Eclogites consist primarily of green pyroxene (omphacite) and red garnet (pyrope), with small amounts of various other stable minerals—e.g., rutile. Nordfjord, Western Norway. 6. Group C eclogites bear amphiboles, epidote, and rutile5. Asthenosphere at depth of 100 km and it’s temprature is 300-500 so how can be 400 degrees at 45 km depth only . Eclogite may also contain kyanite (small blue spots, abundant but visible only if you look carefully (esp. Selje, Norway. Where sedimentary rocks have been metamorphosed under eclogite facies conditions, schist or gneiss forms instead of eclogite5. This is important as these rocks nearly reached the depth at which normal eclogite becomes denser than the surrounding mantle, at which point subduction becomes irreversible. Our data point to a 497±24 (2σ) Ma age, in excellent agreement with U-Pb results (Ménot et al. Nordfjord, Norway. More mica in the composition of eclogite. In some retrogressed eclogites and accompanying more silica-rich rocks, UHP (ultrahigh-pressure) metamorphism has been recognized only because of the preservation of coesite and/or diamond inclusions within trace minerals such as zircon and titanite. but seriously i think there’s a mistake in this line ( 400-500 degrees at 45 km depth is below the crustal average (25 °C per kilometer of depth). ) We report the results of a Sm-Nd isotopic study of whole-rock samples from the Chamrousse ophiolite complex, in the Variscan basement of the Western Alps, France. The generation of TTGs during the Archaean marked the transition from a simatic (mafic) to a sialic (felsic) crust, and represents the magmatic contribution to the cratonization6. The foliation is … Eclogite:A high-pressure, high-temperature, coarse-grained metamorphic rock consisting primarily of pink-red garnet (almadine-pyrope variety) and green pyroxene (omphacite, a sodium-rich variety). Eclogite. Interestingly, eclogites somewhat resemble chondritic meteorites in composition (see chondrite). That may look somewhat complicated but here is the same thing expressed in another way: plagioclase (first two formulas put together give as a plagioclase with a composition of labradorite) + olivine (Mg-rich variety forsterite) + diopside = omphacite (first two formulas are jadeite and diopside, respectively) + garnet (there is no such garnet group endmember as the formula suggests but I guess it was needed to make the equation work) + quartz. Updates? It is a rare but geologically significant rock type. He mentions 400-500 degrees at 45 km depth is below the crustal average (25 °C per kilometer of depth). Many investigators believe that eclogite is representative of numerous parts of the upper mantle. Hence, not all eclogite facies rocks are eclogites, nor are all eclogites formed under the conditions of eclogite facies (some eclogites formed at the conditions of amphibolite or blueschist facies). Our editors will review what you’ve submitted and determine whether to revise the article. Width of view 18 cm. Eclogite is a metamorphic rock formed when mafic igneous rock is subjected to high pressure. Fertile mantle (wehrlite or lherzolite) melts partially by giving away basaltic magma and transforming itself to harzburgite or dunite (depleted mantle). Eclogite also melts partially but by doing that magma with a more evolved composition will form. Eclogite may be more fine-grained and darker in appearance. Eclogite as a rock type was first defined by a French mineralogist René Just Haüy in 18222. The physical properties of Eclogite rock are vital in determining its Eclogite Texture and Eclogite Uses. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. Eclogite, any member of a small group of igneous and metamorphic rocks whose composition is similar to that of basalt. Garnet in eclogite is usually iron-rich pyrope (contains similar amount of Mg and Fe). 45 km depth is about 12 kbar of pressure. Omphacite is a pyroxene group mineral with a composition in the middle between jadeite and diopside. Width of sample 9 cm. Eclogite is a very beautiful rock. This is possible because geothermal gradient is much lower in subduction zones where cold oceanic crust is diving and takes lots of time to heat up. Eclogite GR 30c is a massive medium-grained rock, consisting of garnet, omphacite, glaucophane, epidote, phengite, apatite, quartz, and rutile. :). Eclogite, however, is already basaltic in composition. Elles se répartissent en deux groupes. Request PDF | On Jan 1, 2015, M. J. Caddick and others published Origin of Metamorphic Rocks | Find, read and cite all the research you need on ResearchGate Abstract The eclogites exposed along northeastern boundary of the Belomorian orogen in the eastern Fennoscandian Shield were formed as a result of Mesoarchean–Neoarchean subduction … Smulikowski, K. (1990). 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. Eclogite xenoliths are present in kimberlites, lamproites and the like and come from mantle depths. It is not very common for the rocks once buried that deep to somehow raise again to the upper parts of the lithosphere. Aside from being an absolutely gorgeous rock, eclogite is intriguing because it provides direct evidence that basalt and gabbro descend deep within the Earth. The protoliths of eclogites are igneous rocks with a basaltic composition (basalt, diabase, gabbro). Three groups of eclogites are referred to as group A (former basaltic intrusions within metamorphic rocks of the amphibolite facies), group B (inclusions or xenoliths from great depths), and group C eclogites (former subducting oceanic lithosphere). Some types of rocks have exceptional properties and can be used in medical industry. Rapp, R. P., Watson, E. B., & Miller, C. F. (1991). The lack of relatively light-weight plagioclase is the reason why it is so dense compared to its protoliths. Sm-Nd analyses on the eclogite sample give a Grt±Cpx±whole-rock age of 362 25 Ma, consistent with the U-Pb age of 356 8 Ma (recalculated) obtained from the same sample by J. L. Paquette in 1987. (1996). Eclogite forms at pressures greater than those typical of the crust of the Earth. Thanks for the article of your share, it is very useful to me. eclogite rock isolated over white - Buy this stock photo and explore similar images at Adobe Stock McGraw-Hill. 17, 637-652 Hareidlandet Compare Metamorphic Rocks » … Rapp, R. P., Watson, E. B., & Miller, C. F. (1991). Eclogite is a metamorphic rock consisting of pyroxene omphacite and pyrope-rich garnet. In: The Encyclopedia of Igneous and Metamorphic Petrology (Encyclopedia of Earth Sciences Series) (Ed. Will form data point to a 497±24 ( 2σ ) Ma age, in agreement... The lookout for your Britannica newsletter to get trusted stories delivered right to your inbox lithosphere..., Howie, R. a true as well: eclogite, any member of small. Its denser solid equivalent, eclogite can play an important role in driving convection within the Earth!, trondhjemite, granodiorite ) is usually iron-rich pyrope ( contains similar amount of Mg and )... ( requires login ), or other metamorphic rocks in inclusions such as titanite,,. 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