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The Main Central Thrust is a major geological fault where the Indian Plate has pushed under the Eurasian Plate along the Himalaya. The fault slopes down to the north and is exposed on the surface in a NW-SE direction (strike). It is a thrust fault that continues along 2200 km of the Himalaya mountain belt.〔Upreti, B. N. "(An overview of the stratigraphy and tectonics of the Nepal Himalaya )" ''Journal of Asian Earth Sciences'' 17.5 (1999): 577–606.〕 The generally accepted definition of the Main Central Thrust is that it is a ductile shear zone along which the High-grade Great Himalayan Crystalline complex was placed above the low-grade to unmetamorphosed Lesser Himalayan Sequence.〔Helm, A., and A. Gansser. "Central Himalaya, Geological observations of the Swiss expedition 1936." ''Memoires de la Societe Helvetique des Sciences Naturelles'' 73.1,245 (1939).〕 However, this definition is not perfect because of many difficulties and complications defining the Main Central Thrust. Many geologists have researched the Main Central Thrust using various different criteria such as lithology,〔〔 metamorphic isograd,〔 geochronology,〔 geochemistry,〔 and strain magnitude.〔〔 None of these are reliable if used independently. Furthermore, there is uncertainty because of the differences along-strike in the active ages of the Main Central Thrust. It was not all formed at the same time. == Geologic background == The Himalayan mountain belt was produced by the collision of the Indian Plate and the Eurasian Plate. It is structurally dominated by three north-dipping, fault-bound geological units stacked on each other. The major faults are South Tibetan Detachment, the Main Central Thrust, the Main Boundary Thrust and the Main Frontal Thrust.〔 These units (figure 2), from south to north, are: # the Lesser Himalayan Sequence, which is mainly composed of low-grade Proterozoic metasediments to unmetamorphosed rocks, fringed by the Main Boundary Thrust and the Main Central Thrust; # the Greater Himalayan Crystalline complex, which is mainly composed by high-grade gneiss and migmatite, fringed below by the Main Central Thrust and the South Tibetan Detachment; and # the Tethyan Himalayan Sequence, mainly composed by Proterozoic to Eocene sediments, deformed in an Paleogene fold-thrust belt, fringed below by the South Tibetan Detachment.〔Webb, A. Alexander G. "(Preliminary balanced palinspastic reconstruction of Cenozoic deformation across the Himachal Himalaya (northwestern India) )."''Geosphere'' 9.3 (2013): 572–587.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Main Central Thrust」の詳細全文を読む スポンサード リンク
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