Extract
The Himalaya comprise the earth’s largest mountain range, an orogenic belt in which crustal shortening of hundreds of kilometres is firmly established, shortening related to northward movement of peninsular India. It is a classic region for study of orogenic development, but it is notable for its lack of geosynclinal basins in the conventional sense. The rocks of which it is made up are entirely of shield material and platform sediments, except for a narrow ophiolitic belt in the north.
Segment: this has a length, measured along the strike, of 2400 km. The southern margin of the orogenic belt, which is also the north margin of the Indo-Gangetic plain, is narrowly gradational (½ to 3 km). The north margin, with the Tibetan Block, is broadly gradational (> 3 km). The width of the belt varies from 230 to 320 km and averages 270 km.
Zones: the segment is described in terms of zones from north to south. The northernmost zone (1) is a northward thrust mass of Cretaceous flysch with basic and ultrabasic exotics, resting on Palaeogene molasse. Next south (zone 2) is the Ophiolitic zone, with contemporaneously intruded Jurassic and Cretaceous radiolarites, flysch and ultrabasic rocks, deformed by southward thrusting and gliding. Zone 3, the Tibetan Himalaya, is a broad thrust belt of thick normal sediments (Mesozoic on partly metamorphosed Palaeozoic). In zone 4, the Higher Himalaya, the line of greatest vertical uplift, pre-existing sediments are almost entirely removed and the belt consists of pre-Ordovician metamorphic rocks intruded by granites
- © The Geological Society, London 1974
Extract
The Himalaya comprise the earth’s largest mountain range, an orogenic belt in which crustal shortening of hundreds of kilometres is firmly established, shortening related to northward movement of peninsular India. It is a classic region for study of orogenic development, but it is notable for its lack of geosynclinal basins in the conventional sense. The rocks of which it is made up are entirely of shield material and platform sediments, except for a narrow ophiolitic belt in the north.
Segment: this has a length, measured along the strike, of 2400 km. The southern margin of the orogenic belt, which is also the north margin of the Indo-Gangetic plain, is narrowly gradational (½ to 3 km). The north margin, with the Tibetan Block, is broadly gradational (> 3 km). The width of the belt varies from 230 to 320 km and averages 270 km.
Zones: the segment is described in terms of zones from north to south. The northernmost zone (1) is a northward thrust mass of Cretaceous flysch with basic and ultrabasic exotics, resting on Palaeogene molasse. Next south (zone 2) is the Ophiolitic zone, with contemporaneously intruded Jurassic and Cretaceous radiolarites, flysch and ultrabasic rocks, deformed by southward thrusting and gliding. Zone 3, the Tibetan Himalaya, is a broad thrust belt of thick normal sediments (Mesozoic on partly metamorphosed Palaeozoic). In zone 4, the Higher Himalaya, the line of greatest vertical uplift, pre-existing sediments are almost entirely removed and the belt consists of pre-Ordovician metamorphic rocks intruded by granites
- © The Geological Society, London 1974
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