Eclogite may completely retrogress to amphibolite or granulite during exhumation. ... eclogite residues is primarily ‘east-to-west’, and not ‘north-to-south’, as the amphibolite. Eclogite ( /ˈɛklədʒaɪt/) is a metamorphic rock formed when mafic igneous rock is subjected to high pressure. 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. ids. 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. Eclogites are beautiful rocks that form deep within subduction zones. Eclogite, any member of a small group of igneous and metamorphic rocks whose composition is similar to that of basalt. Hardness and Strength of Eclogite The physical properties of Eclogite depend on its formation. Instead, basalts can be modelled as having been produced by 1 to 25% partial melting of peridotite, such as harzburgite and lherzolite. This is high-pressure, medium- to high-temperature metamorphism. 1. Eclogite, any member of a small group of igneous and metamorphic rocks whose composition is similar to that of basalt. Journal of Metamorphic Geology. Eclogite importance jamesbalmes208 is waiting for your help. The intrusive complexes contain a lot of eclogite inclusions which belong to eclogite and garnet-pyroxenite. Eclogites consist primarily of green pyroxene (omphacite) and red garnet (pyrope), with small amounts of various other stable minerals—e.g., rutile. Eclogite forms at pressures greater than those typical of the crust of the Earth. ... must be an important constituent of the lower mantle and that it is seismologically conspicuous. Hensen and R. Armstrong, This page was last edited on 10 August 2020, at 13:48. 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. The inclusions had undergone eclogite facies high-pressure metamorphism and amphibolite facies retrogressive metamorphism. Importance of eclogite Photomicrograph of a thin section of eclogite from Turkey. Physical properties of rocks play an important role in determining its applications in various fields. Eclogite plays an important role in mantle convection and geodynamics in subduction zones. Glaucophane-eclogites occur in Italy and the Pennine Alps. New findings of foliated eclogite in the Seba and Kotsu areas show that eclogite facies … Updates? 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. Introduction [2] Crustal rocks metamorphosed at high-pressure (HP) to ultrahigh pressure conditions provide important geody- Our editors will review what you’ve submitted and determine whether to revise the article. An unusually dense rock, eclogite can play an important role in driving convection within the solid Earth. The carbon isotopic differences between harzburgitic and eclogitic diamonds supports the hypothesis that those eclogite xenoliths formed from basalt carried down within subduction zones. Likewise, peridotite is a much more important source rock of common magmas. 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. Harzburgitic diamonds typically have titaniferous pyrope, chromian spinel and chromian diopside inclusions, minerals which are not typically found in eclogites. 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. 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. 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. 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. … [1] They are generally formed from precursor mineral assemblages typical of blueschist-facies metamorphism. Xenoliths of eclogite occur in kimberlite pipes of Africa, Russia, Canada, and elsewhere. Eclogite-derived melts may be common in the mantle, and contribute to volcanic regions where unusually large volumes of magma are erupted. 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. A few eclogites also occur in the northwest highlands of Scotland and the Massif Central of France. Known eclogite occurrences in the Sanbagawa metamorphic belt of SW Japan are dominantly in metagabbro bodies which have complex polyphase metamorphic histories. [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. Examples are known in Saxony, Bavaria, Carinthia, Norway and Newfoundland. 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. Occurrences exist in western North America, including the southwest[6] and the Franciscan Formation of the California Coast Ranges. Let us know if you have suggestions to improve this article (requires login). 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. Eclogite is a rare and important rock because it is formed only by conditions typically found in the mantle or … "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. 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). An unusually dense rock, eclogite can play an important role in driving convection within the solid Earth. It is common in the upper mantle, especially in regions occupied by subducted oceanic plates. 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. 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. 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). 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. 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. [7] Transitional granulite-eclogite facies granitoid, felsic volcanics, mafic rocks and granulites occur in the Musgrave Block of the Petermann Orogeny, central Australia. [4], The eclogite melt may then react with enclosing peridotite to produce pyroxenite, which in turn melts to produce basalt.[5]. 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. Eclogite-facies metamorphic conditions encompass a wide range of pressure–temperature space from deep crustal to mantle depths, reflecting tectonic setting. Eclogite consists mainly of omphacite and garnet. Phase changes can be more important in the mantle. Norsk Bergverksmuseum Skrift. Eclogite is a metamorphic rock consisting of pyroxene omphacite and pyrope-rich garnet. Eclogite-rich layers would be intermittent because of low melting points and the temperature-dependency of the relevant phase changes. I suggest that under certain circumstances the lower crust transforms to dense eclogite and delaminates. 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. To get a basalt from melting an eclogite (i.e. shales or limestones, are not known to show … ; a rock with basalt composition) it has to undergo 100% partial melting. Eclogites consist primarily of green pyroxene (omphacite) and red garnet (pyrope), with small amounts of various other stable minerals— e.g., rutile. They are formed when volcanic or metamorphic rocks rich in such mafic minerals are subjected to extremely high pressures and … Information and translations of eclogite in the most comprehensive dictionary definitions resource on the web. Eclogite rheology is an important piece of information for understanding the subduction of continental crust to great depth and then return to the surface. The melting curves have a positive slope, as the solids are denser than their equivalent melts and are thus favoured (enlarged) with increasing pressure.…. [8] The oldest coesite-bearing eclogites are about 650 and 620 million years old and they are located in Brazil and Mali, respectively. C This article has been rated as C-Class on the project's quality scale. melting model would predict. Eclogite is the highest pressure metamorphic facies and is usually the result of advancement from blueschist metamorphic conditions. Unreasonably high degrees of partial melting are required to attain basaltic compositions. Accessory minerals include kyanite, rutile, quartz, lawsonite, coesite, amphibole, phengite, paragonite, zoisite, dolomite, corundum, and, rarely, diamond. Posted on 24 October, 2012 by Metageologist. 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. 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). Interestingly, eclogites somewhat resemble chondritic meteorites in composition (see chondrite). Eclogite is denser than the surrounding asthenosphere. Likewise, partial melting of eclogite has been modeled to produce tonalite-trondhjemite-granodiorite melts. Some UHP rocks appear to record burial at depths greater than 120 km (75 mi) if diamond occurs in these 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). Peridotite is the dominant rock type of the upper mantle, not eclogite, as established by seismic and petrologic evidence. Eclogite forms at pressures greater than those typical of the crust of the Earth. The early Jurassic intrusive complex is chiefly made of monzodioritic porphyry in northern Anhui and northern Jiangsu, which emplaced in 191 Ma. Corrections? Melting of eclogite to produce basalt directly is generally not supported in modern petrology. 17, 637-652: Hareidlandet ⓘ Eiksund; Nordrum, F.S. 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. 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. important strategy for establishing control over organic epitaxy. If we have to define Eclogite in general, Eclogite is an extreme metamorphic rock, formed by regional metamorphism of … [2] The rarity of lawsonite eclogites therefore does not reflect unusual formation conditions but unusual exhumation processes. Plagioclase is not stable in eclogite. 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