Crustal deformation of the Tibetan Plateau revealed by high-resolution shear wave velocity and azimuthal anisotropy models

Abstract:

The Tibetan Plateau was generated by the continental collision between the Indian plate and the Eurasian plate. The thickened Tibetan lithosphere has undergone complicated deformation, characterized by widespread active faults, and several stages of magmatism and metamorphism. With over 10000 Rayleigh wave phase velocity dispersion curves based on the ambient noise method from stations distributed inside and around the plateau, we have inverted for a high-resolution shear wave velocity and azimuthal anisotropy model of the Tibetan crust from the newly developed direct surface tomographic methods. From our model, we observed a few detailed velocity anomalies, including four prominent low-velocity anomalies and one high-velocity anomaly. Regarding the subduction of Indian lithosphere, mantle contribution is important during the formation of middle crustal low-velocity zones and Cenozoic magmatism, especially in the Lhasa terrane. We also found evidences showing the interactions between widespread weak zones in the crust and regional rigid anomalies within the plateau, which influenced the patterns of conjugate strike slip faults in central plateau as well as material transport under the continental convergence. For example, regional eastward ductile flow probably developed in central Tibet, and was blocked by a rigid block in Amdo in central eastern Tibet. Moreover, from shear wave velocity azimuthal anisotropy results of the Tibetan crust, decoupled crustal deformation of the plateau is revealed, especially in the regions of the plateau margin. Ductile deformations probably control the mid-lower crustal anisotropy pattern and further lead the growth of plateau margin. Decoupled deformation also developed in center and southern Tibet, with vertical variations of anisotropy patterns, which are controlled by different mechanisms.