Koalin Loess(Glacier&Periglacial landscapes) - Essay Example

HIMALAYAN MOUNTAINS The Himalayan Range or the Himalayas is the youngest mountains in the world. It lies in the Asian Continent separating the IndianSub continent from the Tibetan plateau. These youngest mountains have the highest peaks in the world. Fig 1: 2004 photo mosaic from the International Space Station, Expedition 8.It extends to over 2500 kms from west to east in a curve. The latitude of Mt.Everest, the highest peak of Himalaya is 275917 N and Longitude is 865531 E.There are various theories about the origin of Himalayas.

The prominent one among those theories is the theory of collision of land masses due to tectonic process, resulting in rising of Himalayas. In this background and context, let us examine the concept of an accreted terrain.Let us begin by comprehending what exactly is a terrain: A terrane is a crustal block or fragment that preserves a distinctive geologic history that is different from the surrounding areas and that is usually bounded by faults.Accreted terranes are those that become attached to a continent as a result of tectonic processes.

In more elaborate words, it is a large geographical feature, often a mountain range, that geomorphologists believe was once a group of islands that sat on one tectonic plate that was being subducted under a continental plate. When the part of the plate on which the islands rode began to be subducted, the islands jammed up the subduction zone and the plate behind it broke. As a result, the islands became attached to the side of the continent. As this happened again and again, the island arc became an inland mountain range.

The Himalayas ,according to the modern theory of plate tectonics, was formed as a result of a continental collision or orogeny along the convergent boundary between the Indo-Australian Plate and the Eurasian Plate. This is referred to as a fold mountain. The collision began in the Upper Cretaceous period about 70 million years ago, when the north-moving Indo-Australian Plate, moving at about 15 cm per year, collided with the Eurasian Plate. About 50 million years ago, this fast moving Indo-Australian plate had completely closed the Tethys Ocean, the existence of which has been determined by sedimentary rocks settled on the ocean floor and the volcanoes that fringed its edges.

Since these sediments were light, they crumpled into mountain ranges rather than sinking to the floor. The Indo-Australian plate continues to be driven horizontally below the Tibetan plateau, which forces the plateau to move upwards. The Indo-Australian plate is still moving at 67 mm per year, and over the next 10 million years it will travel about 1,500 km into Asia. About 20 mm per year of the India-Asia convergence is absorbed by thrusting along the Himalaya southern front. This leads to the Himalayas rising by about 5 mm per year, making them geologically active.

The movement of the Indian plate into the Asian plate also makes this region seismically active, leading to earthquakes from time to time. Fig 2: The accreted terrain model. P.G. DeCelles, G.E. Gehrels, J. Quade, B.N. Lareau & M.S. Spurlin, 2000(as cited in Earth and Planetary Science Letters 212 (2003) 433-441 found the following: ‘Accreted terrane’, model in which the Greater Himalayas represents the basement of an exotic terrane that accreted to the northern Indian margin during the Late Cambrian- Early Ordovician, and that the Tethyan Himalaya sedimentary succession is an overlying cover sequence.

The accreted terrane model is based on published detrital zircon age spectra of the GH and TH that show a wide range of Precambrian to Late Cambrian zircons, in contrast to LH bedrock samples that contain zircons exclusively older than 1.6 Gyr.The accreted terrain model postulates that the Greater Himalayas sutured to India along the MCT during the Cambrian^Ordovician event and that the Tethyan Himalayan succession was deposited subsequently.References:1. DeCelles, P.G., Gehrels, G.E. , Quade, J.

, Lareau, B.N. & Spurlin, M.S. (2000) Tectonic implications of U-Pb zircon ages of the Himalyan orogenic belt in Nepal, Science, 288, 497-499.2. Thompson, K.R., Bowring, S.A., Peng, S.C., Ahluwalia, A.D., Myrow, P.M., Hughes, N.C., et al (2003), Integrated tectonostratigraphic analysis of the Himalaya and implications for its tectonic reconstruction, Earth and Planetary Science Letters,212, 433-441 from http://earthscience.ucr.edu/docs/MyrowEPSL03.pdf