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Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than 150 to 200 °C and, often, elevated pressure of 100 megapascals (1,000 bar) or more, causing profound physical or chemical changes. During this process, the rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition. The protolith may be an igneous, sedimentary, or existing metamorphic rock.
Metamorphism is the transformation of existing rock to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of 150 °C (300 °F), and often also at elevated pressure or in the presence of chemically active fluids, but the rock remains mostly solid during the transformation. Metamorphism is distinct from weathering or diagenesis, which are changes that take place at or just beneath Earth's surface.
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 Bahía Mansa Metamorphic Complex or BMMC, also known as the Western Series, is a group of metamorphic geologic formations of the Chilean Coast Range in southern Chile. It consists mainly of pelitic schists, metagreywackes and oceanic type mafic metavolcanics. The complex owes its name to Bahía Mansa.
The Carolina Terrane, also called the Carolina Superterrane or Carolinia, is an exotic terrane running ~370 miles (600 km) approximately North-South from central Georgia to central Virginia in the United States. It constitutes a major part of the eastern Piedmont Province.
The Lewisian complex or Lewisian gneiss is a suite of Precambrian metamorphic rocks that outcrop in the northwestern part of Scotland, forming part of the Hebridean Terrane and the North Atlantic Craton. These rocks are of Archaean and Paleoproterozoic age, ranging from 3.0–1.7 billion years (Ga). They form the basement on which the Torridonian and Moine Supergroup sediments were deposited. The Lewisian consists mainly of granitic gneisses with a minor amount of supracrustal rocks. Rocks of the Lewisian complex were caught up in the Caledonian orogeny, appearing in the hanging walls of many of the thrust faults formed during the late stages of this tectonic event.
The Pichilemu Fault, also referred to as the Pichilemu-Vichuquén Fault, is a Chilean geological fault, located in Libertador General Bernardo O'Higgins Region, some kilometers away from Pichilemu, at a depth of 15 kilometres (9.3 mi). The fault is 40 kilometres (25 mi) long and 20 kilometres (12 mi) wide.
The Famatinian orogeny is an orogeny that predates the rise of the Andes and that took place in what is now western South America during the Paleozoic, leading to the formation of the Famatinian orogen also known as the Famatinian belt. The Famatinian orogeny lasted from the Late Cambrian to at least the Late Devonian and possibly the Early Carboniferous, with orogenic activity peaking about 490 to 460 million years ago. The orogeny involved metamorphism and deformation in the crust and the eruption and intrusion of magma along a Famatinian magmatic arc that formed a chain of volcanoes. The igneous rocks of the Famatinian magmatic arc are of calc-alkaline character and include gabbros, tonalites, granodiorites and trondhjemites. The youngest igneous rocks of the arc are granites.
The Belén Metamorphic Complex is a group of metamorphic and igneous rocks that crops out in the western edge of the Altiplano plateau in the interior of northernmost Chile. The rocks of the complex metamorphosed during the Early Paleozoic era but the original protoliths formed in the Proterozoic eon. This make rocks of the Belén Metamorphic Complex the oldest rocks known in Chile. To the west the rocks of the Belén Metamorphic Complex thrust along Chapiquiña-Belén fault over sediments of Cenozoic age including ignimbrites of the Oxaya Formation and rocks of Lupica Formation. At their peak conditions of metamorphism rocks reached temperatures and pressures of 700 C and 7 kbar. The timing of the metamorphism matches the age of the Famatinian orogeny in the Argentine Northwest. Rocks of the Belén Metamorphic Complex were involved in one or more orogenies in the Early Paleozoic.
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 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 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.
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 Chañaral Epimetamorphic Complex is an accretionary complex composed of metamorphic rocks located in western Atacama Region, Chile. The rocks of the complex are mainly micaschist, greenschist and metasediment of low-grade. The deposition of the sedimentary protoliths occurred in the Carboniferous and Permian being later metamorphosed. Among the protoliths of the complex are turbidites and other sediments. Chañaral Epimetamorphic Complex is thought to represent the shallow and frontal part of an accretionary prism while the nearby Punta de Choros Metamorphic Complex represents the deeper basal part of the very same accretionary prism.
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 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.
The Ashe Metamorphic Suite, also referred to as the Ashe Formation, was named after its type locality, Ashe County, North Carolina. The Ashe Metamorphic Suite is located in the Eastern Blue Ridge providence that extends from North Carolina up to South-Western Virginia. It is a collection of metamorphic rocks of both sedimentary and volcanic origin. Zircon dating indicates an age of 470 to 335 Ma for the unit. The protolith of the Ashe Metamorphic Suite was deposited during the Late Proterozoic and reaching its cooling age during the end of the Devonian. The Ashe Metamorphic Suite is overwhelmingly composed of amphibolites and mica schists.
References
- 1 2 Maksaev, Víctor; Arancibia, Javier; Munizaga, Francisco; Tassinari, Colombo (2015). "Detrital-zircon U-Pb geochronology of the Quebrada del Carrizo Metamorphic Complex and El Jardín Schists and spatially-related granitoids of the Sierra Castillo Batholith". Andean Geology . 42 (3): 285–315. doi: 10.5027/andgeoV42n3-a01 . Retrieved 14 August 2016.
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