The LA-ICP-MS U-Pb dating of detrital zircons from the Nanhua System in Bikou Terrane, northwestern margin of Yangtze Block

The Nanhua System occurs in Hongyangou area, northwestern margin of Yangtze block. Its age is unclear, and the tectonic setting under which the Nanhua System was deposited is in dispute. In this paper, detrital zircons from the feldspar sandstone in the upper Nanhua System are tested by LA-ICP-MS zircon U-Pb dating. The results show that zircons' U-Pb ages can be divided into two groups:the Late Neoproterozoic group (750~800 Ma), with a small peak at 795 Ma, and the Early and Middle Neoproterozoic group (820~920 Ma), with a main peak at 850 Ma. The weighted mean age of the youngest detrital zircons is 750 Ma, representing the maximum depositional age of the coarse-grained rocks of Upper Nanhua System. Considering the relationships of stratigraphic sequences, it is concluded that the depositional age of sedimentary strata of the Nanhua System was late Nanhua period, and it is proposed that the detrital materials of the Nanhua System are mainly from the Neoproterozoic intermediate-acid magmatic rocks in the Bikou terrane, the Hannan-Micangshan complex, and the Longmenshan tectonic belt in the northwestern margin of the Yangtze block, and less from magmatic rocks exposed in the Mianlue tectonic belt. It is suggested that The Nanhua System is the sedimentary response of the Bikou Micro-block to the late Neoproterozoic (~810 Ma) post-collision-crack event of the northwest margin of the Yangtze Block.