Partially Molten Middle Crust Beneath Southern Tibet: Synthesis of Project INDEPTH Results

TLDR

Geophysical and geological data indicate a partially molten, fluid-like midcrustal layer beneath southern Tibet, formed by crustal thickening, confined by Indian crust and mantle, whose southward extrusion during the Neogene records Himalayan deformation. During the Neogene, underthrusting Indian crust acted as a plunger, displacing the molten midcrust northward while adding melt and ductile flow to the layer.

Abstract

INDEPTH geophysical and geological observations imply that a partially molten midcrustal layer exists beneath southern Tibet. This partially molten layer has been produced by crustal thickening and behaves as a fluid on the time scale of Himalayan deformation. It is confined on the south by the structurally imbricated Indian crust underlying the Tethyan and High Himalaya and is underlain, apparently, by a stiff Indian mantle lid. The results suggest that during Neogene time the underthrusting Indian crust has acted as a plunger, displacing the molten middle crust to the north while at the same time contributing to this layer by melting and ductile flow. Viewed broadly, the Neogene evolution of the Himalaya is essentially a record of the southward extrusion of the partially molten middle crust underlying southern Tibet.