In order to analysis the effects of the rheological properties against the contemporary tectonic deformation field in the Tibetan Plateau and its adjacent region, this article carries out numerical simulation by building up a 3-D finite element viscoelastic model which use the standard linear solid model's constitutive relation. The results show following characteristics:
Under the control of crustal medium's rheological mechanism in the Tibetan plateau, the eastward displacement components become bigger and bigger from west to east in the Tibetan plateau. The maximum appears in the region south to Ganzi - Yushu - Xianshuihe fault belt. It implies that the mass under the Tibetan plateau flow eastward.
The model simulated this region's contemporary tectonic movement characteristics, which show that the southwest parts of Sichuan-Yunnan Region clockwise rotate around the Himalaya eastern tectonic joint. As to the middle and south part of Sichuan-Yunnan rhombus block, the crust moves southeastward in the east while southwestward in the west.
The results of two models with stronger rheological property in middle crust and in lower crust respectively have similar characteristics: both can modeled the patterns of eastward flow in plateau and clockwise rotation around the Himalaya eastern tectonic joint.
The crustal rheological mechanism plays an important role in the tectonic deformation field of Tibetan Plateau.
The tectonic deformation and its evolution in Tibetan Plateau is the key task of geodynamics. Houseman & England (1986) used a finite element method to calculate stresses and strain rates in a thin viscous sheet, representing the continental lithosphere. They studied the relationship of the velocity field, crustal thickness distribution, strain rate and stress index. England & Molnar (1997) used strain rate in deforming zone to infer changes in the viscous stress and found the deforming mechanism controlled by creep equation. Their result showed an average viscosity coefficient of the Tibetan Plateau as in the order of 1022Pa s. Using geodetic, geologic, topographic, and seismic data, Flesh et al. (2001) calculated the deviatoric stress field in the collision zone between Indian plate and Eurasian plate. Both deviatoric stress and effective viscosity displayed an weak intensity of lower crust and the weak lower crust was in favor of eastward movement. Nowadays, Global Positioning System (GPS) data provided the necessary basic data for quantitative research to dynamic mechanism of continental contemporary tectonic deformation. Combined original data from GPS campaigns carried out between 1991 and 2001, Wang et al. (2001) plotted GPS velocity vectors with respect to the stable Eurasia. Zhang et al. (2009) synthesized GPS velocities of 553 control points in the Tibetan Plateau and along its margins to show in which ways the collision between India and Eurasia is accommodated and to shed new insights on the dynamics of the plateau's contemporary tectonic deformation.
