Tomographic imaging of the underthrusting Indian slab and mantle upwelling beneath central Tibet

• Low-velocity zones in South and North Tibet reflect thermal features.
• Discontinuous low-velocity zones indicate complex crustal structures under Tibet.
• Structures under the rifts in southern Tibet show large variations.

To better understand the pattern of convergence between the Indian and Eurasian plates, we determine a high-resolution P-wave tomography of the crust and upper mantle under southern to central Tibet using a large number of high-quality data of local earthquakes and teleseismic events collected by the ANTILOPE-II and Hi-CLIMB projects. A significant low-velocity zone is detected above the northward underthrusting Indian slab beneath the Indus–Tsangpo suture, which may reflect fault zones or (incomplete) fragmentation as well as melts and/or fluids associated with the dehydration of the underthrusting Indian slab. The variations in the diving depth and extending distance of the Indian slab, under the ANTILOPE-II and Hi-CLIMB seismic profiles, may be caused by the differences in the viscosity contrast between the Indian slab and the surrounding mantle as well as strong structural heterogeneities in the upper mantle under the study region. Both high and low velocity anomalies are revealed in the mid- to lower crust under southern Tibet, which may reflect the complex pattern of crustal structure. The rifts in southern Tibet exhibit different velocity images, suggesting that different structures exist beneath those rifts.

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