Geodynamic Modeling of Mantle Evolution of the South China Sea and Surrounding Subduction Systems

The South China Sea (SCS) and adjacent basins are surrounded by multiple subduction zones, including the Sumatra, Java, Philippine, and Manila subduction systems. Previous studies have revealed that the subducting Indian and the Philippine Sea plates may have reached mantle depth of 1000-1200 km beneath the SCS. We first used the plate reconstruction software GPlates to calculate the velocities of the global plates since 100 Ma. We then constructed 3-D models of the global mantle dynamics using the spherical harmonic simulation platform of Advanced Solver for Problems in Earth's ConvecTion (ASPECT). Constant temperatures were assumed at the Earth surface and core-mantle boundary, respectively. The mantle convection was driven from both the surface plate motion as prescribed by the GPlates model and the buoyancy-driven mantle flow. The SCS and its surrounding subduction systems were modeled with much finer grids within the global mantle convection framework. Preliminary results show that the overall geometry of the subduction zone systems in the Southeast Asia has evolved gradually from the early "V" shape to the present-day "U" shape. The Izanagi plate, which has been subducted beneath the Eurasia plate until about 55 Ma, has a profound impact on the mantle evolution of the eastern China and the SCS. Modeling results suggest that the opening of the SCS might have broken up the remnant Izanagi subduction slabs under the SCS. Although the SCS has ceased spreading at 15-16 Ma, the surrounding subduction systems continue to influence the mantle convection and evolution of the SCS and adjacent basins. Furthermore, modeling results reveal that subduction-induced flow may lead to the formation of isolated plume-like mantle upwelling features beneath the SCS.