Mesozoic tectonic evolution of the Proto-South China Sea: A perspective from radiolarian paleobiogeography

The Proto-South China Sea (PSCS)represents the lithosphere that formerly occupied the region southeast of South China where the present-day South China Sea is located. The subduction and demise of the PSCS have attracted wide attention, whereas the pre-subduction history (particular the Mesozoic)of the region remains relatively neglected. In this paper, the radiolarian paleobiogeography of the region is analyzed to identify the paleobiogeographic affinity and paleo-connectivity of the PSCS with the Pacific and Tethys oceans during the Mesozoic. Then the continent–ocean configuration and tectonic evolution of the PSCS and adjacent areas are discussed through the integration of paleobiogeographical results and associated paleomagnetic, stratigraphic, and petrologic data. The main conclusions are as follows: (1)During the Triassic, the PSCS was situated in the transition zone between the Pacific and Tethys oceans, and its paleobiogeography was influenced by both oceans. The PSCS was characterized by complex tectonic overprinting by the Pacific and Tethyan tectonic regimes. (2)In the Early–Middle Jurassic, the PSCS was well connected to the Pacific Ocean but poorly connected to the Tethys Ocean, consistent with the paleobiogeography of the PSCS being mainly constrained by the Pacific Ocean. The PSCS was part of the Paleo-Pacific slab. (3)During the Late Jurassic–Cretaceous, the PSCS was in a semi-closed environment. The Late Jurassic–early Late Cretaceous PSCS was part of a west-facing Andean-type subduction zone, and the late Late Cretaceous PSCS was situated in an extensional tectonic setting.