Lithospheric strength variations in Mainland China: Tectonic implications

Abstract

We present a new thermal and strength model for the lithosphere of Mainland China. To this purpose, we integrate a thermal model for the crust, using a 3-D steady state heat conduction equation, with estimates for the upper mantle thermal structure, obtained by inverting a S wave tomography model. With this new thermal model and assigning to the lithospheric layers a “soft” and “hard” rheology, respectively, we estimate integrated strength of the lithosphere. In the Ordos and the Sichuan basins, characterized by intermediate temperatures, strength is primarily concentrated in the crust, when the rheology is soft, and in both the crust and upper mantle, when the rheology is hard. In turn, the Tibetan Plateau and the Tarim basin have a weak and strong lithosphere mainly on account of their high and low temperatures, respectively. A comparison of temperatures, strength, and effective viscosity variations with earthquakes distribution and their seismic energy released indicates that both the deep part of the crust and the upper mantle of the Tibetan Plateau are weak and prone to flow toward adjacent areas. The high strength of some of the tectonic domains surrounding Tibet (Tarim, Ordos, and Sichuan basins) favors the flow toward the weak western part of South China block.