Petrogenesis of the microcrystalline-dioritic enclaves from Jiuling granitoids in the eastern segment of Jiangnan Orogen and constraints on magma source materials

NumerousdarkenclaveswithdifferentshapesarefoundinJiulingNeoproterozoicgranitoids.PreciseLAICP-MSU-Pbdatingwasconductedonzirconsextractedfromtwomicrocrystallineenclavesamples,yieldingcrystallizationagesof822.6±5.8Maand822.2±6.2Ma,respectively.Theconsistentageswithinanalyticalerrorswiththehostgranitoidssuggestedthattheyweretheproductsofthesamemagmatism.Themicrocrystalline-dioriticenclavescommonlyshowplasticformsandcontainsimilarplagioclasemegacryststothehostrocks,andbothoftheenclavesandhostgranitoidsshowedacomplexcompositionandstructuralimbalanceinplagioclases.Furthermore,theapatiteswithaeuhedralacicularshapeoccurredwidelyinthemicrocrystalline-dioriticenclaves.Allofthesepetrographicfeaturesaboveimplymagmamixingisinvolvedintheirdiagenesis.TheenclavesandhostgranitoidsshowamarkedzircontraceelementdifferenceandHfisotopicsignatureswithoutcorrelationinzircontraceelementpairsbutformtheirownsystembetweenenclavesandhostgranitoids.Additionally,mostofthezirconsshowextremelyhighεHf(t)withεHf(t)=3.54?11.94fromthesouthernsamples,andεHf(t)=1.0?9.09fromthecentralregion.SomezirconswiththehigherεHf(t)aresimilartothezirconsfromthejuvenileislandarcintheeasternsegmentofJiangnanOrogen.IntegratedgeologicalandHfisotopiccharacteristicssuggestmicrocrystalline-dioriticenclaveswerederivedfromthepartialmeltingprocessoftheMesoproterozoiccrustwhichenrichedjuvenileislandarcmaterialsandmixedwiththegraniticmagmathatremeltedfromtheMesoproterozoiccontinentalcrustwhichrelativelyenrichedancientsedimentsandmixedwiththehostgranitoidindiagenesis.