DOCSLIB.ORG

Alteration of Ghromite from the Twin Sisters Dunite, Washington

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Alteration of Ghromite from the Twin Sisters Dunite, Washington American Mineralogist, Volume 59, pages 608412' 1974 Alterationof Ghromitefrom the Twin SistersDunite, Washington ANrnoNv C. ONYracocne' Department of Geological Sciences, Uniuersity of llashington, Seattle, Washington 98 195 Affiact Chromite in the Twin Sistersdunite, an alpine-type ultramafic body some 90 km2, occurs as minor disseminatedeuhedral-subhedral crystals or in clusters forming pods and lenses.Modal proportions of chromite in the pods and lensesare frequently as high as 80 percent.Ferritchromite occurs as rims on chromite crystalsthat are bordered by chlorite and (where still available) olivine' Microprobe analysesof chromite, ferritchromite, chrome-magnetite,olivine, and chlorite show that the chromite-ferritchromite boundary is sharp (lessthan l0 microns) and that, relative to chromite' ferritchromite is enriched in Cr, Fe, Ni, and Mn and impoverished in Mg and Al' However, when chrome-magnetite,found only in association with serpentine,is the alteration product, there is a marked decreasein chromium. Chromite alteration appearsto take place above the upper stability limit of serpentineand below that of chlorite. Inhoduction Two types of chromite alteration were recognized in this study.In one,the alterationproduct is chrome- Alteration of chromite to opaque highly reflecting bearingmagnetite which is associatedwith serpentine. bordershas beenreported by severalauthors (Weiser, In the other, the alteration product is ferritchromite 1967;Kern, 1968;Mih6lik and Saager,1968; Beeson which is in no way associated with serpentine. and Jackson,1969; Frisch, 1971).Because the altera- Serpentineassociated with the magnetite was not tion product is rich in iron, it has been called "gray studiedin detail. magnetite" (Horninger, l94l) or "ferritchromit" (Spangenberg,1943). Several quantitative chemical PehograPhY descriptions of this alteration product have been Chromite crystals in the Twin Sisters dunite worked out (Table l). Most workers, however, (Ragan, 196?)occur either as disseminated,euhedral- investigated only the distribution of the major to-subhedralgrains which constituteless than I per- elements between the chromite and its alteration of the rock, or as concentrationsin bands or product. In this investigation,the behavior of four cent schlieren.They also occur in clustersforming pods major elements(Mg, Fe, Al, and Cr) and also six and lensessome 0.3 metersor more thick. Thesepods minor elements(Ni, Mn, Co, Ti, Zn, and V) were and lensesare distributed irregularly over the entire studied. body. Modal proportions of chromite in these Beesonand Jackson(1969) reported that chromite rock pods and lensesare frequently as high as 80 percent. alteration accompanies the change of associated The chromite crystals in the pods and lenses are olivine and orthopyroxeneto chlorite. Many of the anhedral and some display gran- reported instancesof chromite alteration have been characteristically margins. The dominant, although restricted, related to serpentinizationperhaps caused by late ulated in the original chromite pods and lensesis the pneumatolytic-hydrothermalsolutions (Kern, 1968). change breakdown of chromite plus olivine and enstatite to From a fresh dunite nodule from a basaltic tuff, ferritchromite and chlorite. Frisch (1971) reported chromite alteration that The chromite alteration product in three specimens appears to have resulted from high-temperature, from chromite lenses from locations 2, 5, and 7 late-magmaticprocesses prior to eruption. (Figure 2, Onyeagocha,1973)were studied in detail. developedferrit- I Present address: Department of Mineral Sciences,Smith- Severalchromite crystalswith well sonian Institution, Washington, D. C. 20560. chromite rims were studied, but data are presented 608 ALTERATION OF CHROMITE 609 for only a few that illustrate the extent and nature of Tnsrp 1. Pattern of Chromite Alteration this alteration. These samplesconsist of unaltered chromiteand olivine with local zonesof ferritchromite No Pattern Enrlched in chromite Enriched in Ferrl.tchromlte and light purple chlorite. The chromite grains are Al, Mg Fe, Cr ((reiser, Case I,1967) A1, Mg, Cr fe (Weiser, Case II, 1967) anhedralto subhedral.Chlorite is kinked, representing A1, Mg, Cr Fe (Mlhaltk & Saager, 1968) an adjustmeritto forces exertedby the surrounding A1, Mg. Cr Fe (Beeson & Jackson, 1969) chromite during chlorite growth. Cr At, Mg Fe (Lapham, 1964) There is some A1 Fe (whlte,1966) textural intergrowth of ferritchromite and chlorite Cr Fe (Mulr & Ttlley, 1964) Cr, A1, Mg, Zn Fe, Ti, Ni (Frlsch, 1971) (identified as chlorite by partial microprobe analysis) AI, Mg Fe, Cr, Nl, Mn, Co, T1, much like that shown by Golding and Bayliss(1968, Zn, V (ThIs study) p. 174, Figure 8) which they called "coarsely pitted Cr, A1, Mg Fe, Co, Zn, Ni. (Enriched ln wgnetlte) (Thls study) alteredchromite." At the boundary between a chromite lens and dunite,chromite alteration did not yield ferritchromite and later re-equilibratedat lower temperature.This but instead chrome-bearingmagnetite and books of is corroborated by the data in Table 3 for chrome- kinked green chlorite. The magnetite is associated bearing magnetite where apparent equilibration with serpentine.Instead of the increasein Cr observed temperatures,for what they are worth, are negative. in the other samples,the alteration product showsa No difference in temperature is'apparent between tremendousdecrease in Cr. The lower Cr content olivine-chromite and olivine-ferritchromite in this noted in magnetite relative to ferritchromite is study (Table 3) nor did Frisch (1971) notice any accompaniedby a lower Cr content of coexisting, difference.Since the olivine is, in general,homoge- greenchlorite relativeto the purple chlorite. neous, an alternateinterpretation of re-equilibration Discussion with olivine richer in iron is not applicablehere. In fact, judging from the equation written for alteration Microprobe analyses of phases associatedwith of chromite to ferritchromite using the actual analyt- chromite alteration (Table 2) show that olivine is ical data obtained in this study, it appearsthat the particularly homogeneous.No grain-to-grain-varia- initial olivine is richer in iron. The equation'assumes tions wereobserved, nor did stepscans across individ- that Al, Cr, and Mg wereconserved. ual grains reveal any inhomogeneity. Unaltered go. - * chromitein thesespecimens exhibits no variationsthat 4. 4 4(M zrFe' r uAI0. z u F eBo. oe) On " :lf :-rtr."r could not be accounted for by count statistics. Ferritchromiteand chrome-bearingmagnetite showed * 3.52(Mg.r,.€,Fe'*'. le Sion) slight inhomogeneity.Cr, Fe, and Al in chlorite are remarkably variable within grains and from grain to f 2.54(Meo.:LT:,:.0,SiO3)+ 8 H,O + 0.27O' grain. Within grain a single the Cr-content increases * toward : 3( M 96.55 F"' lo.08 F es o.a u) On the unaltered chromite core and decreases *.::11"".."1l?A towards olivine. For example,specimen 5-5A (near chromite) has 3,2 percent CrrO, whereas 5-5B * ( Mg,o. rrCr6.nrAlr. rTFe'*0.lex Si6.06Alr. s4) O2o o Hr6 (near olivine) only contains 0.10 percent CrrO, (Table 2). ExcessFe and Si were partitioned to form forsterite and Figure I showsstep scansacross a crystal in which enstatitewith the sameFe/Mg ratio. Written in the chromite-ferritchromiteboundary is shdrp (less this manner, the equation showsthat only HrO and than l0 microns). The scansalso show that, relative O, need be introduced. The alteration, therefore, to the chromitc, ferritchromite is enrichedin Cr, Fe, appearsto be a responseto changingoxygen fugacity (Irvine, Ni, and Mn, and impoverishedin Mg and Al. The 1965)and changing/rr,o. pattern is not clear for Co, Zn, andY. A volume-for-volumereplacement of the outcrop as postulatedby Beesonand Jackson(1969, p. 1096) The decreasein the ratios, Mg/(Mg f Fe,*) and Al/(Cr + Al + Fe'*), and the simultaneousincrease z In in Fe'*/(Cr + Al + Fe'*) observedin both types of writing this equation, specimen 2-4Afr1 was used for chromite, ferritchromite, and chlorite. No found chromite alteration olivine was according to Jackson (1969), within severalcm ofthis crystal. Olivine used in the equation is indicatesthat the chromite formed at high temperature from specimen2-4 and is some l0 cm away from2-4A. 610 ANTHONY C, ONYEAGOCHA Tnsle 2. Electron Microprobe Analysesof Chromite, Ferritchromite, Magnetite, Olivine, and Chlorite fro'm the Twjn SistersDunite, Washington CHROMITE FERRITCI{ROMITE MAGNETITE 2-4 2-4A#L 2-4Lll2 5-4B 5-4c 5-4D 5-5 5-5D 5-7 z4Alll 2-4All2 5-5 5-4A 5-48 5-4C 5-7 Tto2 0.03 0.05 0.05 0.10 0.13 0.08 0.08 0.08 0.05 0.12 0.90 0.13 0.02 0.03 0.02 0.02 AL2o3 2r.3 20.6 2t.l LL.7 10.7 16.6 17.5 16.8 18.1 1.8 2.7 9.9 0.48 0,57 0.67 0.56 Cr2O3 47.O 47.7 46.5 51.s 52.7 47.L 51.1 50.8 50.4 56.0 54.9 55.5 0.07 0.25 1.9 4.2 Fe203* 3.8 3.7 4.O 9.7 10.4 5.8 4.L 4.6 3,9 13.1 13.0 1,9 69,5 59.6 67.7 64.9 FeO* 11.0 11.3 10.8 13.9 L3.7 L7.9 t2,4 13.5 12.6 L4.7 t3.7 14.r 25.i 25.5 26,4 27.2 lfnO 0.23 0,24 0.41 0.50 0.58 0.52 0.44 0,47 0.4 o.47 0.63 0.55 o.22 0.18 0.18 0.45 MsO 15.5 L5.2 r5.4 L2.6 12.8 10.3 14.3 L3.4 L4.2 10.1 11,5 L2.4 2.4 2.4 2.O L.7 CoO 0.04 0.03 0.04 0.08 0.11 0.11 0.07 0.08 0.05 0.04 0.08 0.10 o.25 0,23 0.22 0.21 ZnO 0.05 0.07 0.03 0.14 0.14 0,27 0.05 0.08 0.05 0.20 0.14 0.10 0.29 0,29 0.23 0.24 N10 0.10 0, L0 0.09 0.r1 0.15 0,09 0.08 0.09 0.09 0.49 0.34 0.13 1.4 1.5 L.4 0.50 vZ03 0.11 0,12 0.12 0.16 0.19 0.21 0.16 0,18 0.12 0.16 0.16 0.19 0.05 0.07 0.04 0.13 Total 99, 16 99.
Load more

Recommended publications
  • Podiform Chromite Deposits—Database and Grade and Tonnage Models
    Podiform Chromite Deposits—Database and Grade and Tonnage Models Scientific Investigations Report 2012–5157 U.S. Department of the Interior U.S. Geological Survey COVER View of the abandoned Chrome Concentrating Company mill, opened in 1917, near the No. 5 chromite mine in Del Puerto Canyon, Stanislaus County, California (USGS photograph by Dan Mosier, 1972). Insets show (upper right) specimen of massive chromite ore from the Pillikin mine, El Dorado County, California, and (lower left) specimen showing disseminated layers of chromite in dunite from the No. 5 mine, Stanislaus County, California (USGS photographs by Dan Mosier, 2012). Podiform Chromite Deposits—Database and Grade and Tonnage Models By Dan L. Mosier, Donald A. Singer, Barry C. Moring, and John P. Galloway Scientific Investigations Report 2012-5157 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2012 This report and any updates to it are available online at: http://pubs.usgs.gov/sir/2012/5157/ For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Suggested citation: Mosier, D.L., Singer, D.A., Moring, B.C., and Galloway, J.P., 2012, Podiform chromite deposits—database and grade and tonnage models: U.S.
    [Show full text]
  • PRELIMINARY EVALUATION of BEDROCK POTENTIAL for NATURALLY OCCURRING ASBESTOS in ALASKA by Diana N
    Alaska Division of Geological & Geophysical Surveys MISCELLANEOUS PUBLICATION 157 PRELIMINARY EVALUATION OF BEDROCK POTENTIAL FOR NATURALLY OCCURRING ASBESTOS IN ALASKA by Diana N. Solie and Jennifer E. Athey Tremolite (UAMES 34960) displaying the soft, friable fibers of asbestiform minerals. Sample collected from the Cosmos Hills area, Kobuk District, Alaska, by Eskil Anderson. Image courtesy of the University of Alaska Museum Earth Sciences Department. June 2015 Released by STATE OF ALASKA DEPARTMENT OF NATURAL RESOURCES Division of Geological & Geophysical Surveys 3354 College Road, Fairbanks, Alaska 99709-3707 907-451-5020 dggs.alaska.gov [email protected] $2.00 (text only) $13.00 (per map sheet) TABLE OF CONTENTS Abstract ................................................................................................................................................................................................................................. 1 Introduction ........................................................................................................................................................................................................................ 1 General geology of asbestos ......................................................................................................................................................................................... 2 Naturally occurring asbestos potential in Alaska ..............................................................................................................................................
    [Show full text]
  • Oregon Geologic Digital Compilation Rules for Lithology Merge Information Entry
    State of Oregon Department of Geology and Mineral Industries Vicki S. McConnell, State Geologist OREGON GEOLOGIC DIGITAL COMPILATION RULES FOR LITHOLOGY MERGE INFORMATION ENTRY G E O L O G Y F A N O D T N M I E N M E T R R A A L P I E N D D U N S O T G R E I R E S O 1937 2006 Revisions: Feburary 2, 2005 January 1, 2006 NOTICE The Oregon Department of Geology and Mineral Industries is publishing this paper because the infor- mation furthers the mission of the Department. To facilitate timely distribution of the information, this report is published as received from the authors and has not been edited to our usual standards. Oregon Department of Geology and Mineral Industries Oregon Geologic Digital Compilation Published in conformance with ORS 516.030 For copies of this publication or other information about Oregon’s geology and natural resources, contact: Nature of the Northwest Information Center 800 NE Oregon Street #5 Portland, Oregon 97232 (971) 673-1555 http://www.naturenw.org Oregon Department of Geology and Mineral Industries - Oregon Geologic Digital Compilation i RULES FOR LITHOLOGY MERGE INFORMATION ENTRY The lithology merge unit contains 5 parts, separated by periods: Major characteristic.Lithology.Layering.Crystals/Grains.Engineering Lithology Merge Unit label (Lith_Mrg_U field in GIS polygon file): major_characteristic.LITHOLOGY.Layering.Crystals/Grains.Engineering major characteristic - lower case, places the unit into a general category .LITHOLOGY - in upper case, generally the compositional/common chemical lithologic name(s)
    [Show full text]
  • THE WEBSTER-ADDIE ULTRAMAFIC RING, JACKSON COUNTY, NORTH CAROLINA, and SECONDARY ALTERATION of ITS CHROMITE* Roswur Mrrr,Bn III, Drokescorner Road, Princeton, I{
    THE WEBSTER-ADDIE ULTRAMAFIC RING, JACKSON COUNTY, NORTH CAROLINA, AND SECONDARY ALTERATION OF ITS CHROMITE* Roswur Mrrr,Bn III, DrokesCorner Road, Princeton, I{. J. Assrnecr The structure of the webster-Addie ultramafic ring in Jackson county, North caro- lina, is discussed briefly. The ultramafic ring. is almost ever''where concordant with the enclosing and enclosed gneiss and is thought to haVe been intruded as a sheet-like mass and subsequently deformed. The mineralogy of the dunite, websterite, and enstatite pyroxenite is discussed. A table is presented showing that the FezSiOr content of nine olivines from the ultramafic ring varies only ll/6 and shows no "trend" across three quarters of the thickness of the mass. chemical analyses are given for the two types of enstatite from the enstatite pyroxenite, and for two chromite samples and one kammererite sample, The hydrothermal alteration of chromite to kammererite is described and photomicrographs presented to illustrate the progression of this reaction toward an ideal chromite-magnetite solid solution. GnNBner,GBorocy The Webster-Addie ultramafic ring lies in Jackson County, North Carolina, fifty miles southwest of Asheville. The ring, comprisedof dunite, websterite, and enstatite pyroxenite, is an ellipse with a maximum di- mension of six miles and a minimum dimension of three and a half miles. The greatest width of outcrop of the ultramafic rocks, just south of the town of Addie, is a little under four tenths of a mile. Except for very local areas, the Webster-Addie ultramafic rocks are concordant with the enclosing and enclosedgneiss. The gneissforms a dome on the flanks of which lies the thin band of dunite (Fig.
    [Show full text]
  • Medellín Dunite” Published Online 24 April 2020 Revisited: an Algebraic Approach and Proposal
    Volume 2 Quaternary Chapter 2 Neogene https://doi.org/10.32685/pub.esp.36.2019.02 The Petrologic Nature of the “Medellín Dunite” Published online 24 April 2020 Revisited: An Algebraic Approach and Proposal of a New Definition of the Geological Body Paleogene Antonio GARCIA–CASCO1* , Jorge Julián RESTREPO2 , 1 [email protected] Universidad de Granada 3 4 Ana María CORREA–MARTÍNEZ , Idael Francisco BLANCO–QUINTERO , Departamento de Mineralogía y Petrología Avenida Fuente Nueva s/n, 18079 5 6 7 Cretaceous Joaquín Antonio PROENZA , Marion WEBER , and Lidia BUTJOSA Granada, España Instituto Andaluz de Ciencias de la Tierra, Abstract The “Medellín Dunite”, the main ultramafic body of the Central Cordillera of CSIC–UGR Avenida de las Palmeras, 4, 18100 Armilla Colombia, constitutes a fragment of oceanic lithospheric mantle formed at a back–arc Granada, España basin/incipient arc scenario emplaced onto the western continental margin of Pangaea 2 [email protected] Universidad Nacional de Colombia Jurassic during Triassic time. This body has been classically, and is still considered, mainly of Sede Medellín dunite composition. However, in spite of two subsequent metamorphic imprints that GEMMA Research Group Medellín, Colombiaa obscure the primary mantle mineralogical composition, there is petrographic and geo- 3 [email protected] chemical evidence that points to a harzburgitic nature of the unit. In order to overcome Universidade de Brasília Instituto de Geociências Triassic the petrographic effects of medium–T metamorphism, metasomatism, and serpentini- Servicio Geológico Colombiano zation, we analyzed published and new major–element geochemical data by means of Dirección de Geociencias Básicas Grupo de Estudios Geológicos Especiales algebraic methods to approximate the mantle mineralogical composition of ultramafic Calle 75 n.° 79A–51 Medellín, Colombia rocks.
    [Show full text]
  • Mantle Melting and Origin of Basaltic Magma
    Lecture 18 - Mantle Melting Monday, 28th, March, 2005 Mantle Melting and Origin of Basaltic Magma 1 Two principal types of basalt in the ocean basins Tholeiitic Basalt and Alkaline Basalt Table 10-1 Common petrographic differences between tholeiitic and alkaline basalts Tholeiitic Basalt Alkaline Basalt Usually fine-grained, intergranular Usually fairly coarse, intergranular to ophitic Groundmass No olivine Olivine common Clinopyroxene = augite (plus possibly pigeonite) Titaniferous augite (reddish) Orthopyroxene (hypersthene) common, may rim ol. Orthopyroxene absent No alkali feldspar Interstitial alkali feldspar or feldspathoid may occur Interstitial glass and/or quartz common Interstitial glass rare, and quartz absent Olivine rare, unzoned, and may be partially resorbed Olivine common and zoned Phenocrysts or show reaction rims of orthopyroxene Orthopyroxene uncommon Orthopyroxene absent Early plagioclase common Plagioclase less common, and later in sequence Clinopyroxene is pale brown augite Clinopyroxene is titaniferous augite, reddish rims after Hughes (1982) and McBirney (1993). Each is chemically distinct Evolve via FX as separate series along different paths ● Tholeiites are generated at mid-ocean ridges ✦ Also generated at oceanic islands, subduction zones ● Alkaline basalts generated at ocean islands ✦ Also at subduction zones 2 Sources of mantle material ● Ophiolites ✦ Slabs of oceanic crust and upper mantle ✦ Thrust at subduction zones onto edge of continent ● Dredge samples from oceanic fracture zones ● Nodules and xenoliths in some basalts ● Kimberlite xenoliths ✦ Diamond-bearing pipes blasted up from the mantle carrying numerous xenoliths from depth Lherzolite is probably fertile unaltered mantle Dunite and harzburgite are refractory residuum after basalt has been extracted by partial melting 15 Tholeiitic basalt 3 10 O 2 Partial Melting Wt.% Al Wt.% 5 Figure 10-1 Brown and Mussett, A.
    [Show full text]
  • The Halifax County Complex: Oceanic Lithosphere in the Eastern North Carolina Piedmont
    The Halifax County complex: Oceanic lithosphere in the eastern North Carolina Piedmont LUCILLE E. KITE* I Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, EDWARD F. STODDARD J North Carolina 27695 ABSTRACT represents the lower portions of a lithospheric 1979) was followed by Farrar's (1980) report section produced at a mid-ocean ridge or in a on the geology of the eastern North Carolina The Halifax County complex, in the Eastern marginal basin, or, perhaps more likely, it was Piedmont. Slate Belt of North Carolina, consists of the low- formed in the early stages of the development of Prior to this investigation, the Halifax com- grade metamorphic equivalents of the following an intraoceanic volcanic arc. We believe the plex had been studied in a preliminary fashion lithologic groups: (1) an ultramafic group com- Halifax complex is representative of the under- by Stoddard and Teseneer (1978), who sug- posed of peridotite, pyroxenite, and dunite, lo- pinnings of the Eastern Slate Belt volcanic arc. gested a possible early Paleozoic oceanic origin cally preserving cumulate textures; (2) gabbroids for the complex. The important implications of consisting of leucogabbro, anorthosite, and gab- INTRODUCTION an oceanic origin for the Halifax complex, and bro; (3) local quartz diorite and plagiogranite; the constraints it would place upon tectonic and (4) a relatively large volume of porphyritic The Halifax County mafic-ultramafic com- models for the region, accentuate the signifi- and massive basaltic rocks. Within the complex, plex, located in the extreme eastern Piedmont of cance of examining these rocks in detail. This the lithologies conform approximately, from North Carolina, consists of the greenschist to paper, then, reports on the petrology and geo- west to east, to the sequence: peridotite and lowermost amphibolite-facies metamorphic chemistry of the rocks and primary minerals dunite-pyroxenite-anorthosite and leucogabbro- equivalents of associated mafic and ultramafic within the Halifax County complex.
    [Show full text]
  • The Earliest Lunar Magma Ocean Differentiation Recorded in Fe Isotopes ,∗ Kun Wang (王昆) a , Stein B
    Earth and Planetary Science Letters 430 (2015) 202–208 Contents lists available at ScienceDirect Earth and Planetary Science Letters www.elsevier.com/locate/epsl The earliest Lunar Magma Ocean differentiation recorded in Fe isotopes ,∗ Kun Wang (王昆) a , Stein B. Jacobsen a, Fatemeh Sedaghatpour a, Heng Chen b, Randy L. Korotev b a Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA b Department of Earth and Planetary Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA a r t i c l e i n f o a b s t r a c t Article history: Recent high-precision isotopic measurements show that the isotopic similarity of Earth and Moon is Received 25 March 2015 unique among all known planetary bodies in our Solar System. These observations provide fundamental Received in revised form 13 August 2015 constraints on the origin of Earth–Moon system, likely a catastrophic Giant Impact event. However, in Accepted 17 August 2015 contrast to the isotopic composition of many elements (e.g., O, Mg, Si, K, Ti, Cr, and W), the Fe isotopic Available online xxxx compositions of all lunar samples are significantly different from those of the bulk silicate Earth. Such Editor: B. Buffett a global Fe isotopic difference between the Moon and Earth provides an important constraint on the Keywords: lunar formation – such as the amount of Fe evaporation as a result of a Giant Impact origin of the Iron isotopes Moon. Here, we show through high-precision Fe isotopic measurements of one of the oldest lunar rocks Origin of the Moon (4.51 ± 0.10 Gyr dunite 72 415), compared with Fe isotope results of other lunar samples from the Apollo Giant Impact program, and lunar meteorites, that the lunar dunite is enriched in light Fe isotopes, complementing the Lunar Magma Ocean theory heavy Fe isotope enrichment in other lunar samples.
    [Show full text]
  • Significance of the Concentration Gradients Associated with Dunite Bodies in the Josephine and Trinity Ophiolites
    Article Geochemistry 3 Volume 9, Number 7 Geophysics 29 July 2008 Q07025, doi:10.1029/2008GC001954 GeosystemsG G ISSN: 1525-2027 AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES Published by AGU and the Geochemical Society Click Here for Full Article Significance of the concentration gradients associated with dunite bodies in the Josephine and Trinity ophiolites Zachary Morgan and Yan Liang Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA ([email protected]) Peter Kelemen Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA [1] Detailed transects were sampled across dunite bodies in the Josephine and Trinity ophiolites. The major peridotite lithologies sampled in the Josephine transect are a sequence of dunite and harzburgite and in the Trinity transect a sequence of dunite, harzburgite, lherzolite, and plagioclase lherzolite (DHL-PL). Major, minor, and selected trace element abundances in olivine, orthopyroxene, clinopyroxene, and spinel were measured. The composition profile from the Josephine transect has revealed a concentration gradient near the dunite-harzburgite contact. The composition profile from the Trinity transect has revealed several concentration gradients: two within the dunite, one in the harzburgite, and at least two in the plagioclase lherzolite. The composition profiles record complex histories of melt transport, melt-rock reaction, and subsequent subsolidus reequilibration. Analyses of closure distance suggest that compositional variation trends for a majority of major and minor elements in olivine, clinopyroxene, orthopyroxene, and spinel reported in this study were magmatic in origin. Subsolidus reequilibration may reduce the range or magnitude of variations for the 2+ cations such as Fe and Mg in olivine and spinel and significantly redistribute Ca and Li in coexisting minerals.
    [Show full text]
  • Pyroxenes As Tracers of Mantle Water Variations 10.1002/2013JB010328 Jessica M
    PUBLICATIONS Journal of Geophysical Research: Solid Earth RESEARCH ARTICLE Pyroxenes as tracers of mantle water variations 10.1002/2013JB010328 Jessica M. Warren1 and Erik H. Hauri2 Key Points: 1Department of Geological and Environmental Sciences, Stanford University, Stanford, California, USA, 2Department of • Peridotite pyroxenes provide constraints on upper mantle water Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC, USA variations • Water in olivine is calculated from water in pyroxene and partition Abstract The concentration and distribution of volatiles in the Earth’s mantle influence properties such as coefficients melting temperature, conductivity, and viscosity. To constrain upper mantle water content, concentrations of • Peridotites are relatively water rich for the residues of partial melting H2O, P,and F were measured in olivine, orthopyroxene, and clinopyroxene in mantle peridotites by secondary ion mass spectrometry. Analyzed peridotites are xenoliths (Pali Aike, Spitsbergen, Samoa), orogenic peridotites (Josephine Peridotite), and abyssal peridotites (Gakkel Ridge, Southwest Indian Ridge, Tonga Supporting Information: • Readme Trench). The comparison of fresh and altered peridotites demonstrates that low to moderate levels of • Table S1 alteration do not affect H2O concentrations, in agreement with mineral diffusion data. Olivines have • Table S2 diffusively lost water during emplacement, as demonstrated by disequilibrium between olivine and • Table S3 • Table S4 coexisting pyroxenes. In contrast, clinopyroxene and orthopyroxene preserve their high-temperature water contents, and their partitioning agrees with published experiments and other xenoliths. Hence, olivine water Correspondence to: concentrations can be determined from pyroxene concentrations using mineral-mineral partition coefficients. J. M. Warren, Clinopyroxenes have 60–670 ppm H2O, while orthopyroxenes have 10–300 ppm, which gives calculated olivine [email protected] concentrations of 8–34 ppm.
    [Show full text]
  • Melting and Metasomatism/Refertilisation Processes in the Patagonian Sub-Continental Lithospheric Mantle
    Melting and metasomatism/refertilisation processes in the Patagonian sub-continental lithospheric mantle: A review Massimiliano Melchiorre, Barbara Faccini, Michel Grégoire, Mathieu Benoit, Federico Casetta, Massimo Coltorti To cite this version: Massimiliano Melchiorre, Barbara Faccini, Michel Grégoire, Mathieu Benoit, Federico Casetta, et al.. Melting and metasomatism/refertilisation processes in the Patagonian sub-continental lithospheric mantle: A review. Lithos, Elsevier, 2020, 354-355, pp.105324. 10.1016/j.lithos.2019.105324. hal- 03267036 HAL Id: hal-03267036 https://hal.archives-ouvertes.fr/hal-03267036 Submitted on 22 Jun 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/337816314 Melting and metasomatism/refertilisation processes in the Patagonian sub- continental lithospheric mantle: A review Article in Lithos · December 2019 DOI: 10.1016/j.lithos.2019.105324 CITATIONS READS 0 22 6 authors, including: Massimiliano Melchiorre
    [Show full text]
  • W2j980 2B 1986/28
    W2J980_2B 1986/28. Ultramafic-mafic complexes of western Tasmania and Platinum Group Element (PGE) minerals. A.V. Brown Abstract Platinum group element (PGE) minerals have been mined in the past from placer deposits associated with some of the ultramafic­ mafic rocks of western Tasmania. Recent studies have shown that the ultramafic complexes can be divided into three groups on their mineralogy and chemistry. All past 'osmiridium' deposits are associated with one of these groups, the LDH succession. Another of the groups, the LPG succession, has recently been shown to have platinum-palladium sulphide and 'osmiridium' minerals associated with zones of chromite concentrations in one of the ultramafic units. INTRODUCTION Because of the recent interest by exploration companies in the possibility of PGE deposits in western Tasmania, and to requests for information 'in press', the following report has been compiled. The report consists of a brief literature summary of reports on PGE deposits in Tasmania; the abstract of the paper "Geology and platinum-group element (PGE) geochemistry of the Serpentine Hill Complex, Dundas Trough, western Tasmania"; and, as Appendix 1, the section on the ultramafic-mafic complexes of western Tasmania which will be included in Geological Survey Bulletin 62, due to be published in the near future. BACKGROUND Tasmania was a major supplier to the world of 'osmiridium', produced from placer deposits during 1912 to 1925, at which point the production from the Witwatersrand surpassed that of Tasmania. The Os-Ir-Ru alloy grains were mined from alluvial and eluvial deposits associated with some of the ultramafic-mafic complexes in western Tasmania.
    [Show full text]