| The origin of the inverted metamorphism and paired granite belts of the Himalaya has generally been ascribed to development of the Main Central Thrust (MCT). Although a variety of models have been proposed that link Early Miocene anatexis with inverted metamorphism, recent dating studies indicate that peak metamorphic recrystallization of elements of the MCT footwall occurred in the central Himalaya as recently as ca. 6 Ma. The recognition that hanging wall magmatism and footwall metamorphism are not spatially and temporally related renders unnecessary the need for exceptional physical conditions to explain generation of the High Himalayan leucogranites and North Himalayan granites, which differ in age, petrogenesis, and emplacement style. We suggest that their origin is linked to shear heating on a continuously active decollement that cuts through Indian supracrustal rocks that had previously experienced low degrees of partial melting. Numerical simulations assuming a shear stress of 30 MPa indicate that continuous slip on the Himalayan decollement beginning at 25 Ma could trigger partial melting reactions leading to formation of the High Himalayan granite chain between 25-20 Ma and the North Himalayan belt between 17-8 Ma. The ramp-flat geometry we apply to model the Himalayan thrust system requires that the presently exposed rocks of the hanging wall resided at middle crustal levels above the decollement throughout the Early and Middle Miocene. Late Miocene, out-of-sequence thrusting within the broad MCT shear zone provides a mechanism to bring these rocks to the surface in their present location (i.e., well to the north of the present tectonic front) and has the additional benefit of explaining how the inverted metamorphic sequences formed beneath the MCT. We envision that formation of the broad MCT zone involved successive accretion of tectonic slivers of the Lesser Himalayan Formations to the hanging wall and incorporate these effects into the model. The model permits anatexis as much as 400 km north of the Himalayan range. Young (<12 Ma) leucogranites exhumed on the flank of a southern Tibetan rift may be products of such an extended melting episode.. |