![]() Decompression melting peaked with widespread partial melting and formation of migmatites and leucogranites along the highest peaks of the Himalaya. ![]() The GHS metamorphism is all part of one continuum of crustal thickening and shortening, increasing pressure and temperature following a standard clockwise Pressure-Temperature-Time ( PTt) path. The age of the abundant leucogranite sills and dykes along the top of the GHS, beneath the STD, is concomitant with the sillimanite-grade metamorphic event. Peak kyanite grade metamorphism (Late Eocene–Oligocene) pre-dates the regional higher-temperature, lower-pressure sillimanite ± cordierite-grade event, which was accompanied by widespread migmatization and mid-crustal melting during the Oligocene–Mid-Miocene. In broad terms the timing of major events shows little variation along the entire mountain range, with Late Cretaceous–Paleocene obduction of ophiolites onto the passive margin of India, Late Paleocene ultra-high-pressure (UHP) metamorphism at Kaghan (northern Pakistan) and Tso Morari (India), Early Eocene final marine sedimentation prior to the closure of Neo-Tethys, and Late Eocene to Early Miocene regional Barrovian-type metamorphism along the GHS ( Fig. Chamba klippe in India Lingshi klippe in Bhutan), and far-travelled klippen of GHS rocks occur in places south of the main MCT and GHS rocks (e.g. Klippen of low-grade or unmetamorphosed sedimentary rocks lie above the GHS high-grade rocks in places (e.g. Likewise, the major structures, the Indus–Yarlung Tsangpo suture with north-vergent backthrusts, the South Tibetan Detachment (STD) low-angle normal fault, locally called the Zanskar Shear zone in the west, the Main Central Thrust (MCT) zone and the Main Boundary Thrust are all mapped along the entire length of the mountain belt between the western (Nanga Parbat) and eastern (Namche Barwa) syntaxes. The major structural divisions, the Indus–(Yarlung Tsangpo) suture zone, the Tethyan Himalaya sedimentary units, Greater Himalaya Sequence (GHS) metamorphic rocks, the Lesser Himalaya fold-and-thrust belt and the Sub-Himalaya Siwalik molasse basin are present along the entire 2000 km length of the Himalaya ( Figs 1 & 2). The beauty of the Himalaya is that, on a broad scale they form a relatively simple orogenic belt. They are frequently used as the type example of a continental collision orogenic belt in studies of older Phanerozoic orogenic belts. The Himalaya resulted from collision of the Indian plate with Asia and are well known as the highest, youngest and one of the best studied continental collision orogenic belts. ![]()
0 Comments
Leave a Reply. |