Eclogite may completely retrogress to amphibolite or granulite during exhumation. Eclogite Rock: Eclogite (/ˈɛklədʒaɪt/) is a mafic metamorphic rock. I suggest that under certain circumstances the lower crust transforms to dense eclogite and delaminates. Journal of Metamorphic Geology. The vast majority of subducted oceanic crust becomes more dense than the surrounding mantle rocks and travels to the strange world of the deep earth. Information and translations of eclogite in the most comprehensive dictionary definitions resource on the web. Because eclogite is prone to retrogression during exhumation to the surface, the associated changes in physical properties should be understood. Coesite- and glaucophane-bearing eclogites have been found in the northwestern Himalaya. Eclogites consist primarily of green pyroxene (omphacite) and red garnet (pyrope), with small amounts of various other stable minerals— e.g., rutile. It is a rare but geologically significant rock type. Eclogite that is brought to shallow conditions is unstable, and retrograde metamorphism often occurs: secondary amphibole and plagioclase may form reaction rims on the primary pyroxene or garnet, and titanite may form rims about rutile. gins of eclogite lenses and along mesoscopic fracture systems. What does eclogite mean? Eclogite is an important constituent of subduction slabs and plays a critical role in transporting surface materials (e.g., water) into the deep Earth. These bodies are generally described as tectonic blocks and their relationship to the Sanbagawa metamorphism is unclear. Importance of eclogite Eclogite is a rare and important rock because it is formed only by conditions typically found in the mantle or the lowermost part of thickened continental crust. Eclogite forms at pressures greater than those typical of the crust of the Earth. Eclogites typically result from high to ultrahigh pressure metamorphism of mafic rocks at low thermal gradients of <10 °C/km (29 °F/mi) as they were subducted to the lower crust to upper mantle depths in a subduction zone. Diamond and coesite occur as trace constituents in some eclogites and record particularly high pressures. Xenoliths of eclogite occur in kimberlite pipes of Africa, Russia, Canada, and elsewhere. Corrections? If that subducted eclogite is subsequently carried upward with peridotite, as in a mantle plume, it may melt by decompression melting (see discussion in igneous rock) at lower temperature than the accompanying peridotite. Omissions? Eclogites record pressures over 1.2 GPa (170,000 psi) (45 km (28 mi) depth) at about 400 to 1,000 °C (752 to 1,832 °F) and usually over 600–650 °C (1,112–1,202 °F). Eclogite, any member of a small group of igneous and metamorphic rocks whose composition is similar to that of basalt. … and its denser solid equivalent, eclogite (a sodium-pyroxene + garnet rock). Eclogite forms at pressures greater than those typical of the crust of the Earth. [7] Transitional granulite-eclogite facies granitoid, felsic volcanics, mafic rocks and granulites occur in the Musgrave Block of the Petermann Orogeny, central Australia. Eclogite-derived melts may be common in the mantle, and contribute to volcanic regions where unusually large volumes of magma are erupted. Eclogite plays an important role in mantle convection and geodynamics in subduction zones. Occurrences exist in western North America, including the southwest[6] and the Franciscan Formation of the California Coast Ranges. Importance of eclogite Photomicrograph of a thin section of eclogite from Turkey. The inclusions had undergone eclogite facies high-pressure metamorphism and amphibolite facies retrogressive metamorphism. important strategy for establishing control over organic epitaxy. [8] The oldest coesite-bearing eclogites are about 650 and 620 million years old and they are located in Brazil and Mali, respectively. Eclogite forms at pressures greater than those typical of the crust of the Earth. Eclogite diamonds are also typically higher in nitrogen, and will have a different suite of mineral inclusions than harzburgitic diamonds. Therefore, eclogite plays an important role in dynamics of the Earth and distinguishing eclogite from mafic granulite and ultramafic rocks in the present deep crust and mantle is crucial. A few eclogites also occur in the northwest highlands of Scotland and the Massif Central of France. Eclogite is part of WikiProject Geology, an attempt at creating a standardized, informative, comprehensive and easy-to-use geology resource. Introduction [2] Crustal rocks metamorphosed at high-pressure (HP) to ultrahigh pressure conditions provide important geody- If we have to define Eclogite in general, Eclogite is an extreme metamorphic rock, formed by regional metamorphism of … Eclogite definition, a rock consisting of a granular aggregate of green pyroxene and red garnet, often containing kyanite, silvery mica, quartz, and pyrite. [3], Basalt is generally created as a partial melt of peridotite at 20–120 km depth. Eclogite is the highest pressure metamorphic facies and is usually the result of advancement from blueschist metamorphic conditions. Accessory minerals include kyanite, rutile, quartz, lawsonite, coesite, amphibole, phengite, paragonite, zoisite, dolomite, corundum, and, rarely, diamond. Some UHP rocks appear to record burial at depths greater than 120 km (75 mi) if diamond occurs in these rocks. An unusually dense rock, eclogite can play an important role in driving convection within the solid Earth. Many investigators believe that eclogite is representative of numerous parts of the upper mantle. It is a rare but geologically significant rock type. Eclogite is a metamorphic rock formed when mafic igneous rock is subjected to high pressure. Eclogites are helpful in elucidating patterns and processes of plate tectonics because many represent oceanic crust that has been subducted to depths in excess of 35 km and then returned to the surface. See more. When basalt converts to eclogite, or when it melts, there are changes in density that far exceed those associated with thermal expansion. eclogite Very rare, coarse-grained, igneous rock with a chemical composition similar to that of basalt, but noted for the presence of the rare, bright-green pyroxene omphacite, and red, almandine—pyrope garnets.Eclogites may be basalt metamorphosed by high temperatures and pressures. C This article has been rated as C-Class on the project's quality scale. Eclogite is a unique metamorphic rock that forms at high pressure and indicates deeply subducted crust or thick continent crust around Moho depth. Ring in the new year with a Britannica Membership, This article was most recently revised and updated by, https://www.britannica.com/science/eclogite, University of California Santas Barbara - Earth Science - Eclogite Formation and the Rheology, Buoyancy, Seismicity, and H20 Content of Oceanic Crust. Hydrated zones are from 1–50 cm thick, with adjacent wall-rock eclogite replaced by symplectites. Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... …high-pressure and high-temperature rocks called eclogites. Our editors will review what you’ve submitted and determine whether to revise the article. ids. In the crust, eclogites generally occur as xenoliths (i.e., foreign inclusions) in igneous rocks and as isolated blocks measuring as much as 100 m (328 feet) across in metamorphic rocks. 1. It is common in the upper mantle, especially in regions occupied by subducted oceanic plates. Let us know if you have suggestions to improve this article (requires login). Such ultrahigh-pressure (UHP) metamorphism has been defined as metamorphism within the eclogite facies but at pressures more than the quartz-coesite transition (the two minerals have the same composition—silica). They are formed when volcanic or metamorphic rocks rich in such mafic minerals are subjected to extremely high pressures and … Unless the eclogite is created in very young oceanic crust, it is cool at the time of initial subduction and so is carried down into the mantle. 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