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1
Indares, A., and J. Martignole. "Metamorphic constraints on the tectonic evolution of the allochthonous monocyclic belt of the Grenville Province, western Quebec." Canadian Journal of Earth Sciences 27, no. 3 (March 1, 1990): 371–86. http://dx.doi.org/10.1139/e90-034.
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The tectono-metamorphic evolution of Grenvillian monocyclic terranes in western Quebec has been constrained along a northwest–southeast transect from Réservoir Cabonga to the Morin anorthosite by the study of garnet zoning and the application of geothermobarometric techniques to appropriate mineral assemblages. In all three terrenes examined (Réservoir Cabonga, Mont-Laurier, and Morin terranes), the results are consistent with Grenvillian metamorphism induced by thrusting. Additional magmatic heat may have been provided by the cooling of igneous rocks related to the Morin anorthosite complex.After the peak of the Grenvillian metamorphism, the monocyclic rocks were sliced, and three Grenvillian crustal levels, sharing some of their lithologic elements but having contrasting Grenvillian peak-metamorphic conditions, were subsequently juxtaposed. The deepest crustal level exposed in the transect (level A) comprises the Réservoir Cabonga terrene and the margins of the Mont-Laurier terrene. This level consists of metasediments of the "Grenville Supergroup," garnet amphibolites, and synmetamorphic plutonites whose emplacement predated the thrusting. Metamorphic conditions in level A are estimated at 725–875 MPa and 725–800 °C. Level C, which is exclusively in the central part of the Mont-Laurier terrene, comprises metasediments of the Grenville Supergroup that were metamorphosed at 425–600 MPa and 625–725 °C. Synmetamorphic igneous rocks of the Morin plutonic complex in the Morin terrane were metamorphosed at 600–800 MPa and 650–775 °C, probably in an intermediate crustal level B, which is missing in the Mont-Laurier terrane. It is thus suggested that juxtaposition of the Mont-Laurier terrane and the Morin terrane along the Labelle shear belt occurred after the peak of metamorphism.A comparison of the metamorphic evolution of these monocyclic terranes with that of their adjacent polycyclic counterparts suggests that (i) the Réservoir Cabonga terrane was thrust over the parautochthonous Réservoir Dozois terrane after the peak of metamorphism and (ii) level A rocks of the Mont-Laurier terrane and the Réservoir Baskatong terrane were juxtaposed during the peak of metamorphism.
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Li, Zhen, Hao Wang, Qian Zhang, Meng-Yan Shi, Jun-Sheng Lu, Jia-Hui Liu, and Chun-Ming Wu. "Ultra-High Pressure Metamorphism and Geochronology of Garnet Clinopyroxenite in the Paleozoic Dunhuang Orogenic Belt, Northwestern China." Minerals 11, no. 2 (January 24, 2021): 117. http://dx.doi.org/10.3390/min11020117.
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Ultra-high pressure (UHP) metamorphism is recorded by garnet clinopyroxenite enclaves enclosed in an undeformed, unmetamorphosed granitic pluton, northeastern Paleozoic Dunhuang orogenic belt, northwestern China. The protoliths of the garnet clinopyroxenite might be basic or ultrabasic volcanic rocks. Three to four stages of metamorphic mineral assemblages have been found in the garnet clinopyroxenite, and clockwise metamorphic pressure–temperature (P-T) paths were retrieved, indicative of metamorphism in a subduction environment. Peak metamorphic P-T conditions (790–920 °C/28–41 kbar) of garnet clinopyroxenite suggest they experienced UHP metamorphism in the coesite- or diamond-stability field. The UHP metamorphic event is also confirmed by the occurrence of high-Al titanite enclosed in the garnet, along with at least three groups of aligned rutile lamellae exsolved from the garnet. Secondary ion mass spectrometry (SIMS) U-Pb dating of metamorphic titanite indicates that the post-peak, subsequent tectonic exhumation of the UHP rocks occurred in the Devonian period (~389–370 Ma). These data suggest that part of the Paleozoic Dunhuang orogenic belt experienced UHP metamorphism, and diverse metamorphic facies series prevailed in this Paleozoic orogen. It can be further inferred that most of the UHP rocks in this orogen remain buried.
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Crowley, J. L., E. D. Ghent, and R. L. Brown. "Metamorphism in the Clachnacudainn terrane and implications for tectonic setting in the southern Omineca Belt, Canadian Cordillera." Canadian Journal of Earth Sciences 33, no. 11 (November 1, 1996): 1570–82. http://dx.doi.org/10.1139/e96-119.
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New and previously published metamorphic data suggest that the Clachnacudainn terrane of the southern Omineca Belt has tectonic affinities with the overlying Selkirk allochthon, rather than the underlying Shuswap metamorphic complex. This interpretation is based on relationships between metamorphic minerals and deformation phases, plutons, and the upper boundary of the terrane, the Standfast Creek fault. Regional kyanite and staurolite zones in the structurally lowest part of the terrane are overlain by a garnet zone that is continuous upward across the Standfast Creek fault into the Selkirk allochthon. This metamorphism is inferred to be Jurassic age based mainly on the continuity of these zones with those of known age in the allochthon. Textural relationships show that metamorphism occurred at different times relative to deformation across the terrane. Thermobarometry and a petrogenetic grid indicate that the terrane attained lower to middle amphibolitc facies conditions. Sillimanite and andalusite zones in the contact aureoles of posttectonic mid-Cretaceous plutons overprint the regional metamorphic zones and the Standfast Creek fault. Comparison of estimated pressures shows that approximately 5–10 km of exhumation occurred between regional and contact metamorphism. These metamorphic data are interpreted to indicate that the Standfast Creek fault had minor displacement after regional metamorphism and negligible displacement after contact metamorphism. Therefore, the fault cannot be an Eocene ductile to ductile–brittle shear zone that appressed or omitted metamorphic isograds and rapidly exhumed the Clachnacudainn terrane in its footwall, as was previously proposed.
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Brown, Michael. "Metamorphic geology: Tectonics of metamorphism." Nature 318, no. 6044 (November 1985): 314–15. http://dx.doi.org/10.1038/318314a0.
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Grigor’eva, A. V., V. M. Kozlovskiy, G. A. Gridin, and A. A. Ostapchuk. "METAMORPHIC TRANSFORMATIONS OF ROCKS IN THE CENTRAL PART OF THE PRIMORSKY FAULT. WESTERN BAIKALIA." Доклады Российской академии наук. Науки о Земле 511, no. 2 (August 1, 2023): 198–205. http://dx.doi.org/10.31857/s2686739723600807.
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In this paper we compare metamorphic transformations in acid and mafic rocks in a zone of intense tectonic movements. The object of study is the exhumed part of damage zone of Primorsky fault – main collision suture, which connects the Siberian Craton and the Olkhon Terrane. The studied area is located near the Khorga River. Collected metamorphic rock samples are represented by both acid (plagiogranitegneiss) and mafic (amphibole-biotite plagiogneisses) rocks. The samples present two different parent rocks contacting each other but differ in chemical composition. The formation of identical metamorphic minerals belonging to the groups of garnet and epidote is noted in both types of rocks. Mineral formation was associated with high-pressure regional metamorphism and possibly with later collision. Studying chemical composition of rock-forming minerals has allowed to determine the P-T condition of metamorphism in these rocks via the method of multimineral thermobarometry. It was established that conditions of early metamorphism retain in amphibole-biotite plagiogneiss. Early metamorphism is characterized by high-pressure amphibolite facies of medium temperature next to eclogite facies. In plagiogranitegneisses were found conditions of later metamorphism that formed rocks at the same pressure but at a lower temperature in the paragonite-kyanite-zoisite subfacies of the eclogite facies next to the greenschist facies. Minerals formed in the early metamorphism are poorly preserved.
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Pesquera, A., and F. Velasco. "Metamorphism of the Palaeozoic Cinco Villas Massif (Basque Pyrenees): Illite Crystallinity and Graphitization Degree." Mineralogical Magazine 52, no. 368 (December 1988): 615–25. http://dx.doi.org/10.1180/minmag.1988.052.368.06.
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AbstractThe degree of metamorphism affecting the Devonian-Carboniferous rocks of the Palaeozoic Cinco Villas massif has been studied by (a) petrographic techniques, (b) illite crystallinity, and (c) degree of graphitization of the carbonaceous material. Some mineralogical differences have been found between the Devonian and Carboniferous rocks; paragonite and mixed-layer paragonite/muscovite, typical of anchimetamorphic areas, appear in the Devonian but are not found in the Carboniferous rocks. These are characterized by the local appearance of chloritoid, garnet, amphibole, epidote, andalusite and biotite, and the generalized presence of muscovite/chlorite. Illite crystallinity shows a metamorphic zonation (anchizone epizone) towards the granitic Aya massif, and a concentric pattern around the intrusive body.The optical analysis shows that the first effects of the regional metamorphism began before the D2 deformation, reaching its paroxysm during this phase and continuing afterwards. The degree of graphitization evolves progressively with metamorphism, and this fact is reflected in an exponential relationship between d(002) and crystallinity Lc(002). The similarity in the degree of graphitization between homologous materials within and outside the Aya aureole suggests a similar kinetic factor for both the thermal and regional metamorphisms, or a similar duration time. This fact, as well as the distribution and relationship between the deformation and recrystallization of the minerals, suggests a syn-plutonic regional metamorphism developed at low pressures, in accordance with the value of the b0 parameter for the white micas, and probably a maximum temperature of about 500°C.
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MAJKA, JAROSLAW, STANISLAW MAZUR, MACIEJ MANECKI, JERZY CZERNY, and DANIEL K. HOLM. "Late Neoproterozoic amphibolite-facies metamorphism of a pre-Caledonian basement block in southwest Wedel Jarlsberg Land, Spitsbergen: new evidence from U–Th–Pb dating of monazite." Geological Magazine 145, no. 6 (September 10, 2008): 822–30. http://dx.doi.org/10.1017/s001675680800530x.
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AbstractSouthwest Spitsbergen, Wedel Jarlsberg Land, consists of two Proterozoic crustal blocks with differing metamorphic histories. Both blocks experienced Caledonian greenschist-facies metamorphism, but only the southern block records an earlier pervasive M1 amphibolite-facies metamorphism and strong deformational fabric. In situ EMPA total-Pb monazite geochronology from both matrix and porphyroblast inclusion results indicate that the older M1 metamorphism occurred at 643 ± 9 Ma, consistent with published cooling ages of c. 620 Ma (hornblende) and 580 Ma (mica) obtained from these same rocks. This region thus contains a lithostratigraphic profile and metamorphic history which are unique within the Svalbard Archipelago. Documentation of a pervasive late Neoproterozoic Barrovian metamorphism is difficult to reconcile with a quiescent non-tectonic regime typically inferred for this region, based on the occurrence of rift-drift sequences on the Baltic and Laurentian passive margins. Instead, our new metamorphic age implies an exotic origin of the pre-Devonian basement exposed in SW Spitsbergen and supports models of terrane assembly postulated for the Svalbard Archipelago.
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MALUSKI, HENRI, and FRANTIšEK PATOCČKA. "Geochemistry and 40Ar–39Ar geochronology of the mafic metavolcanic rocks from the Rýchory Mountains complex (west Sudetes, Bohemian Massif): palaeotectonic significance." Geological Magazine 134, no. 5 (September 1997): 703–16. http://dx.doi.org/10.1017/s0016756897007498.
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The mafic metavolcanic rocks (blueschists and greenschists) of the Rýchory Mountains crystalline complex (West Sudetes) experienced sea-floor hydrothermal alteration (spilitization?) prior to regional metamorphism. The metabasite geochemistry (namely trace element and REE abundances) indicates that the protolith was comparable in composition with (1) tholeiitic to transitional ocean-floor basalts and (2) transitional and alkaline intra-oceanic island basalts. Two main metamorphic events affected the Rýchory Mountains metabasites. In an earlier high pressure–low temperature metamorphic event, the rocks experienced blueschist facies metamorphism. The results of 40Ar–39Ar geochronology studies on phengites from the mafic blueschists date the end of the earlier metamorphism to 360 Ma. The greenschist metamorphic overprint followed around 340 Ma. The elongated bodies of mafic metavolcanic rocks are situated within the prominent NNE–SSW Leszczyniec shear zone following the trend of the Rýchory Mountains and the Rudawy Janowickie Mountains. Both the geochemical affinities and the blueschist facies metamorphism of the metabasites suggest that this shear zone evolved from the Variscan suture dividing western and central terranes of the West Sudetes. According to the radiometric age for the end of the high pressure–low temperature metamorphism, the terranes accreted during the Famennian. A considerable time-span between the formation of the metabasite protolith and the blueschist metamorphism may indicate long-lasting subduction of a large oceanic plate between Gondwana and Laurussia, possibly accompanied by terrane accretion, prior to the Variscan orogeny.
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Powell, W. G., D. M. Carmichael, and C. J. Hodgson. "Conditions and timing of metamorphism in the southern Abitibi greenstone belt, Quebec." Canadian Journal of Earth Sciences 32, no. 6 (June 1, 1995): 787–805. http://dx.doi.org/10.1139/e95-067.
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Regional metamorphism, ranging in grade from the subgreenschist-facies to the greenschist–amphibolite-facies transition, affects all Archean supracrustal rocks (>2677 Ma) in the Rouyn–Noranda area. Contact metamorphic minerals associated with the posttectonic Preissac–Lacorne batholith (2643 Ma) show no evidence of a regional retrograde event. Accordingly, the age of regional metamorphism can be bracketed between 2677 and 2643 Ma. Three reaction isograds were mapped in subgreenschist-facies metabasites, dividing the low-grade rocks into three metamorphic zones: the pumpellyite–actinolite zone, the prehnite–pumpellyite zone, and the prehnite–epidote zone. In addition, the pumpellyite–actinolite–epidote–quartz bathograd, corresponding to a pressure of approximately 200 MPa, occurs on both sides of the Porcupine–Destor fault. Low-pressure regional metamorphism is also indicated both by the occurrence of an actinolite–oligoclase zone, and the persistence of pre-regional-metamorphic andalusite. The coincidence of andalusite and the actinolite-oligoclase zone indicates that pressure was <330 MPa at the greenschist-amphibolite transition. The geothermal gradient during metamorphism was approximately 30 °C/km. Regionally, isograds dip shallowly to the north and trend subparallel to lithological and structural trends. Metamorphic minerals in metabasites define tectonic fabrics only near major fault zones and in zones of CO2 metasomatism. In biotite zone metasedimentary rocks the schistosity is defined by mica and amphibole. These textures indicate that metamorphism and fabric development were coeval. However, the actinolite–epidote isograd cuts the Porcupine–Destor fault, indicating that regional metamorphism postdates movement along this fault. The strong fabrics associated with the Porcupine–Destor and Larder Lake–Cadillac faults must have developed through a process dominated by flattening strain.
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Biševac, Vanja, Kadosa Balogh, Dražen Balen, and Darko Tibljaš. "Eoalpine (Cretaceous) very low- to low-grade metamorphism recorded on the illite-muscovite-rich fraction of metasediments from South Tisia (eastern Mt Papuk, Croatia)." Geologica Carpathica 61, no. 6 (December 1, 2010): 469–81. http://dx.doi.org/10.2478/v10096-010-0029-9.
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Eoalpine (Cretaceous) very low- to low-grade metamorphism recorded on the illite-muscovite-rich fraction of metasediments from South Tisia (eastern Mt Papuk, Croatia)Eoalpine very low- to low-grade metamorphism related to Cretaceous orogenesis has been investigated in the Slavonian Mts, Croatia. Samples belonging to the Psunj metamorphic complex (PMC), the Radlovac metamorphic complex (RMC) and Permian-Triassic and Triassic sedimentary sequences (PTSS) were studied. The Kübler and Árkai indices of all the analysed samples indicate high-anchizonal to epizonal metamorphism. The degree of Eoalpine metamorphism tends to be constant in all samples implying that the different complexes passed through and recorded the same event. Measurements of illite-white K-micab0-parameter of the RMC samples imply transitional low- to medium-pressure character of the metamorphism. These data together with K-Ar ages (~100-80 Ma) measured on illite-white K-mica rich < 2 μm grain-size fractions point to Late Cretaceous very low- to low-grade regional metamorphism presumably related to the main nappe-forming compressional events in the Pannonian Basin and the Carpathians. The P-T-t (pressure-temperature-time) evolution of the studied area is in good agreement with similar scenarios in the surrounding areas of Tisia, but also in Eastern Alps, Carpathians and Pannonian Basin (ALCAPA).
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Tettelaar, Tanya, and Aphrodite Indares. "Granulite-facies regional and contact metamorphism of the Tasiuyak paragneiss, northern Labrador: textural evolution and interpretation." Canadian Journal of Earth Sciences 44, no. 10 (October 1, 2007): 1413–37. http://dx.doi.org/10.1139/e07-029.
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The Tasiuyak paragneiss at the western margin of the Nain Plutonic Suite has been subjected to two granulite-facies metamorphic events: (i) regional metamorphism during the Paleoproterozoic Torngat orogeny, and (ii) contact metamorphism due to emplacement of the Mesoproterozoic Nain Plutonic Suite. Regional metamorphism led to partial melting of pelitic rocks and the development of a locally well-preserved sequence of prograde and retrograde textures. These textures are partly controlled by bulk composition and formed in the pressure–temperature (P–T) field of the continuous reaction: biotite + sillimanite + plagioclase + quartz = garnet + K-feldspar + melt, along a hairpin P–T path with peak conditions of ~8–10 kbar (0.8–1.0 GPa) and up to 870 °C in the NaKFMASH (Na2O–K2O–FeO–MgO–Al2O3–SiO2–H2O) system. These textures controlled the development of the contact metamorphic assemblages. Contact metamorphism of the pelitic rocks between the Tessiarsuyungoakh intrusion and the Makhavinekh Lake pluton led to growth of orthopyroxene-cordierite symplectite after garnet–biotite, and cordierite–spinel symplectite after garnet–sillimanite. These phase associations attest to reactions in specific microtextural settings, some of which produced a second generation of partial melt. Maximum temperatures were above ~750 °C and pressures were lower than those of the regional metamorphism. The aureole around the Makhavinekh Lake pluton is ~4 km wide and shows a progressive development of the contact metamorphic assemblages toward the pluton. In contrast, the contact metamorphic overprint is incipient around the Tessiarsuyungoakh intrusion, which developed a ~20 m wide contact aureole and is most prominent in screens of paragneiss within that intrusion.
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Prakash, D., DK Patel, MK Yadav, B. Vishal, S. Tewari, R. Yadav, SK Rai, and CK Singh. "Prograde polyphase regional metamorphism of pelitic rocks, NW of Jamshedpur, eastern India: constraints from textural relationship, pseudosection modelling and geothermobarometry." Geological Magazine 157, no. 7 (November 11, 2019): 1045–67. http://dx.doi.org/10.1017/s0016756819001171.
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AbstractThe study area belongs to the Singhbhum metamorphic belt of Jharkhand, situated in the eastern part of India. The spatial distribution of the index minerals in the pelitic schists of the area shows Barrovian type of metamorphism. Three isograds, viz. garnet, staurolite and sillimanite, have been delineated and the textural study of the schists has revealed a time relation between crystallization and deformation. Series of folds with shifting values of plunges in the supracrustal rocks having axial-planar schistosity to the folds have been widely cited. Development of these folds could be attributed to the second phase of deformation. In total, two phases of deformation, D1 and D2, in association with two phases of metamorphism, M1 and M2, have been lined up in the study area. Chemographic plots of reactant and product assemblages corresponding to various metamorphic reactions suggest that the pattern of metamorphic zones mapped in space is in coherence with the temporal-sequential change during prograde metamorphism. The prograde P–T evolution of the study area has been obtained using conventional geothermobarometry, internally consistent winTWQ program and Perple_X software in the MnNCKFMASHTO model system. Our observations suggest that the progressive metamorphism in the area is not related to granitic intrusion or migmatization but that it was possibly the ascending plume that resulted in the M1 phase of metamorphism followed by D1 deformation. The second and prime metamorphic phase, M2, with its possible heat source generated by crustal overloading, was preceded by D1 and it lasted until late- to post-D2 deformation.
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KOZLOV, Pavel Sergeevich. "On the relationships between the Al2SiO5 polymorphs during formation of blastomylonites (North Yenisei Ridge)." NEWS of the Ural State Mining University 1 (March 15, 2021): 25–32. http://dx.doi.org/10.21440/2307-2091-2021-1-25-32.
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Relevance. When mapping the vast areas of the Precambrian polymetamorphic complexes in the North Yenisei Ridge, there is a problem of metamorphism interpretation and phasing of geological development of a particular area along with thrust tectonics. The solution of these issues is also of great importance for the purposes of areas delineation of metamorphic rocks that are favorable for the detection of high-alumina (andalusite, kyanite, sillimanite) schists. Purpose of the work: to substantiate and itemize some geological prospecting, mineralogical and petrological indicator criteria for the development of high-alumina garnet-kyanite-staurolite blastomylonites of dislocation metamorphism formed by andalusite-bearing rocks of regional metamorphism. Research methodology: detailed mapping of structural-metamorphic zoning of dislocation (collisional) metamorphism in the Mayakon key area with sampling of polymetamorphic rocks for petrographic studies of mineral parageneses. Investigation of polished thin sections of polymetamorphic rocks by microprobe analysis with elucidation of minerals zoning, their chemical composition, calculation of the Р–Т paths of metamorphism and determination of the absolute age of blastomylonite formation based on the 40Ar/39Ar dating of biotite. Analysis and generalization of the results obtained for the Mayakon area and their comparison with other key areas of the North Yenisei Ridge. Results. At the Mayakon potential area, a progressive metamorphic zoning of kyanite-bearing blastomylonites has been identified, and the transitional I, outer II, middle III, and inner zones are determined as the dislocation metamorphism intensifies towards the Panimba thrust fault. Based on the compositions of garnets, biotite, and plagioclase, the P–T paths of the early regional metamorphism of andalusite-sillimanite type and late local kyanitesillimanite type were calculated. A list of geological prospecting, petrological and isotope-geochronological criteria for recognizing blastomylonites among rocks of regional metamorphism in thrust zones has been substantiated and itemized. Conclusions. Method of polymetamorphism reconstruction in the North Yenisei Ridge shows that tectonic inversion conditions took place in the Neoproterozoic, in the late Tonian era (~850 Ma ago In terms of occurrences, they are related to the final stage of the Grenville orogeny (1.1–0.85 Ga). The formation of blastomylonites of dislocation (collisional) metamorphism by metapelites of regional metamorphism in thrust zones is accompanied by an increase in the number of mineral phases and leads to a reduction in usable space of high-alumina andalusite schists.
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Zagorchev, Ivan, Constantin Balica, Evgeniya Kozhoukharova, and Ioan Balintoni. "Pirin metamorphic and igneous evolution revisited in a geochronological frame based on U-Pb zircon studies." Geologica Balcanica 46, no. 1 (July 2017): 27–63. http://dx.doi.org/10.52321/geolbalc.46.1.27.
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New isotopic data obtained from zircons by the U-Pb method during the last decade show the necessity of a revision of the tectonometamorphic and igneous evolution of the Pirin–Pangaion Unit of the Alpine Morava–Rhodope tectonic zone. The northern (Pirin) subunit of this unit consists of four areas built up of metamorphic rocks (amphibolite facies) of the Rhodopian supercomplex. These areas are separated by Late Alpine granite plutons of batholithic dimensions. The northernmost (Krupnik) area is built up of rocks of the Rupchos Group (complex) of varied composition and intense multiphase deformation and metamorphism. The oldest metamorphic phase is dated as Cadomian (528–517 Ma), and its products also suffered Hercynian superimposed amphibolite-facies metamorphism and anatexis. A septum of granitised metamorphics preserved between the Krupnik granite pluton (Triassic, ca 240 Ma) and the early Oligocene North Pirin (Kresna) pluton is characterised by Hercynian (330–300 Ma) anatexis. The principal metamorphism within the southern area around the early Oligocene South Pirin (Teshovo) granite pluton is dated both in the Bachkovo quartzo-feldspathic gneisses (named also Kriva-reka metagranites or orthogneisses) and in the Lukovitsa schists and paragneisses as Hercynian (ca 300–290 Ma). Therefore, the polymetamorphic evolution of the Pirin Subunit consists of a Cadomian phase and a strong Hercynian overprint followed by Triassic granitoids. We confirm the Thanetian–early Eocene age (58–55 Ma) of the Spanchevo granite, partially formed by in situ anatexis. Its intrusion was followed by a compression phase during the mid-Eocene thrusting of the Ograzhden Unit over the Pirin–Pangaion Unit, along the Strimon Thrust. The last magmatic phase (ca 34–31 Ma) was represented by a granitoid association formed during the latest Eocene–early Oligocene in extensional conditions and as a result of mixing of anatectic crust-derived magma with magma of mantle origin. It was part of a volcano-plutonic association related to the Macedonian–Rhodope magmatotectonic province. A high-temperature metamorphic overprint of the same age is recorded in the metamorphics as formation of andalusite in the metapelites, and skarns at the contacts of some of the granitoid bodies.
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Kong, Xu, Xueyuan Qi, Wentian Mi, and Xiaoxin Dong. "Zircon U–Pb Dating and Lu-Hf Isotope of the Retrograded Eclogite from Chicheng, Northern Hebei Province, China." Shock and Vibration 2021 (June 16, 2021): 1–11. http://dx.doi.org/10.1155/2021/1445653.
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We report zircon U–Pb ages and Lu-Hf isotopic data from two sample of the retrograded eclogite in the Chicheng area. Two groups of the metamorphic zircons from the Chicheng retrograded eclogite were identified: group one shows characteristics of depletion in LREE and flat in HREE curves and exhibit no significant Eu anomaly, and this may imply that they may form under eclogite facies metamorphic condition; group two is rich in HREE and shows slight negative Eu anomaly indicated that they may form under amphibolite facies metamorphic condition. Zircon Lu-Hf isotopic of εHf from the Chicheng eclogite has larger span range from 6.0 to 18.0, which suggests that the magma of the eclogite protolith may be mixed with partial crustal components. The peak eclogite facies metamorphism of Chicheng eclogite may occur at 348.5–344.2 Ma and its retrograde metamorphism of amphibolite fancies may occur at ca. 325.0 Ma. The Hongqiyingzi Complex may experience multistage metamorphic events mainly including Late Archean (2494–2448 Ma), Late Paleoproterozoic (1900–1734 Ma, peak age = 1824.6 Ma), and Phanerozoic (495–234 Ma, peak age = 323.7 Ma). Thus, the metamorphic event (348.5–325 Ma) of the Chicheng eclogite is in accordance with the Phanerozoic metamorphic event of the Hongqiyingzi Complex. The eclogite facies metamorphic age of the eclogite is in accordance with the metamorphism (granulite facies or amphibolite facies) of its surrounding rocks, which implied that the tectonic subduction and exhumation of the retrograded eclogite may cause the regional metamorphism of garnet biotite plagioclase gneiss.
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Campos, José C. S., Maurício A. Carneiro, and Miguel A. S. Basei. "U-Pb evidence for late Neoarchean crustal reworking in the Southern São Francisco Craton (Minas Gerais, Brazil)." Anais da Academia Brasileira de Ciências 75, no. 4 (December 2003): 497–511. http://dx.doi.org/10.1590/s0001-37652003000400008.
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The Passa Tempo Metamorphic Complex is one of several metamorphic complexes that form the Archean sialic crust of the southern São Francisco Craton. It encompasses hypersthene-bearing gneissic rocks, with subordinateNW- or EW-trending mafic-ultramafic bodies and granodioritic to alkali-granitic, weakly foliated, and light-colored granitoids. These granitoids are the product of generalized migmatization that followed granulite-facies metamorphism. To determine the ages of the granulite-facies metamorphism and granitoid genesis, we obtained U-Pb ages on zircon extracted from the mesosome and leucosome of the migmatitic gneisses. For the mesosome, a discordia that intercepts Concordia at 2622 ± 18 Ma is interpreted as a minimum age for granulite-facies metamorphism. For the leucosome, the upper intercept of discordia at 2599 ± 45 Ma corresponds to migmatization and granitoid genesis. Contemporaneous metamorphism and magmatism have been documented elsewhere in the São Francisco Craton, especially in the southern portion, demonstrating vast and vigorous reworking of sialic crust by the end of the Neoarchean.
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Kyrylyuk, V. P., and O. V. Gaiovskyi. "REGIONAL METAMORPHISM AND STRATIGRAPHY OF THE BASEMENT OF UKRAINIAN SHIELD." Geological Journal, no. 4 (December 28, 2022): 3–30. http://dx.doi.org/10.30836/igs.1025-6814.2022.4.261979.
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Stratigraphic complexes of the Lower Precambrian are everywhere metamorphosed. That is why the stratigraphic dismemberment of the Lower Precambrian has always been inextricably linked with the study of metamorphism. For some time, metamorphism was even used as a sign of the relative age of stratigenic metamorphic complexes according to the principle – “the higher the degree of metamorphism, the older the complex”. The high-temperature complexes of granulite and amphibolite facies belonged to the Archean, while the less metamorphosed complexes belonged to the Proterozoic. But already at the beginning of the widespread use of methods of isotope dating of metamorphic shield complexes, the most ancient age determinations were obtained from weakly metamorphosed complexes. After that, the degree of metamorphism was no longer taken into account in the stratigraphic dismemberment of the shield basement. The degree of metamorphism of the complexes has not been taken into account for a long ago when compiling official stratigraphic schemes of the Precambrian of the Ukrainian Shield, in which isotope dating plays a leading role. This led, according to many geologists, to distortions in the schemes of the real stratigraphy of the basement of the region. The authors of the article believe that the degree of metamorphism can still be used in the development of the stratigraphy of the Ukrainian Shield and, above all, in the stratigraphic study of individual megablocks. The possibility of such use of metamorphism is considered in the cycle of publications in which this is the first article. The article presents the characteristics of stratigraphy and metamorphism of all megablocks of the Ukrainian Shield. In the structure of the megablocks of the Ukrainian Shield, as well as all the shields of ancient platforms, the following stratigenic metamorphic complexes of the Lower Precambrian have been established, differing in the type and degree of metamorphism: a) granulite-gneiss, b) amphibolite-gneiss, c) greenstone (metavolcanogenic), d) ferruginoussiliceous- shale (metavolcanogenic-chemogenic-terrigenous), e) gneiss-shale (metacarbonate-terrigenous). It has been established that in all megablocks granulite-gneiss complexes are represented and are the most ancient, and all younger complexes are always less metamorphosed than the previous ones. Thus, the relationship between the degree of metamorphism and relative age in individual megablocks is preserved, but this feature cannot be extended to the entire shield. Coeval complexes of neighboring megablocks may have different degrees of metamorphism, and younger complexes of one of the megablocks are sometimes more intensely metamorphosed than older ones in the neighboring megablock.
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Webster, Ewan Russell, and David R. M. Pattison. "Spatially overlapping episodes of deformation, metamorphism, and magmatism in the southern Omineca Belt, southeastern British Columbia." Canadian Journal of Earth Sciences 55, no. 1 (January 2018): 84–110. http://dx.doi.org/10.1139/cjes-2017-0036.
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The southeastern Omineca Belt of the Canadian Cordillera preserves a record of overlapping Barrovian and Buchan metamorphism spanning 180–50 Ma. This paper documents the timing, character, and spatial relationships that define separate domains of Middle Jurassic, Early Cretaceous, and Late Cretaceous deformation and metamorphism, and the nature of the geological interfaces that exist between them. A domain of Early Jurassic deformation (D1) and regional greenschist-facies metamorphism (M1) is cross-cut by Middle Jurassic (174–161 Ma) intrusions. Associated contact aureoles are divided into lower pressure (cordierite-dominated; ∼2.5–3.3 kbar; 1 kbar = 100 MPa) and higher pressure (staurolite-bearing; 3.5–4.2 kbar) subtypes; contact metamorphic kyanite occurs rarely in some staurolite-bearing aureoles. Jurassic structures are progressively overprinted northwards by Early Cretaceous deformation and metamorphism (D2M2), manifested in a tightening of Jurassic structures, development of more pervasive ductile fabrics, and Barrovian metamorphism. The D2M2 domain is the southerly continuation of the 600 km long Selkirk–Monashee–Cariboo metamorphic belt. Mid-Cretaceous intrusions (118–90 Ma) were emplaced throughout the D2M2 domain, the earliest of which contain D2 fabrics, but cut M2 isograds. The D2M2 domain makes a continuous, southeasterly transition into a domain of Late Cretaceous regional Barrovian metamorphism and deformation (D3M3; 94–76 Ma). The interface between these two domains is obscured by the coaxial nature of the deformation and the apparent continuity of the metamorphic zones, resulting in a complex and cryptic interface. Similarities between the D3M3 domain and the Selkirk Crest of Idaho and Washington suggest that this domain is the northerly continuation of the northward-plunging Priest River Complex.
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Selyatitskii, A. Yu, O. P. Polyansky, and R. A. Shelepaev. "A High-Pressure Thermal Aureole of the Bayan-Kol Gabbro–Monzodiorite Intrusion (Western Sangilen, Southeastern Tuva): Evidence for Lower-Crust Mafic Magma Chambers." Russian Geology and Geophysics 62, no. 9 (September 1, 2021): 987–1005. http://dx.doi.org/10.2113/rgg20194157.
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Abstract —Thermal metamorphism produced an aureole near the early Paleozoic Bayan-Kol gabbro–monzodiorite intrusion in the Erzin shear zone of western Sangilen (Tuva–Mongolia microcontinent, Central Asian Orogenic Belt). Field observation of intrusive contact, structure–textural and mineral transformations of metamorphic rocks, regular changes in the chemical composition of minerals with approaching the intrusive contact, and high temperature gradient from intrusive to wallrocks verified the occurrence of a contact aureole near the Bayan-Kol intrusion. The high-gradient thermal metamorphism (M2) affected garnet–staurolite–kyanite schists that formed during earlier regional metamorphism (M1) at 6.2–7.9 kbar and 600–670 ºC. The 0.5 km wide M2 metamorphic aureole mapped along the northwestern intrusion margin consists of a muscovite–sillimanite zone adjacent to the sedimentary country rocks and a cordierite–K-feldspar zone on the side of the intrusion. The M2 metamorphic reactions occurred within the granulite facies temperature range 880–910 ºC along the contact with monzodiorites and at ~950 ºC along the boundary with gabbronorites; the temperature on the aureole periphery was about 640 ºC. Pressure estimates indicate deep-seated high-grade metamorphism at 6.9–7.8 kbar, while the intrusion itself crystallized at 7.7–7.8 kbar. The suggested numerical model implying the formation of a thermal aureole at a depth of 26 km (7 kbar) in the lower crust is consistent with the temperature pattern determined by geothermobarometry for several key points of the metamorphic zoning and confirms its deep-level origin. Thus, the aureole near the Bayan-Kol intrusion represents a rare case of contact metamorphism in the lower continental crust. The obtained results, along with published petrological and geochronological evidence, reveal two depth levels of the early Paleozoic M2 metamorphism in the Sangilen area: upper (7–15 km, 2–4 kbar) and lower (26–30 km, 7–8 kbar) crust. The Bayan-Kol gabbro–monzodiorite intrusion is likely a small apophysis or a fragment of a deep-crust intermediate magma chamber, while the moderate-pressure (7–8 kbar) M2 granulites in the Erzin shear zone are products of high-gradient metamorphism related to the Cambrian–Ordovician collisional mafic magmatism in the Sangilen area.
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Yardley, B. W. D. "What Drives Metamorphism and Metamorphic Reactions?" Mineralogical Magazine 63, no. 3 (1999): 442–43. http://dx.doi.org/10.1180/minmag.1999.063.3.17.
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Kozakov, I. K., E. B. Salnikova, I. V. Anisimova, P. Ya Azimov, V. P. Kovach, Yu V. Plotkina, M. V. Stifeeva, and A. M. Fedoseenko. "Tectonic position of the Early Neoproterozoic–Early Paleozoic metamorphic belts within the Tuva–Mongolian terrane of the Central Asian Orogenic Belt." Петрология 27, no. 1 (March 13, 2019): 47–64. http://dx.doi.org/10.31857/s0869-590327147-64.
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The Tuva–Mongolian terrane (TMT) of the Central Asian Orogenic Belt is a composite structure with a Vendian–Cambrian terrigenous-carbonate cover. The formation of the northern part of TMT is marked by the granitoids of the Sumsunur Complex with an age of 785 ± 11 Ma. The Sangilen and Khan-Khukhay blocks of its southern part also form a composite structure, which originated during Early Paleozoic(500–490 Ma) low-moderate pressure regional metamorphism reaching amphibolites-granulite facies. The earlier high-pressure metamorphism was established in the Moren Complex of both the blocks. In the Sangilen block, this metamorphism reached conditions of kyanite-garnet-biotite-orthoclase subfacies of amphibolites facies (temperature ~750oC, pressure 9–10 kbar). The upper age limit of this metamorphism is determined by granites with an age of 536 ± 6 Ma, which cut across migmatized biotite gneisses of the Moren Complex. The latter are intruded by the granitoids of the Ortoadir pluton, which were previously dated at 521 ± ± 12 Ma (U-Pb method, TIMS). Its emplacement predated the Early Paleozoic low-moderate pressure metamorphism, the timing of which is constrained by syn- and postmetamorphic granitoids with ages of 496 ± 4 and 489 ± 3 Ma. The age of 513 ± 4 Ma established for the granitoids of the Ortoadir Complex in the Khan-Khukhay Block more accurately constrains the lower age boundary of collision processes. This determined the amalgamation of the fragments of the high-pressure metamorphic belt with basement and carbonate-shelf cover units of the Tuva–Mongolian terrane, as well as the upper age boundary of early metamorphism. The timing of the main mappable structure of the Khan–Khukhay Block and low-moderate pressure regional metamorphism is marked by the synmetamorphic granitoids with an age of 505 ± ± 2 Ma. In general, the metamorphic rocks of the Sangilen, Khan–Khukhay, and Kaakhem blocks can be considered as fragments of the Late Ediacaran high-pressure metamorphic belt, which were amalgamated to the western margin of TMT within 515–505 Ma, after emplacement of the granitoids of the Ortoadir Complex, and were reworked by regional Early Paleozoic low-moderate pressure metamorphism.
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Sukhorukov, Vasiliy, Valeriya Volkova, Peter Nevolko, and Pavel Kozlov. "Metamorphic Conditions and Raman Spectroscopic Carbonaceous Material Thermometry of Host Schists of Olympiada and Eldorado Gold Deposits (Yenisey Ridge, Russia)." Geosciences 11, no. 11 (November 2, 2021): 452. http://dx.doi.org/10.3390/geosciences11110452.
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Metamorphic processes play a key role in forming orogenic gold deposits. In this paper, we present new evidence that host schists of the two largest gold deposits of the Yenisey ridge (Russia) Olympiada and Eldorado underwent a single stage of metamorphism in contrast to surrounding blocks. This metamorphism is of moderate thermal gradient and belongs to the Barrovian type, which is typical for the collisional event in the time range 800–850 Ma. The new Ar/Ar age data presented in this paper and the review of magmatic and metamorphic events and ore-forming processes indicate that the most productive stage (gold-sulfide-quartz) correlates well in time with the regional metamorphism of the Barrovian type. This indicates that metamorphic processes can have a crucial role in forming gold deposits of the Yenisey ridge. Carbonaceous material thermometry indicates a wide range of obtained temperatures around 90–150 °C around the mean temperature for each sample. The highest temperatures are close to the peak metamorphic temperatures estimated by garnet-biotite thermometry.
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Aoki, K., B. F. Windley, S. Maruyama, and S. Omori. "Discussion of ‘Metamorphic P–T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogen, Scotland’." Geological Magazine 151, no. 4 (March 4, 2014): 758–63. http://dx.doi.org/10.1017/s0016756813001106.
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K. Aoki, B. F. Windley, S. Maruyama & S. Omori reply: First, we thank Viete, Oliver & Wilde for their interesting and thought-provoking comments on the timing of the high-pressure granulite facies (HGR) metamorphism recorded in metamorphic rocks at Cairn Leuchan, Scotland, published by Aoki et al. (2013). Based on new metamorphic data of garnetites and garnet-amphibolites at Cairn Leuchan and new zircon U–Pb ages of amphibolitized eclogite at Tomatin, we suggested in our publication that the HGR metamorphism was retrograde after eclogite facies before the c. 470 Ma ‘Barrovian metamorphism’. Viete, Oliver & Wilde however speculate that the HGR metamorphism at Cairn Leuchan may have occurred at c. 1000 Ma, as a result of their new U–Pb zircon age of the Cowhythe Gneiss at Portsoy and from previous studies of the geological structure and geochronology. We are grateful for this opportunity to describe, albeit in a preliminary manner, our new understanding and tectonic model of the Caledonian orogen in Scotland and western Ireland of which the Barrovian metamorphism is a key component. A reply to a comment is not the correct place to propose an entirely new paradigm for such a classic orogen, but we will present our model more fully in a future publication.
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Kyrylyuk, V. P., and O. V. Gaiovskyi. "REGIONAL METAMORPHISM AND STRATIGRAPHY OF THE BASEMENT OF THE UKRAINIAN SHIELD." Geological Journal, no. 2 (June 26, 2023): 13–29. http://dx.doi.org/10.30836/igs.1025-6814.2023.2.262163.
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The stratigraphic dismembrement of the Lower Precambrian has always been inextricably linked with the study of metamorphism. The degree of metamorphism of the complexes was even used for some time as an indication of their relative age. This sign was not confirmed by isotope dating and was no longer taken into account in the stratigraphic dismembrement of the basement of the shields, including the preparation of official stratigraphic schemes of the Precambrian of the Ukrainian Shield. The authors of the article believe that the degree of metamorphism can still be used in developing the stratigraphy of the Ukrainian Shield. The possibility of such use of metamorphism is considered in a series of publications. The first article describes the stratigraphy and metamorphism of all megablocks of the Ukrainian Shield. It is shown that older stratigenic complexes in each of the megablocks are characterized by higher temperature metamorphism. At the same time, the distinctive features of the composition and metamorphism of the stratigenic complexes, according to the authors, are a reflection of large successive stages of the geological development of the Ukrainian Shield in the Early Precambrian and can serve as the basis for compiling a regional stratigraphic scheme on a historical-geological basis. A version of the regional stratigraphic scheme of the Ukrainian Shield on a historical-geological basis, compiled at the level of complexes, proposed in the second article of the series. In this final article of the cycle, the conditions and duration of lithogenesis and accompanying metamorphism of various sequentially formed stratigenic complexes of the Lower Precambrian are considered. The idea is put forward that the initial pre-metamorphic composition of the complexes and their metamorphism are determined by the temperature state of the upper shells of the Earth and their directed thermal evolution at the early stages of geological history. The existence of hydrospheric, early thermohydrospheric, late thermohydrospheric and normohydrospheric global stages of lithogenesis, lasting from 300 to 700 Ma, and continuous metamorphism from 3.8 to 2.0–1.9 Ga are assumed. During this time, a single metamorphic (paleotemperature) zoning of the basement of the Ukrainian Shield was formed, in which all stratigenic complexes of different ages participate.
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Shawwa, Nabil A., Robert P. Raeside, David W. A. McMullin, and Christopher R. M. McFarlane. "Employing contact metamorphism to assess the conditions of pluton emplacement and timing of recrystallization in southwestern Kellys Mountain, Cape Breton Island, Nova Scotia." Canadian Journal of Earth Sciences 54, no. 11 (November 2017): 1165–78. http://dx.doi.org/10.1139/cjes-2017-0052.
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At Kellys Mountain, Cape Breton Island, Nova Scotia, the late Neoproterozoic Glen Tosh formation (a low-grade metapsammite–metapelite unit of the George River Metamorphic Suite) has been intruded by diorite, granodiorite, and granite plutons, and the diorite hosts a narrow contact metamorphic aureole. New mapping and sampling in the contact aureole reveals that the metasedimentary rocks have reached amphibolite-facies metamorphism resulting in the development of neoformed biotite, muscovite, cordierite, ilmenite, garnet, andalusite, sillimanite, monazite, and spinel within the meta-pelite, a mineral assemblage also found in the Kellys Mountain Gneiss as a result of low-pressure regional metamorphism. Neoformed minerals and the disappearance of foliation defines a contact metamorphic aureole within 300 m of the pluton contacts. Petrographic and microprobe analyses of equilibrium assemblages in metapelitic units of the contact aureole yielded metamorphic pressures of 250 MPa, implying an intrusion depth of ∼9 km, with temperatures ranging from 365 to 590 °C. The presence of earlier-formed andalusite and garnet indicates the rocks may have initially undergone a low-pressure regional metamorphic event prior to contact metamorphism. Monazite in the contact aureole was dated using in-situ U–Pb methods and yielded an age of 480.9 ± 3.7 Ma, interpreted as the time of formation of the contact metamorphic aureole.
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NAKANO, KEISUKE. "Metamorphism in jigsaw." Journal of Functional Programming 23, no. 2 (October 19, 2012): 161–73. http://dx.doi.org/10.1017/s0956796812000391.
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AbstractA metamorphism is an unfold after a fold, consuming an input by the fold then generating an output by the unfold. It is typically useful for converting data representations, e.g., radix conversion of numbers. (Bird and Gibbons, Lecture Notes in Computer Science, vol. 2638, 2003, pp. 1–26) have shown that metamorphisms can be incrementally processed in streaming style when a certain condition holds because part of the output can be determined before the whole input is given. However, whereas radix conversion of fractions is amenable to streaming, radix conversion of natural numbers cannot satisfy the condition because it is impossible to determine part of the output before the whole input is completed. In this paper, we present a jigsaw model in which metamorphisms can be partially processed for outputs even when the streaming condition does not hold. We start with how to describe the 3-to-2 radix conversion of natural numbers using our model. The jigsaw model allows us to process metamorphisms in a flexible way that includes parallel computation. We also apply our model to other examples of metamorphisms.
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Yan, Jun, Ying Cui, and Xiaoyu Liu. "Evolution of Contact Metamorphic Rocks in the Zhoukoudian Area: Evidence from Phase Equilibrium Modelling." Minerals 13, no. 8 (August 10, 2023): 1056. http://dx.doi.org/10.3390/min13081056.
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The Yanshan intraplate tectonic belt is a tectonic-active area in the central part of the North China Craton that has undergone long-term orogenic evolution. Detailed studies on magmatic activity and metamorphism of this belt are significant for restoring its orogenic thermal evolution process. The Fangshan pluton in the Zhoukoudian area within this tectonic belt is a product of the late Mesozoic Yanshan event. However, there is a lack of detailed research on the metamorphic evolution history of the ancient terrane surrounding the Fangshan pluton subjected to contact thermal metamorphism. To further constrain the metamorphic P–T evolution of contact metamorphism associated with the Fangshan pluton, we collected rock samples in the andalusite–biotite contact metamorphic zone of the Fangshan pluton, and conducted petrographic investigations, geochemical and mineral composition analysis, and phase equilibrium modeling. The phase equilibrium modeling in the MnO–Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O system indicates that the peak mineral assemblages of andalusite–biotite schists are pl + q + mu + bi + and ± kfs + ilm + mt, formed at 550 to 610 °C, 1 to 3.5 kbar, and the peak mineral assemblage of garnet–andalusite–cordierite–biotite schists is gt + pl + q + bi + and + cord + ilm + mt, formed at 580 to 620 °C, 1.5 to 2.1 kbar. Therefore, we believe that the rocks in the andalusite biotite contact metamorphic zone of the Fangshan pluton underwent low pressure and medium temperature metamorphism, with the peak metamorphic conditions of about 550–610 °C, <3.5 kbar. The results show that the rocks in contact with the thermal metamorphic zone were rapidly heated by the heat released by the Fangshan pluton, and after reaching the peak metamorphic temperature, they were cooled down simultaneously with the cooling of the rock mass, defined in a nearly isobaric P–T trajectory.
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Treloar, Peter J., Richard M. Palin, and Michael P. Searle. "Towards resolving the metamorphic enigma of the Indian Plate in the NW Himalaya of Pakistan." Geological Society, London, Special Publications 483, no. 1 (2019): 255–79. http://dx.doi.org/10.1144/sp483-2019-22.
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AbstractThe Pakistan part of the Himalaya has major differences in tectonic evolution compared with the main Himalayan range to the east of the Nanga Parbat syntaxis. There is no equivalent of the Tethyan Himalaya sedimentary sequence south of the Indus–Tsangpo suture zone, no equivalent of the Main Central Thrust, and no Miocene metamorphism and leucogranite emplacement. The Kohistan Arc was thrust southward onto the leading edge of continental India. All rocks exposed to the south of the arc in the footwall of the Main Mantle Thrust preserve metamorphic histories. However, these do not all record Cenozoic metamorphism. Basement rocks record Paleo-Proterozoic metamorphism with no Cenozoic heating; Neo-Proterozoic through Cambrian sediments record Ordovician ages for peak kyanite and sillimanite grade metamorphism, although Ar–Ar data indicate a Cenozoic thermal imprint which did not reset the peak metamorphic assemblages. The only rocks that clearly record Cenozoic metamorphism are Upper Paleozoic through Mesozoic cover sediments. Thermobarometric data suggest burial of these rocks along a clockwise pressure–temperature path to pressure–temperature conditions of c. 10–11 kbar and c. 700°C. Resolving this enigma is challenging but implies downward heating into the Indian plate, coupled with later development of unconformity parallel shear zones that detach Upper Paleozoic–Cenozoic cover rocks from Neoproterozoic to Paleozoic basement rocks and also detach those rocks from the Paleoproterozoic basement.
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Timpa, Sean, Kathryn M. Gillis, and Dante Canil. "Accretion-related metamorphism of the Metchosin Igneous Complex, southern Vancouver Island, British Columbia." Canadian Journal of Earth Sciences 42, no. 8 (August 1, 2005): 1467–79. http://dx.doi.org/10.1139/e05-043.
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The metamorphic history of the volcanic sequence of the Metchosin Igneous Complex (MIC), an Eocene ophiolite exposed on southern Vancouver Island, British Columbia, Canada, was studied to examine the roles of seafloor and accretion-related processes. Metamorphic facies in the volcanics vary from prehniteactinolite assemblages in the east to greenschist and amphibolite assemblages in the west. In the east, metamorphism is typified by chlorite ± prehnite ± epidote ± actinolite assemblages that fill vesicles and replace interstitial material; plagioclase is variably albitized, and clinopyroxene is relatively fresh. In the west, the common groundmass assemblage is amphibole + epidote ± chlorite. These assemblages and chlorite geothermometry show a regional eastwest gradient of ∼510 °C/km that is oblique to the volcanic stratigraphy. The regional metamorphic facies distribution for the MIC volcanics is not consistent with seafloor hydrothermal metamorphism documented for ocean crust from mid-ocean ridges, ocean islands, or island arcs. We speculate that underthrusting of the MIC beneath the Pacific Rim Terrane led to the regional metamorphism of the MIC, and that the change in metamorphic grade from east to west results from regional tilting of the complex, perhaps by orographic effects, during or after accretion.
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Xiao, Ling-Ling, and Min-Hua Chen. "Metamorphic Age Comparison and Its Implications between the Zuoquan and Zanhuang Complexes in the Central North China Craton, Based on LA-ICP-MS Zircon U–Pb Dating." Minerals 9, no. 12 (December 13, 2019): 780. http://dx.doi.org/10.3390/min9120780.
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The Trans-North China Orogen (TNCO) is well-known as an early Precambrian orogenic belt in the North China Craton (NCC). Three meaningful groups of metamorphic ages have been reported in the metamorphic complexes throughout the TNCO, including c. 1.85 Ga, c. 1.95 Ga, and c. 2.5 Ga. The spatial distributions and relationships of these ages provide notable insight into the formation timing and tectonic evolution of the NCC basement. The Zuoquan and Zanhuang complexes are exposed in the south–central TNCO and are adjacent to the Eastern Block. In order to place new constraints on the timing of two phases of metamorphism that occurred in the complexes, combined U–Pb and rare earth element analyses were performed on zircons from different types of metamorphic rocks. Uranium–Pb zircon dating in this study shows that two groups of metamorphic ages of 1.88–1.85 Ga and 2.48–2.46 Ga were commonly recorded by metamorphic rocks in the Zanhuang and Zuoquan complexes, respectively. Our previous geochronological studies showed that metamorphic ages of c. 2.51 Ga and c. 1.90 Ga were locally recorded in the Zanhuang and Zuoquan complexes, respectively. These data indicate that metamorphic rocks in the two complexes underwent at least two phases of metamorphism, i.e., 2.51–2.46 Ga (Phase I) and 1.90–1.85 Ga (Phase II). In combination with previous studies regarding reaction microstructures, metamorphic pressure–temperature paths, and geochronology, the Phase II metamorphic ages are interpreted to be linked to the collision between the Western and Eastern Blocks along the TNCO between 1.97 Ga and 1.80 Ga, whereas the Phase I metamorphic ages, as a result of an earlier and extensive tectono-thermal event that occurred in the Eastern and Western Blocks of the NCC, were related to underplating of mantle-derived magma. It is inferred that the rocks with c. 2.51–2.46 Ga metamorphic ages in the two complexes formed in the Eastern Block and underwent regional metamorphism during that period, and then were tectonically involved in the TNCO and experienced c. 1.90–1.85 Ga metamorphism. Metamorphic peaks occurred at different crustal levels in the orogen, resulting in distinct metamorphic ages and peak conditions preserved by metamorphic rocks in the two complexes.
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Talarico, F. M., E. Stump, B. F. Gootee, K. A. Foland, R. Palmeri, W. R. Van Schmus, P. K. Brand, and C. A. Ricci. "First evidence of a “Barrovian”-type metamorphic regime in the Ross orogen of the Byrd Glacier area, central Transantarctic Mountains." Antarctic Science 19, no. 4 (August 2, 2007): 451–70. http://dx.doi.org/10.1017/s0954102007000594.
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AbstractThe Selborne Group comprises two metamorphic rock units, the muscovite±dolomite bearing Madison Marble and the biotite-muscovite±quartz-calcite Contortion Schist, which contains thick lenses of variably deformed metabasalts and metaconglomerates. Petrological and structural data indicate a polyphase metamorphic evolution including: i) an early stage of upper greenschist regional metamorphism (P = ~0.15–0.3 GPa; T = ~380–450°C), ii) prograde metamorphism during D1 up to amphibolite facies peak conditions (P = 0.58–0.8 GPa, T = ~560–645°C), iii) syn-D2 unloading-cooling retrograde metamorphism, iv) a post-D2 contact metamorphic overprint at variable T between 450 and 550°C and ~0.2 GPa connected to the emplacement of granitic plutons and felsic dyke swarms. Geochronological data constrain the polyphase syn-D1/D2 evolution between ~ 510 and 492 Ma. A similar metamorphic path, including a medium P stage but at lower T conditions, is documented in greenschist facies metabasalts within the Byrd Group in the Mount Dick area. The metamorphic pattern and close lithostratigraphic matching between Selborne Group and Byrd Group sharply contrast with the high-grade Horney Formation that is exposed north of the Byrd Glacier and corroborate the hypothesis that the Byrd Glacier discontinuity marks a first-order crustal tectonic boundary crossing the Ross orogen.
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Abu El-Enen, M. M., and M. Okrusch. "The texture and composition of tourmaline in metasediments of the Sinai, Egypt: Implications for the tectono-metamorphic evolution of the Pan-African basement." Mineralogical Magazine 71, no. 1 (February 2007): 17–40. http://dx.doi.org/10.1180/minmag.2007.071.1.17.
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AbstractAccessory tourmaline in metasediments from the Sinai crystalline basement exhibits textural and chemical signatures that relate to the evolution of regional metamorphism and deformation during the Pan-African orogeny and testifies to different P-T path segments. Tourmaline inclusions in various porphyroblasts were formed during the prograde phase of metamorphism; acicular to prismatic crystals in the matrix, oriented sub-parallel to, and enveloped by, the main foliation crystallized syntectonically under prograde and peak metamorphic conditions; tourmaline cross-cutting the main foliation may have formed just after the peak or during the retrograde phase of metamorphism. Some of the cores in tourmaline crystals, showing different colours, are interpreted as former detrital grains. The abundance of tourmaline decreases with increasing peak metamorphic conditions. The tourmaline investigated belongs to the schorl-dravitess group, generally with XMg of 0.42–0.73 and XCa = Ca/(Ca+Na+K+□) of 0.02–0.24, typical of tourmalines in metapelites and metapsammites; whereas detrital cores have been derived from various sources, including former tourmaline-quartz and pre-existing high-metamorphic rocks. Tourmaline of the Sinai metasediments was formed during metamorphism of the sedimentary precursors, essentially in a closed system, where clay minerals and organic matter, together with detrital tourmaline, served as the source of boron. Although a metamorphic facies should be defined by characteristic mineral assemblages present in metamorphic rocks, tourmaline chemistry is a good monitor of P-T conditions in the metapelites and semi-metapelites investigated, showing an increase in XMg with increasing metamorphic grade, where XturMg = 0.60 distinguishes between greenschist and lower-amphibolite facies, while XturMg = 0.65 could distinguish lower- from middle- to upper-amphibolite facies. The results of tourmaline-biotite geothermometry compare well with our former temperature estimates using conventional geothermometry and phase-diagram modelling.
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Zheng, Yong-Fei, and Ren-Xu Chen. "Extreme metamorphism and metamorphic facies series at convergent plate boundaries: Implications for supercontinent dynamics." Geosphere 17, no. 6 (November 1, 2021): 1647–85. http://dx.doi.org/10.1130/ges02334.1.
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Abstract Crustal metamorphism under extreme pressure-temperature conditions produces characteristic ultrahigh-pressure (UHP) and ultrahigh-temperature (UHT) mineral assemblages at convergent plate boundaries. The formation and evolution of these assemblages have important implications, not only for the generation and differentiation of continental crust through the operation of plate tectonics, but also for mountain building along both converging and converged plate boundaries. In principle, extreme metamorphic products can be linked to their lower-grade counterparts in the same metamorphic facies series. They range from UHP through high-pressure (HP) eclogite facies to blueschist facies at low thermal gradients and from UHT through high-temperature (HT) granulite facies to amphibolite facies at high thermal gradients. The former is produced by low-temperature/pressure (T/P) Alpine-type metamorphism during compressional heating in active subduction zones, whereas the latter is generated by high-T/P Buchan-type metamorphism during extensional heating in rifting zones. The thermal gradient of crustal metamorphism at convergent plate boundaries changes in both time and space, with low-T/P ratios in the compressional regime during subduction but high-T/P ratios in the extensional regime during rifting. In particular, bimodal metamorphism, one colder and the other hotter, would develop one after the other at convergent plate boundaries. The first is caused by lithospheric subduction at lower thermal gradients and thus proceeds in the compressional stage of convergent plate boundaries; the second is caused by lithospheric rifting at higher thermal gradients and thus proceeds in the extensional stage of convergent plate boundaries. In this regard, bimodal metamorphism is primarily dictated by changes in both the thermal state and the dynamic regime along plate boundaries. As a consequence, supercontinent assembly is associated with compressional metamorphism during continental collision, whereas supercontinent breakup is associated with extensional metamorphism during active rifting. Nevertheless, aborted rifts are common at convergent plate boundaries, indicating thinning of the previously thickened lithosphere during the attempted breakup of supercontinents in the history of Earth. Therefore, extreme metamorphism has great bearing not only on reworking of accretionary and collisional orogens for mountain building in continental interiors, but also on supercontinent dynamics in the Wilson cycle.
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El Qryefy, Mohamed, Boujemaa Agorram, Said Boubih, Sabah Selmaoui, and Rahma Bouali. "Assessment of Knowledge and Learning Difficulties in Metamorphism Among Future Teachers." European Journal of Theoretical and Applied Sciences 1, no. 5 (September 1, 2023): 230–35. http://dx.doi.org/10.59324/ejtas.2023.1(5).15.
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The present research focuses on evaluating the knowledge and learning difficulties in metamorphism among future teachers. To address our issue, we selected a sample from students at the Ecole Normale Supérieure de Marrakech and employed a questionnaire as our investigative tool. The obtained results indicate that students face learning problems in metamorphism. These difficulties arise in understanding certain key concepts of metamorphism, such as metamorphic facies and migmatite. We also observed that students struggle to establish connections between metamorphism and other geological phenomena. These learning difficulties can be attributed to language barriers, didactic transposition, the persistence of certain misconceptions, and the discipline itself, such as problems in comprehending geological space and time. This research could aid university professors in understanding these difficulties and in designing teaching scenarios that would help students better grasp geological concepts.
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Brown, Michael, and Tim Johnson. "Time's arrow, time's cycle: Granulite metamorphism and geodynamics." Mineralogical Magazine 83, no. 03 (April 12, 2019): 323–38. http://dx.doi.org/10.1180/mgm.2019.19.
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AbstractAlthough the thermal evolution of the mantle before c. 3.0 Ga remains unclear, since c. 3.0 Ga secular cooling has dominated over heat production—this is time's arrow. By contrast, the thermal history of the crust, which is preserved in the record of metamorphism, is more complex. Heat to drive metamorphism is generated by radioactive decay and viscous dissipation, and is augmented by the influx of heat from the mantle. Notwithstanding that reliable data are sparse before the Neoarchean, we use a dataset of temperature (T), pressure (P) and thermobaric ratio (T/P at the metamorphic ‘peak’), and age of metamorphism (t, the timing of the metamorphic ‘peak’) for rocks from 564 localities ranging in age from the Cenozoic to the Eoarchean eras to interrogate the crustal record of metamorphism as a proxy for the heat budget of the crust through time. On the basis of T/P, metamorphic rocks are classified into three natural groups: high T/P type (T/P >775°C/GPa, mean T/P ~1105°C/GPa), including common and ultrahigh-temperature granulites, intermediate T/P type (T/P between 775 and 375°C/GPa, mean T/P ~575°C/GPa), including high-pressure granulites and medium- and high-temperature eclogites, and low T/P type (T/P <375°C/GPa, mean T/P ~255°C/GPa), including blueschists, low-temperature eclogites and ultrahigh-pressure metamorphic rocks. A monotonic increase in the P of intermediate T/P metamorphism from the Neoarchean to the Neoproterozoic reflects strengthening of the lithosphere during secular cooling of the mantle—this is also time's arrow. However, temporal variation in the P of intermediate T/P metamorphism and in the moving means of T and T/P of high T/P metamorphism, combined with the clustered age distribution, demonstrate the cyclicity of collisional orogenesis and cyclic variations in the heat budget of the crust superimposed on secular cooling since c. 3.0 Ga—this is time's cycle. A first cycle began with the widespread appearance/survival of intermediate T/P and high T/P metamorphism in the Neoarchean rock record coeval with amalgamation of dispersed blocks of lithosphere to form protocontinents. This cycle was terminated by the fragmentation of the protocontinents into cratons in the early Paleoproterozoic, which signalled the start of a new cycle. The second cycle continued with the progressive amalgamation of the cratons into the supercontinent Columbia and extended until the breakup of the supercontinent Rodinia in the Neoproterozoic. This cycle represented a period of relative tectonic and environmental stability, and perhaps reduced subduction during at least part of the cycle. During most of the Proterozoic the moving means for both T and T/P of high T/P metamorphism exceeded the arithmetic means, reflecting insulation of the mantle beneath the quasi-integrated lithosphere of Columbia and, after a limited reorganisation, Rodinia. The third cycle began with the steep decline in thermobaric ratios of high T/P metamorphism to their lowest value, synchronous with the breakup of Rodinia and the formation of Pannotia, and the widespread appearance/preservation of low T/P metamorphism in the rock record. The thermobaric ratios for high T/P metamorphism rise to another peak associated with the Pan-African event, again reflecting insulation of the mantle. The subsequent steep decline in thermobaric ratios of high T/P metamorphism associated with the breakup of Pangea at c. 0.175 Ga may indicate the start of a fourth cycle. The limited occurrence of high and intermediate T/P metamorphism before the Neoarchean suggests either that suitable tectonic environments to generate these types of metamorphism were not widely available before then or that the rate of survival was low. We interpret the first cycle to record stabilisation of subduction and the emergence of a network of plate boundaries in a plate tectonics regime once the balance between heat production and heat loss changed in favour of secular cooling, possibly as early as c. 3.0 Ga in some areas. This is inferred to have been a globally linked system by the early Paleoproterozoic, but whether it remained continuous to the present is unclear. The second cycle was characterised by stability from the formation of Columbia to the breakup of Rodinia, generating higher than average T and T/P of high T/P metamorphism. The third cycle reflects colder collisional orogenesis and deep subduction of the continental crust, features that are characteristic of modern plate tectonics, which became possible once the average temperature of the asthenospheric mantle had declined to <100°C warmer than the present day after c. 1.0 Ga.
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Mirčovski, Vojo, Blažo Boev, Goše Petrov, and Orce Spasovski. "Chemical composition of the actinolite-hornblende assemblage as indicator for the P-T metamorphic conditions in chlorite-amphibole schists and metadiabases, Vrteska, Plackovica Mt., Eastern Macedonia." Geologica Balcanica 33, no. 3-4 (December 30, 2003): 23–31. http://dx.doi.org/10.52321/geolbalc.33.3-4.23.
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Microscopic and electronic microprobe studies carried out on the chlorite-amphibole schists and the metadiabases from the vicinity of Vrteska determined an actinolite, Mg-hornblende, biotite, epidote, chorite, albite, calcite, quartz, and ilmenite assemblage. The metamorphic mineral assemblage and structural-textural characteristics indicate that these rocks metamorphosed in conditions of regional dynamothermal metamorphism in a Barovian type series of facies which, according to the degree of metamorphism, corresponds to the transition from quartz-albite-epidote-biotite to quartz-albite-epidote-almnadine subfacies. The chemical composition of actinolite and hornblende indicate that the rocks under investigation metamorphosed in conditions of prograde metamorphism at T = 400-500°C and P = 2-5 kbar.
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Javkhlan, Terbishiinkhen O., Akira Takasu, Md Fazle Kabir, and Dash Batulzii. "Multiple Metamorphic Events Recorded within Eclogites of the Chandman District, SW Mongolia." Minerals 9, no. 8 (August 18, 2019): 495. http://dx.doi.org/10.3390/min9080495.
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The eclogite-bearing Alag Khadny metamorphic complex in the Lake Zone, SW Mongolia occupies the central region of the Central Asian Orogenic Belt, the largest Phanerozoic orogenic belt in the world. The complex consists mainly of orthogneisses intercalated with eclogites and micaschists in a mélange zone. Most of eclogites are strongly amphibolitized. In this study, we examined petrography and mineral chemistry of eclogites and amphibolitized eclogites, respectively. The result of our research shows that Chandman eclogites experienced multiple events of metamorphism in throughout their subduction and subsequent collision history. We revealed that eclogites were subjected to blueschist facies metamorphism before the peak eclogite facies stage. In addition, we have studied amphibolitized eclogite, and revealed that another distinct progressive medium pressure (MP) epidote-amphibolite facies metamorphic event took place in the eclogite, consistent with collision process. The multiple events of metamorphism in eclogites have been revealed by zonation textures of HP amphiboles zoned with glaucophane→barroisite→Mg-hornblende and MP amphiboles zoned with actinolite/winchite→barroisite→Mg-hornblende/tschermakite/Fe-pargasite. These amphiboles with different zonation textures reflect their metamorphic history of subduction to collision events.
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Chakrabarty, A., R. H. Mitchell, M. Ren, P. K. Saha, S. Pal, K. L. Pruseth, and A. K. Sen. "Magmatic, hydrothermal and subsolidus evolution of the agpaitic nepheline syenites of the Sushina Hill Complex, India: implications for the metamorphism of peralkaline syenites." Mineralogical Magazine 80, no. 7 (December 2016): 1161–93. http://dx.doi.org/10.1180/minmag.2016.080.057.
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AbstractThe Proterozoic Sushina Hill Complex is the only agpaitic complex, reported from India and is characterized by a eudialyte-rinkite-bearing nepheline syenite. The complex is considered a ‘metamorphosed agpaitic complex'. This study describes the mineral assemblages formed during successive stages of evolution from magmatic to hydrothermal stages and low-temperature subsolidus re-equilibration assemblage. The primary-late magmatic assemblage is characterized by albite, orthoclase, unaltered nepheline, zoned diopside-hedenbergite, rinkite, late magmatic eudialyte and magnesio-arfvedsonite formed at ∼700°C with maximum aSiO2 of 0.60. In contrast, a deuteric assemblage (400-348°C) is represented by aegirine-jadeite-rich clinopyroxene, post-magmatic eudialyte, sodalite, analcime and the decomposition assemblages formed after eudialyte with decreasing aSiO2 (0.52-0.48). A further low-temperature subsolidus assemblage (≤250°C) represented by late-forming natrolite could be either related to regressive stages of metamorphism or a continuum of the subsolidus processes. Considering the P/T range of the greenschist - lower-amphibolite facies of metamorphism it is evident that the incorporation of a jadeite component within pyroxene is related to a subsolidus process between ∼400°C and 348°C in a silica deficient environment. We emphasize that the deuteric fluid itself acted as an agent of metamorphism and the decomposition assemblage formed after eudialyte is retained even after metamorphism due to the convergence of subsolidus and metamorphic domains. The formation of jadeite-rich aegirine is not considered to result from metamorphism. Overall it is near-impossible to discern any bona fide metamorphic textures or mineral assemblages in these syenites which appear to preserve a relict mineralogy regardless of their occurrence in country rocks which have experienced greenschist - amphibolite facies metamorphism. The Sushina complex is very similar in this respect to the Norra Kärr complex (Sweden).
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Lardeaux, Jean-Marc. "Deciphering orogeny: a metamorphic perspective. Examples from European Alpine and Variscan belts." Bulletin de la Société Géologique de France 185, no. 2 (February 1, 2014): 93–114. http://dx.doi.org/10.2113/gssgfbull.185.2.93.
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AbstractIn this paper we review and discuss, in a synthetic historical way, the main results obtained on Alpine metamorphism in the western Alps. First, we describe the finite metamorphic architecture of the western Alps and discuss its relationships with subduction and collision processes. Second, we portray the progressive metamorphic evolution through time and space with the presentation of 5 metamorphic maps corresponding to critical orogenic periods, namely 85-65 Ma, 60-50 Ma, 48-40 Ma, 38-33 Ma and 30-20 Ma. We underline the lack of temporal data on high-pressure/low-temperature metamorphic rocks as well as the severe uncertainties on the sizes of rock units that have recorded the same metamorphic history (i.e. coherent P-T-t/deformation trajectories). We discuss the role of subduction-driven metamorphism in ocean-derived protoliths and the conflicting models that account for the diachrony of continental subductions in the western Alps.
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Dallmeyer, R. D. "Partial thermal resetting of 40Ar/39Ar mineral ages in western Spitsbergen, Svalbard: possible evidence for Tertiary metamorphism." Geological Magazine 126, no. 5 (September 1989): 587–93. http://dx.doi.org/10.1017/s001675680002286x.
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AbstractHornblende and muscovite within high-grade Caledonian metamorphic rocks exposed in Albert I Land (northwest Spitsbergen) display internally concordant 40Ar/39Ar age spectra providing no record of any post-Silurian thermal history. Both minerals record 420−425 Ma plateau ages indicating that relatively rapid cooling followed Silurian metamorphism. Muscovite within some metamorphic sequences exposed within the Tertiary tectonic zone of Oscar II Land (west-central Spitsbergen) displays a low-temperature 40Ar/39Ar age spectra discordance suggestive of a slight, post-Caledonian thermal disturbance. This is consistent with a post-Palaeozoic thermal overprint documented elsewhere in Oscar II Land and indicates that, at least locally, metamorphism may have accompanied the Tertiary orogeny.
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Skublov, Sergey G., Aleksey V. Berezin, and Laysan I. Salimgaraeva. "Comment on Volodichev et al. Archean Zircons with Omphacite Inclusions from Eclogites of the Belomorian Province, Fennoscandian Shield: The First Finding. Minerals 2021, 11, 1029." Minerals 12, no. 2 (January 25, 2022): 141. http://dx.doi.org/10.3390/min12020141.
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Volodichev et al. (Volodichev et al., 2021) reported on the first finding of omphacite (23%–25% Jd) inclusions in 2.68 Ga metamorphic zircons from Gridino eclogites and presented it as evidence for Archean eclogite-facies metamorphism in the Belomorian Mobile Belt. We believe that the Archean age of the garnets referred to by the above authors was estimated incorrectly. Our interpretation is that omphacite origin is related to Archean high-pressure granulite-facies metamorphism.
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Brunel, Maurice, and Jean-Robert Kienast. "Étude pétro-structurale des chevauchements ductiles himalayens sur la transversale de l'Everest–Makalu (Népal oriental)." Canadian Journal of Earth Sciences 23, no. 8 (August 1, 1986): 1117–37. http://dx.doi.org/10.1139/e86-111.
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Tectonic and microtectonic data in eastern Nepal indicate that the major observed thrusting (100 km) on the Main Central Thrust (MCT) postdates the Barrovian metamorphism of the High Himalaya gneisses. This result, at variance with the famous "reverse metamorphism model," better explains the abnormal metamorphic superpositions in the Himalayas and accounts for the lack of high-pressure assemblages under the thick, allochtonous High Himalaya Tibetan slab.Pressure and temperature estimates by microprobe analysis on plagioclase, biotite, garnet, kyanite, sillimanite, and cordierite assemblages are presented for samples collected along the MCT shear zone and across the gneiss slab in the Everest–Makalu area. Since there is very little difference in pressure at the front of the slab (Kathmandu Klippe) and its root, these estimates support the existence of important late metamorphic thrusting. The decrease of pressure towards the top of the gneiss pile, combined with a small temperature increase, explains the kyanite–sillimanite transition. The reverse metamorphism model, which implies refolded isograds, predicts heat loss by conduction throughout the sole of the thrust; pressure–temperature variations and kyanite–sillimanite transition phases more likely reflect a late heat supply in the upper part of the gneisses. Intrusion of leucogranitic bodies, confined to the interface with the Tethyan sediments, could account for this heat supply.A new tectonic evolution model of the Himalayan intracrustal thrusts is discussed. Without completely denying the existence of a reverse metamorphism synchronous with the phases of early shearing, it can be shown that the metamorphic zonation seen at present was governed by the structure of the later shearing.
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Saunders, James A., and Gilles O. Allard. "The Scott Lake deposit: a contact-metamorphosed volcanogenic massive sulfide deposit, Chibougamau area, Quebec." Canadian Journal of Earth Sciences 27, no. 2 (February 1, 1990): 180–86. http://dx.doi.org/10.1139/e90-018.
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The Scott Lake volcanogenic massive sulfide deposit lies near the margin of a large, early kinematic granitoid intrusion in the vicinity of Chibougamau, Quebec. The deposit was contact metamorphosed by the intrusion, and subsequently it was metamorphosed to the greenschist facies during the Kenoran Orogeny. Pyrite, magnetite, and sphalerite are the most abundant metallic minerals, and minor amounts of chalcopyrite, pyrrhotite, and loellingite are also present. Both pyrite and magnetite locally occur as porphyroblasts up to several centimetres in diameter. Metamorphic textures developed in the massive sulfide ore appear to have formed during contact metamorphism, and they remained intact through the subsequent regional event. However, silicate minerals (biotite and possibly amphibole) that grew during contact metamorphism were largely retrograded during regional metamorphism. The presence of biotite indicates that contact metamorphism took place at 400°–500 °C. Application of the sphalerite geobarometer gives a pressure of approximately 4.5 kbar (450 MPa), which probably reflects the later regional event.
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Liu, Xiaochun, Shuwen Dong, Huaimin Xue, and Jianxiong Zhou. "Significance of allanite-(Ce) in granitic gneisses from the ultrahigh-pressure metamorphic terrane, Dabie Shan, central China." Mineralogical Magazine 63, no. 4 (August 1999): 579–86. http://dx.doi.org/10.1180/minmag.1999.063.4.10.
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AbstractA recent study of granitic gneisses in the ultrahigh-pressure (UHP) metamorphic terrane from Dabie Shan, central China reveals that allanite-(Ce) is a widespread REE-bearing accessory phase. The microprobe analyses show that allanites-(Ce) have nearly uniform chemical compositions, with total REE contents ranging from 23 to 28 wt.% and a La/Ce ratio of 0.57–0.73. All allanites-(Ce) are replaced or rimmed by epidotes and commonly form a relatively REE-poor rim near the interfaces. The textural relations and mineral chemistry suggest that allanite-(Ce) crystallized prior to metamorphism and therefore was of igneous origin, whereas the surrounding epidote was the product of metamorphism. Granitic gneiss, composed chiefly of sodic plagioclase, microcline and quartz with minor amounts of Mn-rich garnet, biotite, low Si phengitic mica, epidote, chlorite and sometimes amphibole, was formed at 495°C and ∼5 kbar, corresponding to the retrograde metamorphism of UHP rocks. Accordingly, it is believed that granitic gneisses have not experienced UHP metamorphism. This implies that a large scale tectonic juxtaposition developed before the epidote-amphibolite facies retrograde metamorphism of UHP rocks during the late continental collision in Dabie Shan.
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Polyansky, O. P., A. Yu Selyatitskii, S. V. Zinoviev, and A. V. Babichev. "Early Paleozoic Tectonothermal Evolution of the Khan-Khukhay Metamorphic Complex (Northern Mongolia)." Петрология 31, no. 5 (September 1, 2023): 510–30. http://dx.doi.org/10.31857/s0869590323050047.
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A reconstruction of metamorphic stages of Moren and Erzin metamorphic Complexes in the Khan-Khuhay block of Nothern Mongolia presented in the paper. Based on it a general geodynamic history of Sangilen terrain of Tuva-Mongolia Massif discussed. Reconstructed “clock-wise” P-T trend demonstrated two stage of metamorphism, the first of which is due to collision metamorphism with P-T parameters of 9 kbar, 740°C, the second one is due to regional magmatic episode with P-T parameters of 6-7 kbar, 860–880°C. Geochemical and petrological peculiarities of rocks in the Khan-Khuhay block demonstrates resemblance with metamorphic block of Western Sangilen in South-East Tuva. In the first time quartz monzodiorite intrusive bodies founded within Khan-Khuhay block. Their geochemical peculiarities are similar to Ordovician gabbro-monzodiorite intrusives of Western Sangilen. Quartz monzodiorite intrusives of Khan-Khuhay are likely a small apophysis of a deep-crust intermediate magma chamber and can present probable thermal source of metamorphic stage M2 in the Khan-Khuhay block. Numerical thermo-mechanical model of metamorphism in the Khan-Khuhay block explain heating in the thickening crust during collision due to higher radiogenic heat source of 1.52 μW/m3. Using computer modeling was show that the P-T parameters of second metamorphic stage can realize only by means of magmatic heat from monzodiorite intrusion. Reconstruction of P-T parameters using mineral thermobarometry, similarity of geochemical characteristics, as well as the results of thermomechanical modeling allow us to conclude that the Erzin and Moren complexes have undergone a joint tectono-metamorphic evolution.
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Abdrakhmanov, I. A. "Physicochemical simulation of the conditions for the mafic granulite formation (Bunger Hills, East Antarctica)." Vestnik of Geosciences 2 (2021): 14–18. http://dx.doi.org/10.19110/geov.2021.2.3.
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The article presents the results of mineral thermobarometry and physico-chemical simulation of the formation of garnet-enstatite gneiss from the Mesoproterozoic metamorphic suite of the Bunger Hills, East Antarctica. As a result, the water activity, temperature and pressure of rock formation were estimated. It is shown that the peak temperature of metamorphism could reach 900 °С or more. Such temperature conditions indicate the prerequisites for the occurrence of UHT-metamorphism during the formation of the East Antarctic Shield.
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Peck, William H., and Matthew P. Quinan. "New age constraints on magmatism and metamorphism in the Morin terrane (Grenville Province, Quebec)." Canadian Journal of Earth Sciences 59, no. 4 (April 2022): 232–42. http://dx.doi.org/10.1139/cjes-2019-0105.
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The Morin terrane is an allochthonous crustal block in the southwestern Grenville Province with a relatively poorly constrained metamorphic history. In this part of the Grenville Province, some terranes were part of the ductile middle crust during the 1.09–1.02 Ga collision of Laurentia with the Amazon craton (the Ottawan phase of the Grenvillian orogeny), while other terranes were part of the orogen’s superstructure. New U–Pb geochronology suggests that the Morin terrane experienced granulite-facies metamorphism during the accretionary Shawinigan orogeny (1.19–1.14 Ga) and again during the Ottawan. Seven zircon samples from the 1.15 Ga Morin anorthosite suite were dated to confirm earlier age determinations, and Ottawan metamorphic rims (1.08–1.07 Ga) were observed in two samples. U–Pb dating of titanite in nine marble samples surrounding the Morin anorthosite suite yielded mixed ages spanning between the Shawinigan and Ottawan metamorphisms (n = 7), and predominantly Ottawan ages (n = 2). Our results show that Ottawan zircon growth and resetting of titanite ages is spatially heterogeneous in the Morin terrane. Ages with a predominantly Ottawan signature are recognized in the Morin shear zone, which deforms the eastern lobe of the anorthosite, in an overprinted skarn zone on the western side of the massif, and in the Labelle shear zone that marks its western boundary. In the rest of the Morin terrane, titanite with Shawinigan ages appear to have been only partially reset during the Ottawan. Further work is needed to better understand the relationship between the character of Ottawan metamorphism and resetting in different parts of the Morin terrane.
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Mihalynuk, M. G., and E. D. Ghent. "Regional depth-controlled hydrothermal metamorphism in the Zymoetz River area, British Columbia." Canadian Journal of Earth Sciences 33, no. 8 (August 1, 1996): 1169–84. http://dx.doi.org/10.1139/e96-088.
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An estimated 6 km of basic to silicic volcanic flows and clastic rocks of the Early Jurassic Telkwa Formation is exposed in moderately east-dipping fault blocks along the Zymoetz River, British Columbia. Extensive wholesale zeolitic replacement of porous tuff beds suggests widespread hydrothermal activity. Metamorphic grade increases regionally from laumontite–albite facies to prehnite–pumpellyite facies with increasing stratigraphic depth. Telkwa Formation strata and the imparted metamorphic zonation are cut and tilted by rotational block faulting, and are repeated in each of the upturned blocks. Late Mesozoic to Tertiary plutonism locally thermally overprinted the regional facies, particularly in the western part of the area. Fluid-inclusion isochores, combined with calculated mineral equilibria, suggest that metamorphism took place at fluid pressures of 2 kbar (1 kbar = 100 MPa) or less, consistent with estimates of stratigraphic burial. Metamorphic fluids were H2O rich and low in dissolved salts. Maximum temperatures during regional depth-controlled hydrothermal metamorphism, based upon the widespread presence of laumontite and the lack of wairakite in the middle to upper parts of the Telkwa Formation, probably did not exceed about 250 °C at H2O pressures of 2 kbar. Mineral zones, estimated paleotemperatures, and geothermal gradients are comparable to regional hydrothermal metamorphism in active volcanic settings such as Iceland.
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Dempster, T. J., and B. Harte. "Polymetamorphism in the Dalradian of the central Scottish Highlands." Geological Magazine 123, no. 2 (March 1986): 95–104. http://dx.doi.org/10.1017/s0016756800029757.
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AbstractSystematic variations in both timing and conditions of metamorphism are observed in the Dalradian rocks of Central Perthshire, Scotland. Early (D2–D3 and syn-D3) relatively low-pressure metamorphism (550 °C, 7 kb) occurs in the Flat belt rocks of the Tay Nappe to the south, and later (post-D3) higher-pressure conditions (550 °C, 9 kb) dominate the Steep belt to the north. The latter appear to be superimposed on earlier low pressure assemblages (chloritoid–biotite) with the pressure increase probably relating to formation of the Tummel Steep Belt, possibly near 460 Ma. This polymetamorphism, in addition to the generally high pressures of Barrovian metamorphism throughout Perthshire, may account for the poor development of the metamorphic zonal pattern in this region compared to the eastern Dalradian.
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Primmer, T. J. "A transition from diagenesis to greenschist facies within a major Variscan fold/thrust complex in SW England." Mineralogical Magazine 49, no. 352 (June 1985): 365–74. http://dx.doi.org/10.1180/minmag.1985.049.352.07.
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AbstractThe north coast of Cornwall, from Bude to Newquay, provides a continuous section through a major Variscan fold/thrust complex. Illite crystallinity studies have revealed a transition from diagenesis in the north to greenschist facies metamorphism in the south in the Upper Palaeozoic succession. More detailed studies of mineral assemblages in both metabasites and pelitic rocks support the regional pattern of metamorphism indicated by illite crystallinity, and show that locally in the Tintagel district, the grade of metamorphism may have reached middle to upper greenschist facies. An attempt to correlate the above data with temperatures (108–985°C) derived from O-isotope geothermometers is made. Interpretation of the metamorphic data presented helps to emphasize the tectonic importance of the major structures seen in the fold/thrust complex.