Episodic crustal growth in the Tanzania Craton:evidence from Nd isotope compositions

(整期优先)网络出版时间:2018-02-12
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TheanalysisofavailableNdisotopedatafromtheTanzaniaCratonplacesimportantconstraintsonthecrest-mantleseparationages,andeventsmarkingjuvenilecrustaladditionandcrustalrecycling.Ndmodelagesdatetheoldestcrustextractionto3.16GaintheTanzaniaCraton,althougharockrecordofsuchantiquityisyettobefoundthere.Themostsignificantperiodofjuvenilecrustaladditionaswellascrustalrecyclingis2.7-2.6Ga.TheNdisotopesofmariesamplesshowthatchemicalheterogeneityexistedinthemantlebeneaththeTanzaniaCraton,withsomesamplesoriginatingfromsignificantlydepletedmantle,andmostsamplesoriginatingfromthemixtureofprimitivemantleanddepletedmantle.TheNdisotopesectionrevealssignificantdifferencesinNdisotopesbetweenthenortheratonandcentralcraton;comparedtothenorthcraton,thecentralcratonyieldsaNdmodelagethatisapproximately100Maolder,anditsεNd(t)valuesaremorenegative,indicatingthatthetwopartsofthecratonhavedifferentmantlesourceregions.DifferenttypesofgranitoidsaredistributedintheTanzaniaCraton,suchashigh-Kandlow-Algranite,ealc-alkalinegranite,peraluminousgraniteandtransitionaltypesoftonalite-trondhjemite-granodiorites(TTGs).Mostofthegranitoidsformedlaterthanthemarierocksinsyn-collisionandpostcollisionevents.