Seismic Tomography of Eastern Tibet: Implications for the Tibetan Plateau Growth

Abstract

The eastern region of the Tibetan Plateau and surrounding regions have gentle to moderate topographic gradients, contrasting the steep margins in northern and southern Tibet. The mechanisms for plateau growth in eastern Tibet are uncertain so far. Here we present a new shear wave tomography model of the Tibetan Plateau derived from S wave traveltimes from teleseismic waveforms recorded by the dense ChinArray seismic network. The model reveals the deep structures beneath the eastern region of the Tibetan Plateau and its adjacent regions, showing clear velocity contrast boundaries roughly along the eastern margins of the Tibetan Plateau. We interpret the slow velocity anomalies beneath the Tibetan Plateau as soft lithosphere, which absorbed most of the northeastward push of the Indian Plate, while the fast velocity anomalies beneath the region surrounding the plateau represent craton‐like rigid block roots. The deformation of the soft/weak lithospheric mantle beneath the Tibetan Plateau is constrained by the convergence between the Indian and Eurasian plates, and the framework of the surrounding rigid blocks. We suggest that weak lithosphere deformation (horizontal shortening and vertical stretching) accounts for the plateau growth in eastern Tibet.

P and S Wave Tomography Beneath the SE Tibetan Plateau: Evidence for Lithospheric Delamination

“…Many previous studies of regional and teleseismic tomography have revealed 3‐D Vp variations beneath the SE Tibetan Plateau (e.g., Huang & Zhao, ; Huang, Wang, Xu, Wang, et al, ; Lei et al, ; Lei & Zhao, ; Li et al, ; Pesicek et al, ; Wei et al, , ; Zhang et al, ). All these results show similar first‐order features, that is, the high‐V body beneath the Yangtze craton and widespread low‐V zones beneath Indochina.…”

“…Lei and Zhao () determined a new model of teleseismic tomography beneath eastern Tibet using travel‐time residuals recorded at 280 permanent stations; they found widespread low‐V zones in the upper mantle and high‐V bodies in the MTZ and so proposed the existence of a big mantle wedge under eastern Tibet (Lei et al, ). Zhang et al () collected more data recorded at the portable seismic stations deployed by the ChinArray project and determined a 3‐D Vs model in eastern Tibet. They focused on different strengths of the lithosphere beneath the plateau (weak due to low velocity) and its adjacent regions (strong due to high velocity) and further discussed their implications for the plateau growth.…”

“…The depressed 660‐km velocity discontinuity (D660) implies that cold material has probably sunk into the mantle transition zone (MTZ; Xu et al, ; Yu et al, ; Zhang et al, ). Beneath the Sichuan basin, the core of the stable Yangtze craton, high‐velocity anomalies are also predominant in the upper mantle (Huang & Zhao, ; Huang, Wang, Xu, Wang, et al, ; Lei & Zhao, ; Tao et al, ; Wei et al, ; Zhang et al, ). In contrast, widespread low‐velocity anomalies are significant in the upper mantle beneath the SE Tibetan Plateau (Huang, Zhao, et al, ; Li et al, ; Wei et al, ; Zhang et al, ), especially under the Tengchong volcano and the Indochina block where the lithospheric thickness is mostly less than 80 km (An & Shi, ; Pasyanos et al, ).…”

Mantle Dynamics Beneath the Sichuan Basin and Eastern Tibet From Teleseismic Tomography

“…Despite these differences, most studies suggest that fast velocities in the mantle beneath the Sichuan Basin show a deep cratonic root is present, a remnant of the South China Block (e.g., Y. Hu & Wang, 2018;Obrebski et al, 2012;F. Zhang et al, 2018).…”

“…Hu & Wang, 2018;Huang & Zhao, 2006;Lei & Zhao, 2016;C. Li & van der Hilst, 2010;Obrebski et al, 2012;F. Zhang et al, 2018).…”