Zircon SHRIMP U-Pb dating of the tuffaceous bed of Xiajiang Group in Guizhou Province and its stratigraphic implication

Abstract：Some zircon dating data of the tuffaceous bed are reported for the first time from the Sibao and Xiajia groups in Guanxi and Guizhou. In combination with the SHRIMP U-Pb dating of the granite that intruded into the Sibao Group, the Xiajia Group is determined to be of Late Neoproterozoic. These isotopic data are very important for us to redefine the age of the Sibao Group and to conduct regional correlation of strata in the corresponding period and tectonic evolution. The Sibao Group (the same as the Fanjingshan, Lengjiaxi and Shuangqiaoshan groups) and the Danzhou Group (the same as the Xiajiang, Banxi and Heshangzheng groups), which are subsequent metamorphosed rocks well developed in the Jiangnan Orogen, formed a metamorphosed basement of the Jiangnan Continent. In the past, the Sibao Group, which constituted the main part of the Sibao Movement, was designed to Mesoproterozoic, and the determined age still affects the stratigraphic subdivision and correlation of the metamorphosed rocks in whole Jiangnan Continent and restricts the determination of the geological background and metallogenic conditions of the Jiangnan Orogen. Based on studying zircon from bentonite in the Sibao Group and overlying strata, the authors accurately dated the zircon at (814.0±6.3) Ma in the Jialu Formation, and (773.6±7.9) Ma in the Qingshuijiang Formation. The series of zircon dating data have solved the problem of the Neoproterozoic ages and also provided a new marker for the Jiangnan Orogen.