SHRIMP zircon U－Pb dating for crystal tuff from Hongzixi Formation of Banxi Group in Xiushan area, Chongqing, and its significance

Abstract：There has long existed considerable controversy concerning the epoch and stratigraphic division of Banxi Group. Based on restudying the sedimentary sequence and evolution of Banxi Group in Xiushan-Fanjingshan area, the authors performed the crystal tuff SHRIMP zircon U-Pb dating for Hongzixi Formation of Banxi Group in Xiushan area. The result suggests that the expansion of the early Banxi basin ended at about 790 Ma, followed immediately by the quick infilling and differential uplifting stage. The deposition epoch of Banxi Group in Xiushan-Fanjingshan area corresponded to that of the lower part of Banxi Group in western Hunan and that of Xiajiang Group in eastern Guizhou, with the deposition duration being between 820Ma and 790Ma. It was the early infilling of the rift basin under the background of the break-up of Rodinia supercontinent in middle Neoproterozoic.