Geodynamics of the South China Sea

The flow-line pattern defined from the seafloor spreading lineaments and the few identified FZs have been used to highlight conjugate segments of continental margins. During the first phases of opening of the SCS, from the fit of continents to chron C10 (30 Ma), the N175° extension observed in the Xisha trough and eventually south of the Macclesfield Bank extends to the Qui Nhon ridge, located along the eastern margin of Vietnam, in the southward prolongation of the Red River fault system. Normal faults curve toward the south with a horsetail geometry interpreted as evidence for a few tens of kilometers of dextral motion along the Qui Nhon ridge. Since chron 10 and until the end of SCS opening, the plate boundary located between the southern South China Sea (SSCS) and EU plates jumped westward several times from the location of the Ulugan fault near Palawan to the western limit of the southwest basin, explaining the progressive formation of the SCS from east to west and giving the characteristic V-shape of the SCS. The opening of the whole SCS is linked and occurred simultaneously with the northward subduction of the proto-SCS whose suture is located south of Palawan and extends westwards in north Borneo.