Zhang et al.，2012-A polyphase metamorphic evolution for the Xitieshan paragneiss of the north Qaidam UHP metamorphic belt.pdf

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1、Lithos136–139(2012)27–45ContentslistsavailableatSciVerseScienceDirectLithosjournalhomepage:www.elsevier.com/locate/lithosApolyphasemetamorphicevolutionfortheXitieshanparagneissofthenorthQaidamUHPmetamorphicbelt,westernChina:In-situEMPmonazite-andU–PbzirconSHRIMPda

2、tinga,bba,⁎,ChrisSpiersbCongZhang,HermanvanRoermund,LifeiZhangaKeyLaboratoryofOrogenicBeltsandCrustalEvolution,MOE,SchoolofEarthandSpaceSciences,PekingUniversity,Beijing100871,ChinabDepartmentofEarthScience,StructuralGeologyandTectonics,UtrechtUniversity,3508TA,Ut

3、recht,TheNetherlandsarticleinfoabstractArticlehistory:In-situelectronmicroprobe(EMP)U–Th–Pbmonazite-,sensitivehigh-resolutionionmicroprobe(SHRIMP)Received10December2010zirconanalyses,metamorphicphaseequilibrium(Domino/Theriak)-andgeothermobarometriccalculationsAcc

4、epted29July2011areperformedonkyanite/sillimanite-bearinggarnetbiotitegneissesformingpartofthedominantrockasso-Availableonline18August2011ciationintheXitieshanultra-highpressuremetamorphicbelt,northQaidam,westernChina.Resultsarecon-sistentwiththefollowingcomplexpol

5、yphasetectono-metamorphicevolution.Keywords:Thekyanite/sillimanitebearinggarnetbiotitegneissescontainmonaziteagesof938±23MaandzirconParagneissEMPmonazitedatingSHRIMPagesof945±7Ma,referringtoaNeoproterozoicmetamorphism,i.e.similartotheageoftheJinningSHRIMPzircondat

6、ingorogenyintheYangtzeblockofsouthernChina.ThiscorrelationsuggeststhattheparagneisshasaffinitiesEarlyProterozoicmetamorphismwiththeYangtzeblock(SouthChinablock).TheNeoproterozoicmonaziteswerefoundinsidecoarsegrainedXitieshanporphyroblasticgarnetscontainingamphiboli

7、tefaciesmineralinclusionassemblages.NorthQaidamUHPMbeltThekyanite/sillimanite-bearinggarnetbiotitegneissesalsocontainearlyPaleozoicmonaziteagesof422–425Maand455–460Ma,detectedinamphibolitefaciesmineralassemblagesassociatedwithmatrixmin-erals.Usingphaseequilibrium-

8、andgeothermobarometriccalculations,PTconditionsof560–610°C/5.8–7.0kbarand610–675°C/4.6–6.5kbarwerecalculatedrespectivelyforbothamphibolitefaciesassembla