PARTIALLY MOLTEN MIDDLE CRUST BENEATH SOUTHERN TIBET - SYNTHESIS OF PROJECT INDEPTH RESULTS

INDEPTH geophysical and geological observations imply that a partially molten mid-crustal layer exists beneath southern Tibet, This partiall y 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 T ethyan and High Himalaya and is underlain, apparently, by a stiff Indi an mantle lid. The results suggest that during Neogene time the undert hrusting Indian crust has acted as a plunger, displacing the molten mi ddle crust to the north while at the same time contributing to this la yer 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.