Extensional styles of the conjugate rifted margins of the South China Sea

To elucidate continental rifting mechanism of the South China Sea (SCS), we characterize crustal structures of the two conjugate rifted margins and calibrate the continental-ocean transition zone (COT) with multi-channel reflection seismic, gravimetric and magnetic data. Narrower than those found in many other magma-poor margins, the COT in the SCS coincides well with a positive-negative gravity boundary, and shows Moho reflection gaps, basement highs and seaward normal faults. Post-rifting/spreading volcanic bodies and igneous intrusions often complicate the structures of the COT. Rifted basins here are often bounded by listric normal faults, the majority of which terminate at the upper-lower crust interface, i.e., the brittle-ductile transition boundary. This observation suggests that the lower crust was weak and played a dominant role in the continental breakup. We propose that the SCS lower crust acted as a decouple layer during extension, but the normal oceanic crust began to establish soon after crustal breakup. We also show how thermal regime affected the extent and timing of continental rifting of the SCS.