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The rocks range in age from Precambrian to Miocene. The geology is complicated due to folding, faulting, and thrusting and are largely unfossiliferous. Tectonically, the entire Lesser Himalayas consists of two sequences of rocks: allochthonous, and autochthonous-para autochthonous units; with various nappes, klippes and tectonic windows.
The Himalayas border the Indo-Gangetic Plain to the south, Pamir Mountains to the west in Central Asia, and the Hengduan Mountains to the east on the China–Myanmar border. From east to west the Himalayas are divided into 3 regions, Eastern Himalaya, Central Himalaya, and Western Himalaya, which collectively house several nations and states.
In geology, metasedimentary rock is a type of metamorphic rock. Such a rock was first formed through the deposition and solidification of sediment. Then, the rock was buried underneath subsequent rock and was subjected to high pressures and temperatures, causing the rock to recrystallize. The overall composition of a metasedimentary rock can be ...
Metasomatism (from the Greek μετά metá "change" and σῶμα sôma "body") is the chemical alteration of a rock by hydrothermal and other fluids. [1] It is traditionally defined as metamorphism which involves a change in the chemical composition, excluding volatile components. [2]
The nappes—large, stacked sheets of rock—found in the Tethys Himalayan mountain range, are primarily composed of sedimentary rocks, such as limestone formed from the accumulation and compression of sediments like sand, mud, and shells deposited in the Neo-Tethys seabed during the Paleogene" (66 Mya–23 Mya). [23]
Plastiglomerate could potentially form a marker horizon of human pollution on the geologic record. [1] [4] [5] [6] and may survive as future fossils. [2] [5] Plastiglomerate may also conceivably form in plastic-polluted regions affected by lava flows or forest fires. [1] [5] [6] They have been found on the surface as well as beneath the sand.
The Greater Himalayan Crystalline complex, also known as the High Himalayan Crystalline Sequence, [14] is composed of high-grade metamorphic rocks aged between Paleoproterozoic and Ordovician. [4] Over the 4.5–8 km thick layer, paragneiss , schist and orthogneiss are observed.
Examples of such islands are found in the Pacific, notably the three phosphate islets of Nauru, Makatea, and Banaba, as well as Maré and Lifou in New Caledonia; Fatu Huku in the Marquesas Islands; and Henderson Island in the Pitcairn Islands. The uplift of these islands is the result of the movement of oceanic tectonic plates.