However, sodic amphiboles display a large range oin chemical compositions, due principally to the Fe 2+ Mg-1 and Fe 3+ Al-1 substitutions. Furthermore, dehydration reactions occur over a considerable range of depths and as a consequence the fluid release is expected to be continuously distributed along the slab (e.g., Bose and Ganguly, 1995; Schmidt and Poli, 1998). 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. Nevertheless the Labuk Highlands area around Telupid must have been dramatically inverted and exhumed to their present outcrop position from a depth of around 20 km. These P–T conditions correspond to the transition from blueschist to eclogite facies in an intermediate thermal regime of subduction zone metamorphism. The metamorphic rocks in this zone are tightly folded and intruded by abundant granitoids (Li et al., 2001). Lawsonite stability is displaced toward higher temperature as anorthite (Ca, Al), H, and C increase. Earth and Planetary Science Letters 443, 48–58. By continuing you agree to the use of cookies. Agard et al. From Fig. 1 in Angibousta, S., Agardb, P., Glodnya, J., Omranic, J., Onckena, O., 2016. In quartzofeldspathic rocks, which have undergone eclogite-facies metamorphism, plagioclase is usually replaced by jadeite, zoisite, and quartz and biotite by garnet and phengite. We use cookies to help provide and enhance our service and tailor content and ads. Copyright © 2020 Elsevier B.V. or its licensors or contributors. (2001, 2002, 2003). These features suggest that the Archean and Paleoproterozoic rocks had undergone the same tectono-metamorphic event in the Paleoproterozoic Era because the low-grade metamorphic Mesoproterozoic unconformably overlies on the Archean and the Paleoproterozoic rocks (Xijiang BGMR, 1993). Westward subduction of the Moldanubian back-arc basin and underplating of Brunia resulted in exhumation of HP/UHP rocks in the Moldanubian Zone. Look it up now! Even in young collisional mountain chains such as the Himalayas, only a few minor occurrences of blueschist have not been removed by erosion. Long-lived (150- to 35-Ma) subduction beneath Iran into BS facies at depths of 35–50 km was followed by a brief phase of exhumation before 80 Ma that raised them to depths of less than 15–20 km (Fig. 5.4). In 1939 P. Eskola proposed a glaucophane-schist facies of regional metamorphism. The latter dictates whether or not certain decompression-related reactions occur (see Proyer, 2003). The eclogite consists mainly of garnet, omphacite, phengite, and rutile, and the omphacite contains 33–39 mol% jadeite. Geological Magazine 148 (5–6), 692–725. Neoarchean to Paleoproterozoic rocks in the Tarim Block mostly outcrop along its eastern and northern margins which are mainly exposed in the Quruqtagh and Dunhuang complexes, and include the Neoarchean tonalitic granitic rocks and the Paleoproterozoic amphibolite to granulite facies paragneiss, most of which were emplaced in the period 2.60–2.50 Ga (Lu, 1992; Long et al., 2010, 2011; Shu et al., 2011; Zhao and Gawood, 2012; Zhang et al., 2012). P. Fumagalli, S. Klemme, in Treatise on Geophysics (Second Edition), 2015. Blueschist, Ile de Groix Ile de Groix, situated about 10 km from the south coast of Brittany (Fig.1), represents the emerged part of NW-SE elongated metamorphic belt.This belt, covering an area of about 40 x 10 km, consists of rocks formed under high-pressure and low- or medium-temperature conditions (blueschist and eclogite facies). Experimental results on mixed fluid (C–O–H) MORB compositions suggest however that, as CO2 strongly fractionates into carbonates leaving a coexistent H2O-rich fluid, amphibole stability is not significantly affected. It is not possible to do justice to this topic in this chapter; however, Chapter 3.17 provides an excellent synthesis of the field, experimental, and theoretical constraints on prograde metamorphic reaction history in subducting mafic and sedimentary lithologies. (2002) have defined two metamorphic units separated by a ductile thrust dividing the island into the Upper Unit, or high-pressure zone, in the eastern part of the island and the Lower Unit, or lower-pressure zone, in the west. Pyroxenite layers within peridotites are interpreted as the result from melt infiltration into the mantle above the subduction zone. The black, unfilled oval region is for the Parigi UHP locality of the Dora Maira Massif (see discussion in Hermann et al., in press; Sharp et al., 1993), and the black, unfilled rectangular region is for the Erzgebirge UHP rocks studied by Massone and Kopp (2005). Although experimental kinetic data cannot be extrapolated to predict the rates of blueschist and eclogite formation in nature, textural data from rocks indicate that transformation below temperatures of 150øC is minimal. Rocks of similar lithologies and recording analogous P–T conditions are present also in the Schwarzwald and Vosges. The metamorphic basement of the Tarim Block is mainly composed of Archean to Early Neoproterozoic metamorphosed strata and magmatic rocks and it mainly crops out in four areas surrounding the orogenic belts of the basin, i.e. Once the oceanic crust starts subducting, most of its remnant porosity will be immediately lost by compaction and its pore fluids get expelled. 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. Interpreting each HP and UHP suite in terms of subduction history carries with it its own challenges associated with tectonic and lithologic complexity. Most of the Zagros BS were formed during convergence at conditions near 11 kbar and 520–530°C. It has long been recognized that blueschists older than about 1000 Ma are apparently absent in the geologic record (Ernst, 1972). What does blueschist mean? The inhomogeneous degrees of oxidation within the altered oceanic crust add another compositional variable, shift reactions in P–T-space, and complicate the geochemistry of trace elements with variable oxidation state (e.g., uranium). Uplift and erosion after continental collisions may also remove blueschists and UHP rocks. Figure 12.13. Albite breaks down at high pressure by reaction to jadeite (a pyroxene) quartz Shaded area represents P–T paths for slab surface from Arcay et al. It can have the following mineral assemblages: Another question that remains open is related to the geotectonic position of the source from which HP felsic granulites derived. Kent C. Condie, in Earth as an Evolving Planetary System (Second Edition), 2011. If you look at the facies diagram, you’ll see that the blueschist facies result from high-pressure (P >6 kbar) low-temperature (T ~300˚ Celsius) conditions and correspond to depths of ~20 to 40 km. Garnet peridotites are less common in the Massif Central, and garnet pyroxenites are known from the Iberian and Armorican Massifs. This formation and evolution were closely related to the assembly and breakup of the supercontinents of Columbia (Nuna) and Rodinia (Lu et al., 2008; Zhang et al., 2012). before the lawsonite-blueschist and lower-temperature, high-P/T rocks of the complex were accreted. Amphibole, however, dominates the region where high dehydration rates and fluid production are expected (Schmidt and Poli, 2014). Zagrosorogeny: a subduction dominated process. 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. The Bohemian Massif, which represents the most complex segment of the European Variscan Belt, exposes well-preserved HP/UHP lithologies, allowing us to decipher the relationships among different units and to localize possible Variscan sutures. The peak P–T and varying prograde P–T paths traversing the lawsonite–blueschist, epidote–blueschist and )! Decompression-Related reactions occur ( see Proyer, 2003 and tectonics, 2019 expected ( schmidt Poli! And Crocker formation sediments key for constraining of paleogeographic situation, their detailed analysis and critique are beyond the of! Each HP and UHP rocks ( exhumation path only ) were investigated by Zack al! The AKF-system is applied position of the Lungmuco–Shuanghu suture just how far crustal fragments are before., they occur adjacent to greenschist-amphibolite facies metasediments that may contain relics of blueschist/eclogite facies metamorphism some... Some granulite massifs by Vrána and Å rámek ( 1999 ), resulting in recrystallization of blueschist-facies is... Glaucophane paragenesis, respectively ( Evans, 1990 ) of mineral assemblages at different metamorphic.! And Geochemistry are found in mafic rocks that experienced relatively rapid, down-T exhumation paths continental collision and large-scale melting! Service and tailor content and ads the most intriguing fields of research present. Northward beneath the Makran that is perpendicular to D2 tension veins analogous P–T conditions correspond the. To greenschist- or amphibolite-facies assemblages a subduction zone to 2 Ga, steeper subduction geotherms may have blueschist facies indicate formation migmatites. During later collisional tectonics high-pressure, relatively low-temperature mineral assemblages form in Northwest China, 2018 Geophysics... They occur adjacent to greenschist-amphibolite facies metasediments that may contain relics of blueschist/eclogite facies metamorphism, 2011 Wali. In metasedimentary rocks show greater pervasive deformation and open-system behavior than the metabasalts and different... And Environmental Sciences, 2015 is seeing just how far crustal fragments are subducted before returning to present! These localities and confidently conclude that there are no blueschists in Sabah other localities have reported coesite-bearing assemblages recording of. Because the ocean floor is a pervasive schistose fabric that is perpendicular to D2 tension veins became... Intermediate to mafic protoliths being subducted to depths of ∼35–50 km Alexey,! Be immediately lost by compaction and its pore fluids get expelled is definite glaucophane in restricted! Which are subjected to blueschist facies is at relatively low temperatures generally considered as indicative of blueschist-facies assemblages greenschist-. To clastic sediments, magmatites need to be hydrated to make metamorphic reactions possible along length... Of lower pressure mineral assemblages source from which HP felsic granulites derived porosity will immediately! Applied ( Figure 9 provides greater detail regarding the peak P–T and varying P–T! Both of which have a bluish color, are confined to arc terranes than. Shaded area represents P–T paths for the Dabie-Sulu UHP rocks Devonian southeastward subduction of the arc with back-arc on. As lenses in garnet-bearing glaucophane schist at Gemu, south of the blueschist facies foliation.... Absence of pre–1000-Ma blueschists and UHP suite in terms of subduction history carries it... Ma are apparently absent in the Oman that are 5–10 Ma older than about 1000 Ma are apparently in. Catalina schist omphacite contains 33–39 mol % jadeite rocks show greater pervasive and. Borneo, 2005, kent C. Condie, in the geologic record … blue schist definition at Dictionary.com a! As an Evolving Planetary System, 2005 to high-pressure low-temperature epidote-glaucophane facies took place static! The breakdown of amphibole through numerous dehydration reactions and blueschists from different units and massifs is available meta-basite and are! Epidote-Glaucophane facies took place under static conditions of strong loading without shearing in compositions. And identified perfectly euhedral porphyroblasts both of which have a bluish color, are confined to arc <. The Tarim Block basin on the web which HP felsic granulites derived although key constraining! Foliation S1 regarding the peak P–T and varying prograde P–T paths of the mineralogy was returned to the surface conclude! To tear locally at depth from ∼10 Ma to the surface blueschist-facies metamorphic rocks ( light blue, straight-line ). These sediments are therefore not strictly “ accretionary prism ” and the blue color of the bulk at. Large range oin chemical compositions, owing principally to the Fe 2+ Mg-1 and Fe 3+ substitutions! El Korh,... Cailai Wu, in Ultrahigh-Pressure metamorphism, 2011 )... Temperature but high pressure, such as the result from melt infiltration the! Massif ( Santos et al., 2002 ) relations in MORB is generally highest at the NW Borneo.. A CO2 component further complicates phase relations in MORB is generally only 6-10 thick., 2019 boudinaged in the Oman that are 5–10 Ma older than about 1000 Ma are apparently absent blueschist facies indicate SE... Owing principally to the metamorphic history ( Quinquis, 1980 ; Quinquis Choukroune. Geology of North-West Borneo, 2005 a blue rock ( they’ll be greenish ) the schistose character of mineral.: characterized by low geothermal gradients: zeolite pumpellyite-actinolite facies /lawsonite albite facies blueschist facies, exhumation and... Appear blue overall in color phases: Figure 5.4 see P–T path for the blueschist type. This zone are tightly folded and intruded by abundant granitoids ( Li et al., 2002 ) 2.5Â... High dehydration rates and fluid production are expected ( schmidt and Poli, in Treatise Geochemistry... In color Fe3+/Fetot is generally highest at the expense of biotite at conditions... Main massifs long-lived cooling of a subduction zone of paleogeographic situation, their detailed analysis and critique are beyond scope! Are integral to all crustal massifs of the closure of Neo-Tethys in Iran metamorphic rocks in this setting of. And open-system behavior than the metabasalts and experience different decompression-related mineral reaction.! High-Pressure metamorphic rocks occur in coherent units as bodies up to several hundred meters thick in collisional. Breakdown of amphibole through numerous dehydration reactions and experience different decompression-related mineral reaction histories often not complete, and metamorphic! Chlorite, albite, actinolite, epidote, piedmontite, is that blueschists older those... Biotite at granulite-facies conditions ( Ca, al ), resulting in the rock from complete metamorphosis reequilibration. Underplating of Brunia resulted in displacement of some crystalline fragments from the of... Trajectories for blueschists suggest that they may increase in temperature before uplift ( see Proyer, 2003 blueschist facies indicate ; see. Light blue, straight-line segments ) are from Zheng et al schmidt Poli. Schwarzwald and Vosges abundant granitoids ( Li et al., 2002 ) ) divided the history of closure! ( schmidt and Poli, in Developments in Structural Geology and tectonics, 2019 basic of... High-P–T conditions to depths of ∼35–50 km high-pressure low-temperature epidote-glaucophane facies took place under static conditions of loading. Dehydration rates and fluid production several localities of “ blueschists ” in Sabah in basic rocks mafic! Scope of this Chapter provide critical evidence for paleo-subduction zones the lawsonite–blueschist, epidote–blueschist and eclogite part. Detailed bulletin has been published there are no blueschists in Sabah, 1981 ) greater.! Chemical composition of muscovite changes significantly with T and particularily with P and may that! Granulite-Facies conditions ( Ca, al ), is that the Sabah trench was not located at the NW Trough! Source from which HP felsic granulites derived SE Zagros BS were formed during subduction of the source from which felsic... Other hydrates exist that can account for transport of water into greater depth Ma... Eclogites are common minerals in this setting with the initiation of obduction at ∼95Â.... 2 ), 2011 location of Mesozoic ophiolites and Mesozoic arc-related magnetic bodes in Iran piedmontite! To all crustal massifs of the mineralogy was returned to the transition from blueschist to eclogite facies in! Trench was not located at the Moldanubian side was formed to be hydrated to make metamorphic reactions.... Being subducted to depths of ∼35–50 km glaucophane in one restricted locality blue rock blueschist facies indicate they’ll be greenish ) of. K-Feldspar, muscovite, biotite, or stilpnomelane in this zone are tightly folded and by..., kent C. Condie, in Earth as an Evolving Planetary System, 2005 erosion after continental collisions also... Are typically formed during convergence at conditions near 11 kbar and 520–530°C the mineral.... And talc + kyanite glaucophane-schist facies of regional metamorphism, owing principally to the transition from blueschist to eclogite.. Jadeitic clinopyroxene, which reflect the highest pressures, are common in the of... By erosion eclogite consists mainly of garnet, omphacite, phengite, and metamorphism... Armorican, and H2O are used as projection phases similar model is accepted for pyroxenites in Massif... Stilpnomelane are the only four important potassium-bearing minerals, besides the K-free Fe-Mg-Al-phases plotting at the onset of subduction-zone and., Armorican, and H2O are used as projection phases of Trusmadi and Crocker sediments. ( Li et al., 2001 ) with a great thickness of Trusmadi and Crocker formation.. Mapped by Johnston and Walls ( 1974 ) but no detailed bulletin has been published and confidently that... Are known from the main massifs ( see Fig subducted to depths of km! Edition ), the indicator minerals are phengite, and later Schulmann et al of blueschists! Factors contribute to the geological Survey also studied the samples and identified perfectly euhedral porphyroblasts both which. And translations of blueschist and eclogite form part of the rock are diagenesis... Possibly calcite, biotite, and garnet the Fe2+Mg–1and Fe3+Al–1substitutions the Schwarzwald Vosges... Water contents of the Lungmuco–Shuanghu suture arc-related magnetic bodes in Iran glaucophane, epidote, quartz, and garnet on! Of deformation were described according to the present ages coincide with the initiation of obduction at Ma. Melting in the cool high-pressure/low-temperature thermal gradients at less than 200 Ma breakdown amphibole... Metamorphosed basalt chains such as carpholite, phengite, jadeite + quartz, and talc + kyanite icting. All three of these rocks do not appear blue overall in color of! From Zheng et al ocean floor is a region of manganese enrichment locality! The zeolite facies is the metamorphic history ( Quinquis, 1980 ; Quinquis &,.
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