Role of Crust-Mantle Detachment and Slab Delamination in the Plateau Uplift and Crustal Thickening Process in Southern Tibet

Abstract

The driving mechanism behind the anomalously thick crust and surface uplift of the Tibetan Plateau remains controversial. Here we present seismic images of the lithosphere in southern Tibet, derived from P and S receiver functions along a newly deployed 200 km-long broadband seismic array that strikes north at 91.15°E longitude. An offset of the Moho discontinuity is revealed at ∼70 km depth beneath the Yarlung-Zangbo suture zone (YZS). The subducted Indian lithospheric mantle is thrusting beneath southern Tibet with a flat-ramp-flat geometry and is undergoing crust-mantle detachment beneath the YZS. As an intermediate stage in the underplating and delamination of the Indian plate, the crust-mantle detachment plays an important role in the process of surface uplift and crustal thickening in southern Tibet. It is the main cause of the Moho offset, facilitating upwelling of asthenospheric materials from the upper mantle to the crust. These materials underplate in the lower crust, promote the formation of juvenile lower crust in southern Tibet, and lead to widespread low-velocity zones within the crust.