The collision of India and Asia can be defined as a process that started with the closing of the Tethyan ocean that, during Mesozoic and early Tertiary times, separated the two continental plates. Following initial contact of Indian and Asian continental crust, the Indian plate continued its northward drift into Asia, a process which continues to this day. In the Ladakh–Zanskar Himalaya the youngest marine sediments, both in the Indus suture zone and along the northern continental margin of India, are lowermost Eocene Nummulitic limestones dated at ∼54 Ma. Along the north Indian shelf margin, southwest-facing folded Palaeocene–Lower Eocene shallow-marine limestones unconformably overlie highly deformed Mesozoic shelf carbonates and allochthonous Upper Cretaceous shales, indicating an initial deformation event during the latest Cretaceous–early Palaeocene, corresponding with the timing of obduction of the Spontang ophiolite onto the Indian margin. It is suggested here that all the ophiolites from Oman, along western Pakistan (Bela, Muslim Bagh, Zhob and Waziristan) to the Spontang and Amlang-la ophiolites in the Himalaya were obducted during the late Cretaceous and earliest Palaeocene, prior to the closing of Tethys.The major phase of crustal shortening followed the India–Asia collision producing spectacular folds and thrusts across the Zanskar range. A new structural profile across the Indian continental margin along the Zanskar River gorge is presented here. Four main units are separated by major detachments including both normal faults (e.g. Zanskar, Karsha Detachments), southwest-directed thrusts reactivated as northeast-directed normal faults (e.g. Zangla Detachment), breakback thrusts (e.g. Photoksar Thrust) and late Tertiary backthrusts (e.g. Zanskar Backthrust). The normal faults place younger rocks onto older and separate two units, both showing compressional tectonics, but have no net crustal extension across them. Rather, they are related to rapid exhumation of the structurally lower, middle and deep crustal metamorphic rocks of the High Himalaya along the footwall of the Zanskar Detachment. The backthrusting affects the northern margin of the Zanskar shelf and the entire Indus suture zone, including the mid-Eocene–Miocene post-collisional fluvial and lacustrine molasse sediments (Indus Group), and therefore must be Pliocene–Pleistocene in age. Minimum amounts of crustal shortening across the Indian continental margin are 150–170 km although extreme ductile folding makes any balancing exercise questionable.

The Main Central Thrust is a crustal-scale ductile shear zone between 1.5 and 3 km wide which places the Oligocene–Miocene metamorphic rocks of the High Himalayan zone south or SW over the unmetamorphosed or weakly metamorphosed rocks of the Lesser Himalaya. The high strain zone of the Main Central Thrust is coincident with an inverted metamorphic field gradient from biotite to kyanite grade over a structural thickness of 1500 m. Kyanite-grade rocks metamorphosed at 9.5–10 kbar were exhumed from depths of 33–37 km along the Main Central Thrust hanging wall and emplaced over Lesser Himalayan rocks never buried deeper than 10–12 km. Exhumation of the deepest buried kyanite-grade rocks occurred along the zone. Above the Main Central Thrust zone approximately 45 km width (28 km structural thickness) of the High Himalaya exposes sillimanite-grade gneisses, migmatites and 19.5–21.5 Ma old leucogranites formed at pressures between 4.5 and 7 kbar and depths of 16–25 km. A NE-dipping normal fault ductile shear zone at the top of the slab (Zanskar Shear Zone) shows condensed but right way-up isograds from sillimanite to chlorite grade over 2–400 metres structural thickness. 40 Ar/ 39 Ar geochronology shows that most of the High Himalayan slab had cooled below 350°C by 16 Ma supporting models linking the two bounding faults of the High Himalaya both kinematically and temporally. There is no evidence of melting along the Main Central Thrust zone and the Himalayan leucogranites were generated 10–30 km structurally above the Main Central Thrust. Frictional heating along the Main Central Thrust could not therefore have played any role in generating the leucogranites. Thus far, there is little evidence for late Miocene reactivation along the Main Central Thrust, as seen elsewhere along the Main Central Thrust in Nepal.

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