Geodynamic characteristics of tectonic extension in the northern margin ofSouth China Sea

Based on the geothermal and gravitation methods, this paper investigated th e theological and thermal structure of the lithosphere under the northern m argin of South China Sea. The result shows that the temperature of the uppe r crust is 150-300 degreesC lower than that of the lower crust, and the vis cous coefficient of the upper crust is 2-3 orders of magnitude larger than that of the lower crust. It reveals that the upper crust is characterized b y brittle deformation while the lower crust by ductile deformation. A chann el of lower-viscosity should be formed between the upper and lower crust wh en the lithosphere is scattered and spreads out toward ocean from northwest to southeast along the northern margin of South China Sea. And, a brittle deformation takes place in the upper part of the lithosphere while a ductil e deformation takes place in the lower part of the lithosphere due to diffe rent viscous coefficients and temperature. The layered deformation leads th e faulted blocks to rotate along the faulting and the marginal grabens to a ppear in the northern margin of South China Sea in Cenozoic tectonic expans ion.