Detrital zircon geochronology of Neoproterozoic-Early Paleozoic sedimentary rocks in Baoshan terrane and its tectonic significance

The Luxi area of west Yun'nan which belongs to Baoshan terrane is located on the southeastern margin of the Tibetan Plateau. It is difficult to confirm the relationship between Baoshan terrane and Tibetan Plateau due to the strong deformation in Cenozoic. Based on the field study and LA-ICP-MS U-Pb dating, the authors hold that most detrital zircons of Neoproterozoic to early Paleozoic strata in Luxi area have high Th/U ratios (>0.1), which corresponds to the features of magmatic zircons. Zircon UPb ages are distributed from Archean to Early Paleozoic, with age peaks showing strong peaks of Cambrian (562Ma), Neoproterozoic (890Ma), Paleoproterozoic (2292Ma), and some weaker age peaks of Mesoproterozoic (1676Ma) and Neoproterozoic (2500Ma). The detrital zircon age distribution pattern in Baoshan terrane is similiar to that in South Qiangtang and Tethys Himalayan sedimentary strata, indicating that they were all derived from the Indian block located on the northern margin of Gondwanaland. From late Neoproterozoic to Early Paleozoic, Baoshen terrane was located on the northern margin of India block, adjacent to the north Qiangtang and Himalayan terrane. During the accretionary orogenic process related to the subduction, the late Newproterozoic to Early Paleozoic sedimentary strata were formed in the Baoshan terrane.