Problems in Accepting Plate Tectonics and Subduction as a Mechanism of Himalaya Evolution.

Abstract

The available geological and structural data from Chaman fault and Indus-Tsangpo regions does not support the new global tectonic concept and the presence of suture zone between Indian and the northern landmass. Instead, it is suggested that the Indus-Tsangpo is a rift valley that appeared in the Triassic and became dormant in the Cretaceous, after a spurt of volcanic activity long before the supposed suturing in the Eocene. The paleontological evidences based on plants, marine and fresh-water invertebrates, insects and vertebrates indicate that Gondwanaland was never a separate entity. Paleoclimatic continuity was maintained over this landmass of India and Tibet from the Paleozoic through Cenozoic eras up to the Pleistocene Epoch. Similarly, the widespread glacial deposits of northern Tibet bespeak of a continental landmass extending from Peninsular India up to northern Tibet, and may be beyond. Thus, Pangaea existed till its breakup beginning in the Triassic and Tethys was an epicontinental sea from west Proto-Pacific to east Proto-Pacific. At no stage was it oceanic in character, although narrow shifting belts along and across it, became rift or geosynclines in the process of crustal development. Thus, the Tethys did not form a wide, funnel shaped gulf, opening into the Pacific as depicted in many reconstructions. On the other hand, the Himalayan sequence is dominantly nongeosynclinals sediments, and therefore, genetically different from such classic mountains as the Caledonian, Hercynian, Urals, and Aravallis etc. It is significant that the Himalayan orogeny was initiated in the Cretaceous, and the major episode was Eocene, i.e. earlier than the supposed collision, rules neither out continental collision and subduction nor even in geosynclines. However, the Himalayas, could, then, not have been borne due to collision of landmasses as suggested by plate-tectonics. Instead, they are an interplatform type of mountain range formed by vertical uplift, by intrusive magmas and gravity gliding played an important part too. Terrestrial gravity, seismic (including DSS), geodetic, geomorphologic and field tectonic studies independently and collectively support the above contention. The Himalaya along with some other ranges in Central Asia may be unique in Earth history, and all the mountain ranges of the past seem apparently to have been originated in geosynclines. The plate tectonic concept, however, considers the term geosynclines redundant.