Ambient-noise anisotropic tomography suggests an episodic growth model for the Tibetan Plateau

How the Tibetan Plateau uplifted and deformed remains vigorously debated and several competing models have been proposed. Recently, we constructed a new azimuthally anisotropic shear-velocity model for the lithosphere beneath Eastern Tibet using ambient-noise tomography from more than 600 seismic stations. In this model, the Tibetan upper crust exhibits strong azimuthal anisotropy with fast directions sub-parallel to surface geologic features and mantle anisotropy, indicative of vertically cohere deformation of the lithosphere. However, a totally different picture emerges in the mid-lower crust of the plateau proper, where the disordered azimuthal anisotropy is much weaker than the plateau margins, in contrast to the prediction of the popular large-scale eastward crustal flow model. Combining the new seismic observation with other studies, they propose an episodic growth model for the plateau, in which heterogeneous crustal thickening was a primary driver at the early stage and the weakened mid-lower crust flowed locally at a later stage without consistent directions. In addition, the southeastern plateau margin was raised likely by upwelling asthenosphere.  

Figure 1. Simplified geologic map (left) and azimuthally anisotropic Vsv model (right) of eastern Tibet. In the Tibetan upper crust, strong azimuthal anisotropy well correlates with surface geology. However, anisotropy in the mid-lower crust beneath the plateau proper is much weaker.

The lead author of this work is Prof. Xuewei Bao at Zhejiang University. Other authors include Prof. Xiaodong Song at Peking University, Prof. David Eaton at University of Calgary, Prof. Yixian Xu and Prof. Hanlin Chen at Zhejiang University. This research was supported by the Natural Science Foundation of China (41774045, 41830212). For more details please refer to the following paper.

Bao, X., Song, X., Eaton, D. W., Xu, Y., & Chen, H. (2020). Episodic lithospheric deformation in eastern Tibet inferred from seismic anisotropy. Geophysical Research Letters, 47, e2019GL085721. https://doi.org/ 10.1029/2019GL085721