Early-Stage Lithospheric Foundering Beneath the Eastern Tibetan Plateau Revealed by Full-Wave Pn Tomography

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The west-east contrast of magmatism in northern Tibet suggests that the lithospheric root has been removed in the west, following continental collision that led to lithospheric thickening and removal, but not in the east where paradoxically larger convergence occurred. Here we show a full-wave Pn tomography model for the eastern Tibetan Plateau, which reveals a high-velocity layer beneath the Moho extending to 150-km depth. The anomalously high velocities and its northward dipping top surface suggest a very depleted and cold mantle consistent with an underthrusted Precambrian Lhasa lithosphere. A high-velocity column connects this layer to another high-velocity layer below 190-km depth, representing early-stage removal of the Tibetan mantle lithosphere and its interaction with the underthrusted Indian lithosphere. The west-east contrast is thus attributed to different stages of lithospheric removal, which may be controlled by varying angles of Indian subduction from the west to the east.

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Geophysical Research Letters