Tornographic evidence for wholesale underthrusting of India beneath the entire Tibetan plateau

We analyzed a global tomographic model for the Tibet-Himalayan collision zone, which indicates that the Indian lithospheric slab has been subducted subhorizontally beneath nearly the entire Tibetan plateau to depths of 165-260 km. Tibetan velocity structure is low in its crust and high in its lithospheric mantle at depths between 75 and 120 km. We interpret an asthenospheric layer positioned above the subducted Indian slab at depths between 120 and 165 km beneath the Tibetan plateau. Beneath the central portion of the plateau a low-velocity anomaly exists from the crust down to 310 km depth, indicating mantle upwelling through a weakened part of the subducted slab. We present a model, which explains that, the uplift history and low relief of the Tibetan plateau is a result of subhorizontal subduction and heating of Indian lithosphere that is separated from Tibetan lithosphere by a thin channel of asthenosphere. Two predictions made by our model are: (1) the amount of shortening in the Himalayas is equivalent to the amount of underthrusted Indian mantle lithosphere; and (2) a young mantle geochemical signature should be present along the entire southern portion of the Tibetan plateau. (c) 2004 Elsevier Ltd. All rights reserved.