Lithospheric deformation under the effect of an extensional stress field

Abstract

The characteristics of lithospheric deformation under the effect of an extensional stress field are investigated, based on two-ship seismic data collected through a joint Sino-US geological investigation project in the South China Sea. A deformation model of layered shear is put forward. In the upper crust the brittle deformation by which the normal faults are produced takes place. The upper part of the lower crust in the lower slope and lithospheric upper mantle are characterized by brittle deformation that produces faults too. In contrast, ductile deformation characterizes both the lower, high velocity component of the lower crust in the lower slope and the lower crust in continental shelf and upper slope as well as the deeper lithosphere that produces rheomorphism. Both models and domains of deformation give rise to the overall lithospheric thinning that produces grabens and half-grabens at the surface; these in turn determine the locations of the sedimentary basins that have developed along the South China Sea margin.