Mantle dynamics beneath the Sichuan Basin and Eastern Tibet from teleseismic tomography

Wang, W. and Wu, J. and Hammond, James O.S. (2021) Mantle dynamics beneath the Sichuan Basin and Eastern Tibet from teleseismic tomography. Tectonics 40 (2), ISSN 0278-7407.

Abstract

The cratonic Sichuan Basin is located east of the Tibetan Plateau, and is surrounded by mountains that have undergone complex deformation and uplift since the Cenozoic. Imaging mantle structure is important for understanding its formation, and to date most models suggest a deep cratonic root underlies the basin, blocking eastward extrusion of lithospheric material beneath Tibet. Here, we obtain detailed upper mantle structure from teleseismic tomography in the region utilizing travel time data from earthquakes recorded at 506 seismic stations, including 25 new stations in the poorly sampled Sichuan Basin. Contrasting to previous models, we show eastward and southeastward dipping high‐velocity anomalies extending eastward ∼150–400 km into the upper mantle from the Sichuan Basin. We suggest, the southeastward subduction of the Yangtze Block occurred in the Mesozoic and may be reactivated in the Cenozoic, with the relatively thin and weak lithosphere to the east of the Sichuan Basin prone to deformation in response to the eastward growth of the Tibetan Plateau. A west‐dipping high‐velocity anomaly beneath eastern Tibet is interpreted as delaminated lithosphere. This delamination may accelerate the development of the Xianshuihe fault zone and the horizontal extrusion of the Tibetan Plateau. Beneath the East Qinling orogen, the eastward extrusion of the plateau material is not obvious suggesting limited horizontal lithospheric extrusion is present north of the Sichuan Basin.

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