Lithospheric Deformation And Active Tectonics Of The Nw Himalayas, Hindukush, And Tibet

The Himalayan Mountain System (HMS) and the Tibetan Plateau (TP) represent an active mountain belt, with continent-continent collision. Geological and geophysical (seismological modeling, seismic reflection, and gravity) data is reviewed herein for an overview of the lithospheric deformation and active tectonics of this orogen. Shallow crustal deformation with dominance of thrusting along the margins of the TP is interpreted with normal faulting in the center and strike-slip deformation with the lateral translation of blocks, over a wedge of ductile deformation. The seismicity is the linear concentration over the margins of the orogen to similar to 20 km depth with exception of the Hindukush and Pamir having seismicity to 300km depth with an interpretation of sinking Indian and Asian lithospheres. The lithospheric structure is represented by mechanically weak surfaces representing decollement to 15 km depth over the basement, low-velocity zone (LVZ) at similar to 20 km, the Moho at similar to 40-82km, and the lithosphere-asthenosphere boundary (LAB) at 130-200 km depth. The decollement, termed as the Himalayan Mountain Thrust (HMT), is inferred to be rooted at the base of the Moho in central Tibet. Along this fault, brittle crustal deformation is interpreted to similar to 15-20 km depth, with brittle-ductile deformation along LVZ and ductile slip with crustal duplexing along the lower crust. The mantle lithosphere of the Indian plate is inferred as duplicated with the wedging of the Asian mantle lithosphere. The active tectonics of the 'IP is proposed to follow the mechanics of thrusting, similar to the foreland deformation of the mountain belts and accretionary prisms.