Numerical Simulation Of Current Crustal Movement And Deformation And Dynamics For Tianshan

Continental dynamics is the frontier field of solid earth science research currently. The kernel problem of continental dynamics is the characteristics of continental tectonic deformation and its dynamical mechanism.As the orogenic belts own the strongest tectonic deformation and the most apparent surface configurations, they had become a focus of continental dynamics research. Tianshan is one of the most active orogenic belts, considered to be the nature laboratory for researching intra-continental orogeny. Dynamics research of Tianshan orogenic belt helps to better understand the formation and evolution of intra-continental orogeny. The paper deals with the crustal movement and deformation and the process of revival orogeny of Tianshan through numerical simulation with the following conclusions.1,A 3-dimension model of research region was set up in the basis of entirely analysing the geological structural and tectonic characteristics of Tianshan and then a numerical simulation of crustal movement and deformation of Tianshan was carried out basing on the model, using the latest GPS observation results of crustal movement as the constraint condition. The paper acquired the velocity field, strain field and stress field of Tianshan east of 81°E and revealed the characteristics of crustal deformation of research region. The dominant direction of curstal horizontal movement is NNE currently, with a gauche trend toward east from west to east. The speed of crustal movement is descending from SW to north and east. The difference of crustal movement between south and north leads to the crustal convergence and shortening of Tianshan near south-north direction and the speed of shortening descends by degree from west to east, changing from 7.71 mm/year in 82°E to 2.42 mm/year in 88°E.The maximum principal strain is compressive strain near south-north direction and the magnitude fo strain rate is 10-8/year, descending from west to east. The principal compressive strain of the mountain body is larger than the bilateral basins, showing that the shortening deformation is mostly absorbed by the mountain body. The shortening deformation absorbed by active fault zones is limited, mainly playing a role of adjusting the movement of two walls of fault in the process of tectonic deformation. All of these show that the crustal shortening near south-north direction of Tianshan is asymmetric but approximately successional deformation. The crustal tectonic stress field of Tianshan mainly is compressive effect near south-north direction and the principal compressive stress descends by degree from west to east. By comprehensive analysis I think that the direct cause of crustal shortening deformation of Tianshan east of 81°E with differences between east and west is the extrusion of Tarim's clockwise rotation and the Junggar's anticlockwise rotation also passively takes a promotion effect in the same time, but the effect of the drag force of mantle convection may be weak.2,The process of orogenic uplift of Tianshan from the beginning of revival at Cenozoic was forward simulated by using the power-rule-creep constitutive model by true of the rock's deformation under the effect of long and persistent force. The deformation pattern and some general characteristics of the uplift of mountain body were presented. Simulation experients show that the interior attribute of crustal medium and the condition of bottom boundary have important influence to the uplift of mountain body. The Tianshan becomes current configuration after 24Ma and 156km of crustal shortening in the persistent extrusion of 6.5mm/year toward north in horizontal direction. The crustal deformation is charactered with shortening and incrassation. The crustal thickness increases to 56km from 40km of original model after 156km of crustal shortening, which is directly responsible for the uplift of mountain body. The uplift model of the mountain body is two-peak uplifting at two sides and intermontane basin forming in middle in the process of orogenic evolution. If not considering the surficial denudation and sedimentation, each part of Tianshan would uplift in a invariable speed respectively under the steady intrusion action but the uplift speed of Southern-and Northern-Tianshan is quicker than Middle-Tianshan. The relative weak medium of mountain body is the necessary condition of uplift. Asymmetric interior mediun of mountain body and inconsistent movement of bottom and upper boundary together result in the difference of uplift configuration of Tianshan.