Margins of the Southwest Sub-Basin of the South China Sea -- A Frontier Exploration Target

摘要

The deep South China Sea Basin is about 500 km narrower (when measured along fracture zone directions) in the southwest sub-basin than in the eastern sub-basin. Reconstruction of the South China Sea Basin to predrift configurations thus creates an unacceptable 500-km overlap of continental or transitional crust in the western half of the proto-South China Basin, In order to maintain continuity through the plate-tectonic evolution of this basin, about 500 km of differential crustal extension must have occurred in the west in relation to that in the east. Virtually no deep-penetration seismic data exist across the northwest and southwest foundered and extended continent-transition crust. However, plate tectonics allows us to place constraints on the effective beta even in the absence of direct information on crustal thickness, heat flow, or subsidence history. The problem here is essentially the inverse of that normally presented. Assuming various end member models and knowing the effective beta (i.e., extension), we can predict the cumulative subsidence (and hence maximum sediment thicknesses), the regional thermal history, and crustal thicknesses. The total continental plus transitional margin crust in the western sub-basin represents a differential stretching factor about twice that inferred for rifted margins of the eastern sub-basin.