7. Bird, P. (1978a) Initiation of intracontinental subduction in the Himalaya, J. Geophys. Res., 83, 4975-4987.
Abstract. Independent arguments based on topographic stress and crustal strength give upper limits of 200 bars and 300 bars, respectively, for the average shear stress on the intracontinental thrust fault that formed the Himalaya. According to either a one-dimensional or a two- dimensional fault model, such stresses could not have produced the Himalayan granites by friction, unless overthrusting velocity exceeded 30 cm/yr. More probably, Himalayan metamorphism was caused by exposure of continental crust to hot asthenosphere prior to the formation of the intracontinental thrust. Crust was exposed by peeling away of Indian subcrustal lithosphere in response to the force and moment exerted by the Tethyan slab. This detachment of buoyant crust from dense lithosphere better explains the metamorphic pattern and also explains why the distributed crustal shortening at the beginning of the collision orogeny was replaced by localized thrusting or intracontinental subduction.
P.S. (1) According to this model, all Himalayan granites in any cross-section should be about the same age. It is now known that the High Himalayan leucogranites formed at 24-17.2 Ma, but the North Himalayan granites formed at 17.6-9.5 Ma (Harrison et al., 1998, JGR). Therefore, the history was more complex, and a second heating mechanism may be necessary. However, this mechanism is still a plausible cause for the first melting event and the formation of the Main Central thrust fault. (2) Bars are not SI. Convert 200 bars = 20 MPa; 300 bars = 30 MPa. P. Bird, 2000.08.31