Numerical simulation of GPS observed clockwise rotation around the eastern Himalayan syntax in the Tibetan Plateau

Abstract

From Global Position System (GPS) measurements, there is a clockwise rotation around the eastern Himalayan syntax in the Tibetan Plateau. This phenomenon is difficult to be interpreted by simple two-dimensional modeling from a geodynamic point of view. Because of the extremely thick crust and the lower crust with relatively high temperature in the Tibetan Plateau, the lithospheric rheology in Tibet and surrounding areas present a complex structure. In general, the tectonic structure of the Tibetan Plateau consists of brittle upper crust, ductile lower crust, high viscosity lithospheric upper mantle, and low viscosity asthenosphere, the same as the case in many other continental regions. However, the lower crust in the Tibetan Plateau is much more ductile with a lower viscosity than those of its surroundings at the same depth, and the effective viscosity is low along the collision fault zone. In this study, we construct a three-dimensional Maxwell visco-elastic model in spherical coordinate system, and simulate the deformation process of the Tibetan Plateau driven by a continuous push from the Indian plate. The results show that the existence of the soft lower crust under the plateau makes the entire plateau uplift as a whole, and the Himalayas and the eastern Himalayan syntax uplift faster. Since the lower crust of surrounding blocks is harder except in the southeastern corner where the high-temperature material is much softer and forms an exit channel for material transfer, after the whole plateau reaches a certain height, the lower crustal and upper mantle material begins to move eastward or southeastward and drag the upper crust to behave same way. Thus, from the macroscopic point of view, a relative rigid motion of the plateau with a clockwise rotation around the eastern Himalayan syntax is developed.