Objective The development of continental rifting and seafloor spreading can be predominated by magmatic upwelling （magma-rich） or tectonic stretching （magma-poor）. Located in the terminal portion of propagating seafloor spreading of the South China Sea （SCS）, the southwestern mid-ridge of the southwest sub-basin （SWSB） of the SCS was found with much thin crust and numerous faulted blocks coupling with magma-poor continental margins along its flanks. Therefore, the southwestern part of the SWSB is most likely to be a tectonic-dominated basin. To justify the hypothesis with further evidence, we investigated the nature of seamounts on the southwestern mid-ridge of the SWSB which may inherit seafloor spreading.
Dongsha waters are poorly studied for gas hydrates. Previous multi-channel seismic reflection and Chirp sub- bottom profiles show that numerous submarine mounds stand up to 100 m high above the seafloor over the continental slope of the SW Dongsha Island in northern margin of the South China Sea （SCS）. These mounds are characterized by hardened seabed, seafloor gas venting and folded structures, which implies the existence of active mud volcanoes. This work aims to confirm this speculation by seafloor sample dredging and to explore the potential of gas hydrates.
