SUBDUCTION OF ASIAN LITHOSPHERIC MANTLE BENEATH TIBET INFERRED FROM MODELS OF CONTINENTAL COLLISION

The relative northward motion of the Indian subcontinent that followed the onset of continental collision with Asia has produced extensive d eformation of the Earth's crust, giving rise to the world's highest mo untains in the Himalayan chain and the world's largest high-elevation region, the Tibetan plateau. The formation of the broad mountain belt implies that, contrary to the original tenets of plate tectonics, the lithospheric plates have experienced widespread deformation far from t he plate boundary(1). Several models have been proposed(2-6) to explai n the manner in which this post-collisional deformation is distributed within the continental lithosphere of the Indian and Asian plates. He re we propose an alternative model in which subduction of the Asian li thospheric mantle develops following the collision of India. Our model is supported by numerical calculations of crustal deformation and thi ckening, and is consistent with available geological and geophysical d ata(7-9). This picture suggests that lithospheric mantle is not deform ed along with the crust, and would imply that continental collision zo nes are more analogous to oceanic subduction zones than was previously believed.