoiopic abundance of RM 8556 (NBS 123) is: Reference Materials 8553-8557 948871 atom percent MS 0.7563 atom percent 33S 4 3463 atom percent MS 8553: Soufre de Lacq (elemental sulfur) 00103 atom percent ^S 8554: NZ1 (silver sulfide) 8555: NZ2 (silver sulfide) 8556: NBSI23 (sphalerite) The sulfur isoiopic composition of ihese RMs relative to CDT is: 8557: NBS127 (barium sulfate) t^Srm. '**> These Reference Materials (RMs) are intended 10 provide samples of known isolopic composition wiih MS/32S and I8O/I6O isotope ratios stated in parts per thousand difference (%o) from ihe Canyon Diablo Troilite (CDT) and ihc Vienna Standard Mean Ocean Water (VSMOW (RM 8535 )| isotope-ratio standards, respectively. RM 8553 (Soufre de + 17.3 m These RMs are not certified, but their use allows comparability of stable sulfur and oxygen isoiope-ratio data Lacq) + 16 m obtained by investigators in different laboratories. RM 8553 (Soufre dc Lacq) and RM 8556 (NBSI23) are RM 8554 (NZI) -0.3 issued in units of 0.5 g and I.S g, respectively. RM 8557 (NBS127) is also intended for oxygen isoiope-ralio RM 8555 (NZ2) + 21.0 J3J calibration of sulfates and is issued in units of 0.5 g. RM8556(NBSI23) + 17.44 |2| + 1709 ± 031 jlj These RM:> are distributed on behalf of the International Atomic Energy Agency (IAEA), Vienna, Austria. RM 8557 (NBSI27) + 20.32 ± 0.36 |1| The overall coordination of preparation for N1ST distribution was carried out by T.B. Coplcn, II S. Geological The uncertainties on the first five items listed above are of the order of 0.3 %o. Survey and R.D. Vockc, Jr.. NIST Inorganic Analytical Research Division. The oxygen isoiopic composition of RM 8557 (NBS 127) relative to RM 8535 (VSMOW) is +9.4 ± 0.3 |l|. The supporting aspects concerning the distribution by NIST of these RMs were coordinated through the Standard Reference Materials Program by J.S. Kane. REFERENCES Material Preparation 1. Hul. G.. Consultants' group meeting on stable isotope reference samples for geochcmical and hydrological investigations. Report to the Director General, International Aiomic Energy Agency, April 1987. RM 8553 (Soufre de Lacq) was prepared by E. Roth. Centre d'Etudcs Nuclcaircs, Saclay. France. RM 8554 (NZ1) was prepared by B.W. Robinson, Department of Scientific and Industrial Research, Lower Hull, New 2. Chang. T.L., and Ding, T, Analysis of Ihe reference material NBS-123 and the atomic weight of sulfur. Zealand, from a sphalerite provided by S. Halas, University Maria Curie-Sklodowska University, Lublin. Chinese Science Bulletin, vol. 34. no. 13. 1086-1089 (1989). Poland, with d^Scoj near 0%o. RM 8557 (NBSI27) was prepared by J.R. O'Nell, U.S. Geological Survey, by ion exchange of sulfate in scawatcr from Montcrey Bay, California. 3. Siichler. W. International Atomic Energy Agency, Vienna, oral communication, I99|. Gaiihcnliuig. MD 20899 William P Reed, Chief June 22, 1992 Standard Reference Materials Program (over) s|i-ii..|'-iM (ruc.n r.r.'ji-iiiyi 'is s.ivr ' 'i-|ii!d n \ p"« M<»«III!:) I.IMIIS- II \\nil>) jslll Illj llllll |ll.I.) I.Ill lll(l|l! '^]: .1111 ln|l|,) )0 A.ll!|.l.l.)i>y{ '.lOllllcl.) I lll|'l|' .lOlllllli^) Jll |UOlll).ll:il.>[ I 'S 'II NBS Standard Reference Materials U S DEPAHTMENT OF COMMFFU t >> National BtitiMti ol St.nul.irils Standard Reference Material 985 Assay-Isotopic Standard for Potassium l-all. 1979 I he NliS Office of Standard Reference Materials announces the availability of a new assay-isotopic standard for potassium. Standard Reference Material 9KS. this SKM is supplied as highly purilial potassium chloride and is certified for assay (99.9Cf,) and lor isotopic composition SKM 985 is intended for use primarily by mass spectroscopists for the calibration ol isotope ratio mass spectrometers. I he material may be dissolved by slamluid techniques to provide solutions ol known puiily and isoiopic composition SUM 985 may be purchased from the OHicco! Standard Kelerence Materials, Koom IUI l.( hcnusiry liuiUluig. National Bureau ol Standards, Washington. I) C 20234, for J5H per I 0 gram sample ureau of Certificate of Standard Reference Material 985 Assay-Isotopic Standard for Potassium Absolute abundance ratios, K/K . . 138566100063 4<>K/ 4I K . 0(K)17143 ±00000061 Potassium - 39, atom percent . . 91 2581 ±00029 Potassium - 40, atom percent . . 0 01167 ± 0 00004 Potassium - 41. atom percent . . 6 7302 ± 0.0029 Atomic weight of Potassium . . . . . 19 (W8304 ± 0 000058 I his Standard Reference Material is supplied as highly purified potassium chloride with a ccriilicd purity of 99.9 weight percent based on determination of the potassium content by a combination of gravimetric and isotope dilution analysis and the chloride content by a coulometric argentimelric procedure. The above value for the purity ol the material is bused on a sample dried over magnesium perchlorate for 24 hours. 1 he absolute isotopic abundance ratios were determined hy two analysis using two different mass spectrometers Samples of known isotopic composition, prepared Irom nearly isotopically pure separated potassium-)9 and potassiurn-41 isotopes, were used In calibrate the mass spectrometers I he indicated uncertainties are overall limits of error based on 95 percent conlideiice limits for the mean and allowances for the ellecls of known souices of possible systematic error. 'I he details of the measurements arc described in a published paper: J Res NBS(U S ). 79A Die technical and support aspects involved in the preparation, certification, and issuance ol ihis Standard Rclcteiue Material were coordinated through the Office of Slandaid Kclcrence Materials hy W P. Kccd Washington. DC 20234 (ieorgc A llnano. Chief August 31, 1979 Olhceol Standard Reference Materials U. S. Dtptrtmut'of Commute Frwkrkk. fc. D»nl The material was examined for compliance with the specifications for reagent grade calcium carbonate as given in Reagent Chemicals, 4th edition, published by The American Chemical Society. The material was found to meet or exceed the minimum requirements in every respect. Examina tion by thermal gravimetric analysis indicated the loss of a minute proportion of weight below 175 ittreau of °C (volatile matter) and the composition was stable above this temperature until a temperature of 625 °C, above which decomposition (evolution of C02 ) set in. of $ A semi-quantitative survey for trace contaminants by emission speclroscopy indicated the presence of less than 0.001 percent of copper, iron, magnesium, manganese and silicon in the Standard Reference Material 915 material. By atomic absorption magnesium was evaluated at 1.0, sodium at 0.4, and strontium 2.1 parts per million (ppm); potassium was less than 0.4, lithium less than 0.05, and barium much less Calcium Carbonate than 10 ppm. Neutron activation analysis indicated copper 0.9, manganese 0.6 and sodium 0.5 ppm. Copper was determined at 1 ppm by spectrophotometry. This Standard Reference Material is intended for "in vitro" diagnostic use only. This Standard Reference Material is certified as a chemical of known purity. It is intended primarily for use in the calibration and standardization of procedures for calcium determinations This material is for use as a standard in clinical chemistry. It may be used to prepare calcium employed in clinical anarysis and for routine critical evaluation of the daily working standards used standard solutions for either atomic absorption or titrimetric methods of analysis. in these procedures. Standard stock solutions of calcium for atomic absorption (Reference Method) (11: Prepare a The sample consists of highly purified calcium carbonate, and chemical assay as well as analysis minimum of three concentrations at 2.00, 2.50, and 3.00 mmol of calcium per liter, with each to for specific impurities indicate that the material may be considered to be essentially pure. contain 140 mmol of sodium chloride and 5.0 mmol of potassium chloride per liter. To each of three 1 liter volumetric flasks, add 8.18 g NaC! and 373 mg of KCI. To the first flask (2.00 mmol of P»nty ...... 99.9+percent Ca per liter) add 200.2 mg of SRM 915 (dried at 200 °C for 4 hours), to the second flask (2.50 w*«er ...... 0.01 ± 0.005 percent mmol of Ca per liter) add 250.2 mgof SRM 915, and to the third flask (3.00 mmol of Ca per liter) add 300.3 mg of SRM 915. To etch flask add a few milliliters of water and 1 ml of concentrated Replicate samples taken from a randomly selected region of the undried material were assayed ' HCI. Make sure that all the calcium carbonate is in solution before diluting with water up to the by a coulometric leidimetric procedure. The results from nine independent determinations, based neck. When at ambient temperature, dilute each flask to the calibrated volume and mix by inverting on expression of the assay as calcium carbonate, indicate a purity of 99.99+percenl with a standard the flask 30 times. Pipettings and dilutions of this material should follow the instructions given in deviation of 0.003 percent. Samples equilibrated at a relative humidity of 90 percent and assayed reference [ 1 ]. by this coulometric procedure showed a maximum moisture adsorption of 0.02 percent as com pared to sample* thai were dried for 6 hours at 210 °C. The moisture content, similarly measured. Stprk aolution of calcium for titrimetric procedure: Place 0.250 g of dried SRM 915 into a on samples equilibrated at 75 percent relative humidity, was found to be 0.01 percent. The water 1000-ml volumetric flask. Add approximately 9 ml of deionized water and 1 ml concentrated HCI. content was determined by the Karl Fischer method. Shake until dissolved. Fill to the mark with deionized water and store in a pyrex bottle. This solution contains 10.0 mg per 100 ml or 5.00 meq. per liter. The calcium carbonate used for this Standard Reference Material was obtained from the J. T. Baker Chemical Company, of Phillipsburg. New Jersey. Analyses were performed by C. E. Cham This Standard Reference Material should be stored in a well-stoppered bottle (preferably the pion, E. R. Deardorff, G. Marinenko, 0. Menis, T. C. Rains, T. A. Rush, W. P. S'chmidt B F original bottle) at room temperature. Calcium carbonate is stable material. Under proper storage, Scrihner, V. C. Stewart. J. K. Taylor, and D. W. Vomhof. experience at NBS indicates this material to be stable for at least 10 years. If the material purity degrades beyond the limits certified, purchasers will be notified by NBS. It is recommended that the The overall direction and coordination of technical measurements leading to the certification material not be used after 5 years from the date of purchase. were under the chairmanship of R. Schaffer. Solutions prepared from SRM 915, Calcium Carbonate, are stable indefinitely when stored in The technical and support aspects concerning the preparation, certification, and issuance of this an glass-stoppered bottle. All such solutions should be clear and display no turbidity. Standard Reference Material were coordinated through the Office of Standard Reference Materials by J. L. Hague. Washington, D. C. 20234 J. Paul Cali, Chief March 4, 1969 Office of Standard Reference Materials Revised November 21, 1973 References: (11 J. P. Cali. G. N. Bowers, Jr., and D. S. Young, Clin. Chem. 19. 1208 1213 (1973) (2| N. W. Tied, Fundamentals of Clinical Chemistry, pp. 636-648, W. B. Saunders Co., Phila delphia. Pa., 19105(1970). This Standard Reference Material has been measured and certified at the laboratories of the National Bureau of Standards, Gaithersburg, Maryland. All inquiries should be addressed to: Office of Standard Reference Materials B311, Chemistry Building National Bureau of Standards Washington, D.C. 20234 The date of issuance and certification of this Standard Reference Material was March 4, 1969. cn I'. S. hi p.iiInieut tif Commerce J«ihu T t'nnjRjr; Secretary N;,li...,.il l|u>kitK4ilf SUii.lar.l- \ \ A»W*"fi|m-l... Certificate of SUnalptfitf Staiularil Reference Material 979 Isotopie Standard lor Chromium Alisolule Aliunilancu Itatm, Ci 50 Cr-.YJ OO.'ilHIi IHHIIIIII Al)so)ule Aliimikmee Italio. Ci Tilt (Y YJ li :(:(!) nun ir, Alisiiliilr Abundance Italio, Cr '< I Ci .Y_' .OJH'Jli IMIOIIIi Chromium fill, atom penenl l:>lf> > (Mm!) Chromium .VJ, atom percent x:i 7rt!i in..' ('hromiuiu r>:l, atom peicenl '.If.lll Mil Cliriiliiium .11, alum peri-enl 'I'lii1 |irfparatioii furmslieil is a coinuirrt ial .s.n mitim nitrate (CrtNO.) OIIO). Measinenients n> !>>' single lilanii'iil (|ilatinum) niitss speetronietry, IIMIIR mixtures of k paicil from high-purity .separated iMilopcs a.s rompa nil limits of error are liaseil on ',) "> pen cut eonlidcn e limits I'm Hie im-an uf the ratio measurements, ami on allowances for Hie km.u n som U'ASIIINGTIIN. D. <' \\'. \Va\nc M.-iiiKc. M.>v :t, litiiii (Illi,,. ,.| Sl.inil.il>! Krlrl, IM IbLUMM-NBb-UL i \ Commission of the (-iiropon Communities Geel LstaljIisliiMtiiit NOIFS JOINT Central Bureau fur Nuclear Measurements Sl««tiweg op H>-tie. 2440 Geel. Belgium | RESEARCH Tel (014) 571.711 Tele. J3bM LtlRAI 8 1. Ihls Isotopic Reference Material is supplied as metallic iron, which is ! CENTRE Telcfai OH/b8 42 73 either available in the form of wires or as small cubes. One unit contains approximately 50 rag (wires) or 250 mg (cubes) of material. The material' is stored In glass containers and was encapsulated under argon. i CERTIFiCAlt ?. All uncertainties Indicated are acuiracles, computed on a 2s basis, I ISOIOPIC RErERCNCt MATERIAL CBNH IRM-014 3. The relative dtomic masses, used fnr the calculations of mass abundance and atomic weight, are i 54Fe 53.93g 61? 7 i 0.000 001 5 Ihe IRM is supplied with a molar isotope ratio certified as 56fe S5.934 939 3 t 0.000 001 6 56.935 395 8 0.000 001 6 n(54Fc)/n(!>6Fe) - 0.063 70 t 0.000 27 57.933 277 3 t 0.000 001 6 n(&/Fe)/n(56|e) - 0.023 096 t 0.000 072 4. The measurements were carried out using a thermal (animation mass spectrometer. The samples were loaded onto the filaments In the form of Iron n(58re )/n(56Fe) = 0.003 071 ± 0.000 029 chloride and a sll Icagel/borlc acid ionisation enhancer was used. The measurements were calibrated against a set of five synthetic isotqpo mixtures, the n(54Fe)/n(56Fe) ratio of which varied from 0.1 to 10. This corresponds to an Isotopic composition with the following abundances : CBNM IRM-014 was made up from the neutron dosimetry reference material EC- Hole X Mass X Uncertainty 5. HUM 5?4. The cubes were prepared by melting pieces of foil, rolling the melt Inlo a plate and then cutting the plate with a diamond wheel (Frans 54pt 5.845 b.645 ! O.OiM Pen lei mans and Paul do Vos). The wires were taken as such from the EC-NRM 524 56Fe 91.754 91.902 t O.OP3 stock. Both the cubes and the wires were cleaned with an organic solvent and 57pe 2.119 1 ?.160 6 t 0.006 6 acid leached, before being put Into vials (Reinhold Maeck and Daniella Sflfe 0.281 9 0.292 4 t 0.002 8 Clymans). The encapsulation was carried out under argon. The Atomic weight of Iron In this sample Is 55.845 15 i 0.000 48 The purity of the material . determined by Philip Taylor using Spark Source This IRM is Intended for use in calibrating measurements of iron isotope abundance Mass Spectrometry. was 99.99 X t 0.01 X . ratios of iron (including those for Isotope dilution). The purification of the enriched isotope carrier compounds and the preparation of the synthetic isotope mixtures was carried out by Reinhold Maeck. Frans Hendrlckx performed the mctrologlcal weighings. The Isotopic medsurcmnnts on the enriched isotope carrier compounds, on the synthetic isotope mixtures and on the IRH was performed by Reinhold Haeck; at CBNM dnd the los Alamos National Lahoratories (for the enriched mdtcridls). 6. Full details of the characterisation of this IRM can be found in GE/MS/R/r)2/1992 H 2110 GeeI Paul OE BIEVRE Hay 1992 Head CflNM Mass Spectromctry CX) Statistical analysis of the data was performed by K.R. Eberbardt and S.B. Schiller, NIST Statistical Engineering ' m*' National Snatitutc nf ^tanbarba & Division. The overall direction and coordination of the technical measurements leading in certification were under the (Hcrttftcatc of Analu0ifi chairmanship of I.L. Itarnes. Issuance nf this Standard Reference Material was coordinated through the Standard Reference Materials Program Standard Reference Material 986 by J.C. Coll.cn. REFERENCES Isotopic Standard Tor Nickel |l) Gramlich. J.W.. Macblan, L.A., Barnes, I.L. and Paulsen P. J.. J. Res. Natl. Insl Stand. Tcchnol. 94. 347 (1989) This Standard Reference Material (SRM) is intended primarily for use as an isolopic standard. SRM 986 consists of 0.50 g of a commercial, higb-purily nickel metal, 99999+ % pure. The certified isolopic compositions are given below together with the atomic weight of nickel. The atomic weight is calculated from the isolopic com position given on Ibis certificate. Absolute Isi.topic Abundance Ratios: S8Ni/60Ni 2.596061 ± 0 000728 Ji 0.043469 ± 0.000015 "Ni/°Ni 0 138600 ± 01X10045 0.035295 ± 0000024 l&olopic Composition: Ni. Atom Percent 68076886 ± 0.005919 "Ni. Atom Percent 26.223146 + 0005144 61 -JD Ni, Atom Percent 1.139894 ± 0.000433 62Ni, Atom Percent 3.634528 ±0.001142 wNi, Atom Percenl 0.925546 ± 0.000599 Nickel Atomic Weight 58.6934 ±0.0002 The indicated uncertainties are overall limits of error based on two standard deviations of the mean and allowances for the effects of known sources of possible systematic error. The absolute abundance ratios of "Ni/^Ni. 61 Ni/60Ni, "Ni/^Ni and MNi/*°Ni were determined by thermal ioni/ai' mass spcclrometry. Mixtures of synthetic isolopic standards were used to calibrate the mass spectroim. _rs. These synthetic standards were grivimctrically prepared from chemically pure and neatly isotopi- cally pure isotopes. The bias correction (calculated isolopic ratio/observed isotopic ratio), that these standards provide, allows absolute ratios to be calculated for the sample. Details of the preparation and measurements for this SRM are described by Gramlich, J.W., Machlao, L.A., Baroes, I.L., ind Paulsen. P.J., "Absolute Isotopic Abundance Ratios and Atomic Weight of a Reference Sample of Nickel'|l). The analytical measurements leading to the certification of this material were performed in the NIST Inorganic Analytical Research Division. Mass speclromeiric measurements on the calibration mixes were made by J.W. Gramlicb and I.L. Barnes. The calibration mixes were prepared by L.A. Machlan. The nickel metal used for SRM 986 was obtained from Alomergic Chemicals Corporation (Lot F-3625). Trace element impurities were determined by ICP-MS using isotope dilution and external standards. Gaithersburg. MD 20899 William P. Reed, Acting Chief May 1, 1990 Standard Reference Materials Program ^National ^Bureau of (Kertificate of JVnalgsis Standard Reference Material 976 Isotopic Standard for Copper This Standard Reference Material (SRM) is intended for use as an isolopic standard. SRM 976 consists of 0.4 g of a commcrical copper metal. The certified isotopic compositions are given below together with the atomic weight of copper. The atomic weight of this copper SRM was calculated from the isolopic composition and nuclidit mass es, 62.929598 for"3Cu and 64.927792 for "Cu reported by Wapstra and Audi [ l|. Absolute Isotopic Abundance Ratio, "Cu/^Cu: 2.2440 ± 00021 Isotopic Composition: 63Cu. Atom Percent 69 174 ± 0020 "Cu, Atom Percent 30.826 ± 0.020 Atomic Weight: 65.5456 ±00004 The indicated uncertainties are overall limits of error based on the sum of 95 percent confidence limits for the means and upper bounds for the effects of known sources of possible systematic error. The absolute abundance ratio of Cur Cu was determined by thermal ioni/ation mass spectromctry. Mixtures of known Cu/ Cu prepared from high-purity separated copper isotopes were used to calibrate the mass spectrometers. Details of the preparation and measurements of this SRM are described by Shields, W.R., Mur phy, T J , and (iarner, L.L., "Absolute Isolopic Abundance Ratio and ihc Atomic Weight of .1 Reference Sample of Copper [2| The analytical measurements leading to certification of this material were performed in the NHS Inorganic Analyti cal Research Division (formerly the NBS Analytical Chemistry Division). Mass spectrometric measurements were made by W.R. Shields and E.L. Garner on calibration mixes prepared by T.J. Murphy. Statistical analysis of the data was performed by H.H. Ku, NBS Statistical Engineering Division References |l| Wapslra, All and Audi, Ci., Nuclear Physics A432(l), 1-55(1985). |2| Shields, W.U, Murphy, T.J., and Garner, E.I.., J. Res. N..I Bur. Stand .(US ), 6KA, (I'l.vs and Chem ), No. 6. 58')-592(l%4). (iailhershnrg, Ml)2l)8'W Stanley I) Ra.sberry, Chief February 14, I'M8 Office of Standard Reference Materials (Revision of Certificate dated March 24, 1965) NBS Standard Reference Materials U S DEPARTMENT OF COMMCRCE £ ^ National Bureau ol Standards Standard Reference Material 994, Gallium Standard Reference Material 997, Thallium UK- NIIS Olluc of Siumhinl Kf ciuc Maicii.ils .nniciniKCs ilu- availability o| two new Sland.nd Releieiue M.ilcii.ds SKM 'W4. (i.illin.n, and SKM W. lli.illium Tltcsc IK-W SKM's, like |>ii i issued isolopu SKM's. ,ne mlcndcd lor use HI .issessni)' sin.ill cimi|Xisiiiou and fur evaluating i aiss dlstriiniu.iiniii elicits eiuoiinlereil in I lie opcr.mon ol m.iss s|x> iir SKM ^M. die uhsoluic abundance rail of ""(ia/"lia was (omul n> k- I MK>7(.; wlnle Im SKM W7. ilic ta '!! was 2 38714 llnih SRM's arc In^li pi in mcials ccrlilicil lur ipu ioiii|Misiuoii. I'm ncillici arc leinlie l assay. SKM ')'>). (l.illiuill. is issucil .is a (I :.S )> mill, .iiul SKM ^>1 . Ikilliiim. is ISMICI! .is y I) S f nun Itoili ol I|K-SC SKM\ arc .iv.nliihlc lor SID2 pet mill Itoin Oilier ol Sl.indai.l Ki-K-ictue M.ilri i.,h R.MMII H3II. Chemistry Riiildmt: Nalidiul Bureau nl Si.md.iiiK (iailliershurg. Ml) 2(I8«W Iclcplioiic Rational ^Bureau of (EedtftcalE of (Analysis The gallium metal used for Standard Reference Material 994 was obtained from Matenal Research Corporation. Orangeburg. N.Y. Standard Reference Material 994 References Isotopic Standard for Gallium [I] Wapstra, A.M. and Audi, G.. Nuclear Physics A432(l), 1-55 (1985). [2] Eberhardt, K.R.. J. Res. Nat. Bur. Stand. (U.S.). (In Press). [3] Machlan. L.A , Gramlich. J.W.. Powell. L.J. and Lambert. G.M.. J. Res. Nat. Bur. Stand. (U.S.). (In Press). This Standard Reference Material (SRM) is intended for use as an isotopic standard. SRM 994 consists of 0 25 g of a commercial, high-purity gallium metal. The certified isotopic compositions arc given below together with the atomic weight of gallium. The atomic weight of this gallium SRM was calculated from the isotopic composition and nuclidic masses. 68.02SS80 and 709247005 reported by Wapstra and Audi [I]. Absolute Isotopic Abundance Ratio, Ga/ Ga: 1.50676 + 000039 SRM 994 Isolopic Composition: Page 2 Ga, Atomic Percent 60.1079 +00062 Ga, Atomic Percent 398921 ±00062 Atomic Weight: (69.72307 ±0.00013) The indicated uncertainties are overall limits of error based on the sum of 95 percent confidence limits lor the means and upper bounds for the effects of known sources of possible systematic error. Details of the statistical analysis and deviation of the uncertainty limits are given by Ebcrhardt, K.R., "Statistical Evaluation of Uncertainties for the Absolute Isolopic Abundance and Atomic Weight of a Reference Sample of Gallium" [2]. The absolute abundance ratio of Ga/ Ga was determined by thermal ionization mass spectrometry. Mixtures of known * Ga/ *Ga prepared from nearly pure separated gallium isotopes were used to calibrate the mass spectrometers. Details of the preparation and measurements of this SRM are described by Machlan, L.A.,Gramlich. J.W., Powell. L.J.. and Lambert, G. M., "Absolute Isotopic Abundance and Atomic Weight of a Reference Sample of Gallium" [3]. The analytical measurements leading to the certification of this material were performed in the NBS Inorganic Analytical Research Division. Mass spectromelric measurements were made by J.W. Gramlich and L.J. Powell on calibration mixes prepared by L.A. Machlan. The purity of the separated isotopes was determined by G. M. Lambert using spark source mass specirometry. Statistical analysis of the data was performed by K.R. Eberhardt, NBS Statistical Engineering Division. The overall direction and coordination of the technical measurements leading to the certification were under the chair manship of J.R. DeVoe of the NBS Inorganic Analytical Research Division. Issuance of this Standard Reference Material was coordinated through the Office of Standard Reference Materials by R.W Seward. Gailhersburg. MD 20899 Stanley D Rasberry. Chief February 3. 1986 Office of Standard Reference Materials (over) ( I % I > liGtJ-tUiiJ i|.) 15. s.\i|.n ' V H9 SUN >I I1 '"PPIilS >! A\ l""! 'Jau.<"0 A"I| |Mi|s;|i|inl .1.111 t;)u.iiu,).ins)ioui pin: ';ii<)))i:.n;(l,i.i(l ,i\|| JD s|M!|,)(| MM.I.I.) .11 |i!Ul.i|s\s' O|(|{Kso<| jo sa.vlnus JO si: s,>ild|osi |),i)i:.n>i|,is A'JI.I UIO.IJ j« -.1.1111x1111 jliiiMi 'A'.IJ.HUO -" 'IV ''.'(>! "N M'liints 'I'""" "I l«IM|H)s- jo ,l|(IUi ,-(1(1 4: ilH'.HI'j IX Joj pjnpuiuvj .">iii()4osj JO U 3 Dcpirimnt'uf Comiinni- M.urice H 3i.n. Certificate nf Standard Reference Material 984 Rubidium Chloride II h<:i. rubidium .i-.jv. u. n-bl pi u i nl .... . >MI Oil t II !! ' Absolute ahiind.im e i.iln.. " ' II I./" ' II l> ..... J Ti1 ).') t II 1102 This lot of rubidium chloride w;.s prepared (o ensure material of intermediate purity and high homogeneity. The maleiial is soiiietvh.il hygroscopic, absorbing appro\im-ilrlv 0.6 percent moisture in a 7"> percent relative humidity al room temperature, bill can be dried In the original weight hy desiccation over freshl) rxpnscil I')O, or Mg((JO 4 ) ; lor Iwenlv four Imnrv The m.ilcrial should Iliereloic he slurcd itilh .1 di lii-c.int such a.-. I'j (),. The as-ay of this malcrial is based on (he d< (erriiiii.ilion ol iiiliidiiini l>\ .1 i nmhinalion of graviinclr) and isotope dilution an.ily-i- on i i»lil -ample., <,l ulionl J g each nf the dried HbU. More than '>')'r of the riibidinin wiis prei ipilaled. tillered and weighed ,is rnhidinni pen Idoralc The r\ % weight of HbCI()4 was corneled for pn|,i.--inni .md i csinm perchlorali . The soluble rubidium was /C_/ determined by isnlopr dilution in as.- >peelroiin Irv 'llic total rubidium was the sum of llic rubidium *. from the rubidium pen-Morale and the rubidium Irnin the filtrate. All weighing* were i orrecled lo ~-J vacuum and the atomic weight* used in the c.ilcul.ilions were from the 1969 Table of Atomic __ r~ tt'eighlj.. Tlir indicated loler.im c i*. al lea-l a- laijM- .is thi- 'IS pin cut innfiilrncr level for a single *~ deleiimnalioii. (Jilorulc was dclermineil b\ silver loulomclr) lo be 29.32 weigh! permit I'n-fi renli.il oxidation of iodide and bromide showed that the material contains <~O.ODI!t I and <0 Od.^t Hr. Flame emission spcclrnmrlry indicated lithium, <0 02 ppm; .sodium, 2.3 ppm, polankinrn. 420 ppm; and ('('Muni l!t ppm. Kiuissinn ^pel lropraplllc ctammalion indicated, in addition, calcium. The absolute abundance ratio of * 5 ltd/' 1 Kb was determined by Inpir filament solid-cample maaa spcclromclry. Mixliirt's of known 'llic following members nl the Anal) lical (!licriii->lry Divi.sion conlnbiiled to llie t liarai lenzilion ol lliia in.ilcrial: T |. Murphy and P. J. Panlsen nibidium asuay, G. Marinrnko chloride a*M\ ; T. (!. Itan^ and T. \. Hush- flame cnii.s-ion delerniinalinns; E. K. Muhbard einis-nui speclro gi.iphu .m.il> sis; .lilil I.. |. I ..i|.in/..no .mil I, (..(lamer ah-olnle lalio dclcrmiiijlioii I In oxer.ill din i lion and coordin.illon of tin li-ilmn.il iiica-iircmcnl'< b adm^ h. i iiiin alion »vcn pciloimed inidei tin i liairmaiiship nl U II. Sim Ids. The lei Imical and support a.-peels involved in the pirparabori, certification, and iiwoancr of this bl.ind.iid referem e nialeri.il vtere conrdinaled llirnngh llic Office of Standard lirfcrrncc Materials bx I I. ll. 1(;uc. U.i-bmglon, D.C. JOJ.II J Paul Call. Ai Img (.bief Jnlv J7. l')70 Olfiic of Standard Kcicrcmc Material,. Sccntiiy' >l ftump Kl .1 Ambk. It Rational £8ureau of j^tandarrb (ttertifteate of JVnalgsts 1 he strontium carhnnaic used lor this Standard Reference Material was obtained from Spex Industries, Inc ol Metuchen. New Jersey I he material, when received, was ol high purity in relation lo canonic impurities but assayed Standard Reference Material 987 only 99 0%duc to moisture and other volatile impurities. Igmiionat 800°C (or 16 hours under an atmosphere ol carbon dioxide removed the moisture and other volatile impurities and converted the compound to essentially stoichiometric Assay-lsotopic Standard for Strontium strontium carbonate (Other commercial high purity lots of strontium carbonate exhibited the same order of low assay.) The material is only slightly hygroscopic, absorbing 0.02 percent moisture al 90 percent relative humidity but can be dried 10 ihe anhydrous stale by healing for one hour at 110 °C The material should therefore be dried al 110° C for one SrCOi. Alkalimelric assay, weight percent ._ _ . . ______99 9K < 002 hour hclorc use Absolute Abundance Ratios "Sr/'Sr = 8 37861 ± 0011325 *'Sr/"".Sr = 0 71034 ± 000026 M Sr/"*Sr = 005655 ± 000014 which yields atom perccnts ol. "Sr - 82 5845 i 00066 " ? Sr = 70015 ± 00026 "*Sr = 9 8566 ± 00034 * 4 Sr - 05574100015 1 he atomic weight calculated Irom these abundances is 87 61681 1 0 00012 I hit Stanil.iiil Hclcrencc Mlllcrial it cerliltcd lor use as an assay ..ml isolopic siandaul I he material consists of highly purified slioiilium carboiiutc mid ti ul high homogeneity I he assay was determined by using a coulomelric procedure in which an excess ol accurately stand.iidi/ed hydrochloric acid is leaded with a known weight ol the dried sample and the excess hydiochlouc acid is determined coiilometrically. Hie results Irom eleven independent determinations showed a total alkalinity equivalent to 99 98 percent strontium catbonatc. This material was used as the rclerence sample in a determination of abundance ratios and atomic weight of strontium (I) I he indicated uncertainties are overall limits ol emu based on the 95 percent confidence limits for the means and allowances for the effects of possible systematic ctror The only detecied impurities in the material are lithium, 4 ppm, sodium, 6 ppm. potassium. I ppm, magnesium. <2 ppm; calcium, 5 ppm; barium, < I5ppm, copper, <3 ppm, iron. <3 ppm; aluminum. < I ppm, and silicon, < I ppm. 1 he following members of the Center lor Analytical Chemist. > contributed to the characicn/aiion of this material: (.. Ma.mciiko, L E f.d. I) (i I'riend, I I llarnes. I J Mooie, I t Rains. I A Rush. I A Machlan. I J. Murphy, and I'.J I'aulsen I he overall direction and cooidiii.ilion ol the leclinual mcasmcmcnis le.idnif! to the ceitilii.tiiuii and i iiiienl update ol this SRM wcie perfoimei.) under the chairmanship ol I I Dailies and W R Shields 1 he technical and support aspects involved iri the prepatalion. cciiilicalion. and issuance ol this Standard Releicnce Material were coordinated through the Ollicc ol Standard Reference Maleii.il. b> I W. Mears (I) I J Moore. I I Murphy. I I. llarnes. and I' I I'aulsen. I ol Ucs (MIS). £7 18 (1982) Washington, I) I 20234 (icotge A Uiiano. C hid October I. 1982 Ollice ol Sl.iiul.iril Rcltrience Materials (Revision of Certilicales dated \\ H l\ & 3-6-72) (over) U S n»p»riA»-«k'of Commerce Frederick iB I>«nt SeortUry I*..*w..A.*,0, tM5tTtottai Ijntrtttit of (Certificate uf Aualngjg I or llu .inal\M> lli. lollouin.; valne> were assumed from SKM 9117: V_ *9 Ital'ms Mom l-'raelion IIII/II6 Il.:i7.r)2 M = 0.005.r>76 Standard Reference Material 988 H7/H6 0.71014 116 - 0.0911601 iU/ltd 0.05655 07 = 0.070020 Oil = O.II25M03 Strontium-84 Spike Assay and Isotopic Solution Standard Minnie Weight = 87.6167 'I lie ni.ileri.il fur lliis SKM was supplied li\ llieOKNI. lsolit|ii- Development Center. Oak Kid»e, 'ri-|iiir>see. '('lie liillDWin^ iitemlicr 1- of the NILS Anal) lir;il (,'lieinislrv Division parlieip;i|ed in the eharaeteri- This Standard Kefe.rcnce Material is certified for use as an assay and isolopn: standard. SKM 988, /.ilinnof SKM 'HtH: Slrunlinm-84 Spike, is a solution scaled in purr i|iiait/. ampoules. Kadi ampoule contains a nominal 10 grains of the solution, uliich i.-. approximate!) 0.5N in UNO). |MI|O|MC Measiirenienls - I. I., llarnes and I.. J. Moore ( lii-iiiii al I'repar.ilioiis -I.. \. M.nlilan and j. It. Moodv The isotopic composition and concentration of strontium in SKM 988 were determined using (wo mass spectrometers and two operators. The concentration was determined hy comparison of I lie overall direction and eoordinalion of the lechnical measurements leadiiif; to eerlifiealion ten Slronliuni-84 alitpiols from five different ampoules with a series of solutions of SKM 987, t\< re under (lie t li;iirnians|iip of W. |(. Shields. Strontium Carbonate. The leehnieal iind support a>pee(S eonecriilli^ the preparation, eerlifiealion, and issuance of (his All isotopic measurements luxe heeii corrected for frarlionation hased on the pseuilo ahsolute Si.mil.ml Iteferenee Material tvere coordinated through the Ol'fiee of Standard Reference \1alerials scale of a "natural" 'Sr/^Sr ratio of 0.1 194. Isolopic Composition Measured Katiiis \loin" 0()0()r>ll9 Jit O'MfJWU j. I'anl Call. Chief 116 ^ OOOOf)') t O.OOOOI 1)7/111 OOIMI09I1 Office of Standard Itefereine Malcn.ils I(H/IH (I OOO.'lllfi 117 - 0 0001010 00001 III! ' 0000.)') i 0.00001 \lomie Weight «:».<) I l..r. niiilcd error limits Ix-rans.- of llit inaKniliidf of llif inrj.Mirnl ntiu Slrniiliuin ( liiiieeiilraliiin 1' p moles/ g of Sulnlidii PK/a of Soliiliiin Analyst I 1.1906 t 0.0004 'iy.91 10.0:1 Anal) si 2 I.IOOUi O000.r> 99.92 t (Mil Average I.I«MI7 t 0.00(1.1 »r limili >rr Ihr (oxer) rnmiinsjiu'i I CFRTIHCATt 2. The IKM solution has a molality of 0.5 m IINOj (I.e. O.b mol IIM03 kg' 1 of solvent) or a molarlty of 0.5 M IIN03 (I.e. 0.5 raal IIN03 1~* of solution). I I ISOTOPIC REFFRENCF HAIFRIAL CDHH IRM-618 3. The Avoyudro constant used Is (6.022 136 9 ± 0.000 OO/ ?) 1023 . 4. The atomic masses, used In the calculations, are I he IKM 1s supplied with a 8?Rb atonic Isotope concentration certified as 85Rb 84.914 390 i 0.000 OOa 1(6.753 iO.010)-1019 atoms 87Rfkg-l of solution 87Rb 86.911 794 ± 0.000 006 From the certified Isotope concentration, the following concentrations are derived : 5. Using this Spike IRM, 85Rb concentrations in unknown samples can be (1.121 3 i 0.001 7J-10-4 mol fl/R^-kg-l of solution determined by Isotope Dilution Mass Spcctrometry, through a measurement of (9.713 ± 0.015)-10-6 kg O/Rb-kg-l of solution the atomic Isotope dilution ratio RB ' 8bRb/87Rb In the blend. They should be computed with the aid of the following formula which allows an easy Olhur Rubidium Isotopes present are related to the 8/Kb atomic Isotope Identification of the sources of the uncertainties In the procedure : i concentration through the following atonic Isotope ratio : I 85Rb/87Rb : 0.020 498 * 0.000 024 This corresponds to an isotoptc composition with following Isotope abundances : where i Isotoplc atom % Isotopic Mass X Rx atomic Isotope ratio 8!"Rb/87Rb | n the unknown sample material RY atomic Isotope ratio 85Rb/87Rb in the spike Material 2.008 7 i 0.002 3 1.963 4 t 0.002 2 MX mass of the unknown sample 87Rb 97.991 3 ± 0.002 3 98.036 6 t 0.002 2 MY mass of the sample of spike solution used C85 number of atoms *"Rb kg~^ sample material C87 number of atoms 87Rb kg" 1 spike solution. The atomic weight of the Rubidium is 86.869 066 1 0.000 045 From the certified Isotope concentration, the following element concentrations are derived : (1.144 3 t 0.001 7)-10-'1 mol Rb-kg-1 of solution (9.940 ± 0.015)-10-6 kg Rb-kg-1 Of solution i Chemical preparation of this IRM was accomplished by Andre Verbruggcn and Gaida Lapltajs. fsotopic measurements by Thermal lonisation Mass Spectrometry were carried out by Gaida Lapitajs. Hetrologlcal aspects involved in the preparation and certification were performed by frans Hendrickx. < The purity of ^RbCI was determined by Spark Source Mass Spectrometry by Willy Lycke. ' The ampoulatlon of this IRM was accomplished by Andre Verbruggcn, Adolfu Alonso- Hunoz and Oatda Lapltajs. ' The overall coordination of the establishment leading to the certification and issuance of this IRM was performed by Andre Verbruggen. I B-2440 Geel Paul DE OIEVRE Head CBHH Mass Spectrometry 00 Rational ^Bureau of Certificate of Standard Reference Material 978a Assay-lsotopic Standard for Silver Standard Referenc- Material 978a was prepared from S R M 748. Silver Vapor Pressure, which is high purity silver metal (greater than 99.99 percent) in rod form. SRM 748 was used by V.E. Bower and R.S. Davis to redetermine the electro chemical equivalent of silver [3]. Based on their work and the silver data presented here, the silver Faraday was This Standard Reference Material (SRM) is certified for use as an assay and isotopic standard It consists of 0.25 gof recalculated with a high level of accuracy [4]. A portion of the metal was converted to silver nitrate and used as the silver nitrate, AgNO), made from high purity silver metal and high purity nitric acid. isotopic reference sample for the redetermination of the atomic weight of silver [I]. Silver nitrate is non-hygroscopic up to about 80 percent relative humidity. At this relative humidity, or above, ii will attract water and form a saturated AgNOj, Silver Assay, weight percent 9999 1002 solution. Whjle this salt would not normally be exposed to such high humidities, as a precaution, it should be dried before use Drying either in an oven for I hour at 105 °C or for approximately 15 hours in a desiccator over MgCIO^s Absolute Isotopic Abundant* Ralio, '" Ag/""Ag I 07618 1000022 satisfactory Isoiopic Composition Ag. Atom Percenl SI 8392 ±00051 [I] Powell, L.J.. Murphy, T.J., and Gramlich. J.W.. J. Res. Nat. Bur. Stand. (U.S.) 87(1). 9, (1982.) IO9 Ag, Atom I'eiccnt 48 1608 100051 [2] Wapstra. A.II. and Bos. K.. At. Data Nucl. Data Tables. 19. 175(1977). [3] Bower, V E and Davis. R.S., J. Res. Nat. Bur. Stand (U.S.). 85(3). 175 (1980). Stl\cr Atomic Weight 10786815 tO 00011 (4) Bower. V.E., Davis, R.S . Murphy. T.J., Paulsen, P.J., Gramlich. J.W., and Powell. I.J., J. Res. Nat. Bur. Stand. (U.S), 87(1). 21 (1982) Ihc indicated uiiceitainties are overall limits of error based on lliesum of the 95 perrenl confidence liiniis for the means and allowances for the effects of known sources of possible systematic error. The assay shown is bused on the determination of silver in the dried silver nilrate in which most of ihe silver is determined gravimetncally as silver iodide and the remainder by isotope dilution mass spectroinetry. Dciailt of ihis procedure are SRM 97Xa published [I). The molecular weight of silver nitrate employed in this calculation is 169.8731 Page 2 The absolute abundance ratio of Ag/'° Ag was determined by thermal ionizaiion mass spectiometry. Mixtures of known Ag/ Ag, prepared from nearly pure separated silver isotopes, were used to calibrate the mass spectro meters. Details of the preparation and measurements are described by Powell, L.J.. Murphy, T.J., and Gramlich, J.W. "The Absolute Isotopic Abundance and Atomic Weight of a Reference Sample of Silver" [I) 'Hie atomic weight of silver was calculated from the isoiopic composition and nuclidic masses 106.905095 and 108 904754 from Wapstra and Bos [2]. The analytical measurements leading to the certification of this material were performed in the N HS Inorganic Analytical Research Division. Mass spectromctric measurements were made by J.W. (iramlich and I..J. I'owell on calibration mixes prepared by T.J. Murphy. The purity of the separated isotopes and this SRM weie determined by P J. Paulsen. using spark source mass spectroinetry Statistical analysis of the data was performed by K R. Hberhardt, NHS Statistical rngineeimg Division. The overall direction and coordination of the technical measurements leading to the certification were under the chairmanship of E.L. Garner ol ihe NDS Inorganic Analytical Research Division The technical and support aspects involved in the preparation, certification, and issuance of this Standard Reference Material weir coordinated through the Office of Standard Reference Material*, by I..J I'owell Gait her shiny. Ml) 2089') Stanley I) Rasherry. Chief September 21 l'»84 Otfkeof Staiul:>id Reference Materials 1) S II. iMilnit.il ..f C..I Kink rick B. |)«nl N..I.....I Union ol Sl» Rich. i.l » ll..l~m. Uu ureau of (Herttfieate of JVnalgsis Standard Reference Material Assay-Isotopic Standard lor Rhenium \li ,,lnli-.iliiiinl.iii., rah... '""'Hi-/'" 7 ii -,'17:1111 o.iMxny Illl.'11111111 111'), al.llll jl.-l.l III . . :i7..i'>» t oiiU) Kin iiiinii 1117. .limn |M r, ,-nl ... . . (ii'.l.OJ i n (IK) 00 MIIIMH- wrijjil ...... Dili JIM,7') i II DIM):) I Ilils Slamlaril Id Irirn. r \l.il. n.il I- Mi|i|ili, .1 .1- iliri l.il in (In- luriii 1.1 .1 iilili.ni ;i|i|iroxi O iii.il.l) (>.()(i:irin lis (I.(I7( M-.l mi ini|Miril il.l.. ictl l.y IM,|.,|M ililnl n r IM.I.-> ^ 111.1.111,1- ratio "ir'H.-/ IHT H.- u;i> ili-lrrnn I ll> Iw S;nii|il,-s kllnUII isilll>|>H- .-(|||||>.IM pri| rl\ I, ;ill\ jinrr M-|i.irali il I VM ir iiM'd lii i alihralr III li'l.T-. h, .id il inn. rl.iinlus an «u all liinil> ul'rrr li.i-ril mi 'Ifl |irn i-lll rnilli I (III I W.IIH-I-s I'nr Ilir .-(!,, I- f kiiiittii -onrr ,1' , >\ .-li'iu.iln rrn i. in.-nU air ilf-i nliril in .1 | Hi-". NILS (ItiS.). 77\(l'li\>. .Hid Ch. .). No. (>. ( ')! < M.INS -|l( i llulllrlnr lllr.l-lln UK III- \\rrr in. nil' lit I \\ ( If. llllln II .mil I I I ..IIIMT nil -.IIM|>lr.s |Mrnl li\ ')'. | \lnr|(li\. I lir im l.lll ilni'i linn .mil riiiinlin.llliiM ul III hi lilllr.il ni, .l-lllrill, ill- li In rrrlllh .ilinil ir inillrr (In i 1 1. II I Ml.lll-lli|l nl \\ . 1 1. M in-Ill-. I In Iri Imiiiil .mil Mipjiorl .i>|n i I- rniiii riling (In- |iu|i.ii.iliun. i rrlil u.iln'ii. .MM! i-v-n.nii r nf (his Sl.uxl.inl Id fi-n in i- Nl.iliii.il urn- . nuiilin.ili il llin.n^li llir (Illirr .if M.iiiil.n ,1 li , |, rnirr M.ili rials lix \\. I'. Id nl vM \\.i lininl.in. I l.C. JOJ 11 I I'.iuH ,ili Cliirf r( '*J IV|.m.ir\ I'). I')7I (Hln i- nl Sl.mliiil Idl. rriu r \l.il. ri.ils NBS Standard Reference Materials II S DEPARIMENI Of COMMI H< t N.iiional Bin.MII of Si.ind.in's Standard Reference Material 994, Gallium Standard Reference Material 997, Thallium UK' MIS I >llii r nl Sl.inil.ilil K> Kiriin- M.il,l|.iK .IMIIOHII, , - Hi, ,t \ .ul.ihiliu nl n\,i n, u Si.in.l.u.l |(. I. i. IK > M.ili i i.iK (SKM M I..i is.H.ipu OMII|I..M|I..,I SUM 'I'M (,.ill,n.n .in.l SUM >> III' 1.0 pU-MI'llvl \ INMK',1 IM nip. SKM s iiik-mlc,! l»f use n JSM'SMIIg s lull t. II. Ill, HIS Ihc ..|H'I. -1 ""l I o( .SKM 1,1.111,1- 1. II 1,1 iii ''"( ;., '« i s 1,. 1111,1 1,1 K- 1 S(K,7(,. »llll.- l.il SKM 4'I7. i i, i.ii,, SKM 'I'M (,.,||,,,,,, is INSIK,! .is ., II JS ^ mill. .in,l SKM "'I'' I Ii.illiiiui is I-MI,,! .is .1 II S f uni II,xli .'I id. .. SKM'v .,c,- .i^.nl.ihU l,,i Mil.1 |Hi nun li.nu ii| Si.in,I.,,,! K, I, I,'IKC M.iun.iN K»»l N.IIK l.ll III,I, .Ml ,l| Sl.lll,l.ll.|x (..ml isl-in,: Ml) MlN'J'l U S l>cnjnm..ll«l I .. Rational ^Bureau of (Eertificate of JVnalysis Standard Reference Material 997 Isotopic Standard for Thallium Thii Staml.ird Reference Material (SRM) ii certified for u*e as. an iMHopic standard SRM 997 consists ol 0 5 grain of a commercial, high-purity thallium metal. Note: While this SRM is a high-purity material for isotopit purposes, it oxidi/es rupidly and cannot be used for assay purposes. The certified isotopic compoMtiom .ire gixen below together wiih the atomic weight of thallium. Absolute Abundance Ratio 2<"TI/2WTI 2 38714 ± 0.00101 Isoiopic Composition WJ T). Atom Percent 29 5235 ± 0.0088 WSTI. Atom Percent 70 4765 ± 0 0088 Thallium Atomic Weight 204 38333 i 0.00018 The above indicated uncertainties are the overall limits of error based on the sum of 95 percent confidence limits for the mean and allowances for the effects of known sources of possible systematic error. This SRM was Used In the determination of the absolute abundance ratio and atomic weight of thallium. (I) The absolute abundance ratio of Tl/ Tl was determined by single filament thermal iontzalion mass spcctromeiry. Mixtures of known °TI/ 'Tl, prepared from nearly pure separated thallium isotopes, were used to calibrate the mass spectrometers. The analytical measurements leading to the certification of this material were performed in the NBS Inorganic Analytical Research Division. Mass spcctrometric measurements were made by L.J. Powell and J.W. Gramlich on calibration mixes prepared by L. 1. Powell. The purity of the separated isotopes was determined by P.J. Paulsen using spark source mass spectrometry. Statistical analysis of the data was performed by H.H. Ku. NBS Statistical Engineering Division. The overall direction and coordination of the technical measurements leading to certification of this SRM were performed under the chairmanship of I.L. Bames, NBS Inorganic Analytical Chemistry Division, and W.C. Purdy. McGill University. Montreal. Quebec. Canada. Issuance of this Standard Reference Material was coordinated through the Office of Standard Reference Materials by R W. Seward Gailhcrsbiirg. MD 20899 Stanley D Raibcrry. Chief July 23. 1986 Office of Standard Reference Maienals Reference. I. Dimitan. L P.. Gramlich. J.W.. Barnes. I.L. and Purdy. W C . J Res. Nat. Bur Stand (U S ). 85, No I. 1-10(1980). I _=-- - National ^Institute of ^tanbarfca & uecn,nologu (Certificate of National 3natitute of £>tauaaraa & aeclinuluiju Standard Reference Material 982 (Certificate of Analjffiifi Equal-Atom Lead Isotopic Standard I In-. Standard Reference Material (SRM) is intended primarily for use as an tsotopic standard SRM 982 COIIMMS nl I israin Standard Reference Material 981 ol a u ue i hat was prepared by mixing commercial and radiogenic leads to obtain essentially equal-atom amounts ol LcaJ- 2iMi and Lead-208. It is chemically pure to at least 99.9+ percent purily. The atomic weight of the material is calculated lo be Common Lead Isotopic Standard 206 9429 using the nuclidic masses 203.971044. 205.974468. 206.975903. and 207.976650. The certified isolopic compositions aic given below. I hii Standard Kcfcrence Material (SRM) is intended primarily for use as an isolopic standard SRM )« 11 onsiMs ol I ue.im of a commercially available, high purity lead metal, of 99.9 + percent purity, that was extruded into wire form The ai'nnnc Alomic Abundance Ratio. Lead-204/Lead-206 ... 0 027219 ± O.IXXKI27 wi-ii-hi of the material is calculated to be 207.215 using the nuclidic masses 203 9730-W, 205 9744(,«, 2d6'J759ta .md 207 'J7(i Atomic Abundance Ratio. Lead 204/Lead 206 . 0059042 ± OOUXH7 Alomic Abundance Ratio, Lead -208/Lcad- 206 ... 1.00016 ± 0.00036 Atomic Abundance Ratio. Lead-2fl7/Lead-206 ... 0.9146-4 ± 001X133 Lead-204, atom percent ...... 1.0912 ±00012 Atomic Abundance Ratio, Lead-208/Lead-206 ... 2 1681 ± 0 0008 Lead-206, atom percent ...... 40.0890 ± 0.0072 00 Lead-204, atom percent ...... 1 4255 ± 0.0012 Lead-207, atom percent ...... 18.7244 ± 0.0023 Lead-206, atom percent ...... 24.1442 ± 0 0057 Lead-208, atom percent ...... '40.0954 ± 0.0077 Lead-207. atom percent ...... 22 0833 ± 0.0027 Overall limits of error arc based on 95 percent confidence litnils for the mean of the ratio mcasurcmenis and on .ill. >« .inn. > for i he known sources of possible systematic error. Lead-208, atom percent ...... 52 .1470 ± 0 0086 Nnhie to User: SRM 982 is radioactive, containing Lead-210 4.2xlOJBq -g"1 of natural origin (sec allathed Re|iori .>! (he-rail limits of error are based on 95 percent confidence limits for the mean of (he r.iiiomcaMireim'iiis .>i»l on allow.nuc.-, Tesi) All users and purchasers must comply with all state and federal regulations regarding (he use and ili'.pos.il »l lliis lor the known sources of possible systematic error. niaienal. Measurements for certification were by triple filament solid-sample mass spectromctry. Mixtures with known :"HPh/:"''Ph Measurements for certification were by triple filament solid-sample mass spectromctry. Mixtures with known " Ph." 'I'h ratio, prepared from high-purity separated isotope solutions, were usedascomparisonstandards. Details of (he preparation ratio, prepared from high-purity separated isotope solutions, were used as comparison standards. Details of (he preparation and measurements were published by EJ. Catanzaro. TJ. Murphy, W R Shields, and EL. Garner J Research NBS 7">A and measurements were published by EJ. Catanzaro, TJ. Murphy, W.R. Shields, and E.L. Garner. J. Rcseari h NBS 72A, No. 3,261(1968). ' " ' No 3.261 (l')68). The analytical measurements leading to the certification of this material were performed in the NISI Inorganic Analvin.il The anal>lical measurements leading to the certification of this material were performed in the NIST Inorganic . Xn.ilvliiMl Research Division. Research Division. The overall coordination of efforts leading to the update and revision of this certificate was cooidmaicd through (he The overall coordination of efforts leading to Ihe update and revision of this certificate was coordinated through the Siandard Referencecncc Materials Program by TT. E. Gills. Siandard Reference Materials Program by T. E. Gills. .'Jailhcrsburg, MO 20899 W'llli.nn P Reed. Chief March 25, I99I Siandard Reference Materials Program (Jaiihee-.hurg.MD 20899 William P Reed, thief (Revision of ceilificatc dated 4-10-73) March 25. 1991 Standard Reference Material s Program (Revision of certificate dated 6-1- 68) U.S. DEPARTMENT OF COMMERCE National Institute of Standards & Technology UtiBtitute of *tanfcarbe & aecljnologu Gailhersburg. MD 20899 (Certificate of REPORT OF TEST Standard Reference Material 983 for Radiogenic Lead Isotopic Standard National Institute of Standards and Technology Office of Standard Reference Materials lliu Standard Reference Material (SRM) is intended primarily for use as an isotopic standard SRM 'MKonMiUui I cram Gallhersburt, MD 20899 of a wire (hat was prepared from radiogenic lead. It is chemically pure toal least 999 -t- percent punlv. andcxiruJjj inio wire form. The atomic weight of the material is calculated to be 206.0646 using the nuclidic masses 203 973044 2t)5 i"4-i«,.S. 2ik> '>75'X)3, and 207.976650. The certified isotopic compositions are given below. Radionuclidc Lead-210 Atomic Abundance Ratio, Lead 204/Lead-206 .. 0 000371 ± 0 000020 Source identification SRM 983 Atomic Abundance Ratio. Lead-207,Lead-206 ... 0.071201 ± 0000041) Source description Radiogenic lead isotopic standard y^_) Atomic Abundance Ratio. Lead 208/Lead-206 . . 0 013619 ± 0 000024 Source composition Radiogenic lead in wire form "" Q>Q Lead-204, atom percent ...... 0 0342 ± 0 0020 Reference time November 1. 1990 - |- Lead-206, atom percent ...... 92 1497 ± 0 0041 Lead-207, atom percent ...... 6.5611 ± 0 0025 Radioactivity concentration 2.6 x JO4 Bq g ' Lead-208, atom percent ...... 1 2550 ± 0 0022 Overall uncertainly 10.1 percent (2> Overall limits of error are based on 95 percent confidence limits for ihc mean of the ratio measure me ins and on allowances Photon-emitting impurities None observed foi the known sources of possible systematic error. Half life 22.3 ± 0.2 years Measurements for certification were by triple filament solid-sample mass specirometry. Mixtures with known :MPb, :o<'Pb rano. prepared from high-purity separated isotope solutions, were used as comparison standards. Details of ihe preparation For the Director. and measurements were published by EJ. Calanzaro, TJ. Murphy. W.R. Shields, and E.L. Gainer. 1. Research NBS 72A. Ni>. 3,261(1968). The analytical measurements leading to the certification of this material were performed in the NIST Inorganic Analytical Dale D. Hoppes, Or Research Division. Gailhersburg. MD 20899 December. 1990 Radioactivity Group The overall coordination of efforts leading to tbe update and revision of this certificate was coordinated through (he Center for Radiation Standard Reference Materials Program by T. E. Gills. Notes on hack Ciaithersburg, MD 20899 William P Reed. Chief March 15. 1991 Standard Reference Materials Program (Revision of certificate dated 6-1-68) NOTES '" A master solution containing a centimeter of lead wire was measured .UK! dissoKcd in nitric acid. Gravimelrical measurements were made for lx>th (he wire and the' nitric acid. Liquid scintillation vials were prepared using a commercial viniill.uor and and gravimclrical aliquois of the active master solution. ' ' The overall uncertainty was formed by taking three limes the quadratic combination nl the standard deviations of the mean, or approximations thereof, for the following: U\ a) liquid scintillation measurements 0.15 percent b) sample preparation 0.10 percent c) gravimetric measurements 0.15 percent d) detection efficiency 3.0 percent e) background 0.24 percent f) progeny contribution 1.5 percent NCKP llandlxxik 58, 2nd L'dillnn. IW5. p. !%. Commercial counter with two phototubes which count in coincidence For additional inlormation please contact Jncqucline M. Calhoun at (301) ^75-3518. I .S. l)i-|i.irlini-nl uf ('iimmrrrc Cllini I.. Hirhard.siin. Si-rrclar) Stimuli Hun .u *.l SUiidiidH Bureau of (Certificate Standard Reference Material 991 Lead 206 Spike Assay and Isotopic Solution Standard This Slaml.inl Id lemur M.ili n.il (SltM) i- nrlilieil l»i IIM- .1.- .in .i^.n .nnl i-..l..pi. -l.mil.inl. The primary inlrmlril n.-e is ;i> .1 *pikr I'nr le.nl ileleriiiiii.iliuii- h\ iMilnpe ihlnlion m.i >pee- Iriunelry. SUM 'I'll. Li-uil-^OC) Spike, is .1 Milnlion til le.nl nilr.ile M-.I|K| in ipi.irl/ imiponlex. K.ieli .inipuiile eunliiiii- n iiiniiiii.il I.') [zr;ini> of M ill 11 KHI. uliii h i- II ~> N in UNO ,. (!iiin enli .iliini nl I.e.nl (».:U_Vil t l.-i>liipic eiiiiipii-iliiui (.ilniii 11.n liun) - li: l'l, IIIIIKIIIII ! 000(111 1 -' "I'd II 11(101 t i (IIIIKIdl \li.ini. \\n»li| 2ll.ri<»7."i Tin 1 ruin rnll.iliini nl li'iiil in SUM 'I'll u.i- ilclri iniin-il li\ ,in IM.IHJIC illinium IM.I--, >p. i lii Ilii- lli;i-> -|H< Inilinll} liir.iMMi-Mii Ml- .il MIS UIH iii.nh In I I MIMHI .mil | \\ ( i i.milli II ii-in^ -ii|iilnni> pn |,,iri-il li\ I., \.\l.nlihin Tin- iiM-r.ill iliri I'liiui .mil i iiiinlin.iliuii nl ll>. in linn .il iiii-.i-iiniiirnl^ li .i.lin;: In i ri din .ilimi \\. M iiniliT I lie rli.iirniilir-llip nl I. I.. Iliiinr.-. 'I In- li-rllllii-.ll .mil >ll|i|inil ,i-pi i I- rum ( iinnu II" pirp.n.ilmn. < rrlllii .ilmn .mil i^n.nn r ul llii> M.mil.inl llrfi I. lin M.ilt ri.il urn niixirm.ilril lliionu'li lln I II In r .il x| .nid.n .1 U. h n in r \l.i|. n,il> lit \\. I'. Id nl U.i-lmi"!...!. D.C. JD.MI .1 I'.n.K ..li ( In, I M.inh I'). I'lTd Dlln. PROVISIONAL CERTIFICATE 2. Ih« I!!M solution has a molality nf 6 m IINOj (i.e. 0 mol llflO-j ' kg" of solvent) or a molarity of 5 M HN03 (i.e. 5 mol HN03 ' I" 1 of solution). ISOTOPIC REFERENCE MATERIAL CBNM-IRM-060 3. I he Avogadro constant used is (6.022 045 +/- 0.000 031) ' 1023 . 230 The IRM is. supplied with a Th atomic Isotope concentration certified as 4. The atomic masses, used in the calculations, are ?30 rh 230.033 130 7 (/- 0.000 003 1 (1.056 9 +/- 0.007 9) ' 102° atoms 230Th ' kg" of solution 23?Th 232.038 053 8 +/- 0.000 002 5 , 900 i 5. Th concentrations In unknown samples can be determined by Isotope j From the certified Isotope concentration, following concnntrat Ions .ire niluLion Mass Spectrometry, using this Spike IHM, through e measurement (if derived : the atomic isotope dilution ratio Rg = 230 Th/ 232 In in the blend. Thfiy should bo computed with the aid nf tha following formula which allows an (1.755 +/- 0.013) ' 10~4 mol 230Th ' kg" 1 of solution | easy idontifIcntion of the sources of the uncertainties in the procedure : (4.03fl +/- 0.030) ' 10"5 kg 230 fh ' kg" 1 of solution i R Y ' R8 Mv "232 230 The Th isotope present Is related to the In atomic isotope concentration Mv through the following atomic isotope ratio : where . R), - atomic isotope ratio Th/ Th In the unknown sample m.iterial R ¥ = atomic Isotope ratio Th/ 'Th In the spika material M mass of the unknown sample This correspond* lo an itnloplc uxnpiriltioii with the follnwlnij «tmii ;. ' Tlu> Sl.indanl Urfrrrnrr Malrrial (SUM) i- trrhlnd lor n-r ,i- an ,i-.i) and IM.IOJII, -l.iinl.iid. : Ilif |inin.iry iiilrndrd n.-i is as .1 spikr for nr.niiinn drlrrinnialions li\ !.-.>!.I|H- dilution ma V s|>r< Irosrnpy. SUM ')'K|, tlraliinin 2:l!">Spikr. i^ a -olnlioii -r.ili-,1 in ^l.is- ain|ion|i - I'.aili ani|Hinlr .!. ion).nn. .1 noiiiiil.il |.r> -i.nil- of--olnlioii, uliitl, i- .(|i| lr ,,Minal ;. Con. cnlralion of I railinin ; ( 1*11270 ' 0 O.'il mi, romo|,-.-/;;r.im '.' l-olo|ii. , olll|>ii-ll lull (aloin |ii r :; -"H HO 112 o ooDi - r'll «l«) lU'C) ' 0001.1 ] ' -"'ii onr»7i ooooi -'"II 00711'! ' 001)01 jf^-j Tin- i oiirriilr.ilion of iir.iiiiiiin in SUM 'I').! »a~ ilr|rrinnii-il It) an i>olo|i,- dilnlion MI.I-- -|i. . Ifomclr) Iri lini,|iii . which is dr-i rilinl in MIS Tr, linn.il Nolr .'i Ki. A rorici lion for i.-o|o|iir fia. lion.ilioii was di'lcrniincil \>y anal)/in>; Slt\l tl HOO. Tlir nuliialid mi, i-rlainl\ for llir i oni rnlralion i> llir 'IT) jirrrrnl lidrranrr linnl* for io\cr.(^r of .il Ic.i-l ')') |MI,.II| of mra-itrrd \alnr-. ol lliis lo| of ain|ionlr> of SUM ')<>:!. Tin- Ir.isii: rlicmiial and ina-^ ijii'i Ironirlrn |>rorrdnrr-< o-< il lor llir iiiaiiiinn i-ol»|>n «ini|>o-iliiin »iiiil\«ih arc dorrilird in NHS S|irt ial I'nldii alion L'(.l) 27. Tlir -"l ami - :"'U saints \vl'|i' drlrrillilli'il |i\ iMdnln' dilnlion iisin^ -"(I.TIir -M"|l \alnr \»;i«. dr|i rinniril li) a dirrt I llli-.iMiirinrill of -'"II will) n>|ii'i I In - iri ll C.iinri lions I'or i,.o|o|iii li ,n li.ni.ilion rffn I- SM'IC iddaiurd liy anillysis of SUM 11.10(1 and a ltrl»iinn ('.on^o nalnral iii.iiiiimi vl.iinl.iiil \- is I li, nia» s|irrlroinrlr\ inra>nrrnirn|> .il MIS \\rrr in.id, |,\ ) . I (i.inni ii-m^ -olnlioii- |ir. |Mr,d h) I,. A. Marld.ni. Tin overall dim lion and rooi dm.ilioii ol lln I,, lmn.il im'.i-mno. nl- I, .,,lni<: lo < n lift, alion \\,-rr midrr llir < hairm.ni-lil|i ol I. I.. Itarnr.-. Tlir Irrluiiriil ami support asprt l> runrrrnin^ llir |irr|iaralion. (frlil'ii alum, and i^-nanrr of (Ins Sl.iiiil.ini Hrfrrriirr Mali-rial wrrr «iortlinal.-d llironnh llir Ofli. r ol Slaiid.nd Id f, rrnrr Malt rials I.) \\. I'. U.T.I. VV. IMP- It. IV Uulr ..( MjluUnl Ui-lrrrnir MalnuK li, \|. .,-,,r. m.-nl >)>l.-m. Ml> \|,.n,.,'l.,|,li I I" I 1 "."- II"' ."M,.-|.l "I 1,.1,-rji,,,' Innil is J|M> ilbriiMU-.l mChapIrr 2. Kx|« cum i,l.,l Mjli-n,. MIS lljiiill.uok Ml. I'11,1, In I.IH f. ,( wr lu.l nu.U ,,.mr,,lial«>n inruM.r. »l- . > ,11 II,, sli.iill.l fall wilhil, Hi, iiuliralril 1.,1,-cjn,,- lunils »(ll, a o.ull.l, n | I'.llll C.lll I In, I Ollin- of Sl.indard It, |rr< n«- Malin.iU urea it nf (Certificate nf Standard Reference Material 960 Uranium Metal llemovaj of Surface Impurities Ihe lollovMiig i leaning proeedtire was n.sed on all nraninin assay sani|des after bring enl lo the. Uranium i IHII7 I'ereenl .ipproximalr M/C for analysis. Kcir aecurale anaJ) tieal work, this proceilnn1 or un ei|iiivulent one should he followed. This metal standard nf normal inolnpie eompusilioti la i.v-ned a- .1 primary .iv-ay standard fur ni.mium determinations. The value of llie. aluiuic weigh) of ibis in.id-n.il ib 2:ilt.Ul!H') .1.-, determined Dip Ihe uranium sample in 1:1 IINOj for a period of up to 10 minutes to remove all visible al MtS l>y Ilicrnial ioni/ation mass .-peelrometrv . Mirfaee oxide. Kiuse iii distilled water. Etch in 1:3 HCl for 5 minutes. Rinse thoroughly in distilled water. »emo\e excess surface water before placing the sample in a vacuum desiccator for attain Tin1 nraiiiilill a.v,ay is based mi llu- roiisl.inl enrrenl roiilmneliie ledm Inm nl iiran\l inn uith ment of eonslant weight. Removal of surface moisture U accelerated and re-oxidation of the metal i-leetrogciicrutcd tit.iinms inn in 7M biill'urie. ai:id. I In- v.ilni: <>f llu avay ha-, been correeted for Mirfac e is retarded by drying under vacuum for a suitable length of time (evacuation for 1/2 hour is 12 |>|»m of iron and 4 ppm of vunailiuni whieh an: llu- tilratahle impurities pn-.-ent in the nn'tal. The Milfiiienl). rrrlificd value, (V). ()75 weight |H-rrrfit, rcftriMiilb the 1111 an of 2\ ih lcriiiiiKiliun> Tln> proriMotl of llu method, expressed in terms of llu: Manilard deviation of a Mnylr di-li-rinni.il ion ib 3.0011 percent. The estimated value of (lie IIIK i-rlainly of the mean a.xsay ib O.OOd jierccnl. Tlu> figure iueludes tin: e^limali-s of all knnun .sunrees of error inherent to (hi* determination: llu random error com- ponent, 0.004 |MTI:CII| (the '>5 pen rut eonfidenee inlerv.il for (lie iin'ati lia-. d on 20 decrees of freerloin), and an additional 0.002 pen cut error lertn as an allowanee for all known |>o:>Ml>le >oiin-es of .sybteniatic error. An ovi'rall nia^b lialanee ol 'ID.'J'JTO perrenl ib ohlaitieil uli.n the e^lini.ile of CO lol.ii impurities prix nl in the material (22il ppm) is taken uilo aeeonnl. The nneertaifil\ ,i.s4 rilieil lo the rerlilied a>.-a\ value nei- inlerx.d lor a ij^c determination. Tin* niclal ab reeei\ed will eon I.mi a Mpiilieanl .1 mount ol Miilaee oxide. In .i-v-.i) inj; I he m.ilerial, (he oxide was removed from the uranium samples jiibt prior to wei^hin^. I he metal Mirf.ui' was i le.un:il hy (he proi cdnri- outlined on (he li.uk of ||ii> eerlilii ale. This material was prepared l>\ (lie United Sljli-5 \lonne l'.ner(;\ (!oiniiii~~ion I npimlie- were .nialy/.ed hy tin' \\'.C. I'arhieah l..iltinalor), 1'ailiirah, Kenlnekv. ,'W.i) ol' llu- material u.i> per- foriiutd |>y (i. M.iriin-nkn anil K. S. I'.t/, the iron eontenl wa> ileli rnnncil pol.iro^raplnenll) li\ !>'.. J. Maietilhal, and the alomie wei^hl uas delennitied li\ i-olopn i.ilio nn .i-ouDM II|N pi-rl'iirnied hy I.. I., (iannr, all of llie NHS Anal) heal Clieini.-lrt |)iM>i<>n. The overall direelioti and eoordinalioti o| (he lei lnm.il m, .1 nn in. nl, h .idin^ In tin- < i rlil'n ation ui u performed nnder Ihe eliairmaiibliip ul' \\ . It. ShiehK. The teehnieal and Mippnrl a>pee|> in\id\ed in llie piep.ir.ilmn, eeililiealion. and i.----iiain e of this Sl.milanl llrfeu nee Material win < onidmah d llnon^h llie Olfne ol .Slaiiil.ini lie h renee M,il. rials h\ \V. P. Uee.l. U.i-liingliifi, HI. Jirj.t I. I'.mll .>h. I.In. I Max 12, IK72 I Illi. it Sl.iml.nd Hi l< r. me Mal.ri.il> (over) IViunriKiM >il C miunciic ^Bureau of j^tandards Rational ^Bureau of (Eerttfttate of JVttalgsts dUeritficate of Standard Reference Material U-930 Standard Reference Material (J-970 Uranium Isotopic Standard Uranium Isotopic Standard (Nominally 93% Enriched) (Nominally 98% Enriched) 2J5U 216U 2J»U Atom Percent 1.0812 93.336 0.2027 5.380 214u 2J5 U 2)IU ±00020 ±0010 ±.0006 ±0005 Atom Percent 1.6653 97.663 0.1491 0.5229 Weight Percent 1.0759 93.276 .2034 5445 ±0005 ±.0006 ±00017 ±0003 This Siandard Reference Material (SRM) is certified for use as an isoiopic standard. The primary intended is for the Weight Percent 1.6582 97.663 .1497 .5296 evaluation of mass discrimination effects encountered in the operation of a mass spectrometer. This Standard Reference Material (SRM) is certified for use as an isoiopic standard. The primary intended use is for the The material consists of highly purified uranium oxide. U)O8. The atomic weight of the material is cjleulaied 10 be 10 evaluation of mass discrimination effects encountered in the operation of a mass spectrometer 235.197, using the nuclidic masses 234.0409; 235.0439; 236.0457; and 238.0508. The material consists of highly purified uranium oxide, UjOg. The atomic weight of the material is calculated (o be The values for U and U were calculated from measurements at the National Bureau of Standards. The samples were 235 045. using the nuclidic masses 234.0409. 235.0439; 236 0457; and 238 0508. spiked with high-puniy U to approximate the 2)4U concentration, the ratios 2I)U to 2I4 U and 2)1 U to I) were measured on a triple-filament equipped surface ionization mass spectrometer with d-c amplifier circuits. The values for U and I) are calculated from measurements made on samples spiked wuh high-purity U (o approximate the 214 U and 2)6U concentrations, the ratios 2U U to 2)< U and 2JJ U to U were measured on a triple- The values for' U and U were calculated from measurements made at the National Bureau of Standards, at Union filament equipped surface ioni/aiion mass spectrometer with d-c amplifier circuits. Ratio deter initiations were cor reeled Carbide Nuclear Co., Oak Ridge. Tenn.. and at Goodyear Atomic Corp.. Portsmouth, Ohio, each laboratory's value for mass discrimination by measurements made under similar conditions on SRM U-500 being given equal weight. Values obtained at NBS are the result of direct measurement of the 2)iU to 2)IU ratio using The value for 1JIU is calculated from measurements of the ratio 2)SU to 2J*U. and calibrated bv measurements of the triple filament thermal ionuation. The observed ratios were corrected for mass discrimination effects by determining the same ratio on synthetic mixtures prepared from high-purity separated isotopes of U and U to approximate the system bias from measurements on standards U-500 and U-900. Experience at NBS has shown, through imercomnarison composition of the sample. Because of (he response time of the measuring circuit when switching from (he U peak to oHhe standards, and synthetic mixtures at the 10-. 50-. and 90-percent 2)iU level prepared from high-purity U and the U peak, (he 2JIU peak was monitored for I minute and only data from (he last 30 seconds, after the signal had U isotopes, that a constant bias for a given procedure can be maintained over the range of 5- to 95-percent U. Values stablLzed. were used in the calculations. The value for )5U is calculated by difference. from Union Carbide and Goodyear Atomic are based on direct determinations of the 2)IU concentration by oxide dilution and UF6 analysis, and then the ratio calculated using the NBS values for I)4 IJ and 2I*U, and the !1J II value The indicated uncertainties for the isoiopic compositions are at the 95-percent confidence level for a single obtained by diffeience deteimination. and include terms for the inhomogcneitics of the material as well as analytical error The U to U ratio for this standard. 186.78, is known to at least 0.15 percent. The indicated uncertainties for the isoiopic concentrations are at the 95-percent confidence level lor a single determination. Hie 2J5 U to 21*U ratio for this standard. 17.349. is known to at least 0.1 percent: at the .s.inic time the Measurements leading to the certification of this SRM were made by E. I.. Gamer and I. A Maclilan pooled variance for the calibration system is significantly smaller. [he overall direction and coordination of the technical measurements leading to certification were performed under the Measurements leading to (he certification of this SRM were made by I:. L.Garner, I.. A. Maclilan. M S. Riclininmi. and chairmanship of W. R. Shields. W. R. Shields. The technical and support aspects in the preparation, certification, and issuance of this Standard Reference Material The technical and support aspects in the preparation, certification, and issuance of this Scuidaid Rclncmr M.iicn.il were coordinated through the Office of Standard Reference Materials by J. L Hague. were coordinated through (be Office of Standard Reference Materials by J. L. Hague. NO I E: In many industries traceability of their quality control process to (he national measurement system is carried out NO 11: In many industries traceability of I heir quality control process to the national measurement sy»iein is can icd out through the mechanisms of S RM's. It may be therefore of interest to know the details of (he measurements made at NBS through the mechanisms of SRM's. Il may be therefore of interest to know the details of the measurements made ai NI1S in arriving at (he certified values of this SRM. An NBS Special Publication, 260-27, is reserved lor this purpose and is in arriving at the certified values of this SRM. An NBS Special Publication, 260-27, is reserved for (his purpose and is available from the NBS Office of Standard Reference Materials upon request. available from the NBS Office of Siandard Reference Materials upon request. Washington, D.C. 20234 George A llnano, Chief Washington. I) T 20234 George A Uri.ino. C'lucl April 6. 1981 Office of Siandard Reference Materials April 6. 1981 Office ol Slniulanl Kcfcmicc M.ncii.iN (Editorial revision of (Editorial revision of Ceilificale dated 7-30-70) Ccnificaie dated 7-30 7(1) U S DcniilintiMiil ( ..i .(.ki.la» Ail.lint ^National ^Bureau of ureau of Certificate of Certificate of JVnalgaia Standard Reference Material U-850 Standard Reference Material U-900 Uranium laotopic Standard (Nominally 86% Enriched) Uranium laotopic Standard 2) 'U 2)4 U "'U 0.3704 13.848 (Nominally 90% Enriched) Atom Percent 0.6437 85 137 ±0.014 ±.0014 ±0017 ±.0011 .3713 14.001 Weight Percent .6399 84988 mu 216 U 2 "U This Standard Reference Material (SRM) is certified for use as an isotopic standard. The primary intended use is for the evaluation of mass discrimination effects encountered in the operation of a mass spectrometer. Atom Percent 0.7777 90 196 0.3327 8.693 ±.0015 ±0011 ±0010 ±0.008 The material consists of highly purified uranium oxide. U)Oj. The atomic weight of the material is calculated to be Weight Percent .7735 90098 .3337 8.795 235.458. using the nuclidic masses 234.0409; 235.0439; 236.0457; and 238.0508. The values for 4 U and ' U were calculated from measurements at the National Bureau of Standards. The sample* were This Standard Reference Material (SRM) is certified for use as an isotopic standard. The primary intended use is for Ihc spiked with high-purity 21J U to approximate the 214 U concentration, the ratios 2n U to 2)4 U and 2}1 U to U were evaluation of mass discrimination effects encountered in the operation of a mass spectrometer. measured on a triple-filament equipped surface ionization mass spectrometer with d-c amplifier circuits. The material consists of highly purified uranium oxide, U)O8 The atomic weight of Ihc maleiial is calculated to be The values for *U and ' U were calculated from measurements made at the National Bureau of Standards, at Union 235.301. using the nuclidic masses 234.0409; 235.0439; 236.0457. and 238.0508. Carbide Nuclear Co.. Oak Ridge. Tenn., and al Goodyear Atomic Corp.. Portsmouth. Ohio, each laboratory's value The values for Uand U are calculated from measurements al the National Bureau ofStamlaids The samples were being given equal weight. Values obtained al NBS are the result of direct measurement of the 21i U to 2) *U ratio using ipiked willi high-purity 2J) U to approximate the IJ4 U concentration, the ratios 2n U to 2I4 U and 2II U lo 2 *U were triple filament thermal ioniration. The observed ratios were corrected for mass discrimination effects by determining the measured on a triple-filament equipped surface ionizaiton mass spectrometer with d-c amplifier circuits. system bias from measurements on standards U-500 and U-900. Experience al NBS has shown, through intercomparison of the standards, and synthetic mixtures at the 10-, 50-. and 90-percent 215 U level prepared from high-purity 2 U and The values for m U and 2I *U were calculated from measurements made at the National Bureau of Standards of the 2}i U U isotopes, that a constant bias for a given procedure can be maintained over the range of 5- to 95-percent U. Values lo U ratio. I he observed ratios were corrected for mass discrimination effects by inlcrcomparison with five synthetic mixtures at the 90-percent 21J U level prepared from high-purity 23SU and 2} *U. from Union Carbide and Goodyear Atomic are based on direct determinations of the 2 *U concentration by oxide dilution and Ul:6 analysis, and then the ratio calculated using the NBS values for >4 U and 2 6 U. and the 2)5 U value The indicated uncertainties for the isotopic concentrations aic at the 95-percent confidence level for a single obtained by diffcience. determination Ihc U to U ratio for this standard, 10373, is known to al least 0 I percent Hie indicated uncertainties for the isolopic concentrations arc at the 95-percent confidence level for a single Measurement* leading to the certification of this SRM were made by E. L. Garner, I. A Machlan.M S Richmond,and determination Ihc U to U ratio for this standard, 6.148, is known to at least O.I percent; at the same time the W. R Shield* pooled variance foi the calibration system is significantly smaller. I he Id limcal and support aspects in the preparation, certification, and issuance of (his St.nul.ml Reference Material Measurements leading to the certification of this SRM were made by II. L. Gamer, 1.. A Machlan, M.S. Richmond, and were coordinated through the Office of Standard Reference Materials by J. I.. Hague W. R Shields. NO! li: In many industries traceability of their quality control process to the national measurement system is carried out I he technical and support aspects in Ihc preparation, certification, and issuance of this Standard Reference Mateiial tin oiigli the mechanisms of SRM's. It may be therefore of interest to know the details ol the measurements made al NRS wcic coordinated through the Office of Standard Reference Materials by J. L. Hague. in airiving at the certified values ol this SUM. An NI1S Special Publication, 260-27, is received lor this purpose and is NO'1 li: In many industries iraccabilily of their quality control process to the national measurement system is carried out available fiom (lie NF)S Office of Standard Reference Materials upon request. through the mechanisms of SRM's. It may be therefore of interest lo know thedetails of the measurements nude at NUS in arriving al the certified values of this SRM. An NBS Special Publication. 260-27. is reserved for this purpose and is Washington. I>C 20234 George A Uriano, Chief available from the N1IS Office of Standard Reference Materials upon request. April 6. 1981 Office of Standard Reference Materials (lidilorial revision of George A. Uriano. Chief Certificate dated 7-30-701 Washington. I) C. 20234 Office of Standard Reference Materials April 6. 1981 (Editorial revision of Certificate dated 7-30-70) U S IVpinmfVMllmflH.il I* .il fnnm.( nnmiciLC MilcolM-jUldngt mfir ,., »fi n'" ^National ^Bureau of (Eerttfteate of Standard Reference Material U-800 Standard Reference Material U-750 Uranium Isotopic Standard Uranium Isotopic Standard (Nominally 80% Enriched) (Nominally 75% Enriched) 2)S U 2)6 U 2)IU I)4u 2)4 u J)S U J)6U 2J"U Atom Percent 0.6S63 80279 024-15 18820 Atom Percent 0.5923 75.357 0.2499 23.801 ±.0013 ±.0007 10019 ±0021 ±.0009 ±0025 ±.0008 ±0024 .2450 19.015 Weight Percent .6519 80088 Weight Percent .5880 75.129 .2502 24033 This Standard Reference Material (SRM) is certified for use as an isolopic standard 1 he primary intended use is for (he This Standard Reference Material (SRM) is certified for use as an isolopic standard. 1 he primary intended use is for the evaluation of mass discrimination effects encountered in the operation of a mass spectrometer. evaluation of mass discrimination effects encountered in the operation of a mass spectrometer. The material consists of highly purified uranium oxide, UjOj. The atomic weight of the material is calculated to be The material consists of highly purified uranium oxide, UjO|. The atomic weight of the material is calculated to be 235 606. using (he nuclidic masses 234.0409; 2350439; 236 0457; and 238.0508 235 756. using the nuclidic masses 234.0409; 235.0439; 236 0457; and 238.0508. The values for 2J4 U and J56 U were calculated from measurements al the National Bureau of Standards. The samples were 1 he values for 214 U and 2 ' 6U were calculated from measurements at the National Bureau of Standards. The samples were spiked with high-purity J)) U to approximate the JJ4 U concentration, the ratios 2)) U to 2)4 U and 2)) U to 2 6 U were spiked with higlvpurily U to approximate the 2)4 U concentration, the ratios 2)) U to J)4 U and 2J) U to U were measured on I triple-filament equipped surface ionization mass spectrometer with d-c amplifier circuits. measured on a triple-filament equipped surface ionizalion mass spectrometer with d-c amplifier circuits. The values for U ind U were calculated from measurements made at the Naiion.il liureau ol Standards, at Union I he values for U and U were calculated from measurements made at (he National Bureau of Standards, at Union Carbide Nuclear Co., Oak Ridge, Tenn., and at Goodyear Atomic Corp.. Portsmouth, Ohio, each laboratory's value Carbide Nuclear Co.. Oak Ridge, Tenn., and at Goodyear Atomic Corp.. Portsmouth. Ohio, each laboiatory's value being given equal weight. Values obtained at NBS are (he result of direct measurement of the U to U ratio using being given equal weight. Values obtained at NBS are the result of direct measurement of the J15 U to 21 *U ratio using triple filament thermal ionization. The observed ratios were corrected for mass discrimination effects by determining (he triple-filament thermal ionization. The observed ratios were corrected for mass discrimination effects by determining the system bias from measurements on standards U-500 and U-900. Experience at NBS has shown, through intcrcomnarison system bias from measurements on standards U-500and U-900. Experience at NBS has shown, through intcrcomnarison of the standards, and synthetic mixtures at the 10-, 50-, and 90-percent 2IS U level prepared from high-puriiv S U and of the standards, and synthetic mixtures at the 10-, 50-, and 90-percent J1S U level prepared from high-puritv U and U isotopes, (hat a constant bias for a given p rocedure ca n be maintained overt he range of 5- to 95-percent U. Values 2) *U isotopes, that a constant bias for a given procedure can be maintained over the range of 5- to 95-percent"' U. Values from Union Carbide and Goodyear Atomic are based on direct determinations of the U concentration by oxide from Union Carbide and Goodyear Atomic are based on direct determinations of the 2) 'll concentration by oxide dilution and UF« analysis, and then the ratio calculated using (he NBS values for )4 U and "'"'II, and the ' U value dilution and UF» analysis, and then the ratio calculated using the NBS values for 2)4 U and 2)6U, and the Z ' J U value obtained by difference. obtained by difference. Ihc indicated uncertainties for the isolopic concentrations aie al 95-percent confidence level (or a single determination. I he indicated uncertainties for the isolopic concentrations are at (he 95-percent confidence level lor a single Ihe Jli |l to 2>IU ratio for (his standard. 4.266, is known to al least 0 I percent, al the same nine ilie pooled variance for determination I he m ll to 2>> U ratio for this standard. 3.166. is known to at least 0 I percent; al the s.ime lime the the talihiation system is significantly smaller. pooled variance for the calibration system is significantly smaller. Measurements leading to (lie certification of iliiiSK M were made by I: 1 (i.iinci.l. A M.ichl.m, M S Richmond,and Measurements leading to the certification of this SRM were made by E. L. Garner, and I.. A. Maelilan W R. Shields. I he technical and support aspects in the preparation, certification, and issuance of this Standard Reference Material I lie (ethnical and support aspects in the preparation, certification, and issuance of this Sl.iinl.ini Uefeicnce Material were coordinated iluough the Office of Standard Reference Materials by J. L. Hague. were coordinated through the Office of Standard Reference Materials by J. 1.. Hague. NOT E: In many industries traceabilily of (heir quality control process to the national measurement system is carried out NO1 E: In many industries traceability of I heir quality com rot process to I he national measurement system is cairied out through the mechanisms of SRM's. It may be therefore of interest to know (he details of (he measurements made at NBS through I lie mechanisms ofSRM's. It may be therefore of interest to know the details of the measurements made al NBS in arriving al the certified values of this SRM. An NBS Special Publication, 260-27, is reserved for this pin pose and is in arriving at the certified values of this SRM. An NBS Special Publication, 260-27, is reserved for this purpose and is available from the NDS Olficc of Standard Reference Materials upon request. available from (he NIIS Office of Standard Reference Materials upon request Waslimgion, DC 20234 George A. Unano. Clnel Washington. D.C 20234 George A llriano, duel April 6. 1981 Office of Standard Reference Materials April 6, 1981 Oil ice of Sl.iiulaul Reference Materials (Editorial revision of (Editorial revision of Certificate daied 7-30-70) CcMilkaic dated 7-30-7(1) VpJUrnfm nl < onill,cue Milcolfa fuMngc JulU.igc «cai4i)|' ,>r'.r., Rational ^Bureau of Rational ^Bureau of (Certificate of AnaWts (Certificate of JVnalgsis i_ ^ Standard Reference Material U-350 Standard Reference Material U-500 Uranium Isotopic Standard Uranium Isotopic Standard (Nominally 35% Enriched) 2)4u (Nominally 50% Enriched) 21 "U Atom Percent 02498 35.190 0.1673 64.393 ±0006 ±0.035 ±.0005 ±0036 2)4 U 2"u Weight Percent 2467 34.903 .1667 64684 Atom Percent 05181 49.696 0.0755 49.711 This Standard Reference M alenal (SRM) is certified for use as an isotopic standard. The primary intended use is for the ±0.0008 ±0050 ±.0003 ±0050 evaluation of mass discrimination effects encountered in the operation of a mass spectrometer. Weight Percent .5126 49.383 .0754 50.029 The material consists of highly purified uranium oxide, U)O|. The atomic weight of the material is calculated to be 236 979, using the nuclidic masses 234.0409; 235.0439; 236.0457; and 238.0508. This Standard Reference Material (SRM) is certified for use as an isoiopic standard. The primary intended use is for the evaluation of mass discrimination effects encountered in the operation of a mass spectrometer The values fur II and I) were calculated from measurements at the National Bureau of Standards. The sample* were spiked with high purity 211 U to approximate the 2U U concentration, the ratios 2J) U to 2J4 U and 211 U to U were Hie material consists of highly purified uranium oxide, UiOg. The atomic weight of the material is calculated lo be measuied on a triple-filament equipped surface ionizaiion mass spectrometer with d-c amplifier circuits. 236.534. using the nuclidic masses 234.0409; 235.0439; 236.0457; and 238.0508. I lie values for II and U were calculated from measurements made at the National Bureau of Standards, at Union The values for 1) and U were calculated from measurements at the National Bureau of Standards The samples were Carbide Nuclear Co.. Oak Ridge. Tenn., and at Goodyear Atomic Corp.. Portsmouth. Ohio, each laboratoty's value jpikcil with high-purity 2 "ll lo approximate (lie 2M U concentration, the ratios 211 U to 2M U and 2)) U to 2 *U were being given equal weight. Values obtained at NBS are the result of direct measurement of the 2JS U to 2)I U ratio using measiuctl on a triple-filament equipped surface ionifation mass spectrometer with d c amplifier circuits. triple filament thermal ionizaiion. The observed ratios were corrected for mass discrimination effects by determining the The values for 2>J U and 2>> U were calculated from measurements made at the National Bureau of Standards of the U system bias from measurements on standards U-500and U-100. Experience at NBS has shown, through inlercomnarison lo ' II ratio. The observed ratios were corrected for mass discrimination effects by intercompanson with five synthetic of the standards, and synthetic mixtures at the 10-. 50-, and 90-percent 2>S U level prepared from high-purilv 2 S U and mixtures at the 50-percent U level prepared from high-purity U and U. U isotopes, that a constant bias for a given procedure can be maintained over the range of 5- to 95-percent 21 U. Values from Union Carbide and Goodyear Atomic are based on direct determinations of the 2JS U concentration by oxide The indicated uncertainties for the isoiopic concentrations are at the 95 percent confidence level for a single dilution and UF4 analysis, and then the ratio calculated using the NBS values for 2U U and 2I6 U. and the 21I U value determination The 2>1 U to 2>>U ratio for this standard, 0.9997, is known lo at least O.I percent. obtained by difference. Measurements leading to the certification of this SRM were made by E I. Garner. 1.. A Machlan, M S Richmond, and The indicated uncertainties for the isoiopic concentrations are at the 95-percent confidence level for a single W. R Shields. determination Die 15 U 10 21I U ratio for Ibis standard. 0.5465. is known to at least 0 I percent; at the same time the The technical and support aspects in the preparation, certificalion.and issuance of tins Sund.ud Reference Material pooled variance for I lie calibration system is significantly smaller. were coordinated through the Office of Standard Reference Materials by J. I Hague Me asm emails leading 10 ilic certification of Ibis SRM were made by E. I.. Garner. I.. A. Maclilan, M.S. Richmond, Jiid NO1 E: In many industries traceability of their qua lily control process lot he national rnca sine man system is earned out W K Shields through the mechanisms of SRM's. It may be therefore of interest lo know the details of the measurements made at NBS 'I he technical and suppon aspects in the preparation, certification.and issuance of this Standard Reference Material were in arriving at the certified values of this SRM. An NBS Special Publication, 260-27. is icscive.l for this purpose and is coordinated through the OI lice of Standard Reference Materials by J. L. Hague. asailiible from the NUS Office of Standard Reference Materials upon request NO I T. In many industries Iraccahility of their quality control process In the national measurement system is curried out thioiigli the mechanisms of SRM's It may be therefore of interest lo know the details of the measurements made at NIIS Washington. D.C. 20234 George A Hi MHO, duel in aniving at the certified values of this SRM. An NBS Special Publication, 260-27, is reserved for this purpose :md is April 6, 1981 Olfice of Standard Reference Materials available from the NltS Office of Standard Reference Materials upon request. (Editorial icsision of Ccftificaie dated 7-30-7(1) Washington, DC 20214 George A. Uriano, duel April 6, 1981 Office of Standard Reference Materials (Editorial revision of Certificate dated 7-30-70) KUIcolafiildi.fr Rational ^Bureau of ureau of j^tattrfards Certificate of JVnalgsis Certificate of (Analysis Standard Reference Material U-200 Standard Reference Material U-100 Uranium Isotopic Standard Uranium laotopic Standard (Nominally 20% Enriched) (Nominally 10% Enriched) 2)i U 2)g U Atom Percent 0.1246 20013 02116 79.651 ±.0003 ±0020 ±0006 ±0021 2S5 U 2U U Weight Percent .1229 19811 .2103 79.856 Atom Percent 00676 10.190 0.0379 89 704 This Standard Reference Material (SRM) is certified for use as an isotopic standard. The primary intended use is for the 5" ±0002 ±0010 evaluation of mass discrimination effects encountered in the operation of a mass spectrometer. ±.0001 ±0010 Weight Percent .0666 10075 .0376 _£> The material consists of highly purified uranium oxide. UjOg The atomic weight of the material is calculated to be 89821 237 440. using the nuclidic masses 234.0409; 235.0439; 236 0457; and 238.0508 This Standard Reference Material (SRM) is certified for use as an isotopic standard. The primary intended use is for the -P- evaluation of mass discrimination effects encountered in the operation of a mass spectrometer. The values for 2)4,U and,216 U were calculated from measurements at the National Bureau of Standards. The samples were spiked with high-purity 2JJ U to approximate the 2)4 U concentration, the ratios 2JJ U to 2J4 U and J)J U to 2 *U were The material consists of highly purified uranium oxide, UjOg. The atomic weight of the material is calculated to be measured on a triple-filament equipped surface ioniiation mass spectrometer with d< amplifier circuits. 237 741. using the nuclidic masses 234.0409; 235.0439; 236.0457; and 238.0508. The values for " J U and 1J*ll were calculated from measurements made at the National Bureau of Standards, at Onion The values for "l J and "*JJ were calculated from measurements at the National Bureau of Standards. The samples were Carbide Nuclear Co.. Oak Ridge, Tenn., and at Goodyear Atomic Corp.. Portsmouth, Ohio, each laboratory's value spiked with high-purity U to approximate the 2J4 U concentration, the ratios 2JS U to 2M U and 2JJ l) to U were being given equal weight. Values obtained at NBS are the result of direct measurement of the U to U ratio using measured on a triple-filament equipped surface ionization mass spectrometer with d-c amplifier circuits triple filament thermal ionuation The observed ratios were corrected for mass discrimination effects by determining the The values for I) and I) were calculated from measurements made at the National Bureau of Standards ndlio' IS D system bias from measurements on standards U-500and U-IOO F.xperienceat NBS has shown, through intercomparison to U ratio. I lie observed ratios were corrected for mass discrimination effects by interconiparison with five synthetic of the standards, and synthetic mixtures at the 10-. 50-, and 90-percent 2J5 U level prepared from high-puritv U and mixtures at the 10-percent JJ5 U level prepared from high-purity 2S5 U and 2)gU. 2 Jg U isotopes, that a constant bias for a given procedure can be maintained over the range of 5- io95-percent U. Values from Union Carbide and Goodyear Atomic are based on direct determinations of the (I concentration by oxide The indicated uncertainties for the isotopic concentrations are at the 95-percent confidence level foi a single dilution and IIF6 analysis, and then the ratin calculated using the NBS values for 4 (l and U, and the U value deieirninaiion Ihe 2) I) to 2lgU ratio for this standard. O.I 1360, is known to at least O.I percent obtained by difference. Measurements leading to the certificalionof thisSRM werernadeby E. L.Garner.L. A. Machlan M S Kulimond and The indicated uncertainties for the isotopic concentrations are at the 95-percent confidence level for a single W. R Shields. determination. The 2S5 U to 2)g U taiio for this standard, 0.25126, is known to at least 0 I percent; at the same time the I lie technical and support aspects in the preparation, certification, and issuance of this Standard Kolerciuc M.itciiul pooled variance for the calibration system is significantly smaller. were coordinated through the Office of Standard Reference Materials by J. L. Hague. Measurements leading to the certification of this SRM were made by E. I..Garner, L. A Maclilan. M S Richmond, und NOTE: In many industries traceability of their quality control process to the national measurement system i* carnal out W. R. Shields. through the mechanisms of SRM's. It may be therefore of interest to know the details of the measurements made at NIIS The technical and support aspects in the preparation, certification, and issuance of this Standard Reference Material in arriving at the certified values of this SRM. An NBS Special Publication, 260-27, is reserved for this purpose and is were coordinated through the Office of Standuid Reference Materials by J. L. Hague. available from the NUS Office of Standard Reference Materials upon request. NO'IE: In many industries traceability of their quality control process to the national measurement system is carried out through the mechanisms of SRM's. It may be therefore of interest to know the details of the measurements made at NBS Washington. DC 20234 George A. Uriano. C'liicl in arriving at the certified values of this SRM. An NBS Special Publication, 260-27. is reserved for this purpose and is April 6. 1981 Office of Standard RefcienccM:itcriiils available from the NBS Office of Standard Reference Materials upon request. (Editorial revision of Certificate dated 7-30-70) Washington, DC. 20234 George A. Dnano, Chief April 6. I9KI (Mike ol Standard Reference Materials (iidunrial revision of Certificate dated 7-30-7(1) ^National ^Bureau of ^Bureau of Certificate Certificate Standard Reference Material U030a Standard Reference Material U-050 Uranium Isotopic Standard Uranium Isotopic Standard (Nominally 3.0% Enriched) (Nominally 6% Enriched) 2J4u Atom Percent 0.02778 30404 0.000599 969312 ±000006 ±00016 ±0000005 ±0.0016 Atom Percent 0.0279 5010 00480 94915 Weight Percent 002732 30032 0000594 96.9689 ±.0001 ±0005 ±0002 ±0005 ±0.00006 ±00016 ±0000005 ±0.0016 Weight Percent 0.0275 4.949 00476 94975 This Standard Reference Material (SRM) is certified for use asanisotopicstandard. The primary intended use is for the This Standard Reference Material (SRM) is certified for use as an isotopic standard The primat) intended use is for the evaluation of mass discrimination effects encountered in the operation of a mass spectrometer. evaluation of mass discrimination effects encountered in the operation of a mass spectrometer SRM U-030a is a highly purified uranium oxide. UjOj. which is certified for isotopic composition and I'/' II ratio. The material is a highly purified uranium oxide. UjOj. The atomic weight of the material is cakul.ued to be 237.898. I he atomic weiglii of the uranium is provided for informational purposes only and is calculated to be 237 958 using the using the nuclidic masses 234.0409; 2350439. 2360457. and 2380508 nuclidic masses 234 0409. 235.0439. 236.0456. and 238 0508 The values for U and U were calculated from measurements at the National Bureau of Standards The samples were The certified isotopic compositions are based on measurements made at the National Bureau of Standards using a spiked with high-purity >JU to approximate the 2)4 U concentration, the ratios 2U U to JI4 U and 2!) U to U were thermal ionizalion mass spectrometer equipped with a triple-filament ion source and Faraday cage collector. The measured on a triple-filament equipped surface ionization mass spectrometer with ion-multiplier amplifier circuits. ohserved isotopic ratios were corrected for mass discrimination effects by intercomparison wiih synthetic mixtures The values (ur Uand U wctc calculated from iiieastiiciiicnts of the II to II iaiioinailr.it the National llurcau piepiired fiom high-purity I) and U teparated isotopes, and blended to closely bracket the I)/ U ratio of of Standards on a triple-filament, surface ionization mass spectrometer equipped with d-c amplifier circuits. The theSKM The abundances of the minor isotopes. 4 |J and U, were determined by isotope dilution after spiking with observed ratios were corrected for mass discrimination effects by inlercomparison with synthetic mixtures prepared at 2) 'l) (SRM 995) to provide a 2)) U/ 2U U ratio that approximates unity. the 5 percent IJ1U level from high-purity 211 U and 2U U. Ihe uncertainly of (lie certified values for the U and U isotopic compositions is the95%confidence interval for the The indicated uncertainties for the isotopic concentrations arc at the 95-percent confidence level for a single mean and includes an estimate of possible sources of systematic error. For Ihe minor isotopes, U and U, the determination, and include allowances for inhomogeneities in the material as well as analytical error. The 211 U to U uncertainty is the 95% confidence interval for the mean and an additional bound on the systematic error associated with ratio for this standard, 0.05278, is known to at least O.I percent. the use of SRM's 960 and 995. Measurements leading to the certification of this SRM were made by I:. I. Garner and I. A Machlan. The m ll/ 2 "u ratio of this material is 0 031367 ±0.000017. The associated uncertainty is the 95%confideucc interval for the mean and includes an estimate of possible sources of systematic error. The relative standard deviation of the 1 he overall direction and coordination of the technical measurements leading to certification were performed under the 2 "|J/ 21I U ratio is calculated to be 0000234 with nine degrees of freedom. chairmanship of W. R. Shields Measurements leading to the certification of this SRM were made by J.W. Gramlich, LA Machlan, and J.K. Moody The technical and support aspects in the preparation, ceitifualion, and issuance of this Standard Reference Material of (he Inorganic Analytical Research Division. were coordinated through the Office of Standard Reference Materials by J. L. Hague. The statistical analyses were performed by W.S. l.iggelt of the Statistical Engineering Division. NOTE'. In many industries traceability of their quality control process to Ihe national measurement system is carried out through (he mechanisms of SR M's. It may be therefore of interest to know the details of the measurements made at NBS I tic overall direction and coordination of the technical measurements leading to certification were performed under in arriving at the certified values of.lhis SRM An NBS Special Publication. 260-27, is reserved for this purpose and is ilie chairmanship of I'-.L. Garner, Chief, Inorganic Analytical Research Division. available from the NI1S Olfice of Standard Reference Materials upon request. The technical and support aspects in the preparation, certification, and issuance of this Standard Reference Material were coordinated through the Office of Standard Reference Materials by T.E. Gills. Washington. D C. 20234 George A Uriano, Chief April 6. 1981 Office ol Standard Reference Materials March I. 1985 Siaolcy D Rasbeii>. Chief (Editorial revision of Gaitheisburg. Ml) 20899 Olfice of Slandaid Refeieme Materials Certificate dated 7-30-70) (Revision of Certificate dJled July 12. 1984) Rational ^Bureau of jitattrfarrb Rational ^Bureau of (tterttftcate Certificate Standard Reference Material U-020a Standard Reference Material U-015 Uranium Isotopic Standard Uranium Isotopic Standard (Nominally 2.0% Enriched) (Nominally 1.5% Enriched) 2J4 U 2J5 U 2J6 U J1I U Atom Percent 0.00850 1.5323 0.0164 98.443 Atom Percent 0.01732 2.0262 001179 979447 ±.00009 ±0.0015 ±.0001 ±0002 ±0.00003 ±00011 ±000007 ±00011 Weight Percent .00836 1.5132 .0163 98462 Weight Percent 001703 20011 001169 97.9702 This Standard Reference Material (SRM) is certified for use as an isotopic standard. The primary intended use is for the ±000003 ±00011 ±0.00007 ±00011 evaluation of mass discrimination effects encountered in the operation of a mass spectrometer. 1 his Standard Reference Material (SRM) is certified for use as an isotopic standard. The primary intended use is for the The material is a highly purified uranium oxide, UjO8. The atomic weight of the material is calculated to be 238 004, evaluation of mass discrimination effects encountered in the operation of a mass spectrometer. using the nuclidic masses 234.0409; 235.0439; 236.0457; and 238.0508. SRM U-020a is a highly purified uranium oxide, UiOi, which is certified for isotopic composition and U/ U ratio. The values for U and U were calculated from measurements at the National Bureau of Standards. The samples were The atomic weight of the uranium is provided for informational purposes only and is calculated 10 be 237.989 using tbe spiked with high-purity 2JJ U to approximate the 2J4U concentration, the ratios 2J3 U to 2J4U and 2JJU to 2 *U were nuclidic masses 234.0409. 235.0439. 236.0456, and 238.0508. measured on a triple-filament equipped surface ionization mass spectrometer with ion-multiplier amplifier circuits. The certified isotopic compositions arc based on measurements made at the National Bureau of Standards using a The values for 21i U and J *U were calculated from measurements of the 2JiU to 23*U ratio made at the National Bureau thermal ionualion mass spectrometer equipped with a triple-filament ion source and Faraday cage collector. The of Standards on a triple-filament, surface ionization mass spectrometer equipped with d-c amplifier circuits. The observed isotopic rilioi were corrected for mass discrimination effects by intercomparison with synthetic mixtures observed ratios were corrected for mass discrimination effects by intercomparison with synthetic mixtures prepared at prepared from high-purity U and U separated isotopes, and blended to closely bracket the U/ U ratio of the I 5 percent 2)5U level from high-purity 2J5U and 2 '*U. theSRM The abundances of the minor isotopes, 4 Uand 2 *U, were determined by isotope dilution after spiking with 111 111 5H " The indicated uncertainties for the isotopic concentrations are at the 95-percent confidence level for a single U (SRM 995) to provide a U/ U ratio that approximates unity. determination, and include allowances for inhomogencities in the material as well as analytical error. 'I he II to U The uncertainty of the certified values for the U and U isotopic compositions is t he 95% confidence interval for the ratio for this standard, 0.015565, is known to at least 0.1 percent. mean and includes an estimate of possible sources of systematic error. For the minor isotopes. U and U, the Measurements leading to the certification of this SRM were made by E. L. Garner, and I.. A. Machlan uncertainty is the 95% confidence interval for the mean and an additional bound on the systematic error associated with the use of SRM's 960 and 995. The overall direction and coordination of the technical measurements leading to certification were performed under the The U/ 2 '(I ratio of this material is 0.020687 ± 0.000011. The associated uncertainty is the 95% confidence interval chairmanship of W. R. Shields. for the mean and includes an estimate of possible sources of systematic error. The relative standard deviation of the The technical and support aspects in the preparation, certification, and issuance of this Standard Rcfricncc Material ni l)/ "(J lalio is calculated to be 0.000234 with nine degrees of freedom. were coordinated through die Office of Standard Reference Materials by J. I.. Hague. Measurements leading to the certification of this SRM were made by J.W. Gramlich. I..A MachUn. arid J R Moody NO I E. In many industries traceability of their quality control process to the national measurement system is carried out of the Inorganic Analytical Research Division. through the mechanisms of SRM's. It may be therefore of interest to know the details of the measurements made at NBS The statistical analyses were performed by W.S. I.iggett of the Statistical Engineering Division in arriving at the certified values of this SKM. An NBS Special Publication, 260-27. is reserved for this purpose and is available from the NBS Office of Standard Reference Materials upon request. The overall direction and coordination of the technical measurements leading to certification were performed under the chairmanship of E.L. Garner, Chief, Inorganic Analytical Research Division. Washington. I) C 20234 George A. Uriano, Chicl The technical and support aspects in the preparation, certification, and issuance of this Standard Reference Material April 6. 1981 Office of Standard Reference Materials were coordinated through the Office of Standard Reference Materials by I'.E. Gills. (Editorial revision of Certificate dated 7-30-70) Guiltiershurg. MI> 20899 Stanley D Rasherry, Chief March I. 1985 Office of Siandaid Reference Materials (Revision of Certificate dated July 12. 1984) Rational ^Bureau of J&tatttiards Rational ^Bnraw of J^tanrfarrb fflertificate (Eerttftcatfc Standard Reference Material U-010 Standard Reference Material (J-005a Uranium Isotopic Standard Uranium Isotopic Standard (Nominally 1% Enriched) 2J'lJ 215 U 2 "u Atom Percent 000340 0.5064 0.00118 99.4890 ±000001 ±00003 A loin Percent 0.00541 1.0037 000681 98984 ±000007 ±0.0003 ±.00005 10 0010 ±.00007 ±0001 Weight Percent 000334 05000 000117 994955 ±0.0003 Weigh! I'ercent 0.00532 09911 0.00675 98.997 ±0.00007 ±00003 ±000001 This Standard Reference Material (SRM) is certified for use as an isolopic standard The primary intended use is for Ihe I his Standard Reference Material (SRM) is certified for use as an isolopic standard. The primary intended use is for (he evaluation of mass discrimination effects encountered in (he operation of a mass spectrometer evaluation of mass discrimination effects encountered in (he operation of a mass spectrometer. The material is a highly purified uranium oxide, UjO|. The atomic weight of the material is calculated to be 238 020, SRM t)-005a is a highly purified uranium oxide, UjOi, which is certified for isolopic composition and I)/ U ratio. using the nuclidic masses 234.0409; 2350439. 236.0457, and 238 0508. 1 he atomic weight of the uranium is provided for informational purposes only and is calculated lo be 218 035 using the The values for *U and *U were calculated from measurements at (he National Bureau of Standards I he samples were nuchdic masses 2340409. 23S.0439. 236.0456. and 238 0508. spiked with high-purity 2JJl) to approximate the 2J4 U concentration, the ratios a)1 U to 214U and 211 U to U were The certified isolopic compositions arc based on measurements made al the National Bureau of Standards using a mcasuicd on a triple-filament equipped surface iomzalion mass spectrometer with ion-multiplier amplifier circuits. thermal ioni/adon mass spectrometer equipped with a triple-filament ion source and Faraday cage collector. The observed isolopic ratios were corrected for mass discrimination effects by inlercomparison with synthetic mixtures The values for J15U and 2Jll) were calculated from measurements of the 2)SU to 2UU ratio made at ihe National Bureau 2)5 2)8 2 J5 2)8 of Standards on triple-filament, surface ioni/ation mass spectrometer equipped with d-c amplifier circuits. The prepared from high-purity U and U separated isotopes, and blended to closely bracket (he U/ U ratio of (he SRM 1 he abundances of the minor isotopes, U and U, were determined by isotope dilution after spiking with observed ratios were corrected for mass discrimination effects by inlercomparison with synthetic mixtures prepared at 311 }M 7II rr the 1 percent U level from high-purity U and ' U. n 'l) (SRM 995) 10 provide a 2)1 U/ 2U U ratio that approximates unity. Ihe indicated uncertainties for Ihe isolopic concentrations are at the 95-percent confidence limits for a single I he uncertainly of (lie certified values for Ihe *U and "u isolopic compositions is Ihe95%confidence interval for the determination, and include allowances for inhomogencities in the material as well as analytical error. The 2UU lo 2) U mean and includes an estimate of possible sources of systematic error. For Ihe minor isotopes, U and U, Ihe ratio for this standard, 0.010140. is known lo ai least O.I percent. uncertainly is the 95% confidence interval for the mean and an additional bound on the systematic error associated with the use of SRM's 960 and 995 Measurements leading lo (he certification of this SRM were made by E. I.. Garner and I. A M.iclilan 'I lie m U/ m ll ratio of this material is 0 0050899 ±00000027. The associated uncertainly is the 95%confidcnce interval The overall direction and coordinalion of the technical measuremenis leading lo certification were performed under Ihe foi the mean and includes an estimate of possible sources of systematic error. The relative standard dcviaiinn of the chairmanship of W. R. Shields. U/ II laiio is calculated lo be 00002)4 with nine degrees of freedom. The technical and support aspects in the preparation, certification, and issuance of this Stand.in) Kdcrciuc Mini-rial Measurements leading lo ihe certification of this SRM were made by J W. Gramlich, I..A Machlan. and I R Moody were coordinated through Ihe Office of Standard Reference Materials by J. I.. Hague of i lie Inorganic Analytical Research Division. NO'I E: In many industries traccability of their quality control process to (he national measurement system is carried out Ihe statistical analyses were performed by W.S. l.iggell of Ihe Statistical Engineering Division. through Ihe mechanisms of SRM's. It maybe therefore of interest lo know the details of Ihe measurements made ai NBS Ihe overall direction and coordinalion of the technical measuremenis leading to certification were performed under in arriving ut the certified values of this SRM. An NBS Special Publication, 260-27. is reserved for this purpose and is the chairmanship of I: I Garner. Chief, Inorganic Analytical Research Division. ' available ft inn the NBS Office of Standard Reference Materials upon lequcst I he technical aixl support aspects in Ihe preparation, certification, and issuance of this Standard Refeicnce Material were coordinated through the Office of Standard Reference Materials by T.E. Gills. Washington. D.C. 20234 George A. llriano. Chief April 6, 1981 Office of Standard Reference Materials (Editurial revision of March I, 1985 Stanley D. Rasberry. Chief Certificate dated 7-30-70) Gailhersburg. MD 20899 Office of Standard Reference Materials (Revision of Certificate dalcd July 12. 1984) I/ tl S IkiuumiNiil | ,» .: N^laMol lul.li.(< ureau of (Eertificate of Standard Reference Material LJ-0002 Uranium Isotopic Standard (Nominally depleted to 0.02%) Atom Percent 0(KK)I6 001755 vOIXXNll 999823 ±.00001 ±(KKX)5 ±0.0001 Weight Percent .00016 01733 < 00001 999825 This Standard Reference Material (SRM) is certified for use as an isuiupic standard. The primary intended use is for the evaluation of mass discrimination effects encountered in the operation of a mass spectrometer. 1 he material is a highly purified uranium oxide. IMV The atomic weight of the material is calculated to be 238.0503 using the nuclidic masses 234 0409; 2.35 04)9, and 23H 050K the \aluc for 2I U is calculated from measurements made on samples spiked wnh high-purity " n (J to approximate the 1) concentration, the ratio 2>> U to 215 U was measured on a triple-filament equipped thermal ionizalion mass spectrometer with d-c amplifier circuits. Ratio determinations were corrected for mass discrimination by measurements made under similar conditions on SRM U-SOO. I lie value for II is caluiluted from measurements miide on samples spiked with high pmiiy 1 1, (lie ratio llto U was measured on a two stage mass spectrometer using a pulse counting technique. '[ he indicated uncertainties are al the 95 percent confidence level for a single determination, and include allowances for the inliomogcneities of the material as well as analytical error. Measurements leading in the certification of this SRM were made by E I. Garner, I.. A. Machlan, and I.. .1. Moore. I lie overall direction a ml coordination ol (he technical nic.ismcmciils leading loccilifk.il inn ucie performed under the chairmanship of W. R. Shields. 'I he technical and support aspects in the preparation, certification, and issuance of this Standard Reference Material were coordinated through the Office of Standard Reference Materials hy J. I, Hague NO! E; In many industries traceability of I heir quality control process to the national measurement system is carried out through the mechanisms of SRM's. It may be therefore of interest to know the details of the measurements madeal NBS in arriving al the certified values of this SRM. An NIIS Special Publication, 260-27.is rescivcil for this purpose and is available from the NIIS Office of Standard Reference Materials upon request Washington, DC. 20234 George A Uriano, Chief April 6, 1981 Office of Standard Reference Materials (riditorial revision of Certificate dated 7-30-70) Commission ol Hit) ( mopc.in Coniinnniims JOINT Goel Establishment Omul Burtju lor Nuclear Measurements RESEARCH Sltemieg op H. lie 2440 Gcel. Belgium CFNTRE Tel (Oil) S'1.211 Irlr. 3JiB9 UtriAT 8 IclrCa, 014/SI 12.73 Holes 1. All uncertainties Indicated arc accuracies, computed on a 2s basis. Isotoplc Reference Material CBNM IRM 072/1-15 2. The atomic masses, used In the calculations, are : 23311 : 233.039 628 0 ± 0.000 006 0 Uranium Isotoplc Reference Material for Testing Isotope Mass Spectrometers 234u : 334.040 946 8 ± 0.000 004 8 ?35u : 235.043 924 2 ± 0.000 004 8 236u : 236.045 562 7 t 0.000 004 6 The IRM set Is supplied with atomic 1sotop« ratios certified as ; 23Bu : 238.050 784 7 i 0.000 004 6 3. Ihe Reference Material consists of a uranyl nitrate solution. Ihe amount or U pur unit Is 1.00 t 0.02 rag contained In a 1.00 ± 0.0? ml solution. 4. The IRM solution has a molality of 6 m HNO? (I.e. 6 mol IIN03 kg-l of Coda Atonic Isotope ratios solvent) or a molarity of 5 H HH03 (I.P. 5 mol HN03 l-l of solution). number CBW- 2330/23S(J 233U/238|J 235U/23B[J Chemical purification of the 233U30R. 235IJ30a and 23flu30fl starting materials was performed by Hilly lycke. Preparation of the IRM itt was performed by (V- 0.03% of. value) (l/- 0.03» of value) (I/- 0.000 20) Crans llendrlckx and Hilly Lycka. Characterisation of the enriched Isotopes from which the set was prepared, was performed by Rene Uamen and Kevin Rosman. Verification measurements on the mass spectrometer weru done by Rune Oamen. 072/1 1.000 33 0.991 36 0.991 03 The overall technical coordination of the establishment of the 1RH set was 0/2/2 0.699 67 0.693 OS 0.991 68 performed by Hilly Lycke. 0/2/3 0.499 85 0.49$ 91 0.992 12 ID 072/4 0.299 87 0.297 63 0.992 56 072/5 0.100 OH 0.099 313 0.992 99 -D 072/6 O.OSO 091 0.049 746 0.993 10 B-2440 Guel Paul Oe Blevre 072/7 0.019 994 0.019 857 0.993 17 September 1986 Head 072/8 0.010 165 0.010 095 0.993 19 CBNM Mass Spectrometry 072/9 0.005 000 0 0.004 966 0 0.993 20 072/10 0.002 001 2 0.001 987 6 0.993 21 072/11 0.000 968 92 0.000 9G2 34 0.993 21 072/12 0.000 500 88 0.000 497 48 0.993 21 072/13 0.000 101 B2 0.000 101 13 0.993 21 072/14 0.000 019 996 0.000 0)9 860 0.993 21 072/15 0.000 001 999 S 0.000 001 985 9 0.993 21 Tho IRM Set Is Intended to verify and correct non-linearity of the entire mass spectrometer measurement system. Commission ol (ha European Communities Ceel Establishment JOINT 3. The relative atomic masses, used in the calculations, are fxiiilr.il Bureau lur Nuclear Meaatireiiienls RESEARCH Sleei.weu op Relic. 2*40 Gerl.'Svlijium CENTRE Tel. (OMl 571.211 - Trlrx 33589 EOflAT B M\\ P14.040 946 0 i 0.000 004 8 235U ?3S.043 924 2 ± 0.000 004 B , CERUFICAIE 236U 236.045 562 7 t 0.000 004 0 238U 238.050 784 7 t 0.000 004 G ISOTOPIC REFERENCE MAIERIAL CBNH IHM 0?1 1. Ihis certificate announcns better values and reduced uncertainties coiupurvd to the previous certificate (dated 1 September 1984) for the sanw material. Die IRM Is supplied with an atomic isotope ratio certified as 2351J/238U = 0 004 403 6 1 0.000 002 2 Mass spectromutry measurements were performed by W. Oe Bolle (235u/238u by UFfi) and M. Gallct (IhlMS) on solutions prepared by J. flroothoerls. Utlier uranium isotopes present are related to the 235l> isotope abundance through the following atomic isotope ratios : ?3«U/235u * 0.005 61 1 0.000 4$ | 0-2440 crn Paul Ot SItVRf 236y/235u < 0.000 ? 15 June 1988 Head, CBNH Mass Spectrometry O I Mi corresponds to an Isotoplc compos! tinn with following abundances : 0 Isotoplc atom X Isotopic mass X Uncertainty 0.002 46 0.002 42 t (1.000 ilU 235U 0.438 42 0.432 91 t (1 DUO 21 236 ' 0.000 10 < 0.000 10 238, 99.559 12 99.564 67 t o.nuo 30 lit of the uranium Is 238.0.17 fi(U 0.000 010 NOUS I I- All uncertainties indicated are accuracies, computed on a ?s basis. I 2. The material consists of purified III 6 and is supplied 1n muricl jmpouli^s with about ?0 q of material per ampoule. Commission o( Ihu li if ope an Communities did Establishment JOINT 3. the relative atomic masses, used in the calr.ulai ions, are Ccntitl Bureau (or Unclear Measurements RESEARCH Sleenweg op Nenc. 2«40 Ucel Hrlgiom CENTRE Tel. (OMIJ7I.2I1 - Iclci 33589 fUHAT B ?34U 231.0<10 946 B » 0.000 004 b 235U 235.043 924 2 i O.noO 004 B CFRTiriCAlE 236U 236.015 562 7 t 0.000 004 6 23flU 218.050 784 7 + 0.000 004 6 ISOrOPIC REfERENCf MA1ERIAI CONM 1KM-022 4. This cert if Irate announces better values and reduced uncertainties comp.ired to the previous certificate (dated 1 September 1984) tor the same material. Ihe IRM is supplied with an atomic isotope r.itio certified as 235U/236U =0.007253510.0000036 Mass spectrompfry measurements were performed by U. De Bo He (235u/2JUu by and M. "Gal let (ThIHS) on solutions prepared by J. Broothaerts. Other uranium isotopes present are relatrri to the 23iu isotope abundance through the following atomic Isotope ratios : ' 234n/235u = O.nO/ 32 i 0.000 41 B 2440 GfIL Paul DC QIEVRE ?36u/235u < 0.000 1 IS June I960 Head, I'BNM Mass Spectrometry Ihls Corresponds to an isotopic composition with following abundances : I O Isotopic atom X fsotopic mass X Uncertainty 0.005 27 0.005 IB 1 0.000 30 0.720 09 0.7)1 06 1 0.000 36 < 0.000 10 < 0.000 10 - 99.274 61 99.203 /6 I 0.000 47 |ht of the uranium Is 236.026 921 £ 0.000 016 NOTFS 1. All Uncertainties Indicated arc accuracies, computed on a 2s basis. 2. The dirttcri.il consists of purified Uffi and is supplied in mone I The IRH Is supplied with an atomic Isotope ratio certified as 235U/238U = 0.033 863 ± 0.000 017 Mass spectrornetry measurements were performed by W. De Bulle (?Jt>u/?38u by and M. Gal let (ThIMS) on solutions prepared by J. Uroothaerts. Other uranium Isotopes present are related to the 235u isotope abundance through the following atomic isotope ratios : i 8-2140 CEEL Paul DE RTEVRf 231u/235u - 0.010 01 i 0.000 21 15 June 1988 236u/235u < Q.QOO 03 Head, CBNM Mass S|iectroinetr> This corresponds to an Isotopic composiI ion with following abundances : Ibolopic atom X Isotopic mass * Uncertainty 234y 0.032 8 0.032 2 i 0.000 7 3.274 3 3.234 3 i 0.001 6 < 0.000 I < 0.000 1 23B 96.69? 9 96.733 5 i 0.001 7 The atomic weight of the uranium is 237.951 016 i 0.000 055 MOIES I. All uncertainties indicated are accuracies, computed on a ?s basis. ?. The material consists of purified lltfc and 1s supplied In monel ampoules with about 20 9 of material per ampoule. Commission of the I urnpitan Communities Gee) Establishment JOINT 3. The relative atonic masses, used In the calculations, are Central Buretu for Nucleir Mtlsurcmenfi RESEARCH blecnweg op Bella. 2440 Gttl. Belgium CENTRE Icl (0141 i? I ill Telex 33M9 tUflAT B 234U 234.040 946 B 1 0.000 004 8 235U 235.043 924 2 ± 0.000 004 0 CERTIFICATE 236U 236.045 i62 7 t 0.000 004 6 238U 238.050 784 7 1 0.000 004 6 1SOTOPIC REFERENCE MATERIAL CBHH IRM 023A 4. This certificate announces better values and reduced uncertainties compart> The IRH is supplied with an atomic Isotope ratio certified as 23SU/238U = 0.0338821 0.000017 Mass spectrumotry measurements were performed by H. Ue Do lie by and M. Gallet (ThIMS) on solutions prepared by J. Bronthaerts. Other uranium isotopes present are related to the 235u isotope abundance ttjrough tlic following atomic Isotope ratios : B 2440 GtEI. ?14u/?35u = D.010 07 t 0.000 21 Paul DP BlfVHl 15 June 1988 ?3fiU/?35|j < o.OOO 03 Head. CBNH Mass Spectrometry This corresponds to dn Isotopic compos it ion with following abundance : I Isotopic atom X Isolopic radSb t UncLTldinty 0.033 0 0.032 4 t 0.000 7 235 3.276 1 3.236 1 £ 0.001 6 236,j 0.000 1 < 0.000 1 96.690 9 96.731 S ± 0.001 7 it of the uranium is 237.950 955 1 0.000 055 NOTES I 1. All uncertainties indicated are accuracies, computed on d 2b basis. 2. The material consists of purified UF& and is supplied in monel ampoules with about 20 g of material per ampoule. Commission of Ih* European Communltiw JOINT Geal Establishment 3. The relative atomic masses, used in the calculations, arc RESEARCH Central Bureau lor Nucleir Measurements CENTRE Sleenwry op Heile. 2440 Geal. Belgium lol |OM) S?| .2) t - Ultx 33519 EUflAT B 234U ?34.040 946 B t 0.000 004 8 , 235U 235.043 924 2 t 0.000 004 fl CERTIFICATE 236U 236.045 562 7 t 0.000 004 6 23BU 23B.050 784 7 i 0.000 004 6 ISOTOPIC RCftRENCE MATERIAL CUNM IRM 024 4. This certificate announces better values and reduced uncertainties compared to the previous certificate (dated 1 September 1984) for the same material. The IKM is supplied with an atomic isotope ratio certified 235U/238U =0.05323510.000027 Mass spectrometry measurements were performed by W. Oe Bolle (235u/238u by Ur-(,) and M. Gal-let (ThlMS) on solutions prepared by J. Broothacrts. I Other uranium Isotopes present are related lu the ?35u isotope abundance through Ihe following atomic isotope ratios : I 234u/235y » 0.005 45 t 0.000 16 B-2440 GE£L Paul DE 81EVRF 236U/235U . 0.009 70 ± 0.000 10 15 June 1088 Head, CBNM Mass Spectrometry This corresponds to an isotopic composition with following abundances : Isntopic atom % (sotopic mass % Uncertainty | ?34,j 0.027 5 0.027 1 235,, ± o.ono a 5.050 6 4.990 0 £ 0.002 4 236o^cU 0.049 0 0.048 6 ?3BU 1 0.000 9 94.872 9 94.934 3 t 0.002 7 Ihp atomic weight of the uranium Is 237.B96 835 0.000 002 NOUS 1. All uncertainties indicated are accuracies, computed on a 2s has is. I 2. The material consists of purified Ul 5 and is supplied in monel ampoules with about ?0 g of material per ampoule. i nl ill* Euioiieaii Communities Geel Lstablishiiicnt JOINT Ccmril Bureau for Hudoi Measurements RESEARCH Stecnwcg op Rctu 2»<0 Cccl Belgium Id (U|4| 5/1 in TC>«« 33«S EUHAI B From the certified values, the following element concentrations arc derived CENTRE l«lda» 014/581? 7J UKMFICATC (9.386 7 t 0.017) 10-1 kg 233u kg"' of solution (9.576 t 0.017) ISOTOP1C RFFFRF.NCE HATERIAI CBNM lRM-040a ID'4 kg U kg~* of solution (4.109 2 I 0.007 2) 10'3 no I U leg"* of solution The IRM is supplied with a molar concentration of 233U rpr ufi c(j to be NOILS -3 233 -1 , (4.0278 ± 0.0072)-10 mol U kg of solution 1. All uncertainties Indicated are accuracies, computed on a 2s basis, taking into account both measurement reproducibi1 Ities and uncertainties of systematic nature estimated on a 2s basis. > Other uranium isotopes present are related to the concentration through the following certified molar ratios : 2. The IRM solution has a molallty of 6 m IINOj (i.e. 6 mol IINOs kg-1 of solvent) or a molarlty of 5 M HNOj (I.e. 5 mol HN03 L-l of solution). I 234U/233U . 0. 009 328 t 0 .000 002 0 3. The Avogadro constant used Is (6.022 136 t 0.000 012) 1023 mol 1. 235U7233y . 0. 002 165 t 0 .000 056 236lj/233y . 0.000 246 ± 0.000 003 0 4 The atomic masses, used In the calculations, are 238UX2330 . o.ooa ?02 t 0.000 020 233U 233.039 629 3 t 0.000 007 1 234U 234.040 947 4 t 0.000 005 1 | 235U 235.043 92b 2 I 0.000 OOij 1 236U 236.045 562 9 ± 0.000 004 9 Tins corresponds to an isotopic composition with following abundances : 238U 238.050 785 8 t 0.000 004 7 Hole X Mass X Uncertainty 7. Using this Spike IRM, 2 0 concentrations in unknown samples cun be determined by Isotope Dilution Mass Spectrometry, through a measurement of 233.J 90.042 9 98.020 1 t 0.005 9 the atomic Isotope dilution ratio Ra - 233U/235U in the blend. Ihey should 234U 0.914 6 , 0.918 3 t 0.000 2 be computed with the aid of the following formula which allows >tn e«tsy 235y U.2I4 2 0.216 0 t 0.005 5 identification of the sources of the uncertainties in the procedure : 236U 0.024 1 O.U24 4 i 0.000 3 23BU 0.801 2 0.8/1 2 t 0.002 0 « -« i m.. R -R The atomic weight of the uranium Is 233.094 10 t 0.000 15 c((0 whore K.Y Isotope abundance ratio 233U/23^U In the unknown sample iiwlerldl molar Isntope abundance ratio 233ll/23^ll in the spike mass of the unknown sample mass of the sample of spike solution used , number of moles ^^5U kg'* sample material number of moles ^3(j kg'' spike solution riumher of nules U kg"* sample material c(U)r " numbnr of moles U kg"* spike solution. ihe Isotopic measurements by Thermal lunisalion Mass Spectrometry were performed by A. Alonso-Muricu and K. Hayer. Chemical preparation of the samples for Isotopic measurements was performed hy A, Verbruggcn. Metrological aspects Involved in the preparation and certification were performed by T. Hendrickx. The ampoulation of this 1KH was accomplished by A. Verbruggen and A. Alonso Huhoz. Ihe preparation of this IRH was coordinated by A. Verbruggcn. ' The overall coordination leading to the establishment, certification and Issuance of this IRM, was performed by K. Mayer. OJ B 2440 Geel Paul OE BIEVRE July 1991 Head CBNM Mass Spectrometry This IRH replaces IRH-040/1 (exhausted) Commission of llu> I iirnpean Communities JOINT Goal Establishment Central Bureau lor Nueleii Melsuremftius From the certified molar concentration, following element concentrations are RESEARCH Siccnwcg op lletie 2*4(1 Orrl 8-lginm Id. IOMI 571211 - Irlrx .ITiW FURAT 8 derived : CENTRE Telr!.i< ni4/'iA42 7] (4.256 8 ± 0.001 1) 10-6 mole (U) kg-1 (solution) ISOTOPIC REFERENCt MAFFRIAl CBNH IRH 050 (1.000 55 ± 0.000 25) 1Q-6 kg (U) kg-1 (solution) MOILS The IRM is supplied with a 235U atomic isotope concentration certified as 1. All uncertainties Indicated are accuracies, computed on a 2s basis. (2.562 03 ± 0.000 65) 10 18n (atoms 235U) kg' 1 (solution) 2. The IRM solution has a molality of 6 m HN03 (i.e. 6 mol HN03 kg-1 of solvent) or a molarity of 5 M HHOj (i.e. 5 mol HN03 1-1 of solution). From the certified isotope concentration, following concentrations are derived : 3. The Avotjddro Constant used Is (6.022 134 t 0.000 012) 10^3 rooH. (4.254 3 4 0.001 1) 10-6 mole (235u) kg-1 (solution) ' (9.999 6 1 0.002 5) 10-7 kg (235u) kg-1 (solution) 4. The atomic masses, used In the calculations, ore | 'Other uranium isotopes present are related to the 235U molar concentration through 234u : 234.040 946 8 t 0.000 004 8 u the following moldr ratios : I 235u : 235.043 924 2 t 0.000 004 8 u 236(j : 236.045 562 7 t 0.000 004 6 u 234u/235u : 0.000 360 9 t 0.000 005 2 I 238u : 238.050 784 7 i 0.000 004 6 u 236u/235u : 0.000 095 i 0.000 010 238u/235u : Q.OOO 129 6 t 0.000 003 0 5. Using this Spike IRM, 238U concentrations In unknown samples can be determined by Isotope Dilution Mass Spectrometry, through a measurement of the molar dilution ratio RB = 235u/238u 1n the blend. They should be Ihis corresponds to an Isotopic composition with following abundances computed with the aid of the following formula which readily Identifies the sources of uncertainty In the procedure : mole X mass X c - -**'*' ?34u/u 0.036 I 0.035 9 t 0.000 5 " 235U/U 99.941 4 99.941 4 ± 0.001 8 236u/U 0.009 5 0.009 6 t 0.001 0 where 238U/U 0.013 0 0.013 1 t 0.01X1 3 molar ratio 235u/238u in the unknown sample material RY molar ratio 235u/238u In the spike material MX mass of the unknown sample The atomic weight of the uranium is 235.044 047 + 0.000 014 MY mass of the sample of spike solution used C238 number of atoms 238u kg-1 sample material % C23S number of atoms Z35u . kg-1 spike solution. 6. Chemical preparation and ampouldtfon of this IRH were accomplished by Willy Lycke, Ado 1 To Alonso-Muno/ and Andre Vcrbruggen. The isolopic measurements were carried out by R. Oamen on samples chemically prepared by Andre Verbruggen. i Metrologlral weighings required In the preparation and certification wen: performed by Frans Hendrickx. The overall coordination of the procedures leading to the certification and Issuing of this IKM was performed by Andre Verbruggen. B-2440 Gee) Paul OE BIEVRE June 1990 Head C0NH Mass Spectrometry Oo O 00 Cnniniisslon of Ihe tnropeaii CommuiiiliBS Ciccl txliihlishment JOINT Central Bureau tor Nurleai Meaiurcmenll 4. Ihe Avogadro number used Is (6.022 136 9 ± O.UOO OU/ ?} 1U23. RESEARCH Sieenwrg oo Htlir. 7440 Getf. Belgium Tel. |OM| s,l 2i( - |rl«x 33589 fUHAT 0 CENTRE M*f»« OI4/5M273 5. I ho relative atomic masses, used In the calculations, am CERT1I ICAIF 233u 233.039 628 0 ± 0.000 006 0 234u 234.040 946 8 t 0.000 004 fl ISOTOPIC RtFfRENCF MATCRIAI CUNM IRM 183 235u 235.043 9?4 2 i 0.000 004 8 236u 236.045 562 7 ± 0.000 004 6 ?38u 238.050 784 7 1 0.000 004 6 Ihn IRM is supplied with with atomic isotope ratios cerlifjprt as 6. Ihe Reference Material consists of a uranyl nitrate solution. The .imounr uf Z3Ji//Z38u < 0.000 000 1 uranium per unit 1s 1 g. 234u/238u _ 0.000 020 2 t 0.000 001 2 Chemical preparation and ampoulatlon of this IKM were acrompli'Ju-,1 by Willy Lyc.ke 23b|j/Z38u - 0.003 215 7 i 0.000 001 6 and Andre Verbruggen. ZJ6u/238u * 0.000 14fi 5 t 0.000 008 6 The isotnplc measurements were carried out by Willy Ue Bolle (23!)U/238u dbunrt^ncc ratio by Ufg mass spnctronetry) and Rpne Oamen (all abundance ratios by thermionic mass spectrometry) on samples chemically prepared hy Willy Lycke. , Hetrological weighing required in the preparation was performed by (Vans - This corresponds to an Isotopic composition with following abundances : Mcndrickx. The overall coordlnntion of the technical work leading lo the certification and Isuioplc atom Isotopic mass Issuance of this IRM was performed by Willy Lycke. v^- ~ 233u < 0.000 01 < 0.000 01 o 23<1u 0.002 01 0.001 98 ± 0.000 12 -o 235u 0.320 49 0.316 15 1 0.000 16 8-2110 Gee) Paul UE RltVRC 1 December 19B7 Head 236u 0.014 60 0.014 48 i 0.000 86 C8NM Mass Spci:lromctry 23Bu 99.662 90 99.667 09 i 0.000 68 Ihe atomic weight of the uranium is 238.010 7/!» » 0.000 OI8 HO ITS 1. All uncertainties indicated are accuracies, computrd on a 2s basis. 2. Values for Isotope ratios, isotopic compositions and for Conccnl rat ions ar± valid for 1985.10.10. 3. Ihe IRM solution has a molallty or 6 m HNOj (I.e. 6 mo I IIN03 kq-1 of solveot) or a molarity of 5 M IIN03 (i.e. 5 mol IIMOj 1 1 of solution). REPRODUCED FROM BEST AVAILABLE COPY * go P» i liiS V g.,0 T 1 CJ 4^ 4 U1 ui 10 o S O CM O o o o o o o a o V II « H O M <7i O 3333 o 01 ">CO «nCO mCO mCO 25 r» rj rvj eg eg o c o o ^ c 31 **3 > ^-=> in3 to3 CD= rr ro m r*> rn a» ^- (Xl 233u 233.039 628 0 * 0.000 006 0 CERIIFICAIC 234u 234.040 916 B t 0.000 004 8 ?35u 235.043 924 2 t 0.000 004 8 ISOTOPIC REPtRFNCE MA If RIAL CHNH-IRH 185 236|| 236.045 562 7 1 0.000 004 6 238|j 238.050 7B4 7 t 0.000 004 6 The IRM is supplied with with atomic Isotope ratios certified as 6. The Reference Material consists of a nranyl nitrate solution. The amount of uranium per unit Is 1 g. 233o/238u < 0.000 000 1 Chemical preparation and anpoulatlnn of this IRM were accomplished by Willy lycke 234u/23Bu - 0.000 176 t 0.000 010 and Andre Verbruygon. 235u/23flu «= 0.020 055 2 t 0.000 006 0 Ihe Isotopic measurements were carried out by Willy Ue Bollc (235u/23ilu abundance 236u/238i| , 0.000 002 86 t 0.000 000 5J ratio by UP6 mass spectromctry) and Renc Oamen (all abundance ratios by thermionic mass spectrometry) on samples chemically prepared by Hilly Lyckn. Metrological weighing required In the preparation and certification *ws performed Ihis corresponds l.o an Isotopic composition with following abundances hy Frans llemlrickx. The Overall coordination of the technical work leading to the certification and i Isutopic atom X Isotopic mass X issuance of this IRM was performed by Hilly lycke. 233jj , < 0.000 01 < 0.000 01 234u 0.017 25 0.016 97 1 0.000 90 235u 1.965 75 1.911 40 t 0.000 58 8-2440 Gee I Paul I)F BICVKE ; 1 December 19B7 Head 236» 0.000 28 0.000 78 t 0.000 Ob CBNN Mass Spectrometry 238u 98.016 72 98.041 35 i 0.001 12 The atomic weight of Ihe uranium Is 237.990 980 f 0.000 042 NOUS 1. All uncertainties indicated .ire accuracies, computed on a 2s basis. ?. Values for isotope ratios, Isotopic compositions and for concentrations are valid for 1985.10.10. 1. Ihe IRM solution has a mnlality of 6 m HNOj (I.e. 6 mol HNOj kg-1 of solvent) or a molarity of 5 M IIMOj (I.e. 5 mol UNO.} 1-1 of solution). Commission ol (he (iiiti|ioan Communities Oeel Establishment JOINT Central Bitrou lor Nucltti Meijurtmrnls 4. The Avogadro numher used Is (6.022 136 9 ± 0.000 OO/ 2) I0?1. Siecimra Op Rrli*. 2440 Geel. B«l CtRIIMCATE 233u 233.039 628 0 t 0.000 006 0 234(j 234.010 946 8 ± 0.000 004 B ISOTOPIC REfCRCNCE NAIEKIAL CRNH I KM-186 23Su 235.043 924 2 t 0.000 004 8 236(j 236.045 562 7 t 0.000 004 6 238|J 238.050 784 7 f 0.000 004 6 The IRM Is supplied wllh with atonic Isninpe ratios certified as 6. The Reference Material consists of a uranyl nitrate solution. The amount of 233u/238u < 0.000 000 1 uranium per unit Is 1 g. 231u/238u . o.OOO 289 t 0.000 016 Chemir.aJ preparation and ampoulatlon of this IRM were accomplished by Willy lycke 235u/238|) = 0.030 771 1 i 0.000 009 2 and Andre Verbruggen. 236u/238u . o.OOO 033 6 > 0.000 002 4 The isutopic measurements were carried out by Willy f)e 80He (235u/238u abundance ratio by (If6 mass spectrometry) and Rene (Jamen (all abundance ratios by thermionic mass spectrometry) on samples chemically prepared by Willy Lycke. | Hetrolngical weighing required in the preparation was performed' by l-rdns Ihis corresponds to an tsotoplc composition with following abundances : Hendrlckx. The overall coordination of the technical work leading to the certification jnd Isotoplc atom % Ho topic mass Issuance of tins IRM was performed by Willy Lycke. OJ 233u < 0.000 01 < 0.000 01 234U 0.028 03 0.027 57 > 0.001 55 B 2440 Gnel 235(j 2.984 32 2.947 75 * 0.000 B7 Paul DE BlfVRt 1 December 1987 Head 236(j 0.003 26 0.003 23 i 0.000 23 CRNM Mass Spectrometry ?3Bu 96.984 39 97.021 45 t 0.001 /b The atomic weight of the uranium Is 237.959 861 t 0.000 066 NOIES I. All uncertainties Indicated are accuracies, computed on a 2s ha&is. ?. Values for isotope ratios, Isotoplc compositions and for concentrations ure valid for 1985.10.10. 3. (he iKM solution has a motahty ol 6 m 111103 (i.e. 6 mol HHOj kg 1 of solvent) or a mol.irily of 5 M HH03 (i.e. b owl IIN0.1 1-1 of solution). Ct.iniiur.r.inn ol Hie luropean Commiiniiies (icitl Fbtablisliinent JOINT Central Bureau lor Nuclear M*Muremenls 4. The Avogadro number used is (6.U22 136 9 1 O.OUO Oil/ 2) 10^3. Sieenwcg op Rciin )4tn O*l. Delqmm RESEARCH l«l IOUI ill 211 . lrlr« :ny» CUflAI U CENTRE 5. ihi> ri:lrtlive dtnmic masses, used in the calculations, ars CFR1IHCATE 233u 233.039 620 0 i 0.000 006 0 23<1u 234.040 946 8 i 0.000 004 8 ISOTOMf. REHRtNCE MAFCRIAI fflNH-IHH 18/ ?3!>U 235.013 921 7 « 0.000 004 8 236u 236.045 562 7 t 0.000 004 6 238u 238.050 784 I ± 0.000 004 6 The IRH is supplied with with atomic isotope ratios certified as 6. .The Reference Material consists of a uranyl nitrate solution. The amount of uranium per unit Is 1 g. | 233u/23Uu < 0.000 000 1 ?34u/230u 0.000 38 1 0.000 02 Chemical preparation and ampoulation of this IRM WHTP acinmpl ivheil by willy tyckt 235u/238y 0.047 32b t 0.000 014 and Andrn Verhruggen. 236u/23flu - o.OOO 072 t 0.000 004 The Isotopic measurements were carried out by Willy lie Bulk (235u/238|| ubund.ince ratio by u>6 moss spectrometry) and Rene Damen (all abundance ratios by thermionic mass spectrometry) on samples chemically prepared by Willy Lyckc. Metrologicdl weighing required In the preparation was performed hy I rank This corresponds r.o an Isotoplc composition with following abundances : Hfindrickx. The overall conrrtination or the technical work leading to the certification and Isotoplc atom X Isotnpic iiuss X issuance of this IKM was performed by Willy Lycke. ?33n < 0.000 01 < O.UOO 01 OJ 234u 0.036 2/ 0.035 60 > 0.001 91 235u 4.516 /O 4.462 23 t 0.001 20 Paul UE BltVRF B-2440 Geel 236|j 0.006 87 0.006 B? i 0.000 38 Head UJ 1 December 198/ CBNM Mass SjJRc.lromel ry 238n 95.440 16 95.495 ?7 t 0.002 25 Ihe atomic weight of the uranium is 237.913 382 i 0.000 084 NO ItS 1. All' unr.ei Uinties Indicated are accuracies, computed on a 2s basis. 2. Valuer fur isotope ratios, isotopic rnmpusitions and for concentrations jrc valid fur I9U5. 1(1.10. i. Ihe H'H solution has a molality of 6 m MHO] (i.e. 6 mol liNUj kg-1 of solvent) in a innlurity of fi M MNOj (i.e. 5 inol HIIUj 1 1 of solution). Commission <>' the I uropuan Communities JOINT Ueel EstahlishinHnt RESEARCH Central Rur«uii foi Nuclear Measurements 233 CENTRE Sleemveg op Halie. 7440 Oeel. B«lgmm U : 233.039 628 0 +/- 0.000 006 0 f«l (0(4) SilXlt - Trlr< 3J589 EUI1AT B 234. I rWnO 14/5342.73 U : 234.040 946 6 i/- 0.000 004 8 235 I'ROVISIONAI U : 235.043 924 2 +/- 0.000 004 8 236. U : 236.045 562 7 */- 0.000 004 6 ISOTOPIC REFERFNCE MATCR1AI CC NRM 199 'u : 238.050 784 7 +/- D.OOO 004 6 3. Ihe Reference Material consists of a iiranyl nitrate solution. lh« amount I he IRM is supplied with .ilomlc isotope ratios rrrtified as : uf U per unit Is 10 mg. 233U/2381( , 1.000 01 +/- 0.000 In ?34014 |j/2381 1Ou 4. Ihe IRM solution has a molarity of 6 m HN0 3 (i.n. 6 mol llfiOj ' ky~' uf 0.002 05 /- 0.000 01 235O1C |I/9 IDU - solvent) or a mnlarlty of 5 M IfflOj (i.e. 5 mol llNO^l' 1 uf solution). I. 000 15 I/- 0.000 20 ?16o« u/23aviau - 0.000 25 +/- 0.000 01 Chemical purification of the 233U3Ofl , 235"30g and ?3flU3»a starting materials was performed by Willy Lycke. Preparation of the mixture was performed by Frans llendrickx and Willy Lycke. Isotopic measurements of the starting Hits corresponds l.o the Isotopic composition : materials were performed by Kevin Rosman and Rene Ddinen. Verification measurements uri the IRM were done by Rene Oamen. Isotopic atom % Isotopic mass i 233 U/ll 33.306 4 1?.975 6 234 +/ 0.005 9 u/u 0.068 3 0.067 9 235 +/- 0.000 .1 u/u 33.311 0 33.263 9 ?36'u/u +/- D.004 0 The overall tnchnlcal coordination of the establishment of this IRM. w.is 0.008 2 0.008 2 GJ /- 0.000 3 performed hy Willy Lycke. 33.306 1 33.684 4 */- 0.004 9 Ihe atomic weight of the uranium is 235.377 23 '/ 0.000 ?4 The concentrdlion is specified as : 1.899 >/- 0.00? ' 10 kg U/kg solutiun B-2440 GEEL PAUL DP UltVHt Head Hie IRM is Intended for 1 November l tBNM Mass Sper.Lrometry a) calibration of isotope dilution measurements b) verff(ration of the dependence of m,is$ discrimination upon mass. Notes 1. All uncertainties indicated are accuracies, computed on A 2s basis. ?.. Ihe relative atomic masses, used in the calculations, nre : ureau of ^Standard* I he dccay-adjiisled values for Ihe plulomum isolopic composition, in atom percent, are tabulated hclnw in I ahle I I he hall-life values, in years, used lor the decay-adjustmeni are. '""pu. 87.74; H Pu. 24.119. '"'I'u. 6.56(1. ^'I'u. 14 .14, and (tterttfttate of An 4: Pu. .187.000 (able I Decay-Adjusted Plutonium Isolopic Coniposiiion Standard Reference Material 946 Atom Percent "Pu "Pii -Nip Dale January I. 1982 0232 84464 12.253 2477 0574 Plutonium Isotopic Standard April I. 1982 231 84490 12257 2448 574 July I. 1982 231 84515 12260 2419 575 October I. 1982 230 84 540 12264 2391 .575 January I. 1983 230 84 565 12267 2 363 575 I Ins Si.iudaid Reference Material (SRM) is ccclilicd as an isolnpic standard for use in isoiupic measuremcnls of April I. 1983 230 84590 12270 2.335 575 pliiioniom SUM 946 consists ol approximately 250 mg of plulimium in Ihe form of plulomum sulfale leirahydrale July I. 1983 .229 84614 12274 2.308 575 packaged in a glass microbollle. October I. 1983 .229 84638 12277 2281 575 January I. 1984 .229 84 662 12.280 2.253 576 "Pu ifi» "Pu Pu ' Pu April I. 1984 .228 84 685 12283 2.227 576 July I. 1984 .228 84709 12286 2 201 .576 Atom I'eiccnl* 0232 84 464 12253 2477 0574 October I. 1984 .227 84732 12.290 2 175 576 ±0007 ±0015 ±0015 ±0.005 ±0.003 January I. 1985 227 84.755 12.293 2 149 576 I, I9\?. n-li-r lit Tahlc I /or m which Ihe americium and uranium were removed. Because high-purily pluionium January I. 1986 225 84.843 12.305 2050 577 isotopes have not been used lo prepare known synthetic mixtures, I he accuracy is dependent on uranium and pluionium April I. 1986 .225 84864 12.307 2026 .577 exhibiting similar behav ior 'I he observed mass spectrometer dala were corrected for mass discrimination elfccls using July I. 1986 225 84.885 12.310 2003 577 data Iroin the analysis ol ui.iiiunu isolopic SRM's ilial had been analy/cd under similar conditions. October I. I9H(> .224 84.906 12.313 1 979 577 SUM 'M6c Mejbuicmciii-, leading lo Ihc I'cinlicalion ol this SUM ucie ni.ulc in the IIIOI^.IIHL Analytical Rcscaich Division by I I (iainer anil I .A. Machlan I he ice lin n. .11 and support aspects involved in (he icvision ol llu> C'crlilic.ile were coordinated lluough Ihe Oil ice of Si.iiul.ii>l UcUiciicC Mali-mils h> I.L. (iills Aiigusi I'*. I''h2 (ieorgc A. IJnanu. Chief Washington. DC. 21)234 Ollicc of Standard Reference Maleiials (Revision ul CYrlilicalc dated 12 3-71) ureau of j^tatutartte T he decay-adjusted values for the plutonium isotopic composition, in atom percent, are tabulated below in Table I The ><£ i« '" yCar$> " hC decay-dJu»me"' P". 87 74; " V 24.119. 2 Table I Decay-Adjusted Plutonium Isolopic Composition Standard Reference Material 947 Atom Percent Date January I. 1982 0.278 77089 18.610 2821 1.202 Plutonium Isotopic Standard April I. 1982 .278 77 115 18.616 2789 1 202 July I. 1982 .277 77 142 18622 2756 1.203 October I, 1982 .277 77.168 18.628 2724 1.203 January I. 1983 .276 'I Ins Standard Reference Material (SRM) is certified as an isotopic standard for use in isotopic measurements of 77 194 18.634 2692 1.204 plutonium. SRM 947 consists of approximately 250 mg of pluionium in the form of plutonium sulfale leirahydrate April I. 1983 .276 77219 18.640 2661 1.204 July I, 1983 .275 packaged in a glass microboule 77245 18645 2630 1.205 October I. 1983 .275 77.270 18651 2599 1.205 January I. 1984 .275 C>J 77295 18657 2568 1 20S April I. 1984 .274 77.3.19 18662 2S38 1.206 Aiom Percent* 0278 77.089 18.610 1.202 July I. 1984 .274 77.344 18.668 2509 1 206 ±0006 ±0022 ±0022 ±0004 October I, 1984 .273 77.368 18.673 2479 1.206 *.4i of Januar\ I. IVS2. refer 10 Table I for quarter h decav-culjusled values January I. 1985 .273 77.392 18.679 2450 1 207 April I. 1985 .272 77.415 18684 2422 1 207 July I, 1985 .272 77438 18.689 2393 1 208 1 he pluionium isotopic distribution was determined by thermal ionization mass speclrometry at the National Bureau of October I. 1985 .271 77.461 18694 2365 1 208 Standards (NBS) on samples from which americium and uranium were removed. Because high-purity pluionium January I, 1986 .271 isotopes have not been used to prepare known synthetic mixtures, the accuracy is dependent on uranium and pluionium 77.484 18700 2337 1 208 April I, 1986 .270 exhibiting similar behavior. T he observed mass spectrometer data were corrected for mass discrimination effects using 77.506 18704 2310 1.209 July I. 1986 .270 data from the analysis of uranium isotopic SRM's that had been analyzed under similar conditions. 77.528 18709 2.283 1.209 October I. 1986 .270 77.550 18.714 2.256 S R M 947 contains uranium and americium isotopes, including growing-in daughters of plutonium that are isobaric with 1.209 95% Confidence I.mm: the pluionium isotopes. I n addition, there may be radiation damage to the glass bottle and the teflon cap liner resulting in ±0.006 ±0022 ±0022 ±0006 small glass slivers. Therefure. in its use. a chemical separation that provides a purified pluionium fraction is essential to ±0004 the attainment of high accuracy. Measurements leading to the ccinlicuiion of llub SKM ucie made in the Inorganic Analytical Research Division by LI. Garner and I..A. Machlan. 1 lie technical and support aspects involved in the revision of this Cerlitlcale were coordinaletl through the Office of Siaml.inl Reference Matcnals b> I.I: Gills. Aiigiui 19. 1982 George A. iJriano, Chief Washington. D.C. 20234 Office of Standard Reference Materials (Revision of Certificate dated 12 3-71) (over) Ikruilmtiri ..I t ,.mi,,ri.r Mikolt. IuMti(c Rational (ttertiftcate of I he Jecax-adjusted x allies lot the plulonium tsoiopic composition, in atom percent, arc tabulated hcluu in I able I I he h.ill-hlc xalucs. in jcais. used lor ihe decay-adjustment aic: ?U Pu, K7 74; "' Pu. 24.119. ~ 4"l'u. 0.560, " 4 I'n. 14 14. and 'u. 3K7.000 Standard Reference Material 948 table I Decay-Adjusted Plutonium Isotopic Composition Atom Peicenl Plutonium Isotopic Standard ' ,, January I. 19X2 0010 91 736 7922 0 294 00330 Apul I. 1982 010 91 739 7922 295 0330 Urn Standard Reference Material (SRM) is certified as an isotopic standard (or use in isotopic measurements of Julx I. 1982 010 91 743 7923 292 0330 plulomum'i SKM 948 consists of approximately 250 mg of plutonium in the form of plulonium sulfate letrahydrale Ocinber I. 1482 010 91 746 7 923 288 0330 packaged m a glass microbotlle. Januars I. I'JK.l 010 91 749 7 923 285 0330 Apnl I. 1983 010 91 753 7 923 281 0330 'Pu 'Pu "Pu 'Pu Jnl> I. I'>M3 010 91 756 7 923 278 0330 Pu October t. 1983 010 91.759 7923 274 0330 QJ Aioin I'crccnl" 0.010 91.736 7.922 0299 00330 Januarv I. IVH4 010 91 762 7923 271 0130 ±0.001 ±0.010 ±0.010 ±0001 ±00003 April I. 1984 010 9-1 76$ 7 923 268 0330 -J '-(to/ Juniiari I. ll>82. refer to Table I for quarterly Jecai-ailjuiifd values. July I. 1984 010 91 769 7924 265 0330 October I. 1984 010 ' 91 772 7 924 262 0330 Januaix I. 19X5 010 91 775 7 924 25K 0330 1 he phiioinuiii isoiopic distribution was determined by thermal lomzalion mass spectiometry at the National Bureau of April I. 1985 010 91 778 7 924 255 0330 Standards (NBS) on samples from which americium and uranium were removed. Because high-purity plulonium I ids I. I>JX5 010 91 781 7 924 252 0330 isotopes have not been used to prepare known synthetic mixtures, the accuracy is dependent on uranium and plutonium Ocit.hci I. |yK5 010 91 784 7 924 249 0)30 exhibiting similar behavior. 1 he observed mass spectrometer data were corrected for mass discrimination effects using data from the analysis of uranium isotopic SRM's that had been analyzed under similar conditions. In addition, the l.inuary I. I'JHo 010 91 787 7924 24h 0130 value (or ' Pu was checked by alpha-count of Pu. using the known value for Pu as a ratio check. A pnl I. I9KO .010 91 789 7924 243 01)0 Julx I. I9H6 010 91.791 7924 210 0)10 SRM 948 contains uranium and americium isotopes, including growing-in daughters of plulonium that are isobaric with ()>.ii>hci I. I'Mt, 010 91 795 7 925 21K 01)0 the plutoiiium isotopes. In addition, there may be radiation damage to the glass bottle and teflon cap liner resulting in smjll glass slivers Therefore, in its use, a chemical separation that provides a purified plutonium fraction is essential to JO 001 10 010 M) OllOl the attainment of high accuiacy. Measurements leading to the certification of this SKM ucic nuilc in the Inorganic Analytical Kocjn.li Division h> F 1 Gainer. I A. Machlan. ami W K Shields 1 lie technical and support aspects involved in the revision ol tins Cemlicaic were coordinated iliiongh the Ofluc ol Slamlait) Kclcmice Matenals hy I I Culls August I'). l')H2 George A Iliiano. Chic! Washington. I) C. 20234 OH ice of Standard Kclcicnce Materials (Revision ol Certificate dated 12 371) (o\ci) Commission ul the European Commumlies Gcct establishment From the certified aturn Ic Isotope concentration, following clement concentrations JOINT CeciliBl B'lrrji'i lor Niirlr.ir M^ASUiPrponl J RESEARCH Sltrnwrg 0|i Hrhft JtM 0»«l. Belgium are derived : Trl |OM| fi7l 711 r»lf< J3J89 EUnAT B CENTRE lrMa« ON/58 « 73 (3.830 i 0.008) - 10 6 rool Pu kg-1 of solution (9.346 ± 0.019) 10 7 kg Pu kg-1 of solution ISOIOPIC REFERENCE MATERIAL CBNM IRM-042a NOTES 1. All uncertainties indicated are accuracies, computed nn a 2s basis. The IRM,Is supplied with a 244pu atomic Isotope concentration certified as | ?. Values for Isotope ratios, isotopic compositions and for concentrations J valid for 10 December 1986. (2.257 7 + 0.004 6) 1018 atoms 244pu kg-i of solution 3. Due tn radioactive decay, the Pu element concentration decreases by 0.003 3 % «-l. From the certified Isotope concentration, following concentrations are derived i The half lives, used in the calculations, arc (3.749 t 0.008) 10-6 oral 244pu kg-1 of solution i 238pu (8.774 t 0.009) 10U (9.150 ± 0.019) 10-7 kg H44pu kg-1 of solution 239pu (2.411 t 0.003) lO^a 240pu (6.537 i 0.010) lQ3a Other plutonlum Isotopes present are related to the 244pu atomic Isotope 2*lPu (1.433 ± 0.002) 10'a concentration through the following atomic isotope ratios : ' 242pu (3.763 i 0.020) lQ5a 244pu (8.2 ; 4 0.1 ) 1Q7« 238pu/Z44pu : o.OOO 055 t 0.000 007 00 239pu/244pu : 0.000 342 i 0.000 001 4. The IRM solution has a mol.illty of 6 m HNOa (i.e. 6 mol UNO} kg-1 240PU/244PU : 0.006 918 ± 0.000 012 solvent) or a molarlty of 5 M HN03 (I.e. 5 mol UNO.} 1 I of solution). 21lpu/Z44pu : 0.000 681 1 0.000 005 242pu/244pu ; 0.013 611 t 0.000 010 | 5. Ihe Avogadro constant used is (6.022 136 9 i 0.000 007 2) 10?1. 6. Ihe atomic masses, used In the calculations, are Ihls corresponds to an Isotoplc composition with following abundances : 238pu 238.049 554 6 i 0.000 005 1 Isotoplc atom % Isotoplc mass 239pu 239.052 157 6 t 0.000 005 1 240pu 240.053 808 Z t 0.000 004 9 23Rpu 0.005 4 0.005 3 t 0.000 7 21lPu 241.Ob6 845 9 i 0.000 004 8 339pu 0.033 S 0.032 8 t 0.000 4 242pu 242.058 737 3 i 0.000 004 8 240pu 0.6/7 2 0.666 2 t 0.001 3 244pu 244.064 199 ± 0.000 OOb 241 Pu 0.067 0 0.066 1 ± O.DOO 4 242pu 1.332 3 1.321 7 ± 0.001 1 244pu 97.884 6 97.907 9 i 0.002 4 The atomic weight of the plutonlum is 244.006 306 ± 0.000 D85 Using this Spike IRM, 239pu concentrations in unknown samples can be determined by Isotope Dilution Mass Spectromctry, through a measurement of the atomic Isotope dilution ratio RB - 239pu/244pu }n the blend. They should be computed with the aid of the following formula which allows an easy Identification of the sources of the uncertainties in the procedure : R_-R M where , Rx - atomic isotope ratio 239pu/244pu in the unknown sample material RY » atomic Isotope ratio 239pu/214pu In the spike material NX * mass of the unknown sample MY mass of the sample of spike solution used 0239 - number of atoms 239pu kg-1 sample material C214 - number of atoms 244py . kg-1 spike solution. Chemical preparation and ampoulatlon of this IRM were accomplished by Willy lycke and Andre Vcrbruggen. ^ ^ The Isotoplc measurements were carried out by Marc Gal let on samples chemically prepared by Andre Verbruggen. Isotoplc measurements were calibrated against synthetic plutonium Isotoplc mixtures prepared by Jan Broothaerts. I Hetrological aspects Involved in the preparation and certification were performed by Frans Hendrickx. : The overall coordination of the establishment, leading to the certification and issuance of this IRM was performed by Andre Verbruggcn. B 2440 Geel Paul DE BItVRE revised April 1989 Head CBNH Mass Spectrometry Commission ol (he European Communilies JOINT RESEARCH Geel Establishment rrom the certified atomic isotope concentration, following element Genital Oiiieni lor Nuclear Measufemenis CENTRE Slctnwrg op flvli*. 2440 Geel Belgium 1>I nu/5/1 211 Tula» 33569 FUHAf B concentrations are derived : PROVISIONAL CERTIFICATE (2.082 5 */- O.OOfi 1) 10~ 7 null Pu ' kg" 1 of solution ISOTOPIC REFERENCF MATERIAL CBNM-IRM-043 (5.035 6 */- 0.001 4) ' 10"8 kg Pu ' kg" 1 of solution The IRN Is supplied with a 242 Pu atomic isotope concentration certified as NOTFS (1.100 fl +/- 0.003 3) 10 17 atoms Z4ZPu ' kg" 1 of solution ion 1. All uncertainties indicated are accuracies, computed on a 2s basis. 2. Values for isotope ratios, isotopic compositions and for concentrations From the< certified Isotope concentration, following concentrations are derived : are valid for 8 August 1978. (1.820 +/- 0.006) * 10" 7 mol 242Pu ' kg" 1 of solution 3. Due to radioactive decay the Pu element concentration decreases by (4.425 */- 0.013) 10" 8 kg ?4?Pu ' kg" 1 of solution 0.12X ' a" 1 I lie half lives, used in the calculations, are ' Other plutoiiium isotopes present are related to the 242 Pu atomic Isotope concentration through the following atomic isotope ratios : "BPU (8.774 +/- 0.009) 10*a 239PU (2.411 +/- 0.003) 104, 238Pu/ 242P U 240Pu 0.011 551 +/- 0.000 020 (6.537 +/- 0.010) I03a GJ 239Pu/ 242Pu 24lPu 0.002 759 */- 0.000 014 (1.433 +/- 0,002) 101 , 240Pu/242Pu 242Pu 105 a 0.097 87 +/- 0.000 34 (3.763 +/- 0.020) 241[Pu/242Pt 244Pu 107a 0.026 8SO +/- 0.000 059 (8.2 +/- 0.1 ) "W42P» 0.000 212 i/- 0.000 012 ion has a molallty of 6 m HNO 3 (I.e. 6 mol HN03 kg" 1 of I" 1 of solution) this corresponds to an isotopic composition with following abundances : molaHty of 5 H HNOj (i.e. 5 mol KN03 Isotopic atom X 5. Tho Avogadro constant used is (6.022«o nac045 +/-< / n0.000 nrtn i031)111 1 ' 10^310 238Pu Isotopic mass X 1.013 9 0.998 1 +/- 0.001 6 0.242 1 0.239 4 +/- 0.001 2 240,Pu 8.590 7 8.528 1 '/- 0.027 0 241Pu 2.356 8 2.349 4 */- 0.004 4 07.777 9 87.866 3 */- 0.031 0 ?44Pu 0.018 6 0.018 7 +/- 0.001 0 The atomic weight of the Plutonium Is 241.015 33 »/- 0.000 60 6. The atomir m.isses. used in the calculations, are 510 Pu 238.0-19 555 2 +/- 0.000 DOS 1 Z39Pu 239.052 157 8 t/- 0.000 005 1 ', , 240Pu 210.053 808 7 */- 0.000 004 9 ?41Pu 241.056 846 9 +/- 0.000 004 8 j 242Pu 242.058 738 5 +/- 0.000 004 8 Z44Pu 244.064 200 +/- 0.000 010 ! 7. Usiny this Spike 1RM, 239Pu concentrations in unknown samples can be , determined by Isotope Dilution Mass Spectrometry. through a measurement of 239 ?4? the1 atomic isotope dilution ratio R. * Pu/ Pu in the blend. They j should be computed with the aid of following formula which allows an easy identification of the sources of the uncertainties in the procedure : I T~ ' 242 0 " X HX where Ry 3 atomic isotope ratio 239 Pu/ 242 Pu in the unknown sample material Ry - atomic isutope ratio 239Pu/ 24? Pu In the spike material HX mass of the unknown sample OJ Mv = mass of the sample of spike solution used Coin " number of atoms 239 Pu * kg -I sample material Cy.y s number of atoms 242 Pu ' kg 1 spike solution. The isotopic measurements, as well as the overall technical coordination of the establishment of this IRM, were performed by Marc Gal let. i Chemical preparation of this IRM and of the samples for isotopir measurements! was performed by Audi £ Verbruggen. Paul Ob BIEVRE 0-2440 GEEL ' Mead 16 September 1985 CBNM Mass Spectrometry in no 02 HO: II r\\ IU55 i FEi VNTSiiiiOOi i R 12)1)02 Dil.1 in-tip 02 n{l:18 FAX 1655 Commission of the European Communities Gffil Fsiahlishmcnt JOINT From the certified atomic Isotope concentration, following element concentrations RESEARCH Cenlitl Buieau (or Nucleir MoiuremcntJ Sie*nw«g np flri.r. 2440 G«»l Belgium arp derived : CENTRE » Tel. ((II4)T,7| ?ll - Trie* 3J509 tUHAI B ISOTOPIC REFERENCE MATERIAL C8HM IRM-044 I (3.809 7 ± 0.005 7) 10- b mol Pu kg' 1 of solution (9.222 ± 0.014 ) IO"6 kg Pu kg' 1 of solution ! NOTES The iRM is supplied with a 2^ 2Pu atomic isotope concentration certified as 1. All uncertainties indicated are accuracies, computed on a 2s basis. I (2.292 0 ± 0.003 4) 10'9 atoms 242Pu - kg ' of solution I I I | 2. Values for Isotope ratios. Isotoplc compositions and for concentrations From the certified isotope concentration, following concentrations are derived*: valid for 27 January 1987. (3.806 0 t 0.005 7) 10'5 mol 242l>u kg' 1 of solution 3. Due to radioactive decay, the Pu element concentration decreases by (9.213 t 0.014 ) ID'6 kg 242Pu kg" 1 of solution 0.000 23 X a' 1 . i , ThP half lives, used in the calculations, are Other plutonium isotopes present are related to the 242Pu atomic Isotope concentration through the following atomic Isotope ratios : 238Pu (8.774 f 0.009) 10 la 239Pu (2.411 ± 0.003) I04a 238pu/242Pu : 0.000 009 ! 0.000 006 240Pu (fi.5.37 ± 0.010) 103a 239pu/242pu . o OOQ 827 t 0 000 QO/J 2<11Pit (1.433 t 0.002) lo'a' 240pu/242pu . o. ut)o IQB t 0.000 004 2/12Pu (3.763 t 0.020) I05a 24lPu/242pu . 0 000 oog ± 0 ooo 004 244'Pu (8.2 t 0.1 ) 107 a 244pu/242pu . o goo 015 t 0.000 004 4. The IRM solution has a mo la II ty of 6 m HMOj (I.e. 6 mol HN03 kg" 1 solvent) or a molarity of 5 H HM03 (I.e. 5 mol HH03 T l of solution). This corresponds to an isotoplc composition with following abundances 5. The Avogadro constant used Is (6.022 136 9 ± 0.000 007 2) 1023 . Isotopic atom X Isulopic mass X 6. The atomic masses, used In the calculations, are 238Pu 0.000 9 0.000 9 ± 0.000 6 239Pu 0.082 6 0.081 6 1 0.000 4 238Pu 238.049 554 6 ± 0.000 005 1 240PU 0.010 8 0.010 7 + 0.000 4 239Pu 239.052 157 6 i 0.000 005 1 241pu 0.000 9 0.000 9 i 0.000 4 240Pu 240.053 808 2 t 0.000 004 9 242pu 99.903 3 99.904 4 t 0.001 0 24lPu 241.056 845 9 t 0.000 004 8 244Pu 0.001 5 0.001 5 t 0.000 4 242Pu 242.05H 737 .1 l 0.000 004 8 244Pu 244.064 199 t 0.000 005 The atomic weight of the plutonium is 242.056 020 i 0.000 028 11 r< \\i5iinniti i H Using this Spike IKM, 2 ^ Pu concentrations in unknown samples can he determined by Isotope Dilution Mass Spectromctry, through a measurement or the alumk isotope dilution ratio RB = 239Pu/2<*2Pu in the hlcnd. They should be computed with the aid of the following formula which allows an easy identification of the sources of the uncertainties In the procedure : RX » atomic isotope ratio ^9pu/?4?pu ; n tne unknown sample material Ky - atomic isotope ratio 239Pu/2'I2Pu In the spike material ' MX - mass of the unknown sample My = mass of the sample of spike solution used C239 - number of atoms 2^Pu kg'l sample material C242 * number of atoms 242Pu kg'* spike solution. I Chemical preparation and ampoulation of this IRM were accomplished by Willy Lycke , i and Andre Verbruggen. The Isotoplc measurements were carried out by Marc Gal let on samples chemically prepared by Andre Verbruggen. Isotopic measurements wore calibrated against synthetic plutonlum Isotoplc mixtures prepared by Jan Broothaerts. I Metroloqical aspects Involved In the preparation and certification were performed by Frans Hendrickx. The overall coordination of the establishment leading to the certification and issuance of this IRM was performed by Andie Verbruggen. H 2440 Gee I Paul OE BIEVRE September 1987 Head CBNM Mass Spectromctry Commission ol the F.mupean Communities Geel Es 2. Values for isotope ratios and isotopic composition aro v.il id for Onrral Buietu lor Nuclear Sl«enwrg op nclie. 2440 10 September 1985. RESEARCH [3 M (014) 171 2H Iclcx : CENTRE K3I1 PROVISIONAL UKIIFICATE Iclcltlclclo« OH/56073 3. The relative; atomic masses used in the calculations are : ISOTOPIC REFERENCE MATERIAL CBNN - IRH - 047a 238 'Pu 238.049 554 6 +/- O.OOU 002 4 239,(Pu 239.052 157 6 +/- 0.000 002 4 240, The IRH is supplied with atomic isotope ratios certified as : u 240.053 808 2 « /- 0.000 002 3 241 Pu 241.056 845 9 +/- 0.000 002 3 242 ?18Pu/244Pu : 0.000 080 +/- 0.000 013 Pn 242.058 737 3 +/- 0.000 002 3 ?44 239Po/244Pu : l.?98 37 +/- 0.002 45 'Pu 244.064 199 '/- 0.000 005 240Pu/ Z44Pu : 0.036 385 +/- 0.000 095 24lPu/ 244Pu : 0:001 145 »/- 0.000 023 4. I lie Reference Material consists of dried Pu nitrate. The amount of Pu per 24ZPu/Z44Pu : 0,013 560 +/- 0.000 043 unit is (1.49/ */- 0.015) ' 10" 7 kg. 5. No chfimir.il reriox cycle was performed on the material. Ihis corresponds tn the Isotopic composition : 6. One to radioactive decay, the Pu element concentration decreases by ( 0.004X 'a'1 Isotopic atom X Isotopic mass X Tlie hdlf lives, used In the calculations, arc Z38Pu 0.003 4 0.003 3 i/- 0.000 6 Z39Pu 55.260 7 54. /64 3 +/- 0.045 5 05 238,'PU (8.774 »/- o.ongnrra 240Pn 1.548 6 1.541 1 +/- 0.003 3 239Pu (2.411 */- 0.003)'104 a 241 Pu 0.048 7 0.048 7 +/- 0.001 0 240.(Pu (6.537 */.; 0.010)'103a 242Pu 0.577 1 0.579 1 */- 0.001 9 241. Pu (1.433 +/- 0.002)'10 a 244Pu 42.561 5 43.063 5 +/- 0.045 7 242) Pu (3.763 f/- 0.020)M05 a 244 The atomic weight of the piuton I urn is 241.219 16 +/- 0.002 29 Pu (8.2 +/- 0.1 )'107a I he IKM is intended for Isotopic measurements, as MB)I as the overall technical courdinatiun of tht? a) determining Pu isotope fractionation using the certified Pu/ Pu ratio establishment of this IRM, were performed by Marc Gallet. b) check of isotopic contamination during chemical preparations and 9)Q 7&A 9A9 744 measurements using the Pu/"qPu and "*?ur Pu ratios. Chemical preparation of this IRM and of the samples for Isotopic measurements was performed by And re" Verhruggen. NOTES B-2440 GEEI PAUL DT BirVRE I. All uncertainties indicated are accuracies, computed on a 2s basis. 1 December 1985 Head, Mass Spcctromctry r.r>mmi*»iun of Ihe Euiupcan Communities JOINT Cj««l FsMhlishment From the certified atomic isotope concnntriil. Inn, following element roncentr at iuns RESEARCH Central Bureau for Nuci««r M«ojurimenli Stecnwcg op Hrnc 2410 G««l Belgium are derived : CENTRE Tel. (OH)»f.2U telex 33509 CUfUT 0 (3.772 7 f 0.007 5) 1(1 4 mol Pu - kg ' of solution ISOIOPIC REFERENCE MATERIAL tBNM [RM-0-19 (9.132 ± O.Olfl ) - 10 5 kg Pu - kg ' of solution NOTFS Ihe IRM is supplied with a 242Pu atomic Isotope cnncentratfon certified as I. All uncertainties indicated are accuracies, computed on a 2s hasis. (2.269 8 ± 0.004 5) 1020 atoms 2<12 Pu kg-' of solution ?. Values for isotope ratios, isotopir compositions ami for coni.'rntrdtions an: validjor 21 J.iniinry 1987. From the certified isotope concentration, following concentrations are derived : 3. Fine to radioactive decay, the Pu element concentration dccrensps hy ' 0.000 23 % a" 1 . (3.769 1 ± 0.007 5) 10" 4 mol ?4?Hu kg' 1 of solution Ihe half lives, used in the calculations, are (9.123 t 0.018 ) 10' 5 kg 242Pu kg ' of solution i 238Pu (8.774 t 0.009) 10 l a Other plutoniura isotopes present are related to the 242Pu atomic isotope 239PU (Z.4U t 0-003) I04a concentration through the following atomic. Isotope ratios : ' 240Pu (6.537 t 0.010) I03a | 241Pu (1.433 i 0.002) lo'a 238pu/24?pu . 0,000 009 ± 0.000 006 ' 242Pu (3.763 ± 0.020) lO^a 239pu/242pu . o ooo 627 ± 0.000 004 244Pu (8.2 t O.I ) 107,i 240pu/242Pu . o 000 108 t 0.000 004 241pu/Z42Pu . o.OOO 009 t 0.000 004 4. fhe IRM solution has a molaUty of 6 m HN03 (i.e. 6 mol UNU.i kg' 1 of 241Pu/242Pu . o.OOO 015 + 0.000 004 I solvt;nl) or a molarity of 5 M HNOa (i.e. 5 mol IINOj 1"' of solution). | 5. the Avogadro constant used Is (6.022 136 9 t 0.000 00/ 2) 10?3 . Ihis corresponds to an Isotopic composition with following abundances 6. The atomic, masses, used In the calculations, are I sotopic atom X Isotopic mass 238Pu 238.019 554 6 t 0.000 OU'j I 238Pu 0.000 9 0.000 9 ± 0.000 6 239PU 239.052 157 6 t 0.000 005 1 239PU 0.082 6 0.081 fi ± 0.000 4 210Pu 240.053 BOB ? t 0.000 004 9 240PU 0.010 8 0.010 7 t 0.000 4 24 'Pu 241.056 845 9 t 0.000 004 8 241pu 0.000 9 0.000 9 t 0.000 4 242Pu ?4?.058 737 3 t 0.00(1 004 8 242PU 99.003 3 99.901 4 1 0.001 0 244Pu 244.064 199 i 0.000 OOli 244pu 0.001 5 (1. 001 S ' 0.000 4 The atomic weight of the plutoniura is 2<12.0hfi fl?0 t 0.000 Oi!0 Using this Spike IRM. "9pu concentrations 1n unknown samples can be determined by Isotope Dilution Mass Spectrometry, through a measurement of the atomic isotope dilution ratio Rfl = 2:*9pu/24?pu in the blend. Uiuy should ho. computed with the aid of the following formula whkh allows rin easy Identification of the sources of the uncertainties in the procrdurp : CSK> " R~. where RX B atomic isotope ratio 23"pu/2'l2pll jn ^c un| 'Chemical prepardllon and ampoulation of this IRM weri> iicrnmplished by Willy Lycke, and Andre Verbruyyen. I The Isotopic measurements were carried out by Hare Gallet on samples chemically prepared by AndrA VPrhrnggen. Isotopic measurements were calibrated against) synthetic plutonlum Isotopic mixtures prepared by Jan Droothaerts. Mntrologlcnl aspects involved in the preparation and certification were performed hy Frans Hendrickx. The overall coordination of the establishment leading to the certification and issuance of this IRM was performed by Andre Verbruggcn. B 2440 Geel Paul DE BIEVfiE September 1087 Head CBNM Mass Spectrometry Applications of the Rhenium-Osmium Isotope System to Geologic Problems Richard J. Walker, Isotope Geochemistry Laboratory, Department of Geology, University of Maryland, College Park, MD 20742 Recent advances in the mass spectrometry and chemical purification of the elements of Re and Os have now permitted this isotope system to take its place as a unique companion to the other long-lived radiogenic isotope systems. 187Re decays to 187Os by p with a decay constant of approximately 1.639 x lO^yf1. There is still approximately ±3% uncertainty in this decay constant, but it should be refined over the next several years as studies of terrestrial systems of known age are examined. The Re-Os system serves as an isotopic tool with some singular uses, but primarily should be used in conjunction with other isotopic systems to be most effective. Many of its uses, for example geochronology, overlap with the uses of the Sm-Nd, Rb-Sr, Lu-Hf and U-Th-Pb systems. However, Re and Os are both siderophile and chalcophile elements, in geochemical contrast to the lithophile elements that comprise the other long-lived radiogenic isotope systems. Consequently, the "view" into geologic processes provided by this system is somewhat unique. A good example of this uniqueness is the behavior of the Re-Os isotope system in the mantle. Unlike the elements that comprise the other isotope systems, Os is usually retained in the mantle during melting events. Re, however, is moderately incompatible. This means that Os isotopes in the mantle are reasonably immune to the effects of short-term crustal recycling. In addition, most melting events in the mantle evidently leave Re-depleted residues with retarded l87Os growth. We have shown that ancient subcontinental lithosphere is usually depleted in 187Os relative to a model bulk Earth that approximates the isotopic evolution of carbonaceous chondrites. A number of uses of the Re-Os system will be discussed. One important use of the system is in dating mafic and ultramafic rocks that are difficult to date using other techniques. Most basalts, for example, have relatively high Re/Os ratios, leading to extremely rapid growth of radiogenic Os relative to the common Os. This permits the dating of even young basalts via model age calculations and in some instances isochron dating. The system also has other unique geochronologic applications including the dating of molybdenites and iron meteorites. Os is one of the six platinum group elements, so the system serves as the best tracer of PGE that we will ever have. In one study, we have found the PGE in Sudbury (Ontario) sulfides to have been derived from ancient continental crust. In stark contrast, sulfides from the Noril'sk (Siberia) sulfides were dominantly derived from a mantle plume source. Figure. Re-Os isochron plot and y0s vs. Re/Os ratio plot for suifide samples of the Kharaeiakhsky orebody, Norirsk region, Siberia. Data show closed-system behavior since the igneous event at approx. 250 Ma. y0s values are all greater than zero (chondritic) and are consistent with derivation from a plume source. Kharaeiakhsky Orebody 20 r 10 Os 251.0±5.1 Ma o -10 -20 10 100 1000 187^ .188 Re/ Os 73 O 00 03 73 251.0±5.1 Ma O I=.1393±0.0020 oo 200 400 600 800 1000 187 .188 Re/ Os 3*8 The Pb-Sr-Nd Isotopic Troika Theory and Applications, R. E. Zartman, U.S. Geological Survey, Denver, CO 80225 The radioactive decay systems, U-Th-Pb, Rb-Sr, and Sm-Nd, when locked within individual minerals or hand specimen-sized whole-rocks, provide the basis for several well-established isotopic dating techniques. These same systems viewed at a larger scale serve to isotopically characterize terrestrial reservoirs, and function as natural tracers of geologic processes affecting those reservoirs. Applications can range from the study of local phase equilibrium (mm to m) through the identification of igneous rock/ore deposit source rock (m to 10.km) and the fingerprinting of tectonostratigraphic terranes (km to 102 km) to placing spatial and temporal constraints on planetary differentiation (103 km). In this lecture we'll examine the basic theory underlying the Pb-Sr-Nd isotopic troika-so-called because its coupled relationships give rise to a number of correlation diagrams that emphasize parent-daughter fractionation trends (several other decay systems, such as Lu-Hf, Re-Os, and K-Ca, are also very useful in this respect). Although, historically, the three systems were developed more or less independently and spawned their own nomenclature and data-reporting conventions, some uniformity has been subsequently introduced with the eNd and eSr notation (parts per ten thousand deviation of isotopic ratios from reference values). No corresponding notation for lead has yet gained wide acceptance, but some advantages of the 8(6/4), 8(7/4), and 8(8/4) convention (parts per thousand deviation of isotopic ratios from reference values; first proposed by Stacey, 1986) will be discussed. A vast body of isotopic data now exists, which invites a general synthesis into various petrogenetic models. At the largest scale and providing a framework for interpreting regional and local patterns are the terrestrial differentiation models. One such model-the plumbotectonic model of Doe and Zartman (1979) and Zartman and Doe (1981)-offers a planetary prospective that has proven helpful in describing first- 32.9 order Pb-Sr-Nd isotopic systematics among major Earth reservoirs (upper crust, lower crust, subcontinental lithosphere, mantle, orogene). Rather than by forcing a narrow tectonic scenario upon the observational data, the plumbotectonic model probably finds its greatest value in testing permissible ranges of reservoir compositions and of fluxes carrying material between reservoirs. Another model-the chemical geodynamics model of Allegre (1982) and'Zindler and Hart (1986)-has been particularly effective in describing mantle heterogeneities by defining mantle end- member reservoirs (DMM, PREMA, BSE, HIMU, EM I, EM II). Within the context of these broad terrestrial differentiation models one can then examine the various geologic phenomena that create and destroy isotopic differences. Observed isotopic patterns reflect a dynamic balance between these opposite tendencies and provide important constraints on the extent and timing of differentiation and mixing processes. Examples to be discussed are taken from studies of igneous rocks, ore deposits, seawater, and terrane identification. 330 Suggested Reading Allegre, C.J., 1982, Chemical geodynamlcs: Tectonophyslcs, v. 81, p. 109-132. Allegre, C.J., Hart, S.R., and Minster, J.-F., 1983, Chemical structure and evolution of the mantle and continents determined by Inversion of Nd and Sr Isotopic data. II. Numerical experiments and discussion: Earth and Planetary Science Letters, v. 66, p. 191-213. Anderson, D.L, 1982, Isotopic evolution of the mantle: a model: Earth and Planetary Science Letters, v. 57, p. 13-24. Armstrong, R.L., 1981, Radiogenic isotopes: the case forcrustal recycling on a near steady-state no-continental-growth Earth: Philosophical Transactions of the Royal Society of London, v. A301, p. 443-472. DePaolo, D.J., 1980, Crustal growth and mantle evolution: inferences from models of element transport and Nd and Sr isotopes: Geochimica et Cosmochimica Acta,v. 44, p. 1185-1196. Doe, B.R., and Zartman, R.E., 1979, Plumbotectonics I, The Phanerozoic. In Geochemistry of Hydrothermal Ore Deposits, 2nd. edn. (ed. H.L Barnes), Chapter 2, p. 22-70, Wiley Interscience. Faure, G., 1986, Principles of Isotope Geology, 2nd. edn., 589 p., John Wiley & Sons. Houtermans, F.G., 1946, Die Isotopenhaufigkeiten im naturlichen Blie und das Alter des Urans: Naturwissenschaften, v. 33, p. 185-186, 219. O'Nions, R.K., Evensen, N.M., and Hamilton, P.J., 1979, Geochemical modeling of mantle differentiation and crustal growth: Journal of Geophysical Research, v. 84, p. 6091-6101. Russell, R.D., and Farquhar, R.M., 1960, Lead isotopes in Geology, 234 p., Wiley Interscience. Zartman, R.E., 1984, Lead isotopic provinces in the Cordillera of the Western United States and their geologic significance: Economic Geology, v. 69, p. 792-805. 331 Zartman, R.E., and Doe, B.R., 1981, Plumbotectonics-The model: Tectonophysics, v. 75, p. 135-162. Zartman, R.E., and Haines, S.M., 1988, The plumbotectonic model for Pb isotopic systematics among major terrestrial reservoirs-A case for bi-directional transport: Geochimica et Cosmochimica Acta, v. 52, p. 1327-1339. Zindler, A., and Hart, S., 1986, Chemical geodyhamics: Annual Review of Earth and Planetary Sciences, v. 14, p. 493-571. 332, Basic Equations For a radioactiue species N, dN/dt = -XN -». N = resulting in the production of a radiogenic species D, D = DO + NO - N = DO + N0( 1 - or, in terms of N (today), = D0 + N( If , D ~ D0 N ® D O D 1 fit t = 0 [N nJ D nJ D'l flt t = t [N, D, D 1 ] 333 The basic age equation is t = 1/X-ln[1 + (D-D0)/N1 or, if (D-D0)/N«1 , t ~ (1 /X)-(D-D 0)/N Sometimes we want to calculate the amount of radiogenic daughter produced between two arbitrary times, tj and t2. D(2) - D(1 ) = N(1 ) - N(2) = NCe^i - e^2) Normalizing to a nonradiogenic isotope of the daughter element, D1, we haue [D(2)/D'l - [D(1)/D-] = For example, 33V- Decay Constants Isotope XdO-'g- 1 ) tl/2(1B- 9 y) 238U -» 2B6Pb 8.1551 4.468 235y _»287p b 0.9849 0.7B38 232Th -» 208 Pb 0.04948 14.01 87Rb -» 87Sr 0.0142 48.81 147Sm -» 143Nd 0.00654 106 335 VERTICALLY RECYCLED COMPONENT (v) iJUPPER CRUST (u) LOWER~CRUST (I) SUBCRUSTAL LITHOSPHERE (s) ot p' AGE (Ga) MANTLE (ml 8 SUBOUCTION ZONE \ UPPt LOWE SUI LITHC AGE (Ga) UPPER CRUST (u) LOWER~CRUST'(I> SUBCRUSTAL LITHOSPHERE (s) " o> o AGE (Ga) MANTLE (m» 336 PLUMBOTECTONICS RESERVOIRS 5 (7/4) -- 20 --15 __Ip. 1 0 IE1N1TAL CRUSTl||i UPPER CRUST Is PROXIMAL OROGENE PI ...... x.:.:.:.:.:-:.:.:- 1"^J 5(6/4) H 80 60 40 20 40 60 80 TOTAL OROGENE -- 5 n DISTAL OROGENE MANTLE -4- 1 0 MANTLE WEDGE SUBCRUST >T -- 1 5 LOWER CRUST Ii -- 20 5 (7/4) 337 PLUMBOTECTONICS RESERVOIRS PROXIMAL OROGENE Jj TOTAL OROGENE + 5 (6/4) 20 40 60 80 CONTIINENTA - 10 SUBCRUST MANTLE WEDGE - 15 DISTAL OROGENE - - 20 MANTLE 8 (8/4) 33 S II -I- 120 IV 5 (8/4) 339 II ARCHEAN UPPER MANTLE I -4-10 MORB IV - 8 (7/4) 310 45° E 27° N O OPHIOLITE © MANTLE L. CRUST MIX OLDER CONTINENT 17° N ARABIAN REGION UC Cx) O OPHIOLITE © ENSIMATIC ARC ---80 630 Ma DIORITES MANTLE L. CRUST MIX OLDER CONTINENT ARABIAN REGION 6 (8/4) CP O OPHIOLITE M ENSIMATIC ARC 630 Ma DIORITES MANTLE L. CRUST MIX OLDER CONTINENT itll, 8 (7/4) UPPER CRUST 100 LOWER CRUST Gold Hill, Utah Southern stock (Jurassic) Northern stock (Oligocene) fj Feldspar O Feldspar | Galena Galena T0 = 3700 Ma, H 0 =9.74 T0 = 3700 Ma, =9'74 T, = 2700 Ma, u^ =11.66 ^ = 2700 Ma, = 12.74 T2 = 1640 Ma, \i 2 = 12.07 T2 = 1640 Ma, =7.36 T3 = 150 Ma T = 38 Ma UPPER CRUST PROTEROZOIC Gold Hill, Utah Southern stock (Jurassic) Northern stock (Oligocene) rj Feldspar O Feldspar | Galena Galena TO = 3700 Ma, K Q =3.78 0 = 3700 Ma, K Q =3.78 TT = 2700 Ma, K 1 =4.31 T = 2700 Ma, =4.00 T2 = 1640 Ma, K2 =4.16 T2 = 1640 Ma, K 2 =6.01 T3 = 150 Ma T3 = 38 Ma 3V5* JAPAN - A MODERN OROGEN 5 (7/4) --10 UPPER CRUST --5 TOTAL OROGENE PROXIMAL OROGENE DISTAL OROGENE MANTLE MANTLE SUBCRUST £Nd = +6 to -4 - 5 (7/4) 6sr = -16 to +12 JAPAN - A MODERN OROGEN 8(8/4) I UPPER CRUST --10 PROXIMAL OROGENE ~- 5 LQWEJl [3| TOTAL OROGENE 5 (6/4) + SUBCRUST MANTLE WEDGE DISTAL OROGENE - 8 (8/4) 0.5136 +16 0.51341- -H2 0.5132 4-8 J2J 0-5130 HBfU 5 +4 S ^ 0.5128 vu 0.5126 0.5124 Eastern China 0.5122 -* 0.5120 -12 0.701 0.702 0.703 0.704 0.705 0.706 0.707 87 Sr/°°Sro_ / 86 OJ07 0.706 ^ 0.705 Patagonia 0.704 CO oo Eastern China 0.703 '/1/IMlfAss"// / 0.702 0.701 15 16 17 18 19 20 21 22 n- 61 LI 91 *- tziro 0 fh 8+ on?o znro CL KirO 91+ 16.5 17.0 17.5 18.0 18.5 19.0 19.5 200) 20.5 21.0 21.5 210 206Pb/^Pb204 40.0 r i 1 i i r Linju, Shandong Province 39.0 PL, 38.0 OO o 37.0 36.0 15.6 12.6 ^ 10.6 155 PH 15.4 18.9 13.7 153 15.2 16.0 17.0 175 18.0 185 19.0 Consider the two uranogenic decay equations t - Diuiding, we haue [2B6 pb /2B4 pb ] 2 _ For t 2 = 0 (today) [2B7 pb /2B4 pb J 2 _ [287(315/284,3(5^ Bulk Earth Constraints If we knew the parent and daughter element contents (actually parent-daughter ratio) and daughter element isotopic composition of the Earth at its time of formation, we mould also know the auerage present-day isotopic composition of the daughter element. That is, despite the chemical fractionation and isotopic heterogeneity of its uarious reseruoirs, the bulk Earth must haue an isotopic composition commensurate with its ouerall parent-daughter ratio. Regarding the troika, it is en commonly assumed that (1) the bulk Earth's rare-earth ~^ elements are unfractionated compared to chondritic abundances ( H7Sm/ m Nd = 0.1967), (2) the bulk Earth's Rb/Sr may be determined from the coupled ENd(8)-ESr(8) diagram for young basalts (87Rb/ 86 Sr = 0.0816), and (3) 238U/ 204Pb must be about 9, although its enact ualue is not known; howeuer, the coupled 238U- 235U decay schemes demand that bulk Earth lies on the Geochron. Problems with Bulk Earth Constraints 1. fire important reseruoirs hidden and/or isolated? 2. Did the Earth haue an 'instantaneous' origin? 3. Hre the bulk Earth's rare-earth elements unfractionated? 4. How ualid is the assumption that the Sm-Nd and Rb-Sr systems are coupled? OJ Ol 5. How accurately can we determine the parent and daughter element contents and daughter element isotopic composition of indiuidual reseruoirs; i.e., can a meaningful summation of the parts be made so as to equal the whole? Decay Constants A,(18- 9 y- 1 ) tl/2(18 9 y) 238 U -» 2a6 Pb 0.1551 4.468 235 U -» 207 Pb 0.9849 0.7838 232yh _»2B8 pb 0.04948 14.01 87 Rb -» 87 Sr 0.0142 48.81 147 Sm ^ 143 Nd 0.00654 106 o en VJ»*S XwVJ i i ' i i ' i ' . DMM + 16 0.5134 '/// 0.5132 V ^\, +12 "O \AfOflfl\_ 2 0.5130 \^_ ^F/?£A£4 +8 5 HIMU Y/// a ~ 0.5128 +4 2 BSE vu 2 0.5126 - m 0 § 0.5124 £»ff^ -4 0.5122 -8 - or/^^^^ ~ 0.5120 I , 1 ^^^ 1 .19 0.701 0.702 0.703 0.704 0.705 0.706 0.707 87 c, / 86 358 87Sr/ 86 Sr o o o o o o o K) 8 OJ -P- cr^ tfj K> U.J1JO i i i i i _ + 16 0.5134 DMM //// X^N + 12 -O 0.5132 \MORB\ z +8 5 0.5130 PDKMA Y/T^- ^ r-r-j 7-1 rKEMA \ZJ /// // +4 2 ^ 0.5128 HIMU JT 0.5126 BSE /// 0 Tf . -4 ~ 0.5124 ^. 0.5122 -8 - *"^^ ffify**U 0.5120 ,VVVV^ , -12 15 16 17 18 19 20 21 22 15.2 16.0 16.5 17.0 17.5 18.0 18.5 19.0 19.5 20.0 20.5 21.0 21.5 22.0 206 / 204 STAGEY (1986) | FELDSPAR f TRUE AGE t ^v .a Q. AVE. CRUST O 04 ISOCHRON O CM Yo 3.7 Ga Xo 206 Pb/ 204 Pb DEFINE PARAMETERS Xf -Xt Yf - Yt 5 (6/4) = X1000 5(7/4) = X 1000 Xt -Xo Yt - Yo FOR t = 0 Ga Xf -Xt Yf - Yt 5 (6/4) = X1000 5(7/4) = X 1000 7.548 2.630 ZARTMAN & STAGEY (1992) II FELDSPAR f TRUE AGE t .Q Q. OROGENE O CM ISOCHRON o CM Yo 3.7 Ga Xo 206 Pb/ 204 Pb DEFINE PARAMETERS Yf -Yt 5(6/4)= Xf ~ Xt X1000 5 (7/4) = X1000 Yt FOR t = 0 Ga Yf - Yt 5(6/4)= X100° 6 (7/4) = X 1000 15.628 363 PRESENT-DAY PLUMBOTECTONICS RESERVOIRS 5 (7/4) UPPER CRUST PROXIMAL OROGENE 6(6/4) 20 / 40 60 80 TOTAL OROGENE DISTAL OROGENE MANTLE MANTLE WEDGE SUBCRUST LOWER CRUST - 5 (7/4) PRESENT-DAY PLUMBOTECTONICS RESERVOIRS + 5 (8/4) - - 20 - - 15 UPPER CRUST - - 1 0 PROXIMAL OROGENE 'BULK EARTH" X.. LOWER CRUST 5 (6/4) TOTAL OROGENE + 6 (6/4) H I I h ! I I \ 80 60 40 20 20 40 60 80 -- 5 --10 SUBCRUST - 15 MANTLE WEDGE DISTAL OROGENE [] - - 20 MANTLE 5 (8/4) 0.709 0.708 100 200 300 400 500 600 Geologic Time in Millions of Yearsl I ft 16 (l')69)|