湘东北前寒武纪仓溪岩群变凝灰岩SHRIMP锆石U-Pb年龄

SRHIMP zircon U-Pb dating of metamorphic tuff from the Precambrian Cangxi Complex-Group in northeastern Hunan

在湘东北地区浏阳市文家市仓溪岩群底部枫梓冲岩组（长英质二云母片岩）变凝灰岩中发现近百粒锆石,锆石虽然形态不相同,但CL图像显示出典型的岩浆生长振荡环带和韵律结构。该类锆石的U、Th含量较高,Th/U值变化范围为0.32~0.87,均属于岩浆结晶的产物。获得的SHRIMP锆石U-Pb年龄为855Ma±5Ma,该年龄改变了仓溪岩群枫梓冲岩组的时代,对重新厘定江南造山带的构造格局有着重要意义。

This paper reports a SHRIMP U-Pb age（855 Ma ± 5 Ma） of metamorphic tuff from the Fengzichong Complex-Formation.Although zircons have different forms,their CL images show typical magmatic oscillatory zoning.The zircons have relatively high content of U and Th,with Th/U ratios vary in the range of 0.32~0.87.Therefore,they are of magmatic origin.The new data change the traditional stratigraphic correlation of the Cangxi Complex-Group in northeastern Hunan.Therefore,the SHRIMP U-Pb dating of the metamorphic tuff from the Fengzichong Complex-Formation at the bottom of the Cangxi Complex-Group is of great significance in understanding of the tectonic framework of the ＂Jiangnan Orogenic Belt＂ in Hunan.