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A forearc is the region between an oceanic trench and the associated volcanic arc. Forearc regions are found at convergent margins, and include any accretionary wedge and forearc basin that may be present. Due to tectonic stresses as one tectonic plate rides over another, forearc regions are sources for great thrust earthquakes.
The Lizard Complex, Cornwall is generally accepted to represent a preserved example of an exposed ophiolite complex in the United Kingdom. The rocks found in The Lizard area are analogous to those found in such famous areas as the Troodos Mountains, Cyprus and the Semail Ophiolite, Oman.
An accretionary wedge or accretionary prism forms from sediments accreted onto the non-subducting tectonic plate at a convergent plate boundary. Most of the material in the accretionary wedge consists of marine sediments scraped off from the downgoing slab of oceanic crust, but in some cases the wedge includes the erosional products of volcanic island arcs formed on the overriding plate.
The Western Carpathians are an arc-shaped mountain range, the northern branch of the Alpine-Himalayan fold and thrust system called the Alpide belt, which evolved during the Alpine orogeny. In particular, their pre-Cenozoic evolution is very similar to that of the Eastern Alps, and they constitute a transition between the Eastern Alps and the Eastern Carpathians.
Lanalhue Fault is a northwest-striking fault that marks the contact between two distinct units of continental basement, the Eastern and Western Series in south-central Chile, separating the Nahuelbuta Range Cordillera de Nahuelbuta at the east and the Arauco Peninsula and Basin to the west. The fault takes name from Lanalhue Lake, which is located in part of the fault trace, of elongated shape shows the NW-SE trend. The lanalhue fault makes up a major lithological boundary in the Chilean Coast Range to which Cordillera de Nahuelbuta belongs. The Nahuelbuta Range is composed by Carboniferous granitic core bounded by High-T metasedimentary rocks referred as the Eastern Series. The Arauco Basin contains over 3 km of late Cretaceous to Holocene continental and marine sediments, being a major center of coal mining and hydrocarbon exploration for over a century. From Valparaíso Region to Lanalhue Fault Carboniferous-Permian granitoids makes up a large part of the bedrock of the Chilean Coast Range. These igneous rocks was once part of a proto-Andean magmatic belt. South of Lanalhue Fault most of the Chilean Coast Range is an accretionary wedge formed by at least since the Paleozoic along the subduction zone at South Americas western margin.
The Lapland Granulite Belt is an elongate and arcuate zone of granulite rock in the Cap of the North spanning areas within Norway, Finland and Murmansk Oblast in Russia. At most the belt is 80 km broad. The main rocks of the belt are migmatized greywacke and argillites. Studies of detrital zircon show that the sedimentary protolith of the metamorphic rocks of the belt could not be older than 2900–1940 million years. The belt has norite and enderbite intrusions of calc-alkaline chemistry.
The Coastal Batholith of central Chile is a group of plutons in the Chilean Coast Range of Central Chile appearing contiguously from 33° S to 38° S. At a latitude of 40° S an outlying group of plutons of the batholith appear in a more eastward position in the Andes.
The geology of Germany is heavily influenced by several phases of orogeny in the Paleozoic and the Cenozoic, by sedimentation in shelf seas and epicontinental seas and on plains in the Permian and Mesozoic as well as by the Quaternary glaciations.
The Arauco Basin is a sediment-filled depression –a sedimentary basin– in south-central Chile. In the context of plate tectonics it is classified as a forearc basin. The basin has an approximate area of 8,000 square kilometres (3,100 sq mi) and at its deeper parts the surface of its sedimentary fill reaches 200 metres (660 ft) below sea-level. The basin is interpreted as being part of an uplifted part of the continental shelf. To the west it bounds an active accretionary prism that lies next to the Chile trench and to the east it bounds metamorphic basement representing a fossil Paleozoic accretionary complex that has been intruded by the Coastal Batholith of central Chile.
The Punta de Choros Metamorphic Complex is a large coherent group of metamorphic rocks –in other words a geologic complex– of the Chilean Coast Range in northern Chile. It consists mainly of micaschists, greenschists and other low-grade metasediment. The complex was formed by the metamorphism of sediments and associated mafic rocks at the interface between a subducting plate and the overriding plate.
The Choapa Metamorphic Complex or ChMC is a large coherent but varied group of metamorphic rocks –in other words a geologic complex– that crops out in the Chilean Coast Range in northern Chile. The rocks of the formation have been metamorphosed under greenschist facies metamorphism. After the main phase of metamorphism the rocks of the complex were heated by plutons in the Jurassic. It has been suggested that the protoliths of the formation were similar and equivalent to the Paleozoic-aged Puerto Manso Formation.
The Eastern Andes Metamorphic Complex is a large coherent but varied group of metamorphic and sedimentary rocks –in other words a geologic complex– that crops out in the eastern Patagonian Andes in Chile and Argentina. The metamorphic grade of rocks varies but does not exceed greenschist facies, the only exception to this are rocks near plutons affected by contact metamorphism. The sedimentary protoliths sedimented in the Late Paleozoic. The pressures and temperatures of metamorphism of the Eastern Andes Metamorphic Complex are different those usually expected from accretionary complexes. The sedimentary protoliths of the Eastern Andes Metamorphic Complex were likely deposited in a passive continental margin.
The Cordillera Darwin Metamorphic Complex is a geologic complex composed chiefly of metamorphic rocks located in southern Tierra del Fuego. It has been suggested that the Cordillera Darwin Metamorphic Complex is analogous to the Eastern Andes Metamorphic Complex. The Cordillera Darwin Metamorphic Complex is the only metamorphic complex in the southern Andes known to have amphibolite facies rocks containing kyanite and sillimanite which evidences high-grade metamorphism. High-grade metamorphism took place during the Cretaceous purportedly in association with the closure of the Rocas Verdes Basin.
The Quebrada del Carrizo Metamorphic Complex is a geological complex of metamorphic rocks that crops out in Quebrada del Carrizo Creek next to the Cordillera Domeyko in the Atacama Desert of Chile. The Quebrada del Carrizo Metamorphic Complex is part of a larger accretionary complex in northern Chile that was an active accretionary wedge in the Late Paleozoic.
Tierra del Fuego Igneous and Metamorphic Complex is a geological basement complex known from boreholes in northern Tierra del Fuego. The complex is made up of foliated igneous rocks of Cambrian age including orthogneiss. It underlies unconformably the Jurassic Tobífera Formation. The protoliths of Cordillera Darwin Metamorphic Complex are unrelated to Tierra del Fuego Igneous and Metamorphic Complex despite present-day proximity.
The Chonos Metamorphic Complex is an accretionary complex composed of metamorphic rocks located in western Aysén Region, Chile. The deposition of the sedimentary protoliths occurred in the Triassic and they were later metamorphosed in the Jurassic. The formation has been subdivided into a highly deformed Western belt and an Eastern belt where sedimentary structures are preserved.
The geology of Venezuela includes ancient Precambrian igneous and metamorphic basement rocks, layered with sedimentary rocks from the Paleozoic and Mesozoic and thick geologically recent Cenozoic sediments with extensive oil and gas.
The Western Block of the North China Craton is an ancient micro-continental block mainly composed of Neoarchean and Paleoproterozoic rock basement, with some parts overlain by Cambrian to Cenozoic volcanic and sedimentary rocks. It is one of two sub-blocks within the North China Craton, located in east-central China. The boundaries of the Western Block are slightly different among distinct models, but the shapes and areas are similar. There is a broad consensus that the Western Block covers a large part of the east-central China.
The Toco orogeny was a mountain building affecting the rocks of northern Chile and northwestern Argentina during the Late Carboniferous and Permian. In 1991, researchers Bahlburg and Breitkurz noted that Chilean rocks had a 100 million lull magmatic and metamorphic "lull" from the Silurian to the Carboniferous. They defined the Toco orogeny as the period when active margin conditions returned in the region.
The Chonide orogeny was a mountain building event in the Triassic, preserved in coastal accretionary complexes in southwestern Chile. The Chonos Metamorphic Complex, Madre de Dios Accretionary Complex and Diego de Almagro Complex all crop out west of the South Patagonian Batholith. Rocks in the Chonos Metamorphic Complex include turbidites as well as meta-chert and mafic schist. Some researchers propose that during the Permian, the supercontinent Gondwana moved rapidly northward leading to the formation of back-arc marginal basins. The closure of the basins then resulted in the orogeny.
References
- 1 2 Creixell, C.; Oliveros, V.; Vásquez, P.; Navarro, J.; Vallejos, D.; Valin, X.; Godoy, E.; Ducea, M.N. (2016). "Geodynamics of Late Carboniferous–Early Permian forearc in north Chile (28°30′–29°30′S)". Journal of the Geological Society. doi:10.1144/jgs2016-010.
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