Himalaya—the collided orogen: a plate tectonic evolution on geological evidences

Abstract

The Lesser Himalaya and the Tethys Himalaya constitute two contrasting and distinct geotectonic zones within the realm of the Himalaya separated from each other by the Main Central Thrust (MCT), and of these two zones, the former is continuous with Northern Peninsular India whereas the latter is demarcated by zones of ophiolitic mélange of the Indus Tectonic zone. The MCT constitutes a zone of greatest overthrusting with a horizontal translation of over 130 km and this dislocation possibly represents a continental suture. The Tethys Himalayan zone has all the elements of a micro-continent independent of the Tibetan block (Karakorum-Lhasa) in the north and Gondwanic India-Lesser Himalaya in the south. The upper Carboniferous—Permian period probably withnessed the first event, a drift of the Proto-Tethys plate and its suturing with the Proto-Karakorum—Tibet plate as substantiated by a Permian-Triassic marine sedimentation all along the northern boundary of the Tethys zone and in Karakorum, volcanic activity and emplacement of ophiolite. The second event occurred during the early Cretaceous, that is the drift of Gondwanic India and its collision with the Proto-Tethys along the Proto-MCT. As a consequence opening occurred along the old suture boundary between the Proto-Tethys and the Proto-Karakorum as documented by the development of the Sangeluma and Shyok rift basins, extensive volcanic activity, granitoid emplacement and development of oceanic crust related to slow spreading along a ridge. Simultaneously Gondwanic India became tensile and there was reactivation along the Narmada-Son zone leading to extensive Deccan volcanism. As compression increased there was closing of the Sangeluma and Shyok seas, subduction, dismemberment and obduction of newly formed oceanic crust and development of deltaic Indus basin on the Ladakh Batholith. Along the southern margin of the Proto-Lesser Himalaya the Tertiary basins evolved due to migration of crustal buckle of the Indian Peninsula. With widespread regression of sea and uplift there was divergent tectonic overlap of the Tethys zone over Gondwanic India-Lesser Himalaya in the south and onto the Indus ophiolite belt-Ladakh batholith in the north, leading to the formation of the Himalaya.