Intracontinental subduction, crust-mantle decollement and crustal-stacking wedge in the Himalayas and other collision belts

The Himalayas exhibit the large-scale geometric characteristics of deformation in a classic collision belt. After the continental collision, which occurred 40 Ma ago, the continuous northward motion of India resulted in an important northward subduction of continental lithosphere. The two main consequences of this subduction were (i) building of a crustal-stacking wedge with an average thickness of 70 km; the continental crust was thickened mainly by extensive low-angle (20-30 degrees) overthrusting (crustal duplex) with the width of the wedge increasing with time by southward migration; and (ii) crust-mantle decollement along which the relatively rigid lithospheric mantle slid below the more deformable continental crust during crustal thickening. At the same time, farther N, large-scale strike-slip faulting gave way to lateral E-W crustal extension. Such a model may be applied to other collision belts such as the Alps, the Canadian Cordillera and the Variscan Belt of Europe.