Numerical Simulation of the Graben-Forming Process in Southern Xizang

I.INTRODUCTION It iS generally accepted that the stress state in the upper crust and upper mantle in the southernQinghai—Xiz~g Plateau is essentially extensional(Molnar and Tapponnier,1978;Chen and Molnar,1983:Armijo et a1.,1986).Data offocal.mechanism

Numerical Simulation of the Graben-Forming Process in Southern Xizang

Because of the friction-fracture behavior in the upper crust,the effective viscosity in this layer may be less than that in the median crust; even under the strong push of the Indian plate,the horizontal compressional stress in the upper crust may relax gradually and thus may concentrate in the median crust,so that the vertical compressional stress becomes in the upper crust.Today in the southern part of the plateau,the stress state of the upper crust is extensional,and some grabens have been formed.Under the strong push of the Indian plate,the median and lower crusts are still thickening,so that the plateau is uplifting.A numerical model for confirming the possibility of this hypothesis is constructed by using a three-dimensional(3-D)elasto-viscous finite element method.