India collided with the northern Kohistan/Asian plate at about 55 Ma. Subsequently, Asia has overridden India, developing a wide range of thrust slices at the top of the Indian plate. Balanced sections in the imbricated sedimentary cover of the Indian plate indicate a minimum displacement of more than 470 km since collision. This requires the Kohistan region to the north to be underlain by underthrusted middle to lower Indian crust, the internal ductile deformation and thickening of which accounts for the main overall crustal thickening beneath Kohistan. In the Besham area of north Pakistan, a stratigraphy can be documented for the northern part of the Indian plate that includes basement sequences of quartzo-feldspathic gneisses of the Besham Group, and of Precambrian schists of the Tanawal Formation intruded by the Swat-Mansehra granite. The basement rocks are unconformably overlain by carbonate-rich Paleozoic sedimentary rocks. Sedimentary rocks of both the basement and cover sequences were metamorphosed at an early stage of the Himalayan deformation during tectonic burial associated with crustal thickening. Structures just south of the suture related to this crustal thickening include a sequence of ductile mylonites thickened by thrust-related folding, a folded thrust stack involving basement rocks imbricated with cover strata, and late cross-folds. Much of the thickening of the Indian plate in the footwall of the Main Mantle Thrust can be related to the necessary changes in thrust wedge shape as it climbs through the crust.

Abstract The Pakistan part of the Himalaya has major differences in tectonic evolution compared with the main Himalayan range to the east of the Nanga Parbat syntaxis. There is no equivalent of the Tethyan Himalaya sedimentary sequence south of the Indus–Tsangpo suture zone, no equivalent of the Main Central Thrust, and no Miocene metamorphism and leucogranite emplacement. The Kohistan Arc was thrust southward onto the leading edge of continental India. All rocks exposed to the south of the arc in the footwall of the Main Mantle Thrust preserve metamorphic histories. However, these do not all record Cenozoic metamorphism. Basement rocks record Paleo-Proterozoic metamorphism with no Cenozoic heating; Neo-Proterozoic through Cambrian sediments record Ordovician ages for peak kyanite and sillimanite grade metamorphism, although Ar–Ar data indicate a Cenozoic thermal imprint which did not reset the peak metamorphic assemblages. The only rocks that clearly record Cenozoic metamorphism are Upper Paleozoic through Mesozoic cover sediments. Thermobarometric data suggest burial of these rocks along a clockwise pressure–temperature path to pressure–temperature conditions of c. 10–11 kbar and c. 700°C. Resolving this enigma is challenging but implies downward heating into the Indian plate, coupled with later development of unconformity parallel shear zones that detach Upper Paleozoic–Cenozoic cover rocks from Neoproterozoic to Paleozoic basement rocks and also detach those rocks from the Paleoproterozoic basement.