Tectonic contrast between the conjugate margins of the South China Sea and the implication for the differential extensional model

Abstract

The extensional model of the South China Sea (SCS) has been widely studied, but remains under debate. Based on the latest high-quality multi-channel seismic data, bathymetric data, and other obtained seismic profiles, the asymmetric characteristics between the conjugate margins of the SCS are revealed and extensional model of the SCS margin is discussed further. Spatial variation of morphology, basement structure, and marginal faults are discovered among the SCS margin profiles. As for the NS-trending variation, the basement of northern margin displays in the shape of step downwards to the sea, while the basement of southern margin is composed of wide rotated and tilted blocks, without any obvious bathymetric change. The variation also exists in the development of marginal faults between the conjugate margins, and detachment fault system is identified on the southern margin. Along the southern margin from east to west, the Eastern and Southwestern Basins developed different structural units. Based on the tectonic contrast of the conjugate margins, differential extensional model is proposed to explain the spatial variation of the SCS structure, which introduces detachment faults controlling the evolution of the SCS. The upper crust above the detachment fault was deformed by simple shear, while the lower crust and upper mantle below the detachment fault was deformed by pure shear. Because of the different lateral transfer between the upper brittle faulting and the lower ductile extensional regions, there developed marginal plateau (Liyue basin) and outer rise (Zhenghe massif) on the lower plate margin of the Eastern Basin and the Southwestern Basin, respectively. The evolution of the present SCS may be influenced by the diachronous close of the paleo-SCS.