Plate tectonic interpretation of the Western Himalaya

Abstract

The Western Himalaya, which includes the regions of Kumaun, Garhwal, Himachal, Jammu and Kashmir in India displays a complete cross-section of the Himalayan orogenic belt encompassing the principal tectonic zones of Outer Himalaya, Lesser Himalaya, Higher Himalaya, Tethys Himalaya, and Trans Himalaya. The rock formations of the Lesser Himalaya, which are correlatable to those of the northern part of the Indian Peninsular shield, represent deposits on the northern edge of the Indian craton. The Phanerozoic sequence of the Tethys Himalaya zone is interpreted as representing sedimentary deposits of the continental margin. The Central Crystallines of the Higher Himalaya zone, underlying the Phanerozoic sequence of the Tethys Himalaya zone, have been exposed in their present position as a result of uplift and southward movement along the Main Central Thrust. The Trans-Himalaya zone consists of the Indus Suture, Ladakh magmatic arc, Shyok Suture and Karakoram subzones. The Nidar ophiolite and the Shergol and Zildat ophiolitic melanges of the Indus Suture are the tectonised remnants of the Tethys ocean floor. The Ladakh plutonic complex, the Dras volcanics and other related Cretaceous volcanics belong to the plutonic-volcanic series of the Ladakh magmatic arc. The Shyok Suture is interpreted as a back-arc basin, and the Palaeozoic-Mesozoic sequence of the Karakoram subzone represents continental margin deposits of the Karakoram block. The molasse sedimentary deposits of the Outer Himalaya zone are interpreted as representing post-collision sedimentation in a trough that developed in front of the rising Himalaya. The tectonic evolution of Northwestern Himalaya has been involved in the following sequence of events. 1. (a) Subduction of the Indian oceanic plate under the Karakoram (Tibet) block in the Cretaceous, giving rise to the Ladakh magmatic arc and arc-trench gap sedimentation. 2. (b) Collision of the Indian plate with the Ladakh magmatic arc in the middle Eocene forming the Indus palaeosubduction zone. 3. (c) Closure of the Shyok back-arc basin and collision of the Ladakh magmatic arc with the Karakoram block. 4. (d) Suturing of the lithospheric blocks as a result of collision. The penetrative and non-penetrative deformation, regional metamorphism, generation of S-type granites in the Higher Himalaya zone and the formation of nappes and thrusts owe their origin to crustal shortening in the Oligocene-Miocene.