Submarine volcanism in the southern margin of the South China Sea.

Submarine volcanism is widely developed in the South China Sea (SCS). However, the characteristics, distribution, and genesis of submarine volcanoes in the southern margin of the SCS remain obscure. In this study, we analyzed the characteristics of submarine volcanoes and identified a total of 43 submarine volcanoes in the southern margin of the SCS, based on a newly acquired 310-km seismic reflection profile, along with previous 45 multi-channel seismic (MCS) profiles, petrological results from volcanic rocks sampled by dredging and drilling, nearby ocean bottom seismometer (OBS) wide-angle seismic profiles, and gravity and magnetic data. The study ascertains that most of these volcanoes are located in fault-block belts and graben-horst zones with strong crustal stretching and thinning. These volcanoes exhibit positive high-amplitude external seismic reflections, weak and chaotic internal seismic reflections, and are accompanied by local deformation of the surrounding sedimentary strata. Meanwhile, they have higher positive gravity anomalies and higher magnetic anomalies than the background strata. The petrological dating results show that volcanic ages are primarily in the Pliocene-Pleistocene, with geochemical characteristics indicating dominance of oceanic island basalt (OIB) -type alkali-basalts. Extensional faults have obviously spatial correspondence with post-spreading volcanism, suggesting these faults may provide conduits for submarine volcanism. The high-velocity bodies (HVBs) in the lower crust and magma underplating exist in the southern SCS, which could provide a clue of genesis for submarine volcanism. The inference is that the intensity of post-spreading volcanism in the southern margin might be affected by stretching faults, crustal thinning and magma underplating. [ABSTRACT FROM AUTHOR]