Eclogites are beautiful rocks that form deep within subduction zones. 17, 637-652: Hareidlandet ⓘ Eiksund; Nordrum, F.S. What does eclogite mean? Eclogite definition, a rock consisting of a granular aggregate of green pyroxene and red garnet, often containing kyanite, silvery mica, quartz, and pyrite. Let us know if you have suggestions to improve this article (requires login). Eclogite is a metamorphic rock consisting of pyroxene omphacite and pyrope-rich garnet. Many investigators believe that eclogite is representative of numerous parts of the upper mantle. Some andesite-like rocks could be produced from partial melting of eclogite; for instance, an unusual rock type called adakite (first described from Adak Island in the Aleutians) has been proposed to be a product of partial melting of eclogite in subducting oceanic crust. Known eclogite occurrences in the Sanbagawa metamorphic belt of SW Japan are dominantly in metagabbro bodies which have complex polyphase metamorphic histories. 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. A few eclogites also occur in the northwest highlands of Scotland and the Massif Central of France. 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). 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. An unusually dense rock, eclogite can play an important role in driving convection within the solid Earth. Hydrated zones are from 1–50 cm thick, with adjacent wall-rock eclogite replaced by symplectites. ; a rock with basalt composition) it has to undergo 100% partial melting. [4], The eclogite melt may then react with enclosing peridotite to produce pyroxenite, which in turn melts to produce basalt.[5]. Importance of eclogite Photomicrograph of a thin section of eclogite from Turkey. If we have to define Eclogite in general, Eclogite is an extreme metamorphic rock, formed by regional metamorphism of … The early Jurassic intrusive complex is chiefly made of monzodioritic porphyry in northern Anhui and northern Jiangsu, which emplaced in 191 Ma. 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. 1. Introduction [2] Crustal rocks metamorphosed at high-pressure (HP) to ultrahigh pressure conditions provide important geody- Eclogite is considered rare and important because it is usually formed only at the lowermost part of our Earth’s crust at the boundary with the mantle at some 50 kilometers or more. Eclogites containing lawsonite (a hydrous calcium-aluminium silicate) are rarely exposed at Earth's surface, although they are predicted from experiments and thermal models to form during normal subduction of oceanic crust at depths between about 45–300 km (28–186 mi). To get a basalt from melting an eclogite (i.e. These conditions are found in subduction zones where the ocean floor is forced beneath a continental margin—such as in the Cascadia subduction zone off the coast of western North America and the Sunda Trench subduction zone off the western coast of Sumatra, Indon. Xenoliths of eclogite occur in kimberlite pipes of Africa, Russia, Canada, and elsewhere. Lucky for us, small volumes make it back to the surface. 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 crust. Hensen and R. Armstrong, This page was last edited on 10 August 2020, at 13:48. Eclogite is a metamorphic rock consisting of pyroxene omphacite and pyrope-rich garnet . 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.. 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. 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. Straume, A. K. & Austrheim, H. (1999): Importance of fracturing during retro-metamorphism of eclogites. Posted on 24 October, 2012 by Metageologist. Many diamonds from eclogite xenoliths have a 13C:12C isotope ratio different from that typical of diamonds from peridotite xenoliths. The carbon isotopic differences between harzburgitic and eclogitic diamonds supports the hypothesis that those eclogite xenoliths formed from basalt carried down within subduction zones. The typical eclogite mineral assemblage is garnet (pyrope to almandine) plus clinopyroxene (omphacite). Eclogite plays an important role in mantle convection and geodynamics in subduction zones. Some UHP rocks appear to record burial at depths greater than 120 km (75 mi) if diamond occurs in these rocks. Eclogite Rock: Eclogite (/ˈɛklədʒaɪt/) is a mafic metamorphic rock. Eclogites consist primarily of green pyroxene (omphacite) and red garnet (pyrope), with small amounts of various other stable minerals— e.g., rutile. Eclogite is denser than the surrounding asthenosphere. [2] The rarity of lawsonite eclogites therefore does not reflect unusual formation conditions but unusual exhumation processes. gins of eclogite lenses and along mesoscopic fracture systems. important strategy for establishing control over organic epitaxy. melting model would predict. Instead, basalts can be modelled as having been produced by 1 to 25% partial melting of peridotite, such as harzburgite and lherzolite. … and its denser solid equivalent, eclogite (a sodium-pyroxene + garnet rock). Eclogite is an important constituent of subduction slabs and plays a critical role in transporting surface materials (e.g., water) into the deep Earth. Eclogite, any member of a small group of igneous and metamorphic rocks whose composition is similar to that of basalt. Likewise, peridotite is a much more important source rock of common magmas. Phase changes can be more important in the mantle. Laboratory experiments have revealed that eclogites will crystallize from basaltic magma under very high pressure conditions common to the deeper portions of the Earth’s upper mantle, the mantle constituting the layer that lies between the crust and core and that comprises about two-thirds of the planet’s bulk. Information and translations of eclogite in the most comprehensive dictionary definitions resource on the web. The density contrast between eclogite and peridotitic plume matrix is very important for understanding the transportation mechanism of the … [9][10], A dense metamorphic rock formed under high pressure, William Alexander Deer, R. A. Howie and J. Zussman (1997), https://en.wikipedia.org/w/index.php?title=Eclogite&oldid=972155697, Short description is different from Wikidata, Articles with unsourced statements from June 2009, Creative Commons Attribution-ShareAlike License. Geochronology of granulitized eclogite from the Ama Drime Massif: Implications for the tectonic evolution of the South Tibetan Himalaya, Tectonics, 28, TC1002, doi:10.1029/ 2008TC002256. Eclogite diamonds are also typically higher in nitrogen, and will have a different suite of mineral inclusions than harzburgitic diamonds. Eclogite is the highest pressure metamorphic facies and is usually the result of advancement from blueschist metamorphic conditions. Eclogites occur with garnet peridotites in Greenland and in other ophiolite complexes. New questions in English. The fresh rock can be striking in appearance, with red to pink garnet (almandine-pyrope) in a green matrix of sodium-rich pyroxene (omphacite). Eclogite forms at pressures greater than those typical of the crust of the Earth. Omissions? Plagioclase is not stable in eclogite. Eclogites are helpful in elucidating patterns and processes of plate tectonics because many represent the crustal rocks that were subducted to depths in excess of 35 km and then returned to the surface. 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. Eclogite is part of WikiProject Geology, an attempt at creating a standardized, informative, comprehensive and easy-to-use geology resource. … Eclogite importance jamesbalmes208 is waiting for your help. Eclogites consist primarily of green pyroxene (omphacite) and red garnet (pyrope), with small amounts of various other stable minerals—e.g., rutile. Unreasonably high degrees of partial melting are required to attain basaltic compositions. "The importance of the Raudkleivane locality lies in the prograde metamorphism of eclogite within peridotite" In simpler words: in a 5000km2 large area, metamorphic eclogite can be found as pods in UHP gneiss formed as a part of the caledonian orogeny, in some places olivine bearing eclogite can be found in metamorphosed peridotite. Eclogite forms at pressures greater than those typical of the crust of the Earth. An unusually dense rock, eclogite can play an important role in driving convection within the solid Earth. ... being an unusually dense rock, eclogite can play an important role in driving convection within the solid Earth. Felsic rocks in these terranes contain sillimanite, kyanite, coesite, orthoclase and pyroxene, and are rare, peculiar rocks formed by an unusual tectonic event. When basalt converts to eclogite, or when it melts, there are changes in density that far exceed those associated with thermal expansion. Although nominally anhydrous, omphacite and garnet contain some amount of structural water (OH) in the lattice, which is up to >1500 ppm wt. Because eclogite is prone to retrogression during exhumation to the surface, the associated changes in physical properties should be understood. An unusually dense rock, eclogite can play an important role in driving convection within the solid Earth. Eclogite rheology is an important piece of information for understanding the subduction of continental crust to great depth and then return to the surface. Harzburgitic diamonds typically have titaniferous pyrope, chromian spinel and chromian diopside inclusions, minerals which are not typically found in eclogites. Removal of the dense lower continen­ tal crust is an important element of … Eclogite-rich layers would be intermittent because of low melting points and the temperature-dependency of the relevant phase changes. The melting curves have a positive slope, as the solids are denser than their equivalent melts and are thus favoured (enlarged) with increasing pressure.…. Our editors will review what you’ve submitted and determine whether to revise the article. It is a rare but geologically significant rock type. In some retrogressed eclogites and accompanying more silica-rich rocks, ultrahigh-pressure (UHP) metamorphism has been recognized only because of the preservation of coesite and/or diamond inclusions within trace minerals such as zircon and titanite. The fresh rock can be striking in appearance, with red to pink garnet (almandine-pyrope) in a green matrix of sodium-rich pyroxene (omphacite). Examples are known in Saxony, Bavaria, Carinthia, Norway and Newfoundland. ... must be an important constituent of the lower mantle and that it is seismologically conspicuous. Eclogite forms at pressures greater than those typical of the crust of the Earth. Green omphacite (+ late chlorite) + pink garnet + blue glaucophane + colorless phengite. Eclogite is a metamorphic rock formed when mafic igneous rock is subjected to high pressure. Eclogite is one of the important type of rocks. [3], Basalt is generally created as a partial melt of peridotite at 20–120 km depth. Interestingly, eclogites somewhat resemble chondritic meteorites in composition (see chondrite). These bodies are generally described as tectonic blocks and their relationship to the Sanbagawa metamorphism is unclear. This is high-pressure, medium- to high-temperature metamorphism. ... eclogite residues is primarily ‘east-to-west’, and not ‘north-to-south’, as the amphibolite. Lawsonite eclogite is known from the U.S. (Franciscan Complex of California; xenoliths in Arizona); Guatemala (Motagua fault zone), Corsica, Australia, the Dominican Republic, Canada (British Columbia), and Turkey. They are formed when volcanic or metamorphic rocks rich in such mafic minerals are subjected to extremely high pressures and moderate to relatively high temperatures. Likewise, partial melting of eclogite has been modeled to produce tonalite-trondhjemite-granodiorite melts. social goals in age of 11 to 15 eclogite importance How do you describe the way you perform your roles and responsibilities?Cite a current experience where these things are evident. An unusually dense rock, eclogite can play an important role in driving convection within the solid Earth. Diamond and coesite occur as trace constituents in some eclogites and record particularly high pressures. Eclogite-facies metamorphic conditions encompass a wide range of pressure–temperature space from deep crustal to mantle depths, reflecting tectonic setting. Study of eclogite rocks provides important information about what happens to ocean crust after it plunges into a subduction zone and thus provides insight into very deep mantle processes. ids. Rocks are rated on the on the Moh's Hardness Scale which rates the rocks on the scale from 1 to 10. Melting of eclogite to produce basalt directly is generally not supported in modern petrology. If you would like to participate, you can choose to edit this article, or visit the project page for more information. They are formed when volcanic or metamorphic rocks rich in such mafic minerals are subjected to extremely high pressures and … 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. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. [7] Transitional granulite-eclogite facies granitoid, felsic volcanics, mafic rocks and granulites occur in the Musgrave Block of the Petermann Orogeny, central Australia. Eclogite is an unusually dense metamorphic rock, typically of basaltic composition, that represents a recorder and/or driving force for planetary-scale processes and evolution. 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. (2005): Nyfunn av mineraler i Norge 2004-2005. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. H2O. [1] They are generally formed from precursor mineral assemblages typical of blueschist-facies metamorphism. 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. Updates? An unusually dense rock, eclogite can play an important role in driving convection within the solid Earth. Coesite- and glaucophane-bearing eclogites have been found in the northwestern Himalaya. eclogite facies A set of metamorphic mineral assemblages produced by metamorphism of basic igneous rocks under high-pressure, moderate-temperature conditions and typically characterized by the development of the mineral assemblage pyrope garnet and omphacite (an Na-rich, high-pressure pyroxene).Other rocks of contrasting composition, e.g. Furthermore, many workers postulated that eclogite blocks entrained in the initial plume head play an important roles in the production of voluminous continental flood basalts (e.g., Cordery et al., 1997, Yasuda et al., 1998, Takahashi et al., 1998). A. Camacho, B.J. Occurrences exist in western North America, including the southwest[6] and the Franciscan Formation of the California Coast Ranges. Add your answer and earn points. The intrusive complexes contain a lot of eclogite inclusions which belong to eclogite and garnet-pyroxenite. Eclogite consists mainly of omphacite and garnet. Eclogite may completely retrogress to amphibolite or granulite during exhumation. I suggest that under certain circumstances the lower crust transforms to dense eclogite and delaminates. It is a rare but geologically significant rock type. shales or limestones, are not known to show … Eclogite forms at pressures greater than those typical of the crust of the Earth. [8] The oldest coesite-bearing eclogites are about 650 and 620 million years old and they are located in Brazil and Mali, respectively. Journal of Metamorphic Geology. Eclogite ( /ˈɛklədʒaɪt/) is a metamorphic rock formed when mafic igneous rock is subjected to high pressure. Large amounts of H 2 O released by blueschist → eclogite dehydration reactions could trigger partial melting in the overlying mantle wedge and may play a crucial role in the generation of arc magmas. See more. Norsk Bergverksmuseum Skrift. Eclogite is a unique metamorphic rock that forms at high pressure and indicates deeply subducted crust or thick continent crust around Moho depth. Eclogites in granulite terranes are known from the Musgrave Block of central Australia where a continental collision took place at 550-530 Ma, resulting in burial of rocks to greater than 45 km (15 kilobars) and rapid (in less than 10 million years[citation needed]) exhumation via thrust faults prevented significant melting. It is common in the upper mantle, especially in regions occupied by subducted oceanic plates. 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. 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. 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. 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. 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. Corrections? New findings of foliated eclogite in the Seba and Kotsu areas show that eclogite facies … Eclogite facies is determined by the temperatures and pressures required to metamorphose basaltic rocks to an eclogite assemblage. Eclogite-derived melts may be common in the mantle, and contribute to volcanic regions where unusually large volumes of magma are erupted. Accessory minerals include kyanite, rutile, quartz, lawsonite, coesite, amphibole, phengite, paragonite, zoisite, dolomite, corundum, and, rarely, diamond. Eclogite forms at pressures greater than those typical of the crust of the Earth . Hardness and Strength of Eclogite The physical properties of Eclogite depend on its formation. Glaucophane-eclogites occur in Italy and the Pennine Alps. Peridotite is the dominant rock type of the upper mantle, not eclogite, as established by seismic and petrologic evidence. The inclusions had undergone eclogite facies high-pressure metamorphism and amphibolite facies retrogressive metamorphism. 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