Characteristics and process of the final breakup of the crustal lithosphere at the V-shaped tip of the Southwest Subbasin in South China Sea

Abstract

To clarify the final breakup characteristics of the crustal lithosphere at the tip of the Southwest Subbasin in South China Sea and its evolution stages, this paper interpreted 2D deep seismic lines and analyzed the fault activities, the proto-basin type in different stages, the rates of subsidence and the history of tectonic and subsidence evolutions. It was clear that the distal domain and ocean continental transition consist of the final breakup zone of continental lithosphere at the tip of southwest South China Sea. According to the shape of the crust, this final breakup zone could be subdivided into a box domain, wedge domain and proto-oceanic domain. The basins within the wedge-shaped domain had been divided into the rifting basin (Tg-Sd), the detachment basin (Sd-Pd), and the sag basin (Pd-Bi). The basins within the box-shaped domain were of the rifting type from the Paleocene to Oligocene (Tg-Sd) and then transitioned to the passive sedimentation stage. From the Cenozoic, the sedimentation center on the tip of the Southwest Subbasin migrated from continental to ocean during the tectonic evolution of this region. The magmatism developed strongly and finally broke up the continental crust. The comparison of high-resolution seismic data showed that the tectono-sediments and magma type were different within different domains at the V-shape tip of the Southwest Subbasin. The continental crust of the research area broke apart after the "double detachment faulting". Then, the magma came in and formed the proto-oceanic crust. The research in this paper was of great value for oil and gas exploration in the deep-water basin in the southwest South China Sea.

Keywords

• v-shape tip of the southwest subbasin
• breakup of continental crust
• double detachment
• proto-oceanic crust