Numerical Modeling Of Upper Mantle Convection And Orogeny Of The Tianshan Mountains

Continental dynamics is one of the frontier fields in present earth sciences. The key problems of continental dynamics are the tectonic deformation and their mechanisms. As orogenic belts have strong deformation and apparent surface figures, orogenic dynamics research is an important branch of continental dynamics.The Tianshan orogenic belt is a typical active intracontinental mountain belt, far from either the locus of collision between continents or a subduction zone. It is recognized as an outstanding natural laboratory of intra-continental deformation research. 10 key problems are presented by Liu Qiyuan (2004) about the Tianshan orogenic dynamics. The kernel problems of these are the influence of the horizontal compression of the Tarim plate and the mantle convection to the orogeny of Tianshan, as well as the relationship between these two different forces.The activity of the Tianshan at present is not an original orogenic process of collision. It is a rejuvenation of an old orogenic belt which has been denuded and leveled off. Geophysical studies show that maybe mantle convection has played an important role in the uplift of Tianshan. So, it is the first problem to determine whether the mantle convection exists or not. If exists, how about the pattern and what is the influence of the mantle convection on the Tianshan orogenic process? What is the relationship between the horizontal compression of the Tarim plate and the mantle convection? What is the influence of the structures and properties of the ancient Tianshan? It is necessary to address these problems based on data interpretation and quantitative analysis.Aiming at these issues, a mathematical model is established for the quantitative study of continental deformation and dynamics. The governing equations include the conservation equations of mass, momentum and energy, as well as the state equation.The"ALE FEM + MIC"numerical method is accomplished which means the Arbitrary Lagrangian- Eulerian Finite Element Method combining with the Marker-in-cell technique. In particular, the unknown parameters (velocity and temperature) are calculated using the ALE FEM. The cell-markers in each element carry the material composition and history variables during the flowing process. The momentum and continuity equations are solved in terms of the pressure-stabilizing Petrov-Galerkin (PSPG) method with the equal-order interpolation of the velocity and pressure, and the energy equation is solved using the streamline upwind Petrov-Galerkin (SUPG) method. By means of ALE, the computational region can be tracked with moving boundaries. In the MIC algorithm, the bilinear interpolation corresponds to the interpolation function in the finite elements. The FEM and MIC algorithm are independent each other. The data in these two processes communicate through the nodal points. With the ALE FEM + MIC, the problems can be described for the variable boundary and extremely strong flow, as well as discontinuous boundary conditions. The numerical tests show that the precision and stability of the computational codes...