COLLISIONAL TECTONICS IN WESTERN CHINA: INSIGHT FROM AN INTEGRATED DYNAMIC MODEL

Cenozoic crustal deformation in western China has largely resulted from the Indo-Asian continental collision and continued plate convergence in the past 50-70 Myr. The uplift of the Tibetan plateau is believed to have played an important role in regional climate changes including development of the Asian monsoon. However, the timing of the plateau uplift and the spatial-temporal evolution of crustal deformation in the surrounding regions are uncertain, and the fundamental causes of collisional strain distribution in western China remain elusive. We have investigated the basic mechanics controlling the collisional crustal deformation in western China by integrating geodetic, geophysical and geological studies with geodynamic modeling. The three-dimensional computer model includes both depth-variable and lateral heterogeneous rock rheology and realistic boundary conditions including major faults. The gravitational buoyancy force of mountain ranges is calculated explicitly from the digital topography. Using the present topography and GPS data as constraints, the model predicts a crustal stress pattern consistent with that indicated by modern earthquakes, featuring roughly E-W extension in the south-central Tibetan plateau and thrust or strike-slip faults near the margins of the plateau. Significant crustal extension occurs when the plateau has reached ~70% of its present elevation. Plateau uplift occurs earlier and faster where the lithospheric rheology is weaker. Using the Cenozoic sedimentary records in the Tarim basin, we were able to reconstruct the spatial-temporal evolution of mountain building in the northern Tibetan plateau and the Tian Shan following the Indo-Asian collision. Whereas uplift in the northern Tibetan plateau was faster than in the Tian Shan orogen, large variations within each orogens indicate important control of local geological structure and rheology on the uplift history.