Thermochemical Heterogeneities in the Northern Tibet Lithosphere Could Explain the Lithosphere-Scale Low Seismic Velocities

Abstract

Present-day lithosphere and upper-mantle structure of the Himalaya-Tibet region is key to understanding Tibetan plateau formation. Competing models propose either a thick lithosphere or lateral variations resulting from the destabilisation of the thickened lithospheric mantle. Using integrated geophysical-petrological modelling along north–south profiles across western, central, and eastern Tibet, we jointly model seismic, gravity, geoid, and topographic data within a self-consistent thermodynamic framework. Results show that the Proterozoic Indian lithosphere continues and thickens from the foreland to beneath southern Tibet, whereas northern Tibet shows Phanerozoic lithosphere. Lithosphere-scale low seismic velocities beneath northern Tibet in the central and eastern plateau could be explained by radiogenic heating from thick orogenic crust, provided that thick crust existed before the collision. These findings support a thermally and compositionally modified thick lithosphere beneath Tibet as an alternative to the replacement by asthenosphere.