Geology - Oblique stepwise rise and growth of the Tibet plateau

Two end member models of how the high elevations in Tibet formed are (i) co ntinuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and (ii) time-dependent, localized shear between coheren t lithospheric blocks. Recent studies of Cenozoic deformation, magmatism, a nd seismic structure lend support to the latter. Since India collided with Asia similar to 55 million years ago, the rise of the high Tibetan plateau likely occurred in three main steps, by successive growth and uplift of 300 - to 500-kilometer-wide crustal thrust-wedges. The crust thickened, while t he mantle, decoupled beneath gently dipping shear zones, did not. Sediment infilling, bathtub-like, of dammed intermontane basins formed flat high pla ins at each step. The existence of magmatic belts younging northward implie s that stabs of Asian mantle subducted one after another under ranges north of the Himalayas. Subduction was oblique and accompanied by extrusion alon g the left lateral strike-slip faults that slice Tibet's east side. These m echanisms, akin to plate tectonics hidden by thickening crust, with slip-pa rtitioning, account for the dominant growth of the Tibet Plateau toward the east and northeast.