Numerical Modeling Of A Down-pulling Lithospheric Root Beneath The Collision Mountain Ranges In The Tibetan Plateau

The collision between continental plates is a key to understanding the evolution of continental dynamics. Perhaps the most spectacular large-scale result of plate tectonics is the broad complicated zone of intracontinental convergence between Eurasia and peninsular India following their collision at about 45 Ma. So far, many geologists have brought forward different models to explain the spectacular phenomena. Those models may help us make a clear image about the evolution of the Tibet Plateau. Evidence for the existence of a massive deep-seated lithospheric root beneath the mountain ranges has recently been recognized on the basis of deep lithospheric exploration. Intracontinental subduction and decollement of the deep-seated lithospheric root play an important role on the Tibet Plateau's evolution. According to Guibin-Zhang et. recent research hi this aspect, we propose a model in which the mountain root and lithoshpheric root may contribute more to the regional stress system in collision mountain ranges. The tectonic finite element computer package FEVP was used to model the evolution of collision mountain ranges. The results show that there are two opposing stress systems. The surface loading of the mountains and the associated root of thickened crust produce horizontal deviatoric tension in the strong upper crust. In contrast, the deep, dense lithospheric root and its associated downflexing of the surface produce horizontal compressive deviatoric stress in the strong near-surface layer. The actual state of stress in the strong layer of the upper crust is the combined effect of these twoopposite stress systems together with bending and other local and regional stresses such as due to ridge push. There are obvious differences in the stress systems between the west and east profile in the Tibet Plateau. Those differences show that the East Tibet is in the early stage in the evolution of collision mountain ranges while the West Tibet is in the late stage.