Constraining The Dynamic Characteristics Of Lithosphere And Asthenosphere In Mainland China And Its Adjacent Regions Using GPS, Quaternary Fault Slip Rates And Shear Wave Splitting Data

Mainland China and its adjacent regions are located in the southeastern part of the Eurasian plate where four major plates are interacting with each other, i.e., the subduction of the Pacific and Philippine oceanic plates in the east and the collision with the Indian plate in the west, and form subduction zones, active orogens and broad continental diffusion that spreads thousands of kilometers. Thus, Mainland China and its adjacent regions provide a natural laboratory for studying the geodynamics. An improved knowledge of the deformation characteristics of lithosphere and asthenosphere is very important for a better understanding of the geodynamics in Mainland China and its adjacent regions. The present thesis focuses on determining the extent of crust-mantle coupling in lithosphere and mantle flow in asthenosphere beneath Mainland China and its adjacent regions through the joint analysis of surface and mantle deformation fields.In order to infer the mantle deformation field, we determine the XKS (SKS, SKKS PKS) fast polarization directions and delay time between the fast and slow waves for1800permanent and temporary broadband seismic stations where the fast polarization and delay time for each arrival were determined following the grid searching method of the minimum tangential energy and stacking procedure, and also, we use993previously published results in Mainland China and its adjacent regions. For the continuous surface deformation field, we determine a model strain-rate and velocity field using continuous spline functions to interpolate between observed surface strain rate data inferred from-3600GPS observations and Quaternary fault slip rates.According to the magnitude of strain rate and lithosphere thickness, we divide the study area into two parts, one is high strain rates and thick lithosphere, and another is low strain rates and thin lithosphere. In high strain rates and thick lithosphere area, we measure the deformation pattern (left-lateral simple shear, right-lateral simple shear or pure shear) at each station based on lithosphere deformation model. We can constrain the extent of crust-mantle coupling through comparing the predicted anisotropy orientations with the observed anisotropy. For most parts of the high strain rates and thick lithosphere area, such as the Tibetan plateau, Tianshan orogen, Altay orogen, Taiwan orogen, Ryukyu Island Arc, the comparison showing the crust and lithospheric mantle are deforming coherently, thus arguing for crust-mantle mechanical coupling of lithosphere. However, in the convergence belt of Himalayan orogen, the Japan trech, the Sichuan basin and Tarim basin, vertical coherence in the deformation is no longer present, the crust-mantle decouping within these areas most likely due to the subduction of plate or fossil from past geologic processes.In low strain rates and thin lithosphere area, we can assume the anisotropy is generated by the differential flow between the lithosphere and asthenosphere. The best fit mantle flow is determined in an iterative inversion by comparing the predicted anisotropy, based differential velocities between predicted mantle flow and the velocity field at the surface, with orientations with the observed anisotropy. The studies showing that the asthenospheric mantle flow beneath the East China is split two parts in Changbaishan volcanic region, one is an eastward-directed clockwise rotation of the asthenospheric mantle directed toward the Pacific subduction in the north, and another is a clockwise rotation of the asthenospheric mantle from southward to southwestward in the south, and directed toward the Burma/Sunda slabs. We think that the asthenospheric mantle flow beneath the North China and South China is generated by the subduction and rollback/retreat of Burma/Sunda slabs, and the mantle flow beneath the Northeast China is generated by the subduction and rollback/retreat of Pacific slab, meanwhile, the mantle upwelling beneath Changbaishan volcanic region split the asthenospheric mantle flow beneath the East China into two flows in the opposite direction. The asthenospheric mantle flow beneath Mongolia is a vortex with clockwise rotation which possibly related to the subduction and rollback/retreat of Pacific slab and the geometry of stable Siberia craton with thick lithosphere.