Thermal modeling of the tectonic evolution of the southwest subbasin in the South China Sea

The rifting and seafloor spreading of the southwest subbasin of South China Sea were the most important tectonic events in the forming process of the South China Sea from late Cretaceous to Middle Eocene. We simulate the thermal evolution process of this region with the 3-D finite element method and research the rifting deformation in the southwest subbasin, the duration of seafloor spreading, the rising of mantle materials, the crush and spreading energy of the lithosphere dyke along the spreading center, and the magmatism by the computing deformation and temperature structure. The result indicates that the extension duration of the sea basin is 10 to 15Ma once, because of the deep dynamics condition is insufficient. The rising of mantle materials stops gradually and the lithosphere loses the extensional force, and then the spreading center becomes a death rift valley with the residual spreading center but not a ridge or a central uplift belt. Though the rising potential of the mantle materials in this area is insufficient, there are quite a lot of violent magma spewing activities indicating the growing up of seamounts after the molding of the sea basin in the region with the partial rifting, especially the extension and detachment of the boundary between the basin and the margin.