The continent-ocean transition on the Northwestern South China Sea basin

Abstract

The continent-ocean transition (COT) represents a key to understand lithospheric extension and final break-up processes on rifted margins. We have reprocessed 2250 km of multichannel seismic data collected during cruise Sonne 49 across the NW South China continental margin. Three regional seismic profiles allows us to image the crustal structure from clear base-of-the-crust reflections to continuous top-of-basement reflections and a well imaged syn-rift and post rift stratigraphy and intrusive magmatic layering. Differences in internal reflectivity, faulting style, fault-block geometry, seismic character of the top of the basement, geometry of sediment deposits, and Moho reflections allow us to interpret a continental domain, an abrupt COT and an oceanic domain. Seismic profiles show that rifting in the NW subbasin resulted in asymmetric conjugate margins and a clear change in the tectonic structure from NE to SW. Based on the style and along-strike variation of the continental extension, the architecture of the COT, and the distribution of oceanic crust, we have proposed a new tectonic model of the formation of the NW South China Sea basin. We suggest the 3D interaction between rifting and oceanic spreading center propagation as responsible for the final structural configuration of the basin