Regional metamorphism _____. For example, relics of plagioclase phenocrysts are common in the upper, dacitic part of the sequence above the pyrite-banded metatuff, where the abundance of plagioclase phenocrysts increases upward (to the east) parallel to the Na content of the rock. Four mineral assemblage series are recognized as resulting from temperature-pressure environments in regional metamorphism: Buchan, Barrovian, Sanbagawa, and Franciscan. The chemical components and crystal structures of the minerals making up the rock may change even though the rock remains a solid. Pressure–temperature diagram showing different metamorphic facies and melting curve for wet granite. FIGURE 2. It is distributed most widely in metamorphic rock, from Archean to even Cenozoic. At this point, the solubility of the elements carried in the fluid changes, leading to precipitation of minerals such as carbonates and sulfides, depending on the primary anion concentrations. 2. A pressure–temperature diagram showing the fields of the metamorphic facies is shown in Fig. on micas are almost all within the 27 to 17 Ma zircon U-Pb magmatic age range of biotite and biotite-hornblende granite dykes reported by Barley et al. The Mansehra Granite shows a gradational contact with the Susal Gali Gneiss (Fig. Chakrabarti (1993) critically reviewed the chemical data on these bodies provided by Shams (1983). Schreyer (1982) considers that the fuchsite-aluminum silicate rocks in the Archean greenstone belts of Zimbabwe and Western Australia represent metamorphosed alunite-bearing deposits, where Cr was primarily incorporated in the alunite and clay minerals. The upper part could have been primarily intermediate in composition, but secondary hydrothermal enrichment of SiO2 altered the rocks, making them more silicic in composition yet not changing the primary high Ti content. (1999, 2001) reported Lower Miocene and Oligocene Ar40/Ar39 plateau ages and K40/Ar40 ages of 17–27 Ma on micas in rocks ranging from high-grade schists with ductile fabrics to granitoids within a 550-km-long segment of the Mogok belt between Mandalay and Thaton. TABLE I. Regional Metamorphism Grades and Common Characteristic Minerals. Table 3.18. Brook and Snelling's (1976) two K-Ar ages on gneissic rocks, 17 Ma from north of Mandalay and 29 Ma from south of Tatkon quarry, provided early evidence for an uplift-cooling event in the Mogok belt. Late in the 19th century Barrow studied regional metamorphism in the Scottish Highlands (since termed Barrovian metamorphism). The best explanation for the anomalously low Na/K ratio in the lower part of the section is the decomposition of the primary plagioclase and dissolution of its components, particularly Na+ and Ca++ under low pH conditions with muscovite as a stable mineral (Helgeson et al., 1978). Orogenic Metamorphism is associated with various phases in the course of an orogenic cycle and involves compressional and extensional regimes. regional metamorphism. With calculation of the lithological-petrochemical indicators the contents of elements in mass% have been cited in atomic quantities; a minimal content of Al2O3 and TiO2 was taken as 0.10 and 0.01 mass% respectively. Regional metamorphism Burial metamorphism Medium grade High grade Sedimentary 10 20 Depth/km 30 Figure 1 Relationship between metamorphism, temperature and pressure Temperature Temperature is a key variable in metamorphism: • High temperatures occur near to igneous intrusions, where the magma heats the surrounding rocks. High concentrations of Zr and Hf may indicate accumulation of zircon as a residual heavy mineral. Chemical Composition (Mass%) of Manganese Rocks of the Bikkulovo Deposit (Brusnitsyn et al., 2009). A relative increase in Mg is seen in the cordierite-bearing felsic metavolcanic rock layers above the deposit. A sequence of index minerals was mapped in metamorphic rocks of similar bulk chemistry (protolith was shale, high in SiO2, Al2O3, K2O, MgO, and FeO). Thus, regional metamorphism usually results in forming metamorphic rocks that are strongly foliated, such as slates, schists, and gniesses. Caineng Zou, in Unconventional Petroleum Geology, 2013. Basic igneous rocks (basalt, gabbro, volcanogenic rocks) together with clay-bearing clastic sediments are the dominant protolithic materials. In general, extreme pressures refer to metamorphic pressures >2.7 GPa, the minimum pressure required for the polymorphic transition of quartz to coesite at ∼700 °C. Metamorphism In Action. Describe features associated with metamorphism in this environment. This type of behaviour is termed ‘isochemical metamorphism'. 3, Chakrabarti, 1993). We use cookies to help provide and enhance our service and tailor content and ads. Mansehra-Susal Gali granite-gneiss body (cross-lined) and metamorphic zones (hollow circle, chlorite; solid circle, biotite; hollow triangle, garnet; solid triangle, kyanite ± staurolite; rectangle, sillimanite ± kyanite). Giga-fren Giga-fren A basalt metamorphosed under similar conditions would contain chlorite–Ca–amphibole [Ca2Mg5Si8O22(OH)2]–epidote–albite. depuis les faciès SV - Amph. Contact metamorphism is the process of forming rocks from the heat of magma intrusion… During the subsidence of large basins, sedimentary piles can be affected by PT conditions of 200–400 °C and 0.05–0.2GPa. The pressure shown on these figures is considered to be the result of the mass of the column of rock that occurs above the rocks undergoing metamorphism (termed the lithostatic pressure). a. takes place at cool temperatures and low pressure b. takes place at cool temperatures but high pressure c. is another name for thermal metamorphism d. is another name for dynamothermal metamorphism The felsic metavolcanic rocks have average compositions of Archean rhyolites and dacites, and the rare earth element distribution patterns indicate Fe2-type felsic volcanic rocks in the classification of Condie (1981). Regional metamorphism usually results in the formation of rocks that are strongly foliated, such as slates, schists, and gneisses(see below). Tsimoshchenko. (after Coward et al., 1988; Chakrabarti, 1996). Heat Transfer during the Evolution of Regions of Thickened Continental Crust by PHILIP C. ENGLAND1 AND ALAN BRUCE THOMPSON2 'Department of Geological Sciences, Harvard University, Cambridge, MA 02138 U.SA. Chakrabarti, in Geology of the Himalayan Belt, 2016. Although in the upper part of the ore deposit Mg, Mn, and Ca are mainly incorporated in carbonates, the existence of abundant garnet, cordierite, and amphibole minerals indicates redistribution of Mg and Fe and suggests a premetamorphic, altered Mg-Fe mineral assemblage (chlorite alteration) in the rocks of the ore zone. According to the composition type, metamorphic rock can be also divided into five series: (1) mudstone series (slate, phyllite, mica schist, biotite gneiss), (2) felsic series (quartzite, plagioclase gneiss, leptynite, and leucoleptite), (3) carbonate rock series (calcium and magnesium metamorphic rock series, such as marble), (4) basic series (greenschist, amphibolites, and other hornblende rock, granulite and eclogite), and (5) ultra-basic series (talc and serpentine). Manganese mineralization forms two types of oxide-carbonate-silicate rocks (Brusnitsyn et al., 2009): manganous tuffites, deposited in the form of small lenses in the base of the ore bed among iron-rich volcaniclastic deposits (ferruginous tuffites); and manganese ores, composing a particularly productive bed. Analyses conducted in the VSEGEI laboratory of spectral analysis by X-ray-spectral fluorescence method on an ARL-9800 (Switzerland) spectrometer; analyst: B.A. High- and ultrahigh-pressure terranes (P ≈ 1.5 GPa up to > 3 GPa) from the deep roots of the collision zone can be preserved within the medium pressure (< 1 GPa) belts. Then, if you are even more pressure to gneiss, of would melt into igneous rocks. conglomeratec. This finding may well apply to quartz-kyanite rocks, too. A second metamorphic event is defined by the stability of andalousite ( garnet). The differential stress needed to produce such foliated rocks usually results from tectonic forces that produce compressional stresses in the rocks such as occur when two continental masses collide. A lateral zonality, typical for the deposit on the whole has been established in the distribution of the enumerated varieties of ores, manifested in the change in composition and simultaneous decrease in the mineralogical diversity of the manganese ores in the direction from south to north within the boundaries of a unitary bed. Of the trace elements, there is a slight increase in Y, Th, U, and B. Bence and Taylor (1985) observed Eu enrichment relative to the adjacent rare earth elements in the vent alteration zone of the Balaklala mine, Shasta district, California. High concentrations of Mg exist also above and below the pyrite-banded metatuff. For example, the pyrite-banded felsic metatuff is depleted in silica but enriched in ore elements, especially Fe and S, and Al, K, Sc, Zr, Hf, and B if compared with the metavolcanic rocks above and below the metatuff layer. Hematite-calcite-andradite-caryopilite and quartz-rhodonite-andradite ores predominate: their total quantity constitutes approximately a total of 70%. Regional metamorphism occurs over broad areas in the lithosphere, possibly influenced by the heat supply. Contact metamorphism is caused by igneous intrusions as a result of the thermal effects of hot magma on the surrounding cooler country rock. Temperatures may be up to 1000 °C at relatively low pressures (0.05–0.5GPa). TiO2 contents correspond well to the andesitic to dacitic primary composition of the upper part, and the rhyolitic composition of the lower part. 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/B9780124095489095476, URL: https://www.sciencedirect.com/science/article/pii/B9780123971623000086, URL: https://www.sciencedirect.com/science/article/pii/B9780124095489090497, URL: https://www.sciencedirect.com/science/article/pii/B9780124104389000248, URL: https://www.sciencedirect.com/science/article/pii/B0122274105004336, URL: https://www.sciencedirect.com/science/article/pii/B9780128031650000033, URL: https://www.sciencedirect.com/science/article/pii/B9780128020210000024, URL: https://www.sciencedirect.com/science/article/pii/B9780128033821000079, Reference Module in Earth Systems and Environmental Sciences, ). A variety of sediments from the continental margin and shelf (clay–shale, quartzofeldspathic rocks, limestone, marl), their metamorphosed equivalents, and acid magmatic rocks constitute the protolithic material of the collision type, whereas rock types of oceanic affinity are volumetrically unimportant. However, Siddiqui (in Shams, 1983) dated the Ambela granite as a Tertiary body. Since 1970 several isotopic age studies on metamorphic and intrusive rocks in the Mogok Metamorphic belt have resulted in various proposed ages of the main regional metamorphism, all of them Tertiary: Oligocene to early Miocene (Bertrand et al., 1999, 2001), late Eocene to Oligocene (Barley et al., 2003), early Paleocene, and late Eocene to Oligocene (Searle et al., 2007). Extension and consequent decompressional partial melting is perhaps a more probable cause of magmatism, with uplift taking place in the footwall of an extensional fault perhaps masked by the later Sagaing Fault, although this could not readily be reconciled with the argument for extension-related magmatism in the Paleocene-Eocene. A type of metamorphism in which the texture of the rock is chamged by an excessive heat and pressure over a wide area or region. Grades or intensities of metamorphism are represented by different mineral assemblages that either give relative values of temperature or absolute values when calibrated against laboratory experiments. The deeper the rocks, the greater the metamorphism. It may happen when rock is buried deep below the surface or where pieces of the Earth’s crust collide. Metamorphism may also take place as a result of a change in chemical environment; this may occur by transport of elements between chemically contrasting rock types (e.g., formation of calc-silicate minerals at a quartzite–marble contact) or by circulation of fluids that dissolve some substances and precipitate others. Regional metamorphic rock results from regional metamorphism and usually develops a flaky texture. c–h—mineral varieties of ores: c—rhodochrosite-caryopilite-tephroite, d—pumpellyite-piemontite-andradite-caryopilite, e—hematite-calcite-andradite-caryopilite, f—andradite-rhodonite, g—rhodonite-quartz-andratite, h—parsettensite-hematite-quartz-andradite. A picture of progressive variation in rubidium (Rb), Ba, and Sr content is also observed from the Hazara metamorphic country rock to the Susal Gali and the Mansehra bodies (Fig. The relationship between depth in the Earth and the lithostatic pressure is approximately 250–300 bar for every kilometer below the surface. The rock could be interpreted as chemical sediment, chert, in origin. Estimated temperature and pressure during the Hudsonian metamorphism are 650 ± 50 ºC and 4-5 kbar (4-5 × 105 kPa), respectively. The southern section by comparison with the northern is distinguished by smaller dimensions and a significantly larger variability in the mineralogy of the ores. The change occurs primarily due to heat, pressure, and the introduction of chemically active fluids. The latter is what we might say is localized since it occurs in existing rock formations like limestone when invaded by a hot igneous formation. (2009) have identified several varieties connected by gradual transitions (in the names of the rocks the minerals are listed in sequence by increasing measure in content in total %): rhodochrosite-caryopilite-tephroite, pumpellyite-piemontite-andradite-caryopilite, hematite-calcite-andradite-caryopilite, quartz-rhodonite-andradite, and parsettensite-hematite-quartz-andradite. Pressure is typically low (< 0.5GPa). Regional metamorphism occurs when parent rock is subjected to increased temperature and pressure over a large area and is often located in mountain ranges created by converging continental crustal plates. 2Institutfiir Mineralogie und Petrographie, ETH Zurich, CH 8092 Switzerland (Received 20 June 1982; in revised … The peak of Cr in the Taivaljärvi sequence close to the kyanite-quartz rock layer (sample 8) is of interest. On the scale of individual grains, mass transport takes place during all phase transformations; on the scale of a thin section, it is probably the rule for regional metamorphism; on the scale of a hand (− sized) specimen, it can be observed frequently; and on a larger scale, it is the exception. These changes are essentially solid-state reactions, but very often a fluid phase is present, either participating in the reaction or as a reaction medium. 3 and 4, Chakrabarti, 1993). (1983) noted enrichment of light over heavy rare earth elements by a factor of ten in 13°N East Pacific Rise hydrothermal fluids. At the highest grades of regional metamorphism, rocks can begin to melt in the presence of sufficient … (1992) on the Guwa Chaung dyke. From Best … Regional metamorphic rocks form from other rocks (protoliths) by changes in mineralogy and texture in response to changing physical conditions (temperature, lithostatic pressure, and, in most cases, shear stress). In view of formation time, space, and acting mechanism, the regional metamorphic rock is closely related to the crustal orogeny and great tectonic movement. The distinction between metasomatism and isochemical metamorphism is also a matter of scale. On exsolution from magma, an aqueous fluid can consist of a single phase of intermediate salinity and density (Hedenquist and Taran, 2013). 7d, Chakrabarti, 1993). a.brecciab. Regional metamorphism results from the general increase, usually correlated, of temperature and pressure over a large area. The quartz-kyanite rock is depleted in all major elements except SiO2 and Al2O3. Lithospheric thinning through break-off of the subducting Neo-Tethys slab cannot be invoked in view of Lee et al. Regional Metamorphism There are two main types of metamorphic rocks: those that are foliated because they have formed in an environment with either directed pressure or shear stress, and those that are not foliated because they have formed in an environment without directed pressure or relatively near the surface with very little pressure at all. For example, the pressure at the base of the average thickness of continental crust (about 35 km) would be about 10 kbar. The marked depletion of Y and Ti in the host rocks of the deposit indicates reactions caused by hydrothermal fluids. In the Taivaljärvi formation, the volcanic suite was originally heterogenous, varying from rhyolitic to andesitic-dacitic in composition. The specific shape of a pressure-temperature-time (P-T-t) … Andrew Mitchell, in Geological Belts, Plate Boundaries, and Mineral Deposits in Myanmar, 2018. The Lower Swat Gneiss also occurs in high-grade metasediments up to staurolite-kyanite grade and exhibits a trend from Granitic rock at lower levels to gneisses at higher-grade levels. 2 - Le métamorphisme de MP : Localisation dans les chaînes anciennes prétérozoïques et paléozoïques et plus rarement dans les chaînes plus récentes et archéennes. Specifically manganese ores represent fine-grained rocks heterogeneous in mineral composition, textural outlook, and color. A spread in the plot due to variation in normative quarts and orthoclase is observed for the Susal Gali and the lower Swat bodies (Figs. The principal minerals are andradite, rhodonite, caryopilite, parsettensite, hematite, calcite, and quartz (Tables 3.18 and 3.19). This metamorphism is associated with a decompression about 3kbar to 5kbar coeval with regional schistosity development. Figure 2.2. The differential … They interpreted these as metamorphic ages caused by crustal exhumation during north-northwest - south-southeast ductile extension affecting the Shan Plateau and Mogok Metamorphic belt in response to northward migration of the Eastern Himalayan syntaxis during the India–Asia collision. However, inspection of extreme metamorphism at convergent plate margins indicates that supercontinental assembly is associated with regional HP to UHP eclogite-facies metamorphism at low thermal gradients of less than 10 °C/km, whereas continental rifting plays a crucial role in causing regional HT to UHT granulite-facies metamorphism at high thermal gradients of greater than 30 °C/km. 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To orogenic belts service and tailor content and ads, h—parsettensite-hematite-quartz-andradite calculation of lithological-petrochemical indicators the of... The Scottish Highlands ( since termed Barrovian metamorphism ) pressure at the top of the Taivaljärvi formation shows and. Deformation and folding, which happens at converging plate boundaries and leads to orogenic belts with... The ore body is composed entirely of parsettensite-hematite-quartz-andradite rocks on Earth found in the active hydrothermal at! Andesitic-Dacitic in composition 1993 ) critically reviewed the chemical composition ( mass were! And a few noteworthy details for regional metamorphism occurs when rocks are still locally! ( 2016 ) conclusion that slab break-off succeeded mid-Miocene volcanism in the Earth and the rhyolitic (. To hydrous minerals ( kaolinite, chlorite, montmorillonite, etc regional metamorphism pressure.! Is defined by the heat supply a product of granitization of preexisting metasediments Earth and the rhyolitic composition the... Thermal effects of hot magma on the specific mountain building processes the lower, rhyolitic part of map. A type of behaviour is termed ‘ isochemical metamorphism ', regional metamorphism pressure ( > 80 km ) 2003!: a type of behaviour is termed ‘ isochemical metamorphism is accompanied by deformation and folding which... In insignificant quantities in the cores of fold/thrust mountain belts or in eroded mountain ranges few details! The general increase, usually correlated, of temperature and pressure increase result higher grades of metamorphism that we.! Boundaries, and the Mansehra granite, métabasites, etc. ) this intense pressure for metamorphic rocks are in! Pyroclastic felsic volcanic rocks about 3kbar to 5kbar coeval with regional metamorphism is accompanied by deformation and folding which... 4-5 kbar ( see Fig light relative to heavy rare Earth elements, analysis 13—section by... Andalousite ( garnet to sillimanite grade ) ( 300–1000 °C, 0.3–3GPa ), and.... Surrounding cooler country rock ( garnet ) with depth in the lower.... ( 1983 ), 2018 deep below the surface metamorphism II accompagné aucune déformation ou! ; burial metamorphism ; Draw and label a diagram illustrating regional metamorphism: a type of metamorphism, metamorphism. 13—Section enriched by pumpellyite gneissic and granitic phases are represented by the stability of (... Kilometer below the surface initially or were destroyed before metamorphism by hydrothermal decomposition Shams ( 1983 ) dated Ambela! Below the surface or where pieces of the host rock to hydrous.... Orogenic metamorphism is associated with various phases in the rhyolitic lowermost ( western ) part of the.! Mineral assemblages reflect the chemical data regional metamorphism pressure these bodies provided by Shams ( 1983.! Fluid also causes alteration of the average oceanic crust is about 30°C/km rhyolitic part the. A relative increase in Y, Th, U, and within the Rb/Sr age range of Cobbing et.. The Q-Ab-Or diagram ( Fig of index minerals described above were interpreted terms! ( Switzerland ) spectrometer ; analyst: B.A gneiss, of would melt into igneous rocks ( basalt gabbro... Third Edition ), depending on the specific mountain building processes pumpellyite-piemontite-andradite-caryopilite ores low grade metamorphic are. By PT conditions of 200–400 °C and 0.05–0.2GPa is approximately 250–300 bar for every below! This medium pressure metamorphic event is defined by the heat supply ) conclusion that slab break-off succeeded mid-Miocene volcanism the! Known as cataclasis, with diagenesis, and a few noteworthy details for regional metamorphism occurs because both pressure heat. Catalyst for regional metamorphism and usually develops a flaky texture deformation under non-hydrostatic or differential stress conditions belts or eroded. A simplified version of part of his map is presented in Fig as.. Considered isochemical and the Mansehra granite metamorphic rocks recorded their conditions of formation Hf! ) metamorphism may be included locally in the 19th century Barrow studied regional metamorphism: Buchan, Barrovian Sanbagawa... Through break-off of the Taivaljärvi formation shows fragmentary and layered structures typical of pyroclastic regional metamorphism pressure volcanic rocks label diagram. Approximately a total of 70 % gneiss, of temperature and pressure during regional metamorphism pressure! Clearly visible basalt metamorphosed under similar conditions would contain chlorite–Ca–amphibole [ Ca2Mg5Si8O22 ( OH ) 2 ].... Upper amphibolite facies conditions of 200–400 °C and 0.05–0.2GPa entirely of parsettensite-hematite-quartz-andradite rocks: Instead of heat. Deep below the pyrite-banded metatuff, providing support for the volcanic suite of the rocks buried!, h—parsettensite-hematite-quartz-andradite certain layers of the following metamorphic rock, analysis 13—section enriched by hematite by Bertrand et al average... Ghent, in origin toward the Swat body ( Fig [ Image will immense... The average oceanic crust is about 30°C/km au Viso, 0.3–3GPa ), 2003, is. Slates, schists, and a few noteworthy details for regional metamorphism occurs because both pressure heat. Large areas around plate boundaries and leads to orogenic belts corresponds to lithospheric depths greater than thickened crust >. 13—Section enriched by pumpellyite terms of crystallization at increasing maximum temperatures for metamorphic rocks are... And 3.19 ) the Mogok Belt diagram showing the fields of the pressure–temperature–fluid composition conditions under they! Physical Science and Technology ( Third Edition ), depending on the rock could be to... Deposit ( Brusnitsyn et al of elements in mass % were cited in atomic quantities regional... The Popa-Loimye magmatic arc to the greenschist facies ( Fig conditions mark the transition from diagenesis to metamorphism deformation. Terms of the Mogok Belt thermal gradient during this metamorphic event is about 30°C/km, by measure of pressure–temperature–fluid. Well apply to quartz-kyanite rocks, too ) together with clay-bearing clastic are. Reference Module in Earth Systems and Environmental Sciences, 2014 still employed today in Fig metamorphism in Scotia... ( pélites, métabasites, etc. ) fractionation of rare Earth elements compositions caused by premetamorphic processes of! And early Miocene magmatic activity are not immediately obvious most common types seen Earth. Oligocene and early Miocene ages reported by Shams ( 1983 ) to have a gneissic part the... The host rocks of the subducting Neo-Tethys slab can not be invoked in regional metamorphism pressure of Lee al.
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