eclogite facies mineral assemblage

December 12th, 2020

Garnet–chloritoid–kyanite assemblages: eclogite facies indicators of subduction constraints in orogenic belts A. J. SMYE, L. V. GREENWOOD* AND T. J. The lawsonite (Lws) eclogite facies mineral assemblage [Lws + omphacite (Omp)] was discovered as an inclusion in garnet (Grt) within a unique epidote (Ep)-glaucophane (Gln) eclogite in the Kotsu area of the Sanbagawa belt in eastern Shikoku, Japan. The accessory minerals are kyanite, quartz, rutile, orthopyroxene and coesite. Metamorphic petrologists studying contact metamorphism early in the 20th century introduced the idea of metamorphic facies (part of a rock or group of rocks that differs from the whole formation) to correlate metamorphic events. The typical eclogite mineral assemblage is garnet (pyrope to almandine) plus clinopyroxene (omphacite). A metamorphic facies is a region of pressure-temperature space in which characteristic metamorphic minerals form. The garnet-pyroxenite has a dominant mineral assemblage of garnet, orthopyroxene, clinopyroxene and hornblende, while garnet-amphibolite and garnet-kyanite schist are made up of garnet, hornblende, plagioclase and quartz, and garnet, kyanite, biotite and quartz, respectively. We found that the seismic signatures of each of the eclogite-facies mineral assemblages were different. For X Jd = 0.43 at 770 °C the calibration of Holland (1980) gives a pressure of 16.8 kbar, whilst the ternary solid solution model of Meyre et al. The typical eclogite mineral assemblage is garnet (pyrope to almandine) plus clinopyroxene (omphacite). Multimineral Rb/Sr internal isochrons from eclogite facies rocks of the Eclogite Zone (Tauern Window, Eastern Alps) consistently yield an Early Oligocene age of Crystallization and very rapid exhumation of the youngest Alpine eclogites (Tauern Window, Eastern Alps) from Rb/Sr mineral assemblage analysis Eclogite facies is determined by the temperatures and pressures required to metamorphose basaltic rocks to an eclogite assemblage. Other articles where Eclogite facies is discussed: metamorphic rock: Eclogite facies: The eclogite facies was initially recognized in rocks only of basaltic composition, which are transformed at the pressure-temperature conditions of the eclogite facies into spectacular red and green rocks composed of the anhydrous mineral assemblage garnet plus omphacite. Table I lists mineral assemblages of the eclogite sam-ples investigated. Triassic eclogite and blueschist facies rocks occur as a thrust sheet, 25-km long and over 2-km thick, in an Eocene fold-and-thrust belt in northwest Turkey along the I˙zmir–Ankara suture. Brown, Martin Hand, Laura J. Morrissey, John W. Goodge Zeolite facies describes the mineral assemblage resulting from the pressure and temperature conditions of low-grade metamorphism. Eclogite facies is determined by the temperatures and pressures required to metamorphose basaltic rocks to an eclogite assemblage. A Low-Variance Mineral Assemblage with Talc and Phengite in an Eclogite from the Saxonian ... in principle, coexist in metabasites with the above assemblage at pressure–temperature (P–T) conditions of the eclogite facies. Definitive Mineral Assemblages of Metamorphic Facies Mineral assemblages in mafic rocks of the facies of contact meta-morphism do not differ substantially from that of the corresponding regional facies at higher pressure. Eclogites record pressures in excess of 1.2 GPa (45 km depth) at >400–1000 °C and usually in excess of 600-650 °C. The typical eclogite mineral assemblage is garnet (pyrope to almandine) plus clinopyroxene (omphacite). Eclogites record pressures in excess of 1.2 GPa (45 km depth) at >400–1000 °C and usually in excess of 600-650 °C. 2 Transition from eclogite facies is further supported by ilmenite-plagioclase-amphibole symplectites suggesting replacement of garnet (Bhowmik and Roy, 2003) during decompression. However, the matrix omphacite is commonly replaced by chlorite, and initially coarse–grained glaucophane is reduced in grain–size. 47, No. Eclogites record pressures in excess of 1.2 GPa (45 km depth) at >400–1000 °C and usually in excess of 600-650 °C. The eclogite-facies assemblage of amphibole, diopside, garnet, ... Other studies show that TTG gneiss may rarely preserve an eclogite-facies mineral assemblage in low-strain zones, where it is able to escape late-orogenic deformation and recrystallization (Krabbendam and Wain, 1997, Wain, 1998, Cooke and O'Brien, 2001, Van Gool et al., 2002). (1997) indicates a value of 17.8 kbar. An eclogite-facies assemblage garnet + omphacite + rutile + glaucophane + quartz occurs as inclusions in clinozoisite porphyroblasts in a high-grade blueschist block in the Paleozoic Osayama serpentinite mélange of the Chugoku Mountains, southwest Eclogites and the Eclogite Facies. Some garnets include polycrystalline qvartz aggregates that are pseu-domorphs after coesite, as will be discussed later. Eclogite-Facies Mineral Inclusions in Clinozoisite from Paleozoic Blueschist, Central Chugoku Mountains, Southwest Japan: Evidence of Regional Eclogite-Facies Metamorphism. The primary mineral assemblage in the eclogites consists mainly of garnet, omphacite, amphi-bole, muscovite, apatite, rutile, and zircon. Cambrian eclogite-facies metamorphism in the central Transantarctic Mountains, East Antarctica: extending the record of early Palaeozoic high-pressure metamorphism along … Eclogite facies. In the eclogite facies, metabasaltic rocks contain the characteristic assemblage of omphacitic pyroxene + almandine-pyrope-grossular garnet, creating dense, beautiful green and red rocks (Table 1) .Plagioclase is not present in the eclogite facies rocks due to his stability. Metamorphic facies. A pumpellyite–bearing retrograde blueschist–facies mineral assemblage is found in the gar-net blueschist, an Mg–rich equivalent of the eclogite (Shinji and Tsujimori, 2019). Eclogite facies. 276 Downloads; Abstract . Primarily, the amphibolized protolith experienced a garnet-amphibolite facies metamorphism at ~ 500–700 °C and ~ 0.8–1 GPa. Graduate School of Environmental Studies, Tohoku University Eclogite and blueschist complexes are the most important indicators of the tectonic evolution of the folded system such as … Some of the metabasites in the Çamlıca metamorphics preserve an early eclogite-facies mineral assemblage of garnet + omphacite + glaucophane + rutile ± paragonite, strongly overprinted by greenschist-facies mineral assemblages. eclogite–facies mineral assemblage in the garnet rims. Amphibole compositions vary significantly and reflect lower grade (low Na, Al, Ti actinolite) overprint of earlier amphibolite facies compositions (high Na, Al, Ti magnesio- hornblende). Field evidence and mineral assemblage of eclogite from the Khungui zone, Zavkhan terrane, Western Mongolia *Manzshir Bayarbold1, Atsushi Okamoto1, OTGONBAYAR DANDAR1, Masaoki Uno1, Noriyoshi Tsuchiya1 1. 215-232. Some of the metabasites in the amlÝca metamorphics preserve an early eclogite-facies mineral assemblage of garnet + omphacite + glaucophane + rutile – paragonite, strongly overprinted by greenschist-facies mineral assemblages. The thrust sheet consists mainly of metabasites with minor marble, phyllite and metachert, and rare lenses of serpentinite. Quartz Download PDF (8 MB) Cite . BibTex; Full citation; Abstract. An Sm-Nd whole-rock–garnet isochron and zircon U-Pb dates show that timing of the eclogite facies metamorphism took place ca. The assemblage garnet–chloritoid–kyanite is shown to be quite common in high‐pressure eclogite facies metapelites from orogenic belts around the world, and occurs over a narrowly restricted range of temperature ∼550–600 °C, between 20 and 25 kbar. International Geology Review: Vol. B. HOLLAND Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK (as859@cam.ac.uk) ABSTRACT The assemblage garnet–chloritoid–kyanite is shown to be quite common in high-pressure eclogite facies metapelites … Eclogite facies. Generally considered to be transitional between diagenetic processes which turn sediments into sedimentary rocks, and prehnite-pumpellyite facies, which is a hallmark of subseafloor alteration of the oceanic crust around mid-ocean ridge spreading centres. Most eclogite facies are eclogites– that is, they are basalts or gabbros which have experienced metamorphism at eclogite facies pressures and temperatures. Eclogite facies is determined by the temperature and pressure conditions required to metamorphose basaltic rocks to an eclogite assemblage. However, sometimes other rock types (notably, granodiorites and pelites) may experience eclogite facies … Eclogite facies is determined by the temperatures and pressures required to metamorphose basaltic rocks to an eclogite assemblage. The typical eclogite mineral assemblage is garnet (pyrope to almandine) plus clinopyroxene (omphacite). Equilibration pressures for the eclogite-facies assemblage were calculated on the basis of the jadeite content in clinopyroxene based on the albite breakdown reaction: Ab = Jd + Qtz. (2005). Since the original definition of the name was vague, its meaning was gradually settled through its usage in later years. Eclogite facies metamorphic rocks formed through subduction and collision processes are common in ... (andesine–albite), garnet, clinopyroxene (diopside–omphacite), scapolite (meionite) and calcite are the main mineral assemblage in the metamorphosed mafic rocks from this study. Cambrian eclogite-facies metamorphism in the central Transantarctic Mountains, East Antarctica: Extending the record of early Palaeozoic high-pressure metamorphism along the eastern Gondwanan margin Dillon A. Eclogite pyrope garnet + omphacitic pyroxene (± kyanite) Contact Facies After Spear (1993) Table 25-1. The assemblage garnet–chloritoid–kyanite is shown to be quite common in high‐pressure eclogite facies metapelites from orogenic belts around the world, and occurs over a narrowly restricted range of temperature ∼550–600 °C, between 20 and 25 kbar. The equilibrium mineral assemblage of rocks subjected to greenschist facies conditions depends on primary rock composition. The rock name eclogite was coined by Haüy, a founder of crystallography, in 1822. … Authors; Authors and affiliations; Akiho Miyashiro; Chapter. 3, pp. Here we report a unique natural example of eclogite resembling assemblage in disequilibrium formed through fluid-induced metasomatic reactions under the amphibolite to granulite facies. The assemblage garnet–chloritoid–kyanite is shown to be quite common in high‐pressure eclogite facies metapelites from orogenic belts around the world, and occurs over a narrowly restricted range of temperature ∼550–600 °C, between 20 and 25 kbar. The primary mineral assemblage of garnet + omphacite/augite + quartz + rutile ± pargasite of the eclogite and garnet clinopyroxenite xenoliths defines a minimum pressure of >1.5 GPa, while the estimated peak metamorphic temperatures range from 800 to 1060 °C. 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