Tectonic Evolution and Key Geological Issues of the Proto-South China Sea

There are numerous controversies surrounding the tectonic properties and evolution of the Proto-South China Sea (PSCS). By combining data from previously published works with our geological and paleontological observations of the South China Sea (SCS), we propose that the PSCS should be analyzed within two separate contexts: its paleogeographic location and the history of its oceanic crust. With respect to its paleogeographic location, the tectonic properties of the PSCS vary widely from the Triassic to the mid-Late Cretaceous. In the Triassic, the Paleo-Tethys and the Paleo-Pacific Oceans were the major causes of tectonic changes in the SCS, while the PCSC may have been a remnant sea residing upon Tethys or Paleo-Pacific oceanic crust. In the Jurassic, the Meso-Tethys and the Paleo-Pacific oceans joined, creating a PSCS back-arc basin consisting of Meso-Tethys and/or Paleo-Pacific oceanic crust. From the Early Cretaceous to the mid-Late Cretaceous, the Paleo-Pacific Ocean was the main tectonic body affecting the SCS; the PSCS may have been a marginal sea or a back-arc basin with Paleo-Pacific oceanic crust. With respect to its oceanic crust, due to the subduction and retreat of the Paleo-Pacific plate in Southeast Asia at the end of the Late Cretaceous, the SCS probably produced new oceanic crust, which allowed the PSCS to formally emerge. At this time, the PSCS was most likely a combination of a new marginal sea and a remnant sea; its oceanic crust, which eventually subducted and became extinct, consisted of both new oceanic crust and remnant oceanic crust from the Paleo-Pacific Ocean. In the present day, the remnant PSCS oceanic crust is located in the southwestern Nansha Trough.