A Critical Analysis of North-South Continuity of Landmasses across Indus-Yarlu-Tsangpo Suture Zone: Its Bearing on the Himalayan Evolution
Authors: Zahid A. Khan, Ram Chandra Tewari
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Gondwana glaciations are well known from the India, and therefore the Pole must have lingered long enough in the subcontinent to deposit some 1600 m thick glacio-marine sediments in northern Tibet. Similarities of these deposits with those of basal Gondwana Talchir rocks indicate that India and Tibet (and hence the rest of Asia) were united in the Upper Carboniferous and Lower Permian. Further, paleo-biogeography of the region suggests their continuity through Permian, Triassic and Jurassic, and up to Cretaceous. The collision is supposed to have taken place in the Eocene-Miocene, and there should at least have been a very short time of compression at this stage. Instead, the immense batholiths intrusion in the area strongly suggests tension. Moreover, the ophiolites along the suture have yielded two different ages of emplacement, Jurassic-Lowest Cretaceous, and then a little later in Lower Cretaceous, i.e. the emplacement took place 100 Ma before the supposed collision in the Eocene. It is believed that the Indian Plate is progressively underthrusting the Tibetan Plate, though a large part of central and southern Tibet is traversed by active normal and transform faults and rift valleys, cutting across the Bongong-Nujiang and the Indus-Tsangpo suture zone and entering the Himalayan region imply tension all over the area, and not compression, that is expected from subduction/collision zone. Thus, the modern global plate tectonic concept and subduction/collision mechanism are thus, untenable for Himalaya evolution. Alternatively the Himalayas are formed under tensional regime by vertical uplift, intrusive magmas, boudins, sills sand dykes. Gravity gliding played an important role.
The various geological arguments such as structure, paleo-biogeography, paleoclimate and volcanic history, including the presence of Tibetan glacial deposits therefore, do not convincingly support the concept of collision of two landmasses, as popularly believed today or by the plate convergence and the hypothetical subduction in this part of world. Even the Paleomagnetic data is replete with contradictory evidence. The collisional along the Indus-Tsangpo suture is, therefore, doubtful in as much as India has all along been adjacent to Tibet, certainly at least since the Ordovician, and hence a part of the great Pangaea landmass. The modern global plate tectonic concept and subduction mechanism are, thus, untenable for Himalayan evolution. The Himalaya is formed under tensional regime by vertical uplift and gravity sliding.