Himalayan Thrusts and Structural Belts

Abstract The Himalayan Orogen is characterised by a series of linear and parallel thrusts demarcating individual tectono-stratigraphic units. Two major tectogens, the Lesser Himalayan and the Tethyan, are recognised and these are separated by the Main Central Thrust (MCT). The MCT is the most fundamental of all thrusts in the Himalaya and represents the outermost tectonic transgression of the crystalline thrust nappes with or without Phanerozoic Tethyan cover over the Lesser Himalayan tectogen. The MCT can be recognised all along the Himalaya and is invariably characterised by retrogressive metamorphic characters and schuppen structures. It also comprises sub-nappes like the Salkhala and the Jutogh in the NW Himalaya. The Lesser Himalayan Tectogen has several structural belts demarcated by well-defined thrust planes and imbricate zones. The Himachal Himalaya has the maximum development of these structural belts. Another important aspect of Lesser Himalayan tectogen is the extensive detachment of cover rocks along the planes of unconformity or even bedding. Along the northern margin of the Tethys Himalayan tectogen, the thrust sheets generally have a NE-directed movement, whereas along the southern margin the thrust sheets have SW-directed movement. The highest allochthon in the Himalaya is represented by the Shilakong and Jungbwa ophiolite nappes. The Indus Tectonic Zone borders the Himalaya along its northern margin and is represented by two structural belts viz. the Sangeluma and Indus belts.