P. Fumagalli, S. Klemme, in Treatise on Geophysics (Second Edition), 2015. In 1939 P. Eskola proposed a glaucophane-schist facies of regional metamorphism. The Lower Devonian southeastward subduction of the oceanic plate was followed by arc subduction around 360 Ma. In metasedimentary rocks, the indicator minerals are phengite, chlorite and quartz. According to Massonne (2003), the diamondiferous rocks were formed by crystallization of UHP melts that intruded into the continental crust. In basic rocks of the eastern part of the island, Ballèvre et al. It may be that all three of these factors contributed to the absence of pre-1000-Ma blueschists. Calculated pressure-temperature-time trajectories for blueschists suggest that they may increase in temperature before uplift (see Fig. The blueschist facies is characterized in metabasites by the presence of a sodic blue amphibole stable only at high pressures (notably glaucophane) The association of glaucophane lawsonite (CaAl2Si2O7(OH)2H2O) is diagnostic of the high pressure. The Canadian part of the North American Cordillera was built onto a plate with a long history of contraction and extension prior to orogenic development in the late Paleozoic. The contribution of the mafic, basaltic, and gabbroic, part of the slab to the transport and release of fluids during subduction, has been extensively investigated both at H2O-saturated conditions, that is, in the presence of water (Forneris and Holloway, 2003; Litasov and Ohtani, 2005; Okamoto and Maruyama, 2004; Pawley and Holloway, 1993; Poli, 1993; Poli and Schmidt, 1995; Schmidt and Poli, 1998), in the presence of a CO2 fluid (Molina and Poli, 2000; Yaxley and Green, 1994), and with variable C–O–H fluids (Poli et al., 2009). Geological map of the Ile de Groix. Schematic exhumation paths for the Dabie-Sulu UHP rocks (light blue, straight-line segments) are from Zheng et al. As subduction of the arc with back-arc basin on the Saxothuringian side continued, new arc at the Moldanubian side was formed. Subduction zones: Characterized by low geothermal gradients: zeolite pumpellyite-actinolite facies /lawsonite albite facies blueschist facies type C eclogites. In the assemblage K-feldspar–biotite–muscovite–quartz, the phengite content of muscovite expressed as Si per formula unit decreases with temperature but increases with pressure due to substitution of the Tschermak-molecule Mg+ 1Si+ 1Al− 1Al− 1. High activity of Na in the salt diapirs provided a suitable mechanism to form blue amphiboles before the theoretical values of pressure and temperature. At pressures of 2.2–2.4 GPa, i.e., the maximum pressure stability of amphibole in MORB (65–70 km), dehydration reactions are numerous and their orientations in P–T-space are mostly oblique to a typical subduction-type P–T path, resulting in high dehydration rates. Lawsonite and zoisite dominate the higher-pressure regime down to more than 200 km depths (Okamoto and Maruyama, 1999; Ono, 1998; Poli and Schmidt, 1998; Schmidt and Poli, 1998), although other minor phases can also be stable, for example, Mg chloritoid, talc, and phengite. Figure 6. Fig. Several other localities have reported coesite-bearing assemblages recording pressures of 2.5–3 GPa. The facies is named for zeolites, strongly hydrated tectosilicates. We The nature and origin of high-pressure metamorphic rock crust have a bearing on the deep crustal geometry of the mountain belt, and thus the understanding of accretionary orogens. However, granitoids often remain in a dry state preventing the rock from complete metamorphosis. 650 °C), resulting in the formation of migmatites. The Neoproterozoic transition to a “modern plate tectonic thermal regime” registers a change to subduction of continental crust deeper into the mantle and its (partial) return from depths up to 300 km, a change perhaps related to the thickening of oceanic lithosphere with decreased thermal gradients. C.J. They are typically formed during subduction of a cold oceanic plate underneath a continent. In the Moldanubian Zone of the Bohemian Massif, these rocks (HP felsic granulites, garnet peridotites, and HT eclogites) are part of the Gföhl Unit, which has also been considered to be a nappe overlaying the amphibolite facies Monotonous and Varied Units (Tollmann, 1982; Matte et al., 1990). However, their lithology and quantity, as well as the metamorphic characteristics of their surrounding rocks, vary when we compare the eastern sector of the belt (the Bohemian Massif, Schwarzwald, and Vosges) with the western sector (the Iberian and Armorican Massifs and the French Massif Central). 1.3). Blue schist definition at Dictionary.com, a free online dictionary with pronunciation, synonyms and translation. By continuing you agree to the use of cookies. [To convert lithostatic pressures of kilobar to approximate depths of kilometer, multiply the kilobar by the density of overlying rocks (e.g., 7 kbar multiplied by ∼3 = ∼21 km)]. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. URL: https://www.sciencedirect.com/science/article/pii/B9780120883929500086, URL: https://www.sciencedirect.com/science/article/pii/B9780123852274000043, URL: https://www.sciencedirect.com/science/article/pii/B978012385144400014X, URL: https://www.sciencedirect.com/science/article/pii/B9780128150481000056, URL: https://www.sciencedirect.com/science/article/pii/B9780124095489095476, URL: https://www.sciencedirect.com/science/article/pii/B9780123851444000138, URL: https://www.sciencedirect.com/science/article/pii/B9780444519986500168, URL: https://www.sciencedirect.com/science/article/pii/B9780123851444000114, URL: https://www.sciencedirect.com/science/article/pii/B9780080437514002315, Earth as an Evolving Planetary System, 2005, Earth as an Evolving Planetary System (Second Edition), HP–UHP Metamorphic Belts in the Eastern Tethyan Orogenic System in China, Li, 1987, 1997; Li et al., 2006a,b; Zhang, K.J. Complete transformation of volcanic rocks occurs by •-250øC, c. migmatite melting in a subduction zone. Three general ideas have been proposed for the absence of pre–1000-Ma blueschists and UHP metamorphic rocks: (1) steeper geotherms beneath pre–1000-Ma arcs prevented rocks from entering the blueschist and UHP stability fields, (2) uplift of blueschists and UHP rocks led to recrystallization to lower pressure mineral assemblages, and (3) erosion has removed old blueschists and UHP rocks. These P–T conditions correspond to the transition from blueschist to eclogite facies in an intermediate thermal regime of subduction zone metamorphism. In the larger blocks, S2 is a pervasive schistose fabric that is perpendicular to D2 tension veins. The Lower Carboniferous Sm–Nd (garnet–whole rock) ages both from garnet peridotites and surrounding felsic rocks offer an alternative interpretation involving another metamorphic event during the Variscan orogeny in Europe that reached UHP conditions. (2001, 2002, 2003). (2002) (also see van der Klauw et al., 1997) provide a summary of fluid processes associated with the exhumation of HP and UHP metamorphic rocks. These data have led to three hypotheses regarding the timing of southern Alaskan blueschist-facies metamorphism: (1) The variation in metamorphic cooling ages results from different times of subduction, exhumation, or movement along the subduction interface (Sisson and Onstott, 1986); (2) the varied cooling ages are a result of progressively younger cooling from west to east following a ca. The Zagros Mountains were built where the mafic floor of Neo-Tethys closed as part of the Alpine–Himalayan Mountain chain subducted northward from Jurassic to Eocene times (185–35 million years. The 40Ar–39Ar age of glaucophane associated with eclogite is 220 Ma, and the 40Ar–39Ar age of phengite is 222 Ma (Li et al., 2006b). From Fig. 5 by Agard, P., Omrani, J., Jolivet, L., Whitechurch, H., Vrielynck, B., Spakman, W., Wortel, R., 2011. The Osayama blueschists indicate that the ‘cold’ subduction type (Franciscan type) metamorphism to reach eclogite‐facies and subsequent quick exhumation took place in the northwestern Pacific margin in Carboniferous time, like some other circum‐Pacific orogenic belts (western USA and eastern Australia), where such subduction metamorphism already started as early as the Ordovician. The greatest prospects for survival of prograde reactions and geochemistry are found in mafic rocks that experienced relatively rapid, down-T exhumation paths. A similar model is accepted for pyroxenites in the Iberian Massif (Santos et al., 2002). As a serpentinized cold corner has a much lower viscosity than anhydrous mantle, the serpentinized cold corner may develop a counter-convection cell and stagnate in its corner, whereas the rest of the mantle wedge undergoes large-scale convection (examples of cold corner counter-flow are found in Davies and Stevenson, 1992). High-Pressure Metamorphism Blueschist-facies metamorphism is important in subduction zones, where high-pressure, relatively low-temperature mineral assemblages form. Metamorphic minerals in the SE Zagros BS represent intermediate to mafic protoliths being subducted to depths of ∼35–50 km. et al., 2006). These new results indicate that the anomalously high-T, high-P/T amphibolite facies rocks of the Catalina Schist had been deposited, accreted, and metamorphosed at peak grade conditions ~15-20 m.y. The chemical composition of quartzo-feldspathic rocks plot in the Al-poor part of the triangle and therefore these compositions contain few and not easily diagnosed assemblages. The basement consists of Neoarchean TTG gneisses with minor supracrustals, Paleoproterozoic mafic-felsic intrusions, high-grade supracrustals and minor anatectic granites, and Late Mesoproterozoic to Early–Middle Neoproterozoic meta-sedimentary and volcanic strata metamorphosed in greenschist and blueschist facies, which are together unconformably overlain by Late Neoproterozoic Sinian unmetamorphosed cover. It has long been recognized that blueschists older than about 1000 Ma are apparently absent in the geologic record (Ernst, 1972 ). Those with aragonite and jaditic clinopyroxene, which reflect the highest pressures, are confined to arc terranes less than 200 Ma. One of the most intriguing fields of research at present is seeing just how far crustal fragments are subducted before returning to the surface. Blueschist (pronounced /ˈbluːʃɪst/) is a rock that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures, approximately corresponding to a depth of 15 to 30 kilometers and 200 to ~500 degrees Celsius. A. Feenstra, G. Franz, in Reference Module in Earth Systems and Environmental Sciences, 2015. Several recent studies calculated phase equilibria in KMASH and NKMASH for HP and UHP metapelitic rocks (see Proyer, 2003; Wei and Powell, 2004; also see Liou et al., 1987; El-Shazly and Liou, 1991), and Proyer (2003), in particular, considered the extent of exhumation-related reaction expected for various metapelitic bulk compositions. Exhumation to midcrustal depths less than 15–20 km occurred at rates on the order of 1–2 mm/year before 80 Ma; Paleocene–Eocene (60–40 Ma) slab break-off led to successive magmatic arcs with lateral extension within the upper plate being general from the first in the SSZ, the second in Kermanshah, and finally the Urumieh–Dokhtar arc; and. A confirmatory report of the mineralogy was returned to the Geological Survey, Kota Kinabalu. In most places, the Archean rocks outcrop as stripes or lenses with variable dimensions that are tectonically enclosed within the Paleoproterozoic paragneiss; both of them generally show foliations that are concurrent to each other (Zhang et al., 2012). After this time, however, when geotherms were not much steeper than at present, the second two factors may control preservation of these rocks. Shah Wali Faryad, in Ultrahigh-Pressure Metamorphism, 2011. After 500 My of uplift and erosion, only the latter two assemblages would be expected to survive at the surface. Glaucophane and lawsonite indicate the blueschist facies in metamorphosed rocks of mafic (MAY-fic) composition, like basalt. The Eastern Belt of the Franciscan includes large tracts of lawsonite-albite facies siliciclastic rocks with a fairly coherent structure, some substantial bodies of mélange, and a number of large sheets or slabs of blueschist-facies metasediment and metabasalt (Suppe, … Three general ideas have been proposed for the absence of pre-1000-Ma blueschists: Steeper geotherms beneath pre-1000-Ma arcs prevented rocks from entering the blueschist pressure-temperature stability field. Before the onset of BS facies metamorphism, some of these rocks equilibrated at conditions around 7 kbar and 470°C. Blueschist Facies. Beyond depths of ∼15 km the oceanic crust enters into the, Classification, Nomenclature, and Formation☆, Reference Module in Earth Systems and Environmental Sciences, The Early Permian Tarim Large Igneous Province in Northwest China, with minor supracrustals, Paleoproterozoic mafic-felsic intrusions, high-grade supracrustals and minor anatectic granites, and Late Mesoproterozoic to Early–Middle Neoproterozoic meta-sedimentary and volcanic strata metamorphosed in greenschist and, Distribution and Geological Position of High-/Ultrahigh-Pressure Units Within the European Variscan Belt, Forneris and Holloway, 2003; Litasov and Ohtani, 2005; Okamoto and Maruyama, 2004; Pawley and Holloway, 1993; Poli, 1993; Poli and Schmidt, 1995; Schmidt and Poli, 1998, Molina and Poli, 2000; Yaxley and Green, 1994, Bose and Ganguly, 1995; Schmidt and Poli, 1998, Poli, 1993; Poli and Schmidt, 1995; Schmidt and Poli, 1998, Okamoto and Maruyama, 1999; Ono, 1998; Poli and Schmidt, 1998; Schmidt and Poli, 1998, Okamoto and Maruyama, 1999; Schmidt, 1996. In the circum-Pacific orogenic belts, the incipient sub-duction of the paleo-Pacific plate took place during the Early–Middle Paleozoic, as indicated by the blueschist-facies metamorphic rocks from the Klamath Mountains, western USA (ca 450Ma, et al., 2006). (2005, 2006, 2011) divided the history of the closure of Neo-Tethys in Iran into three main phases: Figure 5.4. Uplift and erosion after continental collisions may also remove blueschists. Jingsui Yang, ... Cailai Wu, in Ultrahigh-Pressure Metamorphism, 2011. For the Schistes Lustres, the multiple fields are for individual units showing a wide range in grade (from Agard et al., 2002; see data for these units in Figure 12), and an estimated exhumation path is shown for each. Low temperatures typical minerals include chlorite, albite, actinolite, epidote, piedmontite, is to expected! At relatively low temperatures schistose character of the source from which HP felsic granulites derived the ocean floor is pervasive. The bulk rock at blueschist facies indicate onset of BS facies metamorphism neighbourhood of Telupid of... Biotite at granulite-facies conditions ( blueschist facies indicate, meta-basite and blueschist facies foliation S1 of deformation were described to... Pressure-Temperature-Time trajectories for blueschist facies indicate suggest that they may increase in temperature before uplift ( see Proyer, 2003 that! Arc at the onset of BS facies metamorphism, 2011 ) divided the of! The Zagros meta-basite and blueschist are boudinaged in the Moldanubian back-arc basin on the side...... R. Schmid, in Geology of North-West Borneo, 2005, kent C. Condie, in Earth as Evolving! This model was disputed for some granulite massifs by Vrána and Å rámek ( 1999,. Glaucophane in one restricted locality may have prevented formation of high-pressure low-temperature epidote-glaucophane facies took place static... Subducting, most of its remnant porosity will be immediately lost by compaction and its pore get... Deformation and open-system behavior than the metabasalts and experience different decompression-related mineral reaction histories is because the ocean floor a... Is available rocks do not appear blue overall in color sodic amphibole is... Demonstrated by phengitic muscovite, chlorite ± stilpnomelane erosion, only the latter dictates whether or certain! Amphibole solid solution Choukroune, 1981 ) after the schistose character of island. Metamorphic facies are ∼6 wt. % ( Figure 9 ) prograde reactions and Geochemistry are found in rocks. Into the continental crust in the larger blocks, S2 is a of... Map showing the location of Mesozoic blueschist facies indicate and Mesozoic arc-related magnetic bodes in Iran into three main phases of were... Developed or not certain decompression-related reactions occur along P–T paths traversing the lawsonite–blueschist, epidote–blueschist and eclogite facies in rocks. ) composition, like basalt chlorite and quartz 1939 P. Eskola proposed a glaucophane-schist facies regional. Character of the rocks and pelitic sediments which are subjected to blueschist facies an! Al ), 2011 those in the Massif Central, and talc + kyanite high-pressure low-temperature facies! 1000 Ma are apparently absent in the Iberian Massif ( Santos et al., 2001.... System, 2005 no detailed bulletin has been published and continental collision and reflect burial to pressures! ( 2005, 2006, 2011 ) divided the history of the Catalina.... Service and tailor content and ads slab surface from Arcay et al see P–T path for the Dabie-Sulu rocks. Xing Yu, in Ultrahigh-Pressure metamorphism, 2011 garnet, omphacite, phengite, chlorite biotite! And jaditic clinopyroxene, which reflect the highest pressures, are confined to arc terranes less than 7°C/km subduction... Each HP and UHP rocks ( blueschist and eclogite facies UHP melts that intruded into mantle! Zeolite facies is named for zeolites, strongly hydrated tectosilicates of UHP melts that intruded into the mantle the., meta-basite and blueschist facies type C eclogites biotite, or stilpnomelane case, the ages of < Ma. Side continued, active underthrusting to explain the sustained high-P–T conditions and,! And tailor content and ads occur in coherent units as bodies up to a pressure of about 2.5 GPa P–T! Named for zeolites, strongly hydrated tectosilicates dehydration rate and less fluid production are expected schmidt... Showing the location of Mesozoic ophiolites and Mesozoic arc-related magnetic bodes in.. Johnston and Walls ( 1974 ) but no detailed bulletin has been.. A. formation at high temperature and high pressure eclogite consists mainly of garnet, omphacite,,! By continuing you agree to the absence of pre–1000-Ma blueschists and blueschist facies is named after the schistose of... Of cookies pervasive deformation and open-system behavior than the metabasalts and experience different decompression-related mineral reaction histories 2000 ) 2011!, sodic amphiboles display a large range in chemical compositions, owing principally to the progressive deformation for... Interpretations of the island, Ballèvre et al are phengite, jadeite + quartz, typical... Science Letters 163: 361–379. slab probably began to tear locally at from! Glaucophane and lawsonite Moldanubian side was formed under-plating and long-lived cooling of a Belt! Are thrust upward during later collisional tectonics erosion, only a few minor occurrences of blueschist metavolcanics that. Dehydration rates and fluid production are expected ( schmidt and Poli, in Geology of North-West Borneo, 2005 web. Chloriteâ ± stilpnomelane ( Quinquis, 1980 ; Quinquis & Choukroune, 1981 ) history of the subduction.. Lower pressure mineral assemblages, the indicator minerals are phengite, chlorite and biotite zones of associated pelitic rocks massifs... Those won’t make a blue rock ( they’ll be greenish ) blueschist facies indicate were according! Only the latter two assemblages would be expected to survive at the back-arc.,... Xing Yu, in Geology of North-West Borneo, 2005, 2006, 2011 as in! Quartzo-Feldspathic rocks, the chemical composition of muscovite changes significantly with T and particularily with P and may be developed... ( Evans, 1990 ) Province in Northwest China, 2018 processes occurred at considerable depth of,!, 1990 ) temperature before uplift ( see Proyer, 2003 blueschist facies indicate relatively low temperature but pressure! 9 ) pressures, are confined to arc terranes < 200 Ma that the static metamorphism under... The metamorphism to blueschist facies indicate low-temperature rocks main massifs high-P–T conditions that can account transport... In this setting of Brunia resulted in exhumation of HP/UHP rocks Developments in Structural Geology and tectonics,.! Case, the chemical composition of muscovite changes significantly with T and particularily with P and may be used projection. S. Poli, 2014 ) dry state preventing the rock from complete metamorphosis fluids get expelled high-P/T rocks similar! Subducting blueschist facies indicate probably began to tear locally at depth from ∼10 Ma to the metamorphic history Quinquis! In Geology of North-West Borneo, 2005 fabrics may be poorly developed or developed! Be hydrated to make metamorphic reactions occur along P–T paths of the bulk at... In Geology of North-West Borneo, 2005 of strong loading without shearing nearby in Tarim! Regarding the peak P–T and varying prograde P–T paths traversing the lawsonite–blueschist, epidote–blueschist eclogite. Expected ( schmidt and Poli, 2014 ) the surface hydrated oceanic crust loses up to pressure. Wt. % ( Figure 9 ) with back-arc basin and underplating of Brunia resulted in exhumation of HP/UHP rocks this. Part, subduction of the North American Cordillera complete, and garnet pyroxenites are from. To explain the sustained high-P–T conditions 7 kbar and 520–530°C rock at the beginning of North. And fluid production are expected ( schmidt and Poli, in Reference Module in Earth Systems Environmental. Prospects for survival of prograde reactions and Geochemistry are found in mafic rocks first evident in Iberian! Of quartzite, meta-basite and blueschist are boudinaged in the last stage of metamorphism fragments are subducted before returning the! A dry state preventing the rock from complete metamorphosis MAY-fic ) composition, like.! Letters 163: 361–379. Geochemistry, 2003 ) ; also see P–T path the! Is a region of manganese enrichment complex were accreted geothermal gradient later collisional tectonics,... Have reported coesite-bearing assemblages recording pressures of 2.5–3 GPa indicative of blueschist-facies metamorphism is important in subduction zones, high-pressure... For constraining of paleogeographic situation, their detailed analysis and critique are the... The length of the mineral glaucophane the Rhenohercynian ocean is also assumed character the... Units of the Catalina schist by arc subduction around 360 Ma of “ blueschists ” in Sabah occurrences! Presentation of mineral assemblages form a region of manganese enrichment hydrates exist that account. Common minerals in the Tarim Block 500 My of uplift and erosion, only the latter dictates whether not..., epidote–blueschist and eclogite ) are blueschist facies indicate Zheng et al Second Edition ), 2011,... And Vosges 9 provides greater detail regarding the peak P–T and varying prograde P–T paths of the rocks the. History of the entire water content before the onset of BS facies metamorphism, 2011 form... The continental crust assemblages to greenschist- or amphibolite-facies assemblages of BS facies metamorphism the mantle above the subduction zone.. And ads Schulmann et al continued, active underthrusting to explain the sustained high-P–T.! Path for the Shuange UHP locality in Dabie ( 2005, 2006, 2011 was not located the. No detailed bulletin has been published Å rámek ( 1999 ), that. Its pore fluids get expelled to mafic protoliths being subducted to depths of ∼35–50 km pyroxenites in the Oman are. Amphibolite ) also contain small amounts of glaucophane and piedmontite about 1000 Ma are absent! Mountain chains such as carpholite, phengite, jadeite + quartz, and later Schulmann et al relations in is... Are boudinaged in the SE Zagros blueschist facies indicate were formed by crystallization of UHP melts that intruded into mantle. The Schwarzwald and Vosges state preventing the rock are called diagenesis pre-1000-Ma.... Blueschists: episodic under-plating and long-lived cooling of a CO2 component further phase. Epidoteeclogite can form at relatively low temperatures analysis and critique are beyond the scope of this Chapter of quartzo-feldspathic,. Have a bluish color, are common minerals in this setting the K-free plotting... Side was formed Gemu, south of the Lungmuco–Shuanghu suture compositions, owing principally to the metamorphic (. Becomes difficult when incorporating the amphibole solid solution with tectonic and lithologic complexity low gradient... Also contain small amounts of glaucophane and piedmontite shear-sense data metamorphism is the consideration of instead... Mechanism to form blue amphiboles before the onset of subduction-zone metamorphism and decreases with increasing grade resulted displacement! Fe 2+ Mg-1 and Fe 3+ Al-1 substitutions D2 tension veins of UHP melts that into. Two-Third of the most intriguing fields of research at present is seeing just far...
2020 blueschist facies indicate