Reconstruction of the South Qiangtang-Zhongba-Tethyan Himalaya continental margin system along the northern Indian Plate: Insights from the paleobiogeography of the Zhongba microterrane

Information regarding the paleobiogeography of the Qinghai-Tibet Plateau can improve our understanding of its tectonic evolution. The Zhongba microterrane has been recognized as a small stratigraphical terrane within the western Yarlung-Zangbo suture zone. Paleobiogeographically, the Zhongba microterrane exhibited a moderate relationship with the Tethyan Himalaya throughout the Permian because they shared several typical Gondwanan/bipolar cool-water brachiopods and bivalves. However, several Cathaysian warm-water brachiopods, bryozoans, fusulines and compound corals appeared in the Zhongba microterrane as early as the Late Cisuralian but were not present in the Tethyan Himalaya until the latest Lopingian, indicating that the Zhongba microterrane drifted away from the northern Indian Plate no later than the Late Cisuralian. Additionally, Early Triassic marine faunas observed in the Zhongba microterrane were characterised by Tethyan ammonoid genera, along with several cosmopolitan/widely distributed ammonoids and bivalves, but Gondwanan/bi-temperate elements observed in the Tethyan Himalaya were lacking in the Zhongba microterrane, suggesting that the Zhongba microterrane had been biogeographically decoupled from the northern Indian Plate during that time. Additionally, both the Zhongba microterrane and Tethyan Himalaya exhibited an abrupt faunal variation from benthic brachiopod- to nektonic ammonoid-dominated assemblages across the P/T boundary, which is thought to be related to harsh and inhospitable oceanic environmental conditions during the Permian-Triassic mass extinction. Our results, together with published paleontologic, paleomagnetic, magmatic, and sedimentary studies, indicated that the Lhasa Block was exotic to the South Qiangtang-Zhongba-Tethyan Himalaya continental margin system along the northern Indian Plate during the Permian.