Platinum-group Mineral (PGM) and Base-metal Sulphide (BMS) Inclusions in Chromitites of the Zedang Ophiolite, Southern Tibet, China and their Petrogenetic Significance

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摘要 Voluminousplatinum-groupmineral(PGM)inclusionsincludingerlichmanite(Os,Ru)S2,laurite(Ru,Os)S2,andirarsite(Ir,Os,Ru,Rh)AsS,aswellasnativeosmiumOs(Ir)andinclusionsofbasemetalsulphides(BMS),includingmillerite(NiS),heazlewoodite(Ni3S2),covellite(CuS)anddigenite(Cu3S2),accompaniedbynativeiron,havebeenidentifiedinchromititesoftheZedangophiolite,Tibet.ThePGMsoccurasbothinclusionsinmagnesiochromitegrainsandassmallinterstitialgranulesbetweenthem;mostarelessthan10μminsizeandvaryinshapefromeuhedraltoanhedral.Theyoccureitherassingleorcomposite(biphaseorpolyphase)grainscomposedsolelyofPGM,orPGMassociatedwithsilicategrains.Os-,Ir-,andRu-richPGMsarethecommonspeciesandPt-,Pd-,andRh-richvarietieshavenotbeenidentified.SulfurfugacityandtemperatureappeartobethemainfactorsthatcontrolledthePGEmineralogyduringcrystallizationofthehostchromititeintheuppermantle.Iftheactivityofchalcogenides(suchasS,andAs)islow,PGEclusterswillremainsuspendedinthesilicatemeltuntiltheycancoalescetoformalloys.Underappropriateconditionsof?S2and?O2,PGEalloysmightreactwiththemelttoformsulfides-sulfarsenides.Thus,wesuggestthattheOs,IrandRumetallicclustersandalloysintheZedangchromititescrystallizedfirstunderhightemperatureandlow?S2,followedbycrystallizationofsulphidesofthelaurite-erlichmanite,solid-solutionseriesasthemagmacooledand?S2increased.TheabundanceofprimaryBMSinthechromititessuggeststhat?S2reachedrelativelyhighvaluesduringthefinalstagesofmagnesiochromitecrystallization.ThediversityofthePGEminerals,incombinationwithdifferencesinthepetrologicalcharacteristicsofthemagnesiochromites,suggestdifferentdegreesofpartialmelting,perhapsatdifferentdepthsinthemantle.Theestimatedparentalmagmacompositionsuggestsformationinasuprasubductionzone
机构地区 不详
出处 《地质学报:英文版》 2016年3期
出版日期 2016年03月13日(中国期刊网平台首次上网日期,不代表论文的发表时间)
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