Abstract Following the c. 50 Ma India–Kohistan arc–Asia collision, crustal thickening uplifted the Himalaya (Indian Plate), and the Karakoram, Pamir and Tibetan Plateau (Asian Plate). Whereas surface geology of Tibet shows limited Cenozoic metamorphism and deformation, and only localized crustal melting, the Karakoram–Pamir show regional sillimanite- and kyanite-grade metamorphism, and crustal melting resulting in major granitic intrusions (Baltoro granites). U/Th–Pb dating shows that metamorphism along the Hunza Karakoram peaked at c. 83–62 and 44 Ma with intrusion of the Hunza dykes at 52–50 Ma and 35 ± 1.0 Ma, and along the Baltoro Karakoram peaked at c. 28–22 Ma, but continued until 5.4–3.5 Ma (Dassu dome). Widespread crustal melting along the Baltoro Batholith spanned 26.4–13 Ma. A series of thrust sheets and gneiss domes (metamorphic core complexes) record crustal thickening and regional metamorphism in the central and south Pamir from 37 to 20 Ma. At 20 Ma, break-off of the Indian slab caused large-scale exhumation of amphibolite-facies crust from depths of 30–55 km, and caused crustal thickening to jump to the fold-and-thrust belt at the northern edge of the Pamir. Crustal thickening, high-grade metamorphism and melting are certainly continuing at depth today in the India–Asia collision zone.

The closing of the Tethys Ocean and continent-continent collision along the Alpine-Himalayan chain ultimately produced large Himalayan-type mountain belts and large plateaux, such as Tibet. Earlier stages in the collision process, however, can be seen in the Oman Mountains of eastern Arabia and the Zagros Mountains of SW Iran. In Oman, a large, intact ophiolite was emplaced onto a Mesozoic passive continental margin, largely by thin-skinned thrust processes, prior to continental collision. The ophiolite and a granulite-amphibolite-greenschist facies inverted metamorphic sole were formed in a subduction zone setting during the early stages of emplacement. Eclogites were formed by the attempted subduction of the continental margin, and its rapid expulsion back up the same subduction zone, during later stages of the orogeny. The early stages of continental collision are best seen in the Zagros Mountains where thick-skinned thrusting and simple folding has resulted in a relatively small amount of crustal shortening (50–70 km) with almost no metamorphic or magmatic consequences. Burial metamorphism may be occurring presently at deep levels of the internal zone and the Turkish-Iranian Plateau where the crust is thicker, but this remains unexposed at the surface. The collision of the Indian plate with Asia since ca. 50 Ma resulted in formation of the Himalaya along the north margin of India, and the Karakoram–Hindu Kush Mountains along the south Asian margin. Together with renewed uplift and crustal thickening of the Tibetan Plateau, this was arguably the largest continental collision in the last 450 m.y. of Earth history. The Himalayan-type orogeny involved large amounts of crustal shortening (∼500–1000 km), early ultrahigh-pressure (UHP) coesite-eclogite facies metamorphism, peak Barrovian facies kyanite and sillimanite metamorphism, and mid-crustal anatexis resulting in garnet, tourmaline, muscovite-bearing migmatites, and leucogranites. Processes involved in the construction of the Tibetan Plateau include crustal shortening and doubling the thickness of the crust to 65–90 km. High-pressure (HP) eclogite and high-temperature/high-pressure (HT-HP) granulite metamorphism may be occurring at depth today in the lower crust beneath Tibet. Widespread ultrapotassic volcanism across Tibet indicates the presence of a hot subcontinental mantle, which was progressively shifted northwards as the cold, Indian lithosphere underthrust southern Tibet. Whereas Tibet shows mainly upper crustal sedimentary and volcanic rocks at the present surface, the Karakoram Range, along strike to the west, shows mostly deep crustal high-grade metamorphic rocks, multiple granite intrusions, and over 60 m.y. of high-temperature metamorphism. This paper reviews the salient geological features of Oman-, Zagros-, Himalayan-, Tibetan-, and Karakoram-type orogenic belts. These features can be used in studies of older orogenic belts to give indications of their tectonic origins.

Recent chronologic and stratigraphic studies in the northwestern Himalayan foreland basin have led to better constrained deformational and depositional histories. In order to test the hypothesis that considerable pre-Pleistocene uplift occurred in the Salt Range of northern Pakistan, the stratigraphic record adjacent to the central and eastern Salt Range has been examined. Unconformities, paleomagnetically documented tectonic rotations across these unconformities, and changes in the paleocurrent directions, provenance, and rates of sediment accumulation serve to delineate an interval of early Pliocene uplift of the Salt Range, as well as several late Pliocene–Pleistocene uplift events in this range and adjacent structures. Stratigraphic, reflection seismic, and structural data indicate that these uplift events resulted from thrusting related to the salt-lubricated Potwar detachment. When considered in conjunction with the chronology of deformation in other parts of the foreland, these data clearly indicate that out-of-sequence thrusting has occurred on a large scale (>100 km) during the past 6 m.y. This pattern of deformation supports the concept that an irregular spatial and temporal distribution of shortening should be expected to occur within an advancing thrust wedge.

Skardu Basin is a northwest-trending intermontane basin along the Indus River in the Karakoram Himalaya Mountains of Pakistan. Seismotectonic domain boundaries in the Karakoram Himalaya commonly cross lithologic and some older structural boundaries. Four major structural-seismotectonic domains exist in the Skardu area: the Himalayan seismic zone, characterized by thrust tectonics; the complex Hindu Kush–Pamir seismic zone; the Skardu quiet zone, characterized by strike-slip, extensional, and rotational tectonics with relatively little seismicity; and the southern edge of Eurasian lithosphere (Tarim–Kun Lun–Tibet) northeast of the Karakoram fault. The Skardu quiet zone is interpreted to be within the Himalayan thrust prism, above an aseismic detachment along which stable sliding or ductile faulting accommodates displacement. Stresses transmitted into the Skardu quiet zone laterally from the Himalayan seismic zone toward Eurasia and perhaps upward from the inferred basal detachment result in gross clockwise rotation, translation to the north-northwest, and a right-lateral sense of shear in the Skardu region. Landsat lineaments defined by major drainages suggest an array of fractures and faults in the Skardu quiet zone. Field data suggest that the lineaments generally reflect distributed shear along myriad small faults rather than displacement exclusively localized on major, discrete fault surfaces. Extensive glacial and fluvial erosion have accentuated trends characterized by relatively dense fracturing and faulting. At its confluence with the Indus at Skardu, the Shigar River flows through a breach that may have originated as a pull-apart structure similar to the pull-apart basin along the upper Sutlej River. The preserved vestiges of the upper Cenozoic Bunthang sedimentary sequence reflect Skardu’s early basin phase. Uplift along the Nanga Parbat–Haramosh syntaxis and along the northeastern margin of the Himalayan seismic zone may have contributed to the ponding of the Indus River in the Skardu Basin during Bunthang time. These axes of uplift may be related to movement of the Himalayan thrust wedge from a region of easy basal slip (Skardu quiet zone) to a region of increased resistance to basal slip (Himalayan seismic zone, or, in the case of the NP-H syntaxis, the Hindu Kush-Pamir seismic areas). Regional uplift within the Skardu quiet zone may reflect thickening of the thrust prism in response to variations in shear resistance along the detachment. Quaternary glacial lake beds located on the floor of Skardu Basin are generally undeformed in the western half of the basin. Local deformation within the lake beds in the eastern half of the basin is probably due to interaction with glaciers.