Geology & Tectonics of the Himalayan Mountains Essay

Geology & Tectonics of the Himalayan Mountains - Essay Example The Himalayas are mountain range in asia separating the indian sub continent and tibetan plateau. The meaning of the word Himalaya in sanskrit is "abode of the snow." The geology of the Himalayan mountain is the most dramatic and creation of modern plate tectonic forces. The Himalayas are a result of orogeny which is a result of a collison between two continental tectonic plates. They are formed due to the denudation processes of weathering and erosion. The Himalayas supplies water for more than one-fifth of the world population and accounts for a quarter of the global sedimentary budget. Himalayas stretch 2,900 km along the border between India and Tibet. With the collision of two large landmasses, India and Eurasia, driven by the plate movement, collided; this mountain began to form between 40 and 50 million years ago. As both the landmasses have the same rock density, one plate could not be subducted under the other. Thus the pressure of these plates started forming the Himalayan peaks. The Himalayas and the Tibetan Plateau to the north have risen very rapidly. In just 50 million years, Mt. Everest has risen to height of more than 9 km. The Himalayas continue to rise more than 1 cm a year -- a growth rate of 10 km in a million years. If that is the case, the Himalayas should be even higher. This made scientists to believe that Eurasian Plate may now be stretching out rather than thrusting up, and such stretching would result in some subsidence due to gravity. Tectonics of Himalayas: The most important property of the Himalayan orogen is its growth laterally. The Himalayan region is divided into four tectonic units for the convenience and better understanding. 1) The sub Himalaya forms the foothills of the Himalayan range and is composed of Miocene and Pleistocene molassic sediments derived from the erosion of Himalaya. The subhimalyan region consist of the quarternery alluvium depsited by the rivers coming from the Himalayas. This explains that the Himalaya is still a young and active orogen. 2) The Upper Proterozoic to Lower Cenozoic Detrital Sediments from the passive Indian margin forms the Lesser Himalaya. These sediments are formed byintercalated with some granites and acid volcanics (1840 70 Ma, Frank et al., 1977). These low-grade sediments are thrust over the SubHimalaya along the Main Boundary Thrust (MBT). The Lesser Himalaya often appears in tectonic windows (Kishtwar or Larji-Kulu-Rampur windows) within the High Himalaya Crystalline Sequence. 3) The Central Himalayan Domain, CHD (or High Himalaya) forms the backbone of the Himalayan orogen and encompasses the areas with the highest topographical relief. It is commonly separated into four zones. a. The High Himalayan Crystalline Sequence, HHCS is a 30 km thick, medium- to high-grade metamorphic sequence of metasedimentary rocks which are frequently intruded by granites of Ordovician ( 500 Ma) and Lower Miocene ( 22 Ma) age. b. The Tethys Himalaya, TH is an approximately 100 km large synclinorium formed by strongly folded and imbricated, weakly metamorphosed sedimentary series. c. The Nyimaling-Tso Morari Metamorphic Dome, NTMD: In the Ladakh region, the Tethys Himalaya synclinorium passes gradually to the north in a large dome of greenshist to eclogitic metamorphic rocks. As with the HHCS, these metamorphic rocks represent the metamorphic equivalent of the sediments forming the base of the Tethys Himalay