The existentce of the ca.860 Ma concealed granite in the central Jiangnan Orogen:Evidence from the xenocrysts in lamproite at Yunyingwo,Ningxiang,Hunan Province
In order to explore the information of deep magmatic record in the central Jiangnan Orogen,this contribution,taken the No.I Yunyingwo lamproite dike of the Ningxiang area,Hunan Province as a′lithoprobe′,and conducted U-Pb geochronological and trace element studies of apatite and zircon xenocryts in the lamproite dike and detrital zircons in wall rocks.The results show that the youngest group of detrital zircons from wall rocks has a 207Pb/206Pb weighted average age of(769±19)Ma,which represents the maximum sedimentary age of ca.770 Ma for the Wuxiangxi Formation of the Neoproterozoic Banxi Group.The weighted average ages of apatite and zircon xenocrysts in the lamproite are(859±9)Ma and(854±21)Ma,respectively,which are consistent within the standard deviation range.It is suggested that the lamproite could have captured a deep magmatic rock with age of about ca.860 Ma.Furthermore,the trace element characteristics of xenocrystic zircons indicate those zircons were sourced from the S-type granite.Based on facts that the S-type granite,metamorphic event,and mafic magmatism in the central Jiangnan orogen,it is suggested that the central Jiangnan orogen was experienced an oceanic slab rollback,implying that the Neoproterozoic oceanic-continental subduction of the Yangtze Block occurred possibly before 860 Ma.
NeoproterozoicapatitezirconS-type graniteYangzte blockYunyingwo,Ningxiang,Human Province
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