Limited southward underthrusting of the Asian lithosphere and material extrusion beneath the northeastern margin of Tibet, inferred from teleseismic Rayleigh wave tomography

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Abstract
The northeastern margin of Tibet is of key importance in understanding the uplift and expansion of Tibetan Plateau. In this research, we perform Rayleigh wave tomography from 20 s to 167 s using the data recorded by China Digital Seismic Network and several portable seismic arrays in Northeastern Tibet and adjacent areas. Our resultant 3‐D shear wave velocity model exhibits strong lateral variations in the lithosphere. High shear wave velocities are observed in the mantle of the cratonic Ordos and Yangtze Blocks, as well as the East Qinling Orogen. The Qilian Orogen is underlain by a ∼120 km thick lithosphere of intermediate velocities and a low‐velocity layer of asthenospheric mantle below the depth of 120 km. Low velocities are characteristic in the middle‐to‐lower crust of the Songpan‐Ganzi Terrane and the West Qinling Orogen, possibly representing the crustal flow penetrating the Kunlun Fault. An uppermost mantle low‐velocity zone is found in the same location, indicating either the asthenosphere upwelling or the transitional crust‐mantle boundary layer. Our observations have two tectonic implications. First, the large‐scale eastward Tibetan material extrusion into Eastern China through the East Qinling Orogen is unlikely to be an ongoing process above 200 km depth; second, the southward subduction of the North China Craton toward Northeastern Tibet may not have fully developed in this region. Furthermore, we propose that the difference in the lithospheric strength between the Qaidam Block and the West Qinling Orogen is a critical element to control the tectonics in the northeastern margin of Tibet.
Funding Information
  • National Natural Science Foundation of China (41125015, 41225016, 41274002, 41404051, 41574056)

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