1 H h..9 .RECEIVED - "5 1.1 -1 2 , . L - R& ... M.I.T.-1381-17. SEVENTEENTH ANNUAL PROGRESS REPORT FOR 1969 U. S. ATOMIC ENERGY COMMISSION CONTRACT AT(30-1)-1381 *%15 VARIATIONS IN ISOTOPIC ABUNDANCES OF STRONTIUM, CALCIUM, AND ARGON AND RELATED TOPICS Contributions by M.I.T. Staff Students, M.I.T. P. M. HURLEY C. M. SPOONER H. W. FAIRBAIRN J. B. REID, JR. W. H. PINSON, JR. T. M. GATES R. 1 NAYLOR B. J. FRYER J. D. AIKEN, JR. Visiting Research Staff and Collaborators Secretary : J. Golden - J. R. RAND V. G. POSADAS Machinist: 0. J. Annese (part-time) G. W. LEO (U. S. Geol. Survey) R. W. WHITE (U. S. Geol. Survey) W. D. MACDONALD (State U. of N. Y.) D. G. BROOKINS (Kansas State' U.) B. M. FRENCH (Goddard Space Flight Center) A. R. BERGER (U. of Toronto) R. H. REESMAN (Geochron Laboratory, Cambridge) . J. RONDOT (Ministry of Natural Resources, Quebec) DEPARTMENT OF EARTH AND PLANETARY SCIENCES MASSACHUSETTS INSTITUTE OF TECHNOLOGY 1 CAMBRIDGE, MASSACHUSETTS 02139, U. S. A. December 1, 1969 DISTRillUTIC)NOFT:25 DOCUMENTIS UtaiMMED DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. M.I.T.-1381-17. SEVENTEENTH ANNUAL PROGRESS REPORT FOR 1969 U. S. ATOMIC ENERGY COMMISSION CONTRACT AT(30-1)-1381 VARIATIONS IN ISOTOPIC ABUNDANCES OF STRONTIUM, CALCIUM, AND ARGON AND RELATED TOPICS LEGAL NOTICE This re pcrt was prepared as an account of Govern ment sponsored work. Nellher the United Suntea, nor the Commission, nor any person acting on behalf of the Commission: A. Makes any warranty or representation. expressed or implied, with respect to the accu- racy. comploteness, or uiefulneia of the information contained in thia report. or that the use of any t nflrmation, apparn tus, method, or process disclosed tn this report may not infringe privately owned righl; or B. Aimmes any liabiltles with rcipect to the use of, or for damages resilling from the use of any informalon, apparms, method, or procesi disclosed in this report. 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December 1, 1969 TlilS DOCUMENT IS UNLIMITED DISTRIBUTION OF -7 x L Table of Contents CONTINENTAL EVOLUTION Page 1 Investigation of'Continental Accretion in 1 Laurasia Northern Appalachian Geochronology as a 11 Model fur Interpreting Ages in Older Orogens REGIONAL STUDIES Preliminary Geochronological Studies in 19 Northeastern Newfoundland Basement Rocks in the Northern Appalachians: 21 Preliminary Data on the Massabesic Gneiss, Manchester Area Further Work on the Archean Complex in 23 Sierra Leone Approximate Location of the Boundary Between 25 the Eburnean and Liberian Orogenic Provinces in Eastern Liberia Rb-Sr Isotopic Investigation of Crater Rocks 27 of Possible Impact Origin Ph.D. THESIS INVESTIGATIONS Progress Report on the Isotopic Composition 31 of Strontium in Minerals from Ultramafic Inclusions in Basaltic Rocks Radiometric Ages and Paleomagnetism of 39 Canadian Diabase Dikes 1 A Test of Rb-Sr Whole-Rock Dating of 41 Diabase Dikes Preliminary Report on Rb-Sr Whole-Rock 43 Measurements on Precambrian Iron Formations of the Canadian Shield 87 86 Sr 1 Sr Initial Ratios and Whole-Rock Ages 45 of Pyroxene Granulite TECHNIQUES and STANDARDS Interlaboratory Comparisons and Rb and Sr 95 Isotope Dilution Analyses Progress Report on Rock Standards 99 Iron Extraction Procedures for Rb-Sr 103 Isotopic Determinations An Isotope Effect Suppressing Absorption 105 in Measuring Concentrations of Spike Solutions by Atomic Absorption Spectrophotometry BIBLIOGRAPHY Bibliography of Age Data on Continental 107 Basement Rocks MISCELLANEOUS Reprints of Published Reports, 1968-1969: Correlation of Radiometric Ages of Nipissing 129 Diabase and Huronian Metasediments with Proterozoic Orogenic Events in Ontario Review of Age Data in West Africa and South 131 America Relative to a Test of Continental Drift A Rb-Sr Geochronologic Study of the 133 Pegmatites of the Middletown Area, Connecticut Pre-Drift Continental Nuclei 137 Strontium Isotopic Compositions of Gangue 143 Minerals from Hydrothermal Vein Deposits Strontium Isotope Variation and Whole-Rock 145 Isochron Studies, Grenville Province of Ontario Precambrian Gneisses from Northern 151 Colombia, South America Abstracts of Papers Presented at Meetings 153 Reviews 155 1t Additions zo the Project Bibliography 157 1 Investigation of Continental Accretion in Laurasia Patrick M. Hurley Int oduction The concept of continental accretion has been examined therefore use this phenomenon to provide a mappable by many investigators. In particular it has been advo- geologic unit, and propose the term "orogenic series" cated by those who have used Sr87/Sr86 initial ratios in in keeping with the usage in stratigraphy. Detailed igneous rocks as an indication that new material has been investigations (see elsewhere in this Volume) have in- added to the crust progressively throughout time in suc- dicated that the scatter plot in Figure 1 is actually cessive and generally peripheral orogenies. The object made up of discrete isochron plots indicating distinct i of this report is a more detailed examination of the hy- episodes o f plutonic and metamorphic acti.vi.ty. Names pothesis, after assuming that continental drift has oc- have been given to these individual episodes here and curred since mid-Phanerozoic times, and that the recon- in Europe, ouch as Caiedonian, Acadian, Hercynian, and stricted cupereontinent of Laurasia presents a more real- Taconic, and there has been much discussion about the istic test. Of particular interest is the distribution continuity of these individual episodes over great dis- of late Precambrian and Phanerozoic orogenies, which may yances. It is proposed that the aggregate or these epi- permit further examination of the suggestion by Hurley sodes be termed an "orogenic series" in that it deline- and Rand (1969) that there was no significant drift ates a province within which there is a limited number prior to this last break-up of the continents. of discrete events which in obscure cases are indicated Geological mapping requires the adoption of uniti. simply by a bounded array of whole-rock Rb-Sr points as Since this is a study of possible continental accretion, „in Figure 1. applied we are interested in the distribution in time and space The name "Appalachian Orogenic Series" might be of some defined unit of new crust in each of several to the band in North America. The same band appears to successive time units. The selection of such mappable be underlying much of western Europe. In view of the units obviously depends upon carefully stated definitions. older age values currently being found in most of the Thus the present continental crust is defined as. that Pan-African of Africa, the Adelaide and Tasman of Aus- material above the moho which has typical crustal seis- tralia, the Carriri and Paraiba of South America, the mic velocities due in major part to the presence of Trans-Antarctic and Paleozoic belts of Antarctica, and feldspar; and furthermore as that material which has the belts south of the Russian and Siberian shields been piled up by undefined geological processes above and north of the alpine orogeny in central Asia, are the mean level of the earth's surface, and currently of the same age span. In addition there is good indi- resides in approximate isostatic equilibrium within cation that a similar zone of geological activity lies the boundaries of the continental This is in slopes. between older and younger belts around northern and contrast to the usage by Zartman and Wasserburg (1969) western South America. (for example), who include the lithosphere below the In this kind of map unit the consideration of the age crust in the definition of the term. Also only the of the sedimentary materials which may be caught up in present··crust will be considered, so that any former the orogenic activity is eliminated. Thus a clear dis- crustal material which has been recycled through the tinction is made between currently used map units and mantle will be said to have an age only equivalent to the new one proposed here. In this case there ic in- that since its last appearance at the earth'R surface. cluded only igneous and metamorphic rocks or their This is a key part of the definition and side-steps metasomatic off-shoots at the time of their intrusion 87 the question of whether radiogenic Sr is constantly of thermal development. This decision stems from the lost by mantle recycling of crustal materials. fact that most whole-rock Rb-Sr measurements to date have It is now necessary to examine the ratio of radiogenic indicated very little difference between the apparent 87 87 Sr /Rb in total rock materials within a single oro- ages of metamorphic rocks and accompanying igneous bo- genic region.