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1
Puffer, John H., John R. McGann, and James O. Brown. "The Manhattan Schist, New York City: Proposed Sedimentary Protolith, Age, Boundaries, and Metamorphic History." Geosciences 14, no. 7 (July 15, 2024): 190. http://dx.doi.org/10.3390/geosciences14070190.
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There are some persistent basic questions pertaining to the bedrock schist of New York City (NYC). How many mappable schist formations are exposed in NYC, and what was the sedimentary protolith of the Manhattan schists? Our proposed answers are based in part on a blending of published paleontological and radiometric dating results that constrain the timing of Taconic subduction and the best choice of a pelitic protolith for the schists of NYC. We have chemically analyzed some samples of schist and shales at key locations to evaluate the plausibility of our proposals. The compelling published evidence indicates that the Taconic Orogeny began about 475 Ma, when peri-Laurentian plates began the process of east-dipping subduction under the Moretown Terrane, resulting in a magmatic flareup of the Shelburne Falls arc that carried the Moretown Terrane west across NYC. East-dipping subduction accounts for early Ordovician metamorphism until an oceanic slab break-off event at about 466 Ma. Our review of the biostratigraphic data indicates a continuation of subduction and the deposition of pelitic sediments until about 455 Ma, during the transition to deep-water turbiditic sediment deposition. This disqualifies all post-455 Ma turbidites as viable protoliths for the NYC Manhattan schists but does include the Late Cambrian to lowermost Late Ordovician pelites of the Jutland Sequence that are exposed directly west of NYC in New Jersey. Our new chemical analyses of Jutland sediments and each of the three named schists from the NYC plot as a single geochemical population. We, therefore, propose that the schists of NYC could collectively be referred to as the Manhattan schist of the Late Cambrian to lower Late Ordovician.
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Obioha, Young Ezenwa. "Geochemistry evolution of Schists of northwest Obudu area southeastern Nigeria." Global Journal of Geological Sciences 19, no. 1 (July 13, 2021): 29–39. http://dx.doi.org/10.4314/gjgs.v19i1.3.
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Geochemistry of schists of Obudu area was carried out using ICP-MS and ICP-ES techniques in order to determine the geochemical evolution of the area. 40 samples were analyzed for their major, trace and REE composition. Field mapping revealed that gneisses, amphibolites and schists comprising migmatitic schists (MS), quartz-mica schists (QMS), garnet-mica schists (GMS), and hornblende biotite schists (HBS), intruded by granites, granodiorites, quartzofeldspathic rocks and dolerites occur in the area. Structural studies revealed that the schists trend approximately NE–SW (5 – 30o ) indicating the Pan-African event. Modal analysis revealed that the schists have average concentration of quartz (15vol.%), plagioclase (An45-19 vol.%), biotite (15vol.%), garnet (9.0vol.%) and muscovite (6vol.%), the remaining consists of accessory minerals. Geochemistry showed that all the schists have molecular Al2O3 > CaO+K2O+Na2O, indicating they are peraluminous metasedimentary pelites. Trace and REE element results show that all the analyzed schist samples are depleted in Hg, Ag, Be, Bi, and Sb below < 1.0ppm, but relatively enriched in Ba, Sr and Zr with average concentration of 996, 675.73, 243.13 ppm respective. The HREE are depleted with ΣHREE < 10.2, but the LREE are relatively enriched with ΣLREE > 289.54. The ΣLREE/ΣHREE ratio ranges from 9.17 to 33.4, with a large positive delta V at Eu. These findings indicate that the schists of Northwest Obudu area are highly fractionated and had attained at least the uppermost amphibolite metamorphic grade. The schists had contributed to the development of the Pan-African continent.
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Esteban, J. J., J. Cuevas, and J. M. Tubía. "Geochemistry and origin of zircon in chlorite schists of the Ronda peridotites (Betic Cordilleras, southern Spain)." Lithosphere 11, no. 6 (November 4, 2019): 855–67. http://dx.doi.org/10.1130/l1088.1.
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Abstract This work deals with scarce chlorite schists scattered through the Ronda peridotites (Betic Cordilleras, Spain). These schists have unusually high zircon contents, which contrast with the usual lack of this mineral in ultramafic rocks. From field data and detailed petrographic, geochemical, and geothermometric studies, we focused on the origin of the zircon, a relevant issue for the interpretation of geochronological results. The chlorite schists appear as concordant sheets with granite dikes and as blackwall zones between dikes and serpentinized peridotites. As the intrusion age of the dikes and chlorite schist zircon crystallization (ca. 22 Ma) is slightly older than the age of serpentinization and related chlorite schist formation (ca. 19 Ma), we propose that the chlorite schists are tied to the intrusion of the granite dikes and the subsequent serpentinization of peridotites. Trace and rare earth elements alone are not indicative of the magmatic or hydrothermal origin of the zircon, but the combination of information about zircon morphology, melt inclusions, geothermometry, and the structural relationships between granite dikes and chlorite schists points to late magmatic melts for the zircon origin. We suggest that high-temperature melts saturated in F and Cl acted as Zr carriers under low-pH conditions. A change of the pH conditions, due to hydrothermal alkaline fluids incoming for the concomitant peridotite serpentinization, would have led to zircon crystallization and concentration at the apical zones of the dikes, and to rodingitization before the extensive observed chloritization.
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Kadir, S., and A. Akbulut. "Mineralogy, geochemistry and genesis of the Taşoluk kaolinite deposits in pre-Early Cambrian metamorphites and Neogene volcanites of Afyonkarahisar, Turkey." Clay Minerals 44, no. 1 (March 2009): 89–112. http://dx.doi.org/10.1180/claymin.2009.044.1.89.
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AbstractThe Taşoluk kaolinite deposits of Afyonkarahisar (western Anatolia) are hosted by both pre-Early Cambrian sericitic mica-chlorite schists and Neogene volcanites, the latter comprising tuffs and agglomerates. These units have been affected by hydrothermal alteration controlled by faults resulting in complex, irregular, lateral mineralogical zonation. The occurrence of a siliceous cap on altered schists and in claystone, of quartz veins in schists and tuffs, and the development of explosion cones and pit fillings indicate that alteration in both the schists and the volcanites is due to hydrothermal processes. Altered schists have generally large (locally small) Fe contents, and claystones are generally silicified and have small Fe contents. Kaolinite predominates south and west of Taşoluk, whereas high (Fe+Ti)-bearing illite + kaolinite predominate in other altered sections. The kaolinite exhibits a stacked micromorphology within altered schists, and the altered volcanites record in situ precipitation, derived from a mechanism of paired dissolution and precipitation. Illite fibres coexist with kaolinite, smectite, chlorite, mica and sericitized feldspar in markedly altered schists, revealing that the illite formed either authigenically or by conversion of smectite to illite. A relative increase in Cr+Ni and decrease in Sr+Ba in the kaolinite deposits and their schistose host rock relative to the upper level of the kaolinite deposits and their volcanic parent rocks came about by the alteration of chlorite, mica and feldspar in the sericitic mica-chlorite schists, and feldspar, glass shards and schist fragments in the volcanites as a result of extensive faulting, fracturing and hydrothermal activity during Late Miocene-Pliocene volcanism, which contributed to the development of kaolinite deposits under acidic environmental conditions. With regard to industrial applications, the low-Fe kaolinized schists are suitable for use in refractories and paper coatings, while the claystone is suitable for use in ceramics and in the white-cement industry.
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Khedr, Mohamed Zaki, Gehad M. Saleh, Khaled M. Abdelfadil, Eiichi Takazawa, Kamal Abdelrahman, Akihiro Tamura, and Shaimaa Ali El-Shafei. "The Geology and Mineral Chemistry of Beryl Mineralization, South Eastern Desert, Egypt: A Deeper Insight into Genesis and Distribution." Minerals 14, no. 5 (April 28, 2024): 465. http://dx.doi.org/10.3390/min14050465.
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Beryl mineralization in the Nugrus-Sikait domain in the South Eastern Desert (SED) of Egypt occurs as disseminated crystals in granitic pegmatite and quartz, as well as pegmatite veins crosscutting mélange schist and ophiolitic rocks. When granitic pegmatite comes into contact with the ophiolitic rocks, phlogopite and amphibole schists are formed due to K metasomatism. The ophiolitic mélange is intruded by leucogranite and related pegmatite along the NNW to NW Nugrus shear zone. Beryl samples have been collected from Um Sleimat, Madinat Nugrus, Wadi Abu Rusheid, and Wadi Sikait. Major oxides and in situ trace and rare earth elements (REEs) of beryl and associated minerals were analyzed through EPMA and LA-ICP-MS, respectively. The investigated beryl, based on its color and chemical compositions, can be classified into the two following types: pegmatitic beryl (type I) and schist-related beryl (type II). The former is colorless to pale green, and is mainly restricted in pegmatite veins; it is poor in Cr2O3 (up to 0.03 wt%) and MgO (Nil). The latter, deep green in color, is rich in Cr2O3 (up to 0.27 wt%) and MgO (up to 2.71 wt%), and occurs within quartz veins, phlogopite schists, and tremolite schists. The abundant beryl mineralization in phlogopite schists and their related quartz veins suggests that granite and associated pegmatite are the source rocks for the Be-bearing fluids that migrate along the NW-SE trending deep-seated tectonic zone, such as the Nugrus shear zone. Therefore, the formation of beryl in schists is attributed to the interaction of granitic/pegmatitic-derived Be-bearing fluids with serpentinite and gabbro interlayered with mélange schists. Variations in the trace and REE contents of both beryl types (I and II) indicate their two-stage formation from different compositions of Be-rich fluids, where light REEs, Zr, Nb, Ba, and Th decrease from type I beryl to type II. These two phases of beryl could be attributed to the magmatic/hydrothermal fluids associated with the pegmatite emplacement. The early phase of the late-stage magmatic-derived fluids was closely related to magma evolution and pegmatite formation, forming euhedral type I beryl. The late phase of pegmatite-derived fluids was mixed with serpentinite/schist-derived fluids that cause high V and Cr content in type II beryl. The composition of parent magmas of felsic rocks, the high degree of magma fractionation or the late stage melts, fluid compositions (rich in Be, Li, Cs, Rb, K), and alkali metasomatism, as well as the linear NW-SE trending deep-seated shear zone, are all factors possibly influencing beryl mineralization in the SED of Egypt.
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Na, Fuchao, Weimin Song, Yingcai Liu, Junyu Fu, Yan Wang, and Wei Sun. "Geochemistry, Chronology and Tectonic Implications of the Hadayang Schists in the Northern Great Xing’an Range, Northeast China." Minerals 13, no. 11 (October 28, 2023): 1379. http://dx.doi.org/10.3390/min13111379.
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The Late Paleozoic tectonic evolution of the Xing’an block in the eastern Central Asian orogenic belt has long been the subject of debate. In this paper, a comprehensive study of U-Pb zircon ages, Lu-Hf isotopes and whole-rock elemental analyses was carried out on Hadayang schists. Representative samples of the epidote-biotite-albite schist and biotite-albite schist yielded the weighted mean 206Pb/238U ages of 360 ± 2 Ma and 355 ± 3 Ma, respectively. This indicated the presence of Late Devonian–Early Carboniferous intermediate-basic rocks in the eastern Xing’an block. The Hadayang schists exhibited a Na-rich, tholeiitic and calc-alkaline affinity in composition with low Mg# (35.2–53.0), Cr (23.7–86.5 ppm), Ni (21.1–40.0 ppm) and Co (12.1–30.6 ppm). They were characterized by enrichment of LILEs, depletion of HFSEs and highly positive zircon εHf(t) values (the average values were +8.93 and +9.29, respectively). The magma source of the Hadayang schists was a mantle that consisted of both spinel and garnet lherzolite, with a partial melting degree of 1%–5%, and it had undergone fractional crystallization of olivine, orthopyroxene and plagioclase. The Hadayang schists, together with other Late Devonian–Early Carboniferous intermediate-basic magmatic rocks in the eastern Xing’an block, were formed in an intracontinental extension tectonic setting similar to that of the North American Basin and Range basalt. Moreover, Late Devonian–Early Carboniferous ophiolite under a similar tectonic background in the western Xing’an block has been reported. We believe that the Xing’an block would have been in the stage of intracontinental extension during the Late Devonian–Early Carboniferous.
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Nurdiana, Astin, Atsushi Okamoto, Masaoki Uno, and Noriyoshi Tsuchiya. "Development of Open Transport of Aqueous Fluid from Pegmatite Revealed by Trace Elements in Garnet." Geofluids 2022 (October 15, 2022): 1–21. http://dx.doi.org/10.1155/2022/8786250.
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We investigated the fluid flow and elemental transport from a granitic body to the middle crust by determining the trace element compositions of garnet in pegmatites related to a quartz diorite intrusion and metamorphic rocks on Kinkasan Island, northeast Japan. Garnet in the pegmatites and biotite schists is characterized by spessartine– (Sps–) almandine- (Alm-) rich compositions of Sps14–69Alm22–70Prp2–14Grs1–13 and Sps16–30Alm54–66Prp9–16Grs3–6, respectively. A garnetite pod in the metamorphic unit has grossular- (Grs-) rich compositions (Sps1–4Alm8–11Prp0.1–0.4Grs80–87Adr3–4). The peak temperature ( T ) and pressure ( P ) conditions of the biotite schist during contact metamorphism were 600–650°C and 0.27–0.41 GPa, respectively. The primary fluid inclusions in quartz crystals within the pegmatites hosted by the quartz diorite and hosted by the metamorphic rocks have a wide range of homogenization temperatures (200–380°C). These correspond to the trapping temperature of 500–700°C, assuming a salinity of 4 wt.% NaClequivalent at pressure of the crystallization of the quartz diorite. Chondrite-normalized rare earth element (REE) patterns of garnets in the pegmatites in the quartz diorite and metamorphic unit are generally characterized by enrichment of heavy REEs and negative Eu anomalies with the REE contents in the schists which are systematically lower than in the pegmatites. However, garnet in the biotite schists close to the pegmatites has similar REE contents to garnet in the adjacent pegmatites. These geochemical features suggest that garnet in the biotite schists grew in response to fluid infiltration from the pegmatites. Besides, the Grs-rich garnet in the garnetite pod and its host quartz schist have flat heavy REE patterns and no Eu anomalies, which probably reflect a metasomatic process related to plagioclase replacement that produced Ca-Al-rich fluids. Our results suggest that the infiltration of pegmatitic fluids enhances elemental transport and metamorphic reactions in the middle crust.
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Han, Zhi Qiang, Jian Liu, Kang Bian, and Quan Chen. "Research on Geological Characteristics and Deformation Law of Surrounding Rock of a Tunnel with Carbonaceous Schist in Northwest Hubei Province." Applied Mechanics and Materials 256-259 (December 2012): 471–76. http://dx.doi.org/10.4028/www.scientific.net/amm.256-259.471.
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Northwest Hubei province is located in Mount Wudang metamorphic zone, where the geological conditions are very complex. The carbonaceous schist is relatively rare in this area, however, compared with other schists, it has some quite special characteristics. This paper focuses on lithologic features, physical and mechanical characteristics of carbonaceous schist, and Huashigou tunnel is researched as the engineering background. Analysis of carbonaceous schist shows that it has typical rheological, anisotropic and water-sensitive properties. Through a large number of monitoring measurement data analysis, deformation law of carbonaceous schist are summarized.
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Rai, Santa Man. "Geology along the Arniko Highway between Barabise and Kodari (China-Nepal Boarder) area, central Himalaya." Journal of Nepal Geological Society 42 (September 24, 2011): 41–50. http://dx.doi.org/10.3126/jngs.v42i0.31447.
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The area between Barabise and Kodari in central Nepal along the Arniko Highway is geologically located into Higher Himalayan Crystallines (HHC) and Lesser Himalayan Sequence (LHS) that is separated by the Main Central Thrust (MCT). The HHC consists of amphibolite facies rocks (pelitic schist, psamitic schist, pelitic gneiss and quartzite), while LHS is comprised by green schist to amphibolite facies rocks (phyllite, calcareous phyllite, garnet-mica schist, black schist, quartzite and augen gneiss) in uppermost section and carbonate (dolomite and limestone) with phyllite, and metasandstone in lower section. The MCT in the area is oriented in E-W direction with about 30° dip due north and S-C structure preserved in augen gneiss of LHS characterizes the top-to-south sense of shearing, which could be related to the movement along the MCT. Mineral lineation marked by stretched mica indicates N to NNE direction in both HHC and LHS.
Metamorphism of inverse grade from biotite at stratigraphically lower most section of Kuncha Formation to garnet at the uppermost section having schist and augen gneiss is obvious close to the MCT in the section. However, the Kuncha Formation contains tiny crystals of garnet in the rocks of greenschist facies. Kyanite and sillimanite isograds are developed in pelitic and psamitic schists, and pelitic schists appeared at the basal part of HHC above the MCT. The transformation of garnet to chlorite at the margin and fractures and formation of chlorite within bulk rocks of the MCT zone and HHC are the indicators of traces of retrograde metamorphism because of dropping in pressure-temperature probably related to post deformation event.
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Carvalho, Cristina, Sílvia Aires, Fernando Noronha, António Casal Moura, and João Farinha Ramos. ""Schist" from Trás-os-Montes and Alto Douro (NE of Portugal): Potential Use as Natural Stone." Key Engineering Materials 548 (April 2013): 205–11. http://dx.doi.org/10.4028/www.scientific.net/kem.548.205.
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The main purpose of this work was to increase the knowledge about the geological resources of Trás-os-Montes and Alto Douro region (TMAD), particularly about their “schists” (slate, phyllite and schist), due to the economic and social effects that their mining and processing can have, not only on the local economy, but also on a national level. This work presents the results of the study conducted on “schists” from TMAD, aiming for their use as natural stone. Special emphasis is given on the results obtained from the following physical and mechanical tests: compressive strength, flexural strength, apparent density, open porosity, water absorption, abrasion resistance and resistance to ageing by thermal shock. These tests were determinant to define the most suitable applications for each schistose stone that was studied, taking into account the existing groups of natural stone products. For defining the recommended applications for each “schist”, European standards for natural stone products were considered, as well as technical specifications that exist in some European countries, which were the basis for the establishment of a proposal of technical specifications for Portugal, already published by one of the authors of this work.
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Popov, V. A., M. A. Rassomakhin, and S. V. Kolisnichenko. "Polyakov log coarse garnet occurrence in the South Urals." МИНЕРАЛОГИЯ (MINERALOGY) 9 (June 29, 2023): 60–66. http://dx.doi.org/10.35597/2313-545x-2023-9-2-5.
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Ontogenic modeling of the origin of coarse garnet of the Polyakov log occurrence (South Urals) in a fne-grained schist sequence allowed the authors to conclude on its metasomatic growth with the replacement of chlorite aggregates. Muscovite, ilmenite, epidote, quartz and apatite remain preserved in the primary schist orientation of individuals. Accessory andesine, cobaltite, pentlandite, pyrrhotite and zircon crystallized together with garnet. The formation of coarse garnet crystals is probably related to fuctuations of supersaturation relative to garnet in areas of schists with abundant chlorite. This allows us to expect the presence of coarse garnet areas in adjacent parts of the schist sequence. Keywords: South Urals, garnet, ontogeny
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Tsar, M. "EXOTIC METAMORPHIC SCHIST FRAGMENTS IN THE OLIGOCENE DEPOSITS OF THE SILESIAN NAPPE (UKRAINIAN CARPATHIANS)." Visnyk of Taras Shevchenko National University of Kyiv. Geology, no. 2(97) (2022): 14–19. http://dx.doi.org/10.17721/1728-2713.97.02.
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The study aims at analyzing the petrographic composition of exotic metamorphic schist clasts in the Oligocene deposits filling the Silesian Nappe in the south-western part of the Ukrainian Carpathians and reconstructing their possible source area. The methodology includes petrographic, sedimentological and comparative geological methods. To achieve this goal, field research was carried out along the first right tributary of the Hysnyi Stream (the village of Uzhok, Velykobereznyanskyi district, Transcarpathian region) and petrographic analysis of the selected samples of the exotic metamorphic schist clasts included in the Oligocene debris-flow deposits was performed. The results of microscopic studies showed that these exotic rocks are represented by mica-quartz schist and garnet-muscovitebiotite-plagioclase-quartz schist with a low content of chlorite, carbonate and epidote. Mineral composition and structure/texture features suggest the rocks were metamorphosed under green schist and epidote-amphibolite facies. Similar exotic rock fragments were identified by Polish scientists in the south-eastern part of the Polish Carpathians in the Silesian Nappe, where possible source area of the exotic rocks is related to the Bukowiec Paleo-Ridge, which had been located between the Dukla and Silesian basins of the Carpathian sedimentary realm. Scientific novelty. For the first time, the petrographic composition and textural and structural features of the exotic schists fragments included in the Oligocene deposits of the Silesian Nappe in the Ukrainian Carpathians (area of the village of Uzhok, Ukrainian Carpathians) are described. These schists are similar to the exotic rocks included in the Oligocene deposits of the Silesian Nappe in the Polish Carpathians, which may indicate the same source area.
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Abdus-Salam, Maryam. "Geochemistry and mineral chemistry of quartz mica schists within Iseyin-Oyan Schist Belt, Southwestern Nigeria." Indian Journal of Science and Technology 13, no. 41 (October 10, 2020): 4319–31. http://dx.doi.org/10.17485/ijst/v13i41.1628.
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Background/Objectives: The Iseyin-Oyan schist belt is made up metasedimentary rocks, gneisses, granites and pegmatite intrusions. The study was aimed at identifying the schist within this belt and assess their metamorphism, geochemical characteristics and tectonic origin. Methods: Detailed geologic field mapping was undertaken where rocks were located, studied in-situ and identified. Samples of the schist were prepared for petrographic studies. Mineralogical contents were determined using X-Ray Diffraction technique. Polished sections were studied for mineral chemistry using Scanning Electron Microscope-Energy Dispersive Spectroscopy. Rock samples were analysed using X-Ray Fluorescence Spectroscopy and Inductively Coupled Plasma Emission Spectrometry. Geochemical data were elucidated using diverse geochemical discrimination diagrams. Findings: The schists are quartz mica schists and occur in close association with amphibolites, intrusive granitoids and pegmatites. The Mineral assemblage indicates upper (at the western part) to lower (at the central part) amphibolite facies grade metamorphism in the area. Pyrope-almandine garnets occur in quartz mica schist at the western parts reinforcing higher pressure-temperature metamorphic conditions. The concentration (in %) of SiO2 ranged from 56.4-71.6; Al2O3, 13.7-21.1; Fe2O3, 2-8; MgO, 0.7-2.4; and K2O, 2.1-5.5 supporting the evidence for differential degrees of metamorphism. Large iron lithophile and high field strength elements are similar to the average upper continental crust. Pronounced negative Europium anomaly pointed to the major roles played by feldspars during the geological processes. Plagioclase ranged from albite-oligoclase and oligoclase- andesine. The precursors of the quartz mica schist are possibly arkosic and greywacke sands deposited within the active continental margins. Evidence of uplift and overturning suggested for the differential metamorphism may be due to these events usually associated with active continental margins. Applications: This study has identified the once named undifferentiated schist in the study area to be quartz mica schist with details in their grades of metamorphism elucidated. Keywords: Quartz mica schist; geochemistry; mineral chemistry; Iseyin-Oyan schist belt; precambrian basement complex
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Adeoti, Blessing, and Chukwuemeka Tony Okonkwo. "Structural Geology of the Basement Complex Rocks in Iwaraja Area, Southwestern Nigeria." International Letters of Natural Sciences 58 (September 2016): 16–28. http://dx.doi.org/10.18052/www.scipress.com/ilns.58.16.
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The geological and structural evolution assessment of the Basement Complex rocks in Iwaraja area, southwestern Nigeria showed that the basement rocks comprise quartzites and quartz-schists of the Effon Psammite Formation, quartz-mica schists, biotite schists, migmatitic gneisses, granitic gneisses, late and post-tectonic granitic rocks including pegmatites, which have been subjected to two phases of deformation. The first phase is mainly a fabric forming deformation that also led to the development of moderately plunging mineral lineation. No minor fold of this phase was recognized. The second deformation phase gave rise to the development of Iwaraja (ductile) shear zone. Mylonitic foliation is sub-vertical and steeply dipping and while the mineral lineation is sub-horizontal and shallowly plunging. Within granitic gneiss mylonites, the shear zone is characterised by early and late open to tight folds of pegmatite dykes. Adjacent the shear zone, ptygmatic folds of quartzo-feldspathic veins in gneisses and crenulated cleavages that overprinted earlier schistosity surfaces in the quartz-mica schist also characterised this deformation phase. Extensional fractures in the various lithologies generally show bimodal orientations mainly in the WNW-ESE and NW-SE directions, which are nearly perpendicular to the regional metamorphic foliations. These deformation conditions depict structural features that are associated with internal zones of orogenic belts. Within the study area, the structures document late-Precambrian deformation during the closing stages of Pan-African orogenesis.
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Santamaría-López, Ángel, Isabel Abad, Fernando Nieto, and Carlos Sanz de Galdeano. "Early Mylonitization in the Nevado-Filábride Complex (Betic Cordillera) during the High-Pressure Episode: Petrological, Geochemical and Thermobarometric Data." Minerals 13, no. 1 (December 23, 2022): 24. http://dx.doi.org/10.3390/min13010024.
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In the western part of the Sierra de los Filabres area, there are fine-grained metamorphic rock bands, showing a field aspect simitar to slates, as previously described in the geological literature of the studied region. They are variable in thickness, from millimeters to tens of meters and appear intercalated in the schist succession. The geochemical resemblance between both types of rocks (major, minor and trace elements), determined by a statistical approach and the comparison of depositional condition indices, points to a similar sedimentary origin of the protolith but different clay content. Mineral facies and illite “crystallinity” indices in the so-called slates indicate that they followed the same metamorphic path and reached the same metamorphic grade than schists. According to compositional zoning detected in micas and garnets present in both lithologies and the P-T conditions deduced from garnets, the mineral nucleation and growth episode of the main mineral paragenesis in these fine-grained schists was more remarkable during the high-pressure event, with a no significant effect of the latter low-pressure–high-temperature episode. In contrast, the coarse-grained schists developed higher size minerals during the low-pressure–high-temperature episode. A differential mylonitization process during the metamorphism is proposed to justify the discrepant field appearance and the contrasting response of both types of metapelitic rocks to the latter metamorphic event.
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Adeoti, Blessing, and Chukwuemeka Tony Okonkwo. "Structural Geology of the Basement Complex Rocks in Iwaraja Area, Southwestern Nigeria." International Letters of Natural Sciences 58 (September 9, 2016): 16–28. http://dx.doi.org/10.56431/p-m654ru.
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The geological and structural evolution assessment of the Basement Complex rocks in Iwaraja area, southwestern Nigeria showed that the basement rocks comprise quartzites and quartz-schists of the Effon Psammite Formation, quartz-mica schists, biotite schists, migmatitic gneisses, granitic gneisses, late and post-tectonic granitic rocks including pegmatites, which have been subjected to two phases of deformation. The first phase is mainly a fabric forming deformation that also led to the development of moderately plunging mineral lineation. No minor fold of this phase was recognized. The second deformation phase gave rise to the development of Iwaraja (ductile) shear zone. Mylonitic foliation is sub-vertical and steeply dipping and while the mineral lineation is sub-horizontal and shallowly plunging. Within granitic gneiss mylonites, the shear zone is characterised by early and late open to tight folds of pegmatite dykes. Adjacent the shear zone, ptygmatic folds of quartzo-feldspathic veins in gneisses and crenulated cleavages that overprinted earlier schistosity surfaces in the quartz-mica schist also characterised this deformation phase. Extensional fractures in the various lithologies generally show bimodal orientations mainly in the WNW-ESE and NW-SE directions, which are nearly perpendicular to the regional metamorphic foliations. These deformation conditions depict structural features that are associated with internal zones of orogenic belts. Within the study area, the structures document late-Precambrian deformation during the closing stages of Pan-African orogenesis.
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Craw, D., and Y. A. Cook. "Retrogressive fluids and vein formation during uplift of the Priestley metamorphic complex, north Victoria Land, Antarctica." Antarctic Science 7, no. 3 (September 1995): 283–91. http://dx.doi.org/10.1017/s0954102095000393.
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The poly-deformed Priestley schist (Wilson Terrane) of north Victoria Land, Antarctica ranges in metamorphic grade from lower greenschist facies to upper amphibolite facies. All grades of schist have been affected by structurally controlled retrogressive H2O-CO2 fluids with 45–70 mole % CO2. The fluids have deposited quartz-carbonate veins with pyrite and chlorite or biotite in late stage structures. Veins typically constitute < 1% of the rock mass, but in one greenschist facies area > 10% of the rock is vein. Veins in higher grade schists have been boudinaged after formation, and many have been annealed. Primary fluid inclusions are preserved in veins in biotite zone schists in two localities. At one locality, entrapment of immiscible fluids (water with c. 8 and 45 mole % CO2) occurred during vein formation, at about 280–300°C and 700 ± 200 bars fluid pressure. The aqueous fluid is slightly saline (4 wt % NaCl equivalent). At the other primary fluid inclusion locality, veins were formed from a single phase fluid (c. 70 mole % CO2) at 200–350°C and 1600 ± 500 bars fluid pressure. Both these vein systems are inferred to have formed between 2 and 8 km depth, near the brittle-ductile transition. Retrogressive fluid mobility and vein formation occurred throughout schist in the Priestly metamorphic complex during uplift in the latter part of the Ross Orogeny (c. 490 Ma), following near-isobaric cooling at metamorphic depths.
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Canil, Dante, Stephen T. Johnston, Rameses J. D’Souza, and Larry M. Heaman. "Protolith of ultramafic rocks in the Kluane Schist, Yukon, and implications for arc collisions in the northern Cordillera." Canadian Journal of Earth Sciences 52, no. 7 (July 2015): 431–43. http://dx.doi.org/10.1139/cjes-2014-0138.
Full textAbstract:
Mafic and ultramafic rocks crop out as decimetre- to centimetre-sized bodies of talc–antigorite–olivine (±orthopyroxene) and chlorite–amphibole schists interleaved in the pelitic Kluane Schist of southwestern Yukon. The metamorphic assemblages in ultramafic rocks exposed at Doghead Point overprint two generations of cleavage and are consistent with metamorphism reaching >550 °C (talc + olivine) and >750 °C (olivine + enstatite) in the contact aureole of the Eocene Ruby Range batholith. The bulk rock major and trace element patterns in the ultramafic schists (>40 wt.% MgO, Mg/(Mg + Fe) > 0.90) are unlike residual mantle from partial melting (i.e., ophiolite, orogenic massif, abyssal ocean floor) but are similar to peridotite or pyroxenite cumulates from arc magmas. Identical trace element concentrations and patterns are observed in several late Triassic basalts, pyroxenites, and websterites occurring to the southeast in Stikinia (present coordinates). A highly discordant U–Pb zircon date for one antigorite–talc–olivine schist sample (200–210 Ma) is within the range of U–Pb zircon ages for the late Triassic Lewes River – Stuhini arc in northwestern Stikinia (200–208 Ma, 216–220 Ma). When combined with other published age information, the ultramafic rocks in the Kluane Schist are interpreted as fragments of deeper arc-related mafic and ultramafic intrusive rocks introduced to the Kluane forearc basin between 95 and 82 Ma by exhumation along shear zones in northwestern Stikinia, most likely the Wann River or Llewellyn Faults. The Kluane Schist represents a west-facing forearc basin bordered to the east by arc-parallel strike-slip fault(s) that served to exhume and imbricate large knockers into the accretionary prism.
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Setiawan, Muhamad Ragil, and Rahmat Nawi Siregar. "Kandungan Mineral dan Struktur Kristal Batu Sekis." Science, and Physics Education Journal (SPEJ) 4, no. 1 (December 31, 2020): 24–30. http://dx.doi.org/10.31539/spej.v4i1.1513.
Full textAbstract:
This study aims to determine the mineral content and crystal structure of schist rocks in South Lampung. The method used in this research is the X-ray diffraction method to see the lattice parameters and the crystal structure of the schist rocks. Based on data processing, information was obtained that two main minerals were found, namely quartz and albite minerals. In conclusion, the Albit minerals found in the two samples of rock crystal schists in South Lampung have the same crystal structure and lattice parameters, while the quartz minerals from the two samples have different crystal structures and lattice parameters.
Keywords: Lampung, Schis, XRD, Crystal Structure
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Ayodele, Olusiji Samuel. "Geochemical Exploration for Heavy Metals in the Stream Sediments of Okemesi-Ijero Area." Journal of Advance Research in Applied Science (ISSN: 2208-2352) 3, no. 4 (April 30, 2018): 01–29. http://dx.doi.org/10.53555/nnas.v3i4.648.
Full textAbstract:
The bedrocks and gold mineralization have been widely studied especially, in the southern extension of the Ilesha schist belt, but information regarding stream sediments in the area is rarely available in literature. The present study therefore, focused on stream sediments geochemical survey of Okemesi/Ijero axis within the northern extension of Ilesha schist belt using an integrated approach to elucidate the heavy metals potentials and its possible controlling environmental geological conditions. Detailed geological survey involved lithological and structural assessment of the bedrocks. Thirty-five (35) stream sediment samples were collected at a depth of 20-25cm. Major oxides of the stream sediments for major elements were determined using atomic emission spectroscopy (AES). Trace and rare earth elemental analysis was done using inductively coupled plasma mass spectrometry (ICP-MS). Data evaluation was carried out using statistical packages for software simulation. Results showed that bedrock types are quartzbiotite-schists, banded-gneiss, granite-gneiss, biotite-gneiss, calc-gneiss, porphyritic granites, charnockites, massive and schistose quartzites, mica-schists. Structural assessment of the bedrocks revealed folds, fractures and veins as products of Precambrian deformations. Sediments have relatively high concentration of heavy metals such as Mn (387-200ppm), Zn(76.5- 18.52ppm), Pb(39.81-20.23ppm), La 36.2-15.5ppm), Cu(12.68-13.65ppm). However, the folds, fractures and veins provided the groundwork for epigenetic type of mineralization in the studied area.
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Erokhin, Yuriy V., Kirill S. Ivanov, Anatoliy V. Zakharov, and Vera V. Khiller. "Accessory and Ore Mineralization of Schists from the Basement of the Yamal Peninsula (Zapadno-Yarotinsky Area, Western Siberia)." UNIVERSITY NEWS. NORTH-CAUCASIAN REGION. NATURAL SCIENCES SERIES, no. 2 (210) (June 28, 2021): 49–55. http://dx.doi.org/10.18522/1026-2237-2021-2-49-55.
Full textAbstract:
The results of studying the mineralogy of metamorphic schists from the Pre-Jurassic base of the Arctic part of the West Siberian plate are presented. The accessory and ore mineralization of schists from the Zapadno-Yarotinsky license area located in the southern part of the Yamal Peninsula is studied. The schists was uncovered by the Zapadno-Yarotinskaya No. 300 well at a depth of 2762 m. Above the section, the metamorphic rocks are overlain by a young Meso-Cenozoic cover. The schists are mainly composed of quartz, plagioclase (albite), carbonates (dolomite and siderite), mica (muscovite) and chlorite (donbassite). The discovered accessory and ore minerals in the metamorphic schists of the Zapadno-Yarotinsky area can be divided into two groups. The first group includes minerals that were formed during the metamorphism of schists, or were preserved as detrital matter. These minerals include zircon, fluorapatite, and rutile as the most stable compounds. The remaining mineralization (pyrite, sphalerite, chalcopyrite, cubanite, galena, cobaltite, barite, xenotime-(Y), goyazite, synchysite-(Nd), native silver and copper) is clearly secondary and was formed as a result of superimposed metasomatic processes. Judging from the described mineralogy, the schists underwent changes as a result of superimposed propyllitization. The temperature range of this process is determined by the formation of cubanite in association with chalcopyrite at a temperature of 200-210 оС.
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Pavlopoulos, Kosmas, and Hampik Maroukian. "Geomorphic and morphotectonic observations in the drainage network of Kakotopia Stream, North East Attica, Greece." Geologica Balcanica 27, no. 3-4 (December 30, 1997): 55–60. http://dx.doi.org/10.52321/geolbalc.27.3-4.55.
Full textAbstract:
The Kakotopia stream, located in north-east Attica, flows north into the South Euboic gulf. The drainage basin of Kakotopia is composed of schists, marbles and fluviotorrential deposits. The contact between the marbles and schist system in most cases is tectonic defined by several fault surfaces; in other instances, the contact is transitional. There are numerous neotectonic faults in the region, having a prevailing SE-NW direction, which form small tectonic horsts and grabens, usually filled with recent deposits. An asymmetric anticlinal structure is also observed plunging towards the SW. A large part of the lower reaches of the drainage system of Kakotopia stream is most probably missing. This is owed to the presence of major faults having an ESE-WNW direction parallel to today's coastline. The creation of the South Euboic gulf depression during the Quaternary is attributed to the presence of these faults. The upper section of the drainage system is controlled to a great extent by the tectonic activity of the area. In this part, we observe the phenomenon of stream piracy which is owed not only to fault tectonism but also to the differential erosion rates of the marbles and the schists.
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NUONG, N. D., T. ITAYA, and Y. NISHIMURA. "Age (K–Ar phengite)–temperature–structure relations: a case study from the Ishigaki high-pressure schist belt, southern Ryukyu Arc, Japan." Geological Magazine 145, no. 5 (July 22, 2008): 677–84. http://dx.doi.org/10.1017/s0016756808004998.
Full textAbstract:
AbstractThe Ishigaki high-pressure schist belt in the southern Ryukyu Arc is correlated with the Suo high-pressure schist belt in southwest Japan. The former metamorphic sequence is composed mainly of basic and pelitic schists and is subdivided into three zones, the lower-grade zone A, the medium-grade zone B and the high-grade zone C, based on the mineral assemblages of the basic schists. The K–Ar phengite age gives 188–205 Ma for zone A, 196–206 Ma for zone B and 208–220 Ma for zone C, while the apparent d002 spacing of carbonaceous materials is 3.590–3.437 Å, 3.415–3.390 Å and 3.387–3.364 Å, respectively. The age–d002 relationships suggest that the ages become older with increasing metamorphic temperature. This positive age–temperature relationship in the Ishigaki area contrasts with a negative relationship in the Nishiki area in the Suo belt. The two areas also display a contrasting thermal structure with the former area having an inverted metamorphic gradient and the latter displaying a normal thermal structure. These contrasting age–temperature–structure relationships in the metamorphic belt could be due to different tectonic styles relating to the exhumation of the metamorphic sequences. We suggest that the ages obtained are related directly to the ductile deformation history of the matrix phengite below the closure temperature (500°C) during exhumation of the host rocks. The duration from the beginning of exhumation to the apparent resetting of the phengite K–Ar system was different between the two metamorphic sequences, and significantly longer in the Ishigaki than the Nishiki.
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Eric, S., D. Milovanovic, and D. Babic. "GARNETS OF MICA-SCHISTS FROM CRNI VRH AND RESAVSKI HUMOVI (SERBIA)." Bulletin of the Geological Society of Greece 36, no. 1 (January 1, 2004): 552. http://dx.doi.org/10.12681/bgsg.16752.
Full textAbstract:
Metamorphic rocks of the Crni Vrh and Resavski Humovi area belong to the north-northwestern part of the Serbo-Macedonian Composite Terrane and consist of different types of mica-schists, gneisses and amphibolites. Mica-schists are composed of biotite, muscovite, garnet, staurolite, kyanite, small quantity of Kfeldspar, acid plagioclase and quartz. Accessory minerals are apatite, zircon, tourmaline and ilmenite. Garnets in mica-schists from both localities occur as subhedral to anhedral porphyroblasts from 0.2 to 10mm in size. Most garnets are oriented parallel to the dominant foliation. Garnets from the Crni Vrh mica-schists contain more spesartine component than garnets from Resavski Humovi, while almandine component show opposite tendency. The difference between those garnets is clearly visible, as well as zonality expressed through the increase of almandine component from center to the grain rim. The spesartine component as mentioned above, shows the opposite tendency. Using different geothermometers and geobarometers it was found that mica-schists from Crni Vrh were formed at temperatures from 550-600°C and pressures from 6-6.2 kbar, while micaschists from Resavski Humovi developed at slightly lower temperatures (520-560°C) and at some higher pressures (7-7.3 kbar).
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Bassi, Ε. Κ., Κ. Soukis, and S. Lekkas. "THE PRESENCE OF VARI - KIROU PIRA UNIT AT PANION HILL (SE ATTICA, GREECE)." Bulletin of the Geological Society of Greece 36, no. 4 (January 1, 2004): 1608. http://dx.doi.org/10.12681/bgsg.16564.
Full textAbstract:
Detailed mapping in the area of Panion Hill (SE Attica, Greece), revealed the existence of three metamorphosed lithological units which are separated by major tectonic contacts. The lower unit is located at the western part of Panion Hill and comprises marble - schist alternations that pass transitionally to massive dolomitic marbles of probable Thassic age. The intermediate unit comprises exclusively massive to thick bedded marbles that occupy the central and eastern part of the hill. The upper unit can be observed mainly at the foothills of Panion and comprises HP/LT schists, exhibiting greenschsist fades retrograde metamorphism. The contact between the lower and the intermediate unit is a low-angle normal fault, dipping to the east-southeast whereas the upper unit, in most cases is juxtaposed against the intermediate and lower units by high angle normal faults. These contacts accommodated the exhumation of the lowermost metamorphic formations of Attica at least in the last stages. The overall structure resembles that of Mt. Hymittos (east of Athens), where the Vari Schists and Dolomitic Marble formations (Vari - Kirou Pira Unit, VKPU) underlie tectonically the Lower Marble, Kesariani Schists and Upper Marble formations (Hymittos Unit, HU) Based on lithological and structural similarities the lower unit of Panion Hill is considered to be part of the Vari - Kirou Pira Unit and the intermediate unit part of the Hymittos Unit, respectively. The upper unit of Panion Hill belongs to the allochthonous Lavrion Unit. The existence of a major tectonic contact separating formations of VKPU and HU in several outcrops in SE Attica signifies that it is of no local character. Furthermore, it supports the suggestion of dividing the relatively autochthonous unit of Attica into two distinct units: the upper Hymittos Unit and the lower Vari - Kirou Pira Unit, the latter standing for the actual autochthonous unit of SE Attica.
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Schulz, Bernhard. "Mineral chemistry, geothermobarometry and pre-Alpine high-pressure metamorphism of eclogitic amphibolites and mica schists from the Schobergruppe, Austroalpine basement, Eastern Alps." Mineralogical Magazine 57, no. 387 (June 1993): 189–202. http://dx.doi.org/10.1180/minmag.1993.057.387.01.
Full textAbstract:
AbstractAlternating eclogitic amphibolites, mica schists and orthogneisses in the Schobergruppe to the south of the Tauern Window suffered a post-Upper-Ordovician progressive deformation D1-D2which produced parallel planar-linear structures in all the rocks. Zoned garnets, preferentially oriented zoned clinopyroxenes (Jd 35-42%) and albite (An 7-9%) give evidence of high-pressure metamorphism (550-650°C 14-16 kbar) of the metabasites. Ca-amphiboles crystallized during subsequent decompression. In a kyanite-staurolite-garnet mica schist 300 metres below the metabasites, garnetbearing assemblages grew synchronous with the development of foliations S1and S2. Garnets are zoned with increasing XMgand decreasing-increasing-rcdecreasing Xcafrom cores to rims. Albitic plagioclase (An 1-3%) and micas are enclosed in garnet cores and rims, are in contact with garnet, and occur with garnet in microlithons. When these minerals are used for geothermobarometry, a prograde P-T evolution (460 to 680°C with coeval pressure variations which reach high-pressure conditions can be estimated. This suggests that garnet-plagioclase geobarometry with albitic plagioclase works in the relevant P-T field. Similar garnet zonation trends and a similarly shaped P-T path from mica schists of an adjacent region with late-Variscan cooling ages, points to an eady-Variscan age of the syn-D1-D2high-pressure and subsequent amphibolite-facies metamorphism.
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Omanayin, Y. A., M. Lawal, I. B. Bolaji, and A. Muhammad. "Field and petrographic studies of Basement Complex rocks in Saigbe and Environs, North-Central, Nigeria." Nigerian Journal of Basic and Applied Sciences 31, no. 1 (October 24, 2023): 49–59. http://dx.doi.org/10.4314/njbas.v31i1.6.
Full textAbstract:
Geological mapping and petrographic studies of rocks provide useful information on texture and mineralogical composition of rocks which can be used in the exploration and exploitation of any associated mineralization. However, few regional studies have been conducted in Minna and environs. Here, preliminary field mapping and petrography of out crops in Saigbe environ were conducted to determine their identification, structural and mineralogical composition. Twenty-one rock samples were collected, eight of which were used for thin section analysis. Joint directions were measured and plotted on rose diagram. Results show that Saigbe is underlain by schist, amphibolite and granite with minor pegmatite intrusions. Joints, faults, fold and foliations constitute main structures. Joints in the schists trend NE-SW, while those in the granites trend NW-SE, suggesting different episodes of emplacement for both rocks. Petrography revealed that the schists comprised quartz, biotite, muscovite, plagioclase and opaque mineral, while the amphibolites are composed largely of quartz, hornblende, plagioclase feldspar and opaque minerals. The granites are composed of quartz, microcline, plagioclase feldspar, muscovite and opaque minerals. The pegmatite dykes in the granites comprised quartz, plagioclase feldspar, orthoclase feldspar, muscovite and gemstones, hence interpreted as product of residual melt. The pegmatites make interesting target for mineral exploration.
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Samuel, Ayodele Olusiji, and AsubiojoFola Emmanuel. "Mineralization Characterization of Psammitic Rocks in Efon-Alaaye and Environs using Remote Sensing and Field Studies." Asian Review of Environmental and Earth Sciences 8, no. 1 (November 26, 2021): 48–61. http://dx.doi.org/10.20448/journal.506.2021.81.48.61.
Full textAbstract:
This paper analyses remotely sensed data over a part of the Psammitic Rocks in Efon-Alaaye and Environs to elucidate its geology and structural framework as well as delineate the potential zones of mineralization. The study area belongs to the Precambrian Basement Complex terrain of Southwestern Nigeria and lies within the eastern unit of the Ilesha schist belt. The lithologic units comprise schistose quartzites, quartz schists, quartz-mica-schists, and granitic gneisses. Landsat 8 satellite imagery and Shuttle Radar Topography Mission imagery (SRTM), both of path 190 and row 055, were used for the purpose of this study. A total of 138 lineaments of total length of 147.948 Km, were automatically extracted from both data. Rose diagram showed that the lineaments are bi-directional, with major lineaments trending NE-SW, E-W and the subsidiary ones in the NW-SE direction. These lineaments are mostly mapped on the schistose quartzites. Also, N-S trending faults were mapped from the Digital Elevation Model map generated from the SRTM data which was confirmed to be reverse fault based on field studies. The mineral alteration map generated revealed signatures of gold, iron oxides and silica minerals, while the mineralization potential map was done with reference to established geological settings of the area in conjunction with the structural elements such as folds, faults, joints and fractures mapped and measured on the field. These structures are typical of gold mineralization and associated metallic minerals in the Ilesha schist belt. This study also confirmed that mineralization in the study area is structurally controlled and type of mineralization is epigenetic in nature as a result of favorable ground preparation.
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Sun, Wenqing, Lidong Dai, Heping Li, Haiying Hu, Changcai Liu, and Mengqi Wang. "Effect of Temperature, Pressure, and Chemical Composition on the Electrical Conductivity of Schist: Implications for Electrical Structures under the Tibetan Plateau." Materials 12, no. 6 (March 22, 2019): 961. http://dx.doi.org/10.3390/ma12060961.
Full textAbstract:
The experimental study on the electrical conductivities of schists with various contents of alkali ions (CA = K2O + Na2O = 3.94, 5.17, and 5.78 wt.%) were performed at high temperatures (623–1073 K) and high pressures (0.5–2.5 GPa). Experimental results indicated that the conductivities of schist markedly increased with the rise of temperature. Pressure influence on the conductivities of schist was extremely weak at the entire range of experimental temperatures. Alkali ion content has a significant influence on the conductivities of the schist samples in a lower temperature range (623–773 K), and the influence gradually decreases with increasing temperature in a higher temperature range (823–1073 K). In addition, the activation enthalpies for the conductivities of three schist samples were fitted as being 44.16–61.44 kJ/mol. Based on the activation enthalpies and previous studies, impurity alkaline ions (K+ and Na+) were proposed as the charge carriers of schist. Furthermore, electrical conductivities of schist (10−3.5–10−1.5 S/m) were lower than those of high-conductivity layers under the Tibetan Plateau (10−1–100 S/m). It was implied that the presence of schist cannot cause the high-conductivity anomalies in the middle to lower crust beneath the Tibetan Plateau.
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Kounis, G. D., and K. G. Kounis. "RELATIONSHIP BETWEEN THE TRANSMISSIBILITY OF THE “ATHENS SCHISTS” AND THE PERCENTAGE OF THEIR COMPETENT ROCK COMPONENT." Bulletin of the Geological Society of Greece 43, no. 4 (January 25, 2017): 1767. http://dx.doi.org/10.12681/bgsg.11362.
Full textAbstract:
Aquitard formations consisted principally of “soft”, ductile schists, crystalline or not, including,as a minor component, thin intercalations of “hard” rocks, like carbonates, quartzites, sandstones, quartz veinlets and the alike, though of low transmissibility, and thus very low yielding, are of great importance in some places where groundwater is demanded, especially in drought periods for irrigation of parks, and other uses. To these formations belong the “Athens Schists“ (from a long ago term, after R.Lepsius). Formations like these, during the orogenic processes and their structural finishing, responded, under the compressive stresses, with a resultant normal extension strain contemporary or late, by folding affecting mostly the “plastic”, ductile “soft”, low rigidity components, by fracturing their competent, more rigid, “hard” components ; a fracturing hydraulically well performing, particularly that in carbonates which are better dissoluble into the circulating water. Further, a very good measure of the yield of the unit saturation front under unit hydraulic head is the transmissibility of the formation, which in turn becomes a good decision making parameter in the exploitation of groundwater. Therefore, the search for the correlation between the transmissibility (T) of the “Athens Schist” and the percentage (Hr) of the brittle, “hard”, hydraulically well performing component arised as a hydrogeologically sound idea. A very good and positive relationship T vs. Hr has been revealed, with an increase of transmissibility (ΔT) of “Athens Schists” per unit increase (ΔΗr) of the percentage found in the range of values. 0.38Χ 10-2 lit/sec.m.Hr < ΔΤ < 0.72 X10-2 lit/sec.m.Hr Values of T are very low, as expected for a formation of the hydrolithology of the “Athens Schist”, and mostly in between 0.4Χ 10-2 lit/sec.m < Τ < 8.5 X10-2 lit/sec.m The percentage (Hr) of the hard member is commonly in the range of values 2.8% < Hr < 17.5% Δελτίο της Ελληνικής Γεωλογικής Εταιρίας, 2010 Bulletin of the Geological Society of Greece, 2010 Πρακτικά 12ου Διεθνούς Συνεδρίου Proceedings of the 12th International Congress Πάτρα, Μάιος 2010 Patras, May, 2010 Transmissibility is calculated under unsteady state conditions of pumping tests in boreholes, using the Jacob approach. Drawdown (s) with time (t) from start of pumping offers, with a very good accuracy, the appropriate linear segment on semi-logarithmic plot. Values of T from pumping test data representing longer pumping time and a more expanded cone of depression to wider rock mass showed recharge condition with delayed yield. However, dependence of T on Hr is again positive and very good. The percentage (Hr) of the “hard” rock component of the “Athens Schist” was measured on drilling cuttings and in outcrops of the formation ( excavations for buildings foundations etc ) in the closer vicinity of boreholes, and results found were well comparable to each other.
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Mohamedai, Moa′awia Adam, and Osman Mohammed Elhassan. "Genesis of Gold Deposit in Um Trambishi Area, NE Atbara, Sudan." Journal of The Faculty of Science and Technology, no. 6 (January 13, 2021): 103–9. http://dx.doi.org/10.52981/jfst.vi6.614.
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Um Trambishi area consists of volcano-sedimentary sequence intruded by syntectonic pluton of granitoids composition with marginal fissures injected by aplite, had been subjected to dynamic metamorphism and obliterated by recrystallization forming different rock units varying in composition, forming greenschist terrains. These are an assemblage of recrystalline schists, meta-acid, cataclastic tonalite, granodiorites, meta-andesite, chlorite schists, quartzite, marble, metabanded chert, together with two generations of unmineralized deformed and undeformed white quartz, which are oriented mainly in E-W and N-S direction following faults trend. The area is subjected to four deformational phases of brittle-ductile transition. The metamorphic grade is Green Schist Facies. The alteration around the endo-contact zone is characterized by minerals: albite, chlorite, epidote, sericite, carbonate and kaolin with anomalous Au=0.91ppm, Ag=1.75ppm, As=44.6XRF, Co=15.70XRF, V=65XRF, Ti=4796XRF, Cr=23XRF, Sr=269XRF, and base metals Pb=1.51ppm, Zn=22.02ppm and Cu=13.59ppm. The first phase of hydrothermal solution carrying gold is related to the magmatic high temperature associated with granitoidal intrusions, deposited into the planar fabric S1 and has a characteristic signature of hypothermal processes .The second mode of occurrence is the regeneration of auriferous quartz stringers filling into the tectonic fissures trending 340⁰ and oblique to S1 as a result of D3 (Keraf Shear Zone) and has a characteristic signature of mesothermal processes.
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Thompson, J. B. "Modal Spaces for Pelitic Schists." Reviews in Mineralogy and Geochemistry 46, no. 1 (January 1, 2002): 449–62. http://dx.doi.org/10.2138/rmg.2002.46.10.
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A. O, Talabi, Awoleke S. O, Akinola O. O, and Afolagboye L. O. "Petrographic Characteristic and Geochemical features of Basement Rocks in Ikogosi, Southwestern Nigeria." International Journal of Applied Science and Research 05, no. 05 (2023): 145–56. http://dx.doi.org/10.56293/ijasr.2022.5441.
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This study investigates and reports petrographic characteristics, geochemical features and the processes of formation of rocks in Ikogosi, southwestern Nigeria. Eighteen (18) rock samples (six quartzite, six migmatite gneiss and six schists) were collected and subjected to optical study. Ten (10) representative samples (six quartzite, three schist and one migmatite gneiss) were evaluated for major elements composition using Energy Dispersive X-Ray Fluorescence (ED-XRF). Petrographic evaluation revealed quartz, feldspar, muscovite, biotite, hornblende, pyroxene and opaque are dominant mineral constituents in quartzite and schist while migmatite gneiss contains the same set of minerals but without opaque constituents. Quartz forms a dominant constituent in quartzite and migmatite gneiss but as subordinate mineral in the schist. The feldspars are mainly plagioclase with albite twinning, associated microcline has characteristic crosshatched twinning. Chemical investigation reveals the rock units are generally siliceous. Three oxides (SiO2, Al2O3 and Fe2O3) constitute 85–90% of the bulk chemical composition of the rocks. SiO2 constituent as applied in rock classification indicates the quartzite is unequivocally felsic, migmatite is intermediate while the schist is mafic to ultramafic. K2O versus SiO2 variation plot revealed that the quartzite and schist are tholeiitic while the migmatite gneiss is shoshonitic. TiO2 versus SiO2 variation diagram depicts igneous antecedent.
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Eskola, T., and V. Peuraniemi. "Secondary sulphate precipitates in the gravel pit at Kumpuselkä esker, northern Finland." Mineralogical Magazine 72, no. 1 (February 2008): 415–17. http://dx.doi.org/10.1180/minmag.2008.072.1.415.
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AbstractWhite and yellowish precipitates were found in a gravel pit in the Kumpuselkäesker chain during the summers of 2004—2007. The esker is located in northern Finland, in the northern Ostrobothnia schist area which contains mica schists with quartz veins, which are locally enriched in Co, Cu, Au, Zn, Pb and Ni. A thin till bed lies between the esker gravel and bedrock. Precipitates were found as small grains on the till surface, encrusting twigs and around small pebbles. Ground-water ponds in the pit measured in the summer of 2006 were very acidic as was the till material. The precipitates comprise secondary sulphates, such as gypsum, pickeringite and Mg-sulphates, which are all water-soluble.
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Laskari, Sofia, Konstantinos Soukis, Stylianos Lozios, Daniel F. Stockli, Eirini M. Poulaki, and Christina Stouraiti. "Structural Study and Detrital Zircon Provenance Analysis of the Cycladic Blueschist Unit Rocks from Iraklia Island: From the Paleozoic Basement Unroofing to the Cenozoic Exhumation." Minerals 12, no. 1 (January 11, 2022): 83. http://dx.doi.org/10.3390/min12010083.
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Detailed mapping and structural observations on the Cycladic Blueschist Unit (CBU) on Iraklia Island integrated with detrital zircon (DZ) U-Pb ages elucidate the Mesozoic pre-subduction and the Cenozoic orogenic evolution. Iraklia tectonostratigraphy includes a heterogeneous Lower Schist Fm., juxtaposed against a Marble Fm. and an overlying Upper Schist Fm. The contact is an extensional ductile-to-brittle-ductile, top-to-N shear zone, kinematically associated with the Oligo-Miocene exhumation. The DZ spectra of the Lower Schist have Gondwanan/peri-Gondwanan provenance signatures and point to Late Triassic Maximum Depositional Ages (MDAs). A quartz-rich schist lens yielded Precambrian DZ ages exclusively and is interpreted as part of the pre-Variscan metasedimentary Cycladic Basement, equivalent to schists of the Ios Island core. The Upper Schist represents a distinctly different stratigraphic package with late Cretaceous MDAs and dominance of Late Paleozoic DZ ages, suggestive of a more internal Pelagonian source. The contrast in the DZ U-Pb record between Lower and Upper Schist likely reflects the difference between a Paleotethyan and Neotethyan geodynamic imprint. The Triassic DZ input from eroded volcanic material is related to the final Paleotethys closure and Pindos/CBU rift basin opening, while late Cretaceous metamorphic/magmatic zircons and ~48–56 Ma zircon rims constrain the onset of Neotethyan convergence and high-pressure subduction metamorphism.
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Μαρίνος, Π., Β. Μαρίνος, Γ. Στούμπος, M. Νόβακ, K. Κορκάρης, and M. Μπενίση. "BEHAVIOUR OF THE "ATHENIAN SCHIST" IN EXCAVATION BY AN OPEN FACE SHIELD BORING MACHINE. EXTENSION LINE TO PERISTERI OF THE METROPOLITAN RAILWAY OF ATHENS." Bulletin of the Geological Society of Greece 36, no. 4 (January 1, 2004): 1790. http://dx.doi.org/10.12681/bgsg.16648.
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The excavation of the Metropolitan Railway of Athens is being opening mainly through the system of "Athenian Schist" which basically is constituted by a sequence of schists and metasandstones and presents high heterogeneity and tectonic disturbance due to faults and shear zones. The excavation is either mechanized or conventional. This paper is focused on the extension line to Peristeri, where an OFS (Open Face Shield) ΤΒΜ was used. This machine is effective in controlling any instabilities in fair quality rock mass, but not when poor quality rock masses are present where the stand-up time is limited. In such cases immediate support of the face or even improvement of the quality of the material is necessary. In this paper a specific classification of "Athenian Schist" is described in order to provide predictions for the behaviour of the rock masses under the conditions of an excavation with an OFS and, to access the risks but also the need of remedial measures
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Shatsky, V. S., A. L. Ragozin, Q. Wang, W. Su, A. A. Ilyin, and M. V. Kolesnichenko. "FEATURES OF THE STRUCTURE AND EVOLUTION OF THE LOWER PARTS OF THE CONTINENTAL CRUST OF THE YAKUTIAN DIAMONDIFEROUS PROVINCE IN THE AREA OF THE UPPER-MUNA KIMBERLITE FIELD." Доклады Российской академии наук. Науки о Земле 508, no. 2 (February 1, 2023): 173–84. http://dx.doi.org/10.31857/s2686739722602393.
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Upper Muna kimberlite field) showed that the crust at different levels is composed of pyroxene, garnet-pyroxene crystalline schists and garnet-pyroxene gneisses. Exsolution textures in pyroxenes and amphiboles, granat rims around grains of ilmenite and pyroxenes indicate that the mineral associations of crystalline schists were formed during cooling at constant pressure. Р–Т equilibrium parameters indicate that garnet-pyroxene crystalline schists are present in the middle crust (P = 7–8 kbar), while garnet-pyroxene gneisses can be considered as rocks of the lower crust (P = 9–10.1 kbar). For the first time, sodalite was found in xenoliths of crystalline schists, which indicates the presence of brines with a high concentration of NaCl at the final stages of rock cooling. The determination of the U–Pb age of zircons testifies to the Neoarchean (2.7 Ma) tectono-thermal event, accompanied by the melting of the crust. In the garnet–pyroxene gneisses, the 1.9 stage is weakly manifistated. The obtained data confirm the earlier conclusion about the vertical and lateral heterogeneity of the crust of the Yakutsk diamondiferous province and the absence of dependence between the degree of crust reworking and spatial location relative to the main collision zones of the Siberian craton.
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Springer, Janet S. "Carbon in Archean rocks of the Abitibi belt (Ontario–Quebec) and its relation to gold distribution." Canadian Journal of Earth Sciences 22, no. 12 (December 1, 1985): 1945–51. http://dx.doi.org/10.1139/e85-210.
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In the Abitibi belt of Ontario and Quebec, sedimentary black argillites with carbon contents of up to 5% C contain up to 0.5 ppm gold. Sheared black argillites, now graphitic schists, reflect the values of the sedimentary precursors, although their appearance is very different. Gold values of 15 ppm and more are found in graphitic schists only where alteration, shown by quartz veins and increased carbonate content, gives independent evidence of a later hydrothermal event. Gold-rich graphitic schists are characterized by veining; raised gold values closely follow vein margins. As mass balancing shows gold leaching and redeposition to be unlikely, gold enrichment is interpreted to reflect introduction of gold and its preferential deposition in carbonaceous rocks by reduction at vein margins. Natural carbons in these rocks may have been surface activated by both shearing and hydrothermal fluids.
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Krstic, Branislav, Ljubinka Maslarevic, and Milan Sudar. "On the graptolite schist's formation, Silurian-Lower Devonian, in the Carpatho-Balkanides of eastern Serbia." Annales g?ologiques de la Peninsule balkanique, no. 66 (2005): 1–8. http://dx.doi.org/10.2298/gabp0566001k.
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The fabric of the Silurian and a part of the Lower Devonian in the Carpatho-Balkanides of eastern Serbia, i.e. in two large geotectonic units, the Kucaj Unit (Getic) and the Luznica Unit (West Kraishte), is reviewed in this paper. Silurian sediments of the Serbian part of the Carpatho-Balkanides are made of the Graptolite Schists Formation, from the lower part of the acuminatus Zone at the Ordovician-Silurian boundary to the transgrediens Zone at the Silurian-Devonian boundary. The presence of all parts of the Silurian is proved on the basis of graptolite faunas: Llandovery (Rhuddnanian, Aeronian, Telychian), Wenlock (Sheinwoodian, Homerian), Ludlow (Gorstian, Ludfordian) and Pridoli. Two Lower Devonian (Lochkovian) zones (uniformis and hercynicus), with which the deposition of the Graptolite Schists Formation ended in eastern Serbia is also described. Data on the geochemical characteristics of the Graptolite Schists Formation are presented as well.
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Crawford, M. L., and W. A. Crawford. "Magma emplacement in a convergent tectonic orogen, southern Revillagigedo Island, southeastern Alaska." Canadian Journal of Earth Sciences 28, no. 6 (June 1, 1991): 929–38. http://dx.doi.org/10.1139/e91-084.
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The western metamorphic belt of the British Columbia – Alaska coastal orogen consists of lithostratigraphic units assigned to the Taku terrane and the Gravina sequence. On Revillagigedo Island and Cleveland Peninsula in the Ketchikan quadrangle of southeastern Alaska, greenschist- and amphibolite-grade schists of the western metamorphic belt are intruded by mid-Cretaceous tonalite and leucotonalite plutons and sills. A number of these igneous bodies are spatially associated with northwest-trending shear zones developed along thrust faults that formed during the main phase of metamorphism of the schists. Observations of field relations and structural fabric in the igneous rocks and the country-rock schist show the following: (i) Along the southern shore of Revillagigedo Island, the Moth Bay pluton was emplaced along a shear zone. Magmatic and submagmatic flow foliation in the southern border zone of the pluton parallels foliations in the sheared country rock; rocks in the interior of the pluton are generally unfoliated. (ii) At Carroll Point a group of sills intrude along the same shear zone. In some of the sills, tabular plagioclase phenocrysts are oriented parallel to the shear fabric. (iii) Foliation-parallel sills lie within a shear zone that separates Gravina sequence and Taku terrane rocks at Point Francis on Cleveland Peninsula. Older sills within the shear zone are deformed, and younger intrusions are unfoliated and cut across the fabric. Based on these and similar observations elsewhere in the area, we suggest the mid-Cretaceous tonalite and leucotonalite magmas in the Ketchikan quadrangle intruded during the regional compressional deformation that formed the shear zones.
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van Loon, A. J., R. Mazumder, and S. De. "Unravelling the depositional environment of the Archaean Rajkharsawan conglomerate (Jharkhand, eastern India)." Netherlands Journal of Geosciences - Geologie en Mijnbouw 91, no. 1-2 (September 2012): 129–35. http://dx.doi.org/10.1017/s0016774600001542.
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AbstractLarge conglomerate lenses occur in a fine-grained siliciclastic succession of the Singhbhum craton, eastern India. They overlie an Archaean orthogneiss, from which they are separated by a palaeosol. Neither the conglomerates nor the directly overlying rocks have been dated, but the conglomerate unit is assumed to have also an Archaean age. The conglomerate lenses occur within a succession of pelitic and mafic schists, and the depositional environment of this conglomerate/schist unit had not been clarified thus far. On the basis of a combination of the vertical and horizontal distribution of the conglomerates, their stratigraphic position and analysis of their sedimentological characteristics and the sedimentological context, it is concluded that the succession must have developed in a fluvial lowland environment where volcanic input contributed significantly to the sediment accumulation.
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Dematteis, Antonio, Riccardo Torri, Bertrand Chereau, and Michel Ducrot. "Groundwater in the Perthus Tunnel: feedback after excavation." Acque Sotterranee - Italian Journal of Groundwater 10, no. 2 (June 24, 2021): 65–71. http://dx.doi.org/10.7343/as-2021-518.
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This work presents the experiences gained during the construction of the Perthus high-speed railway tunnel (8.4 km long), as regards water inflow management, analysis of the impact on surface-waters and groundwater, monitoring of piezometers and water quality control, soil injections. The excavation met granodiorites, schists, diorites, gneisses, black schists and coarse river deposits (pebbles and blocks) near the north portal. Some important tectonic structures, and associated groundwater flow, were also crossed. Finally, a geothermal study on the hydrothermal springs Le Boulou, which were not impacted, is presented.
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Narantsetseg, Tserendash, Yuan Chao, Wang Tao, Ren Zhongyuan, Li Pengfei, Zhang Le, Guo Lei, et al. "Metamorphic rocks from the north-eastern part of the Ereendavaa terrane (Eastern Mongolia) :." Mongolian Geoscientist 26, no. 52 (June 23, 2021): 16–45. http://dx.doi.org/10.5564/mgs.v26i52.1079.
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In this paper, we have conducted geochronological and geochemical studies on the metamorphic rocks of the Khaychingol and Ereendavaa Formations in the Mogoitiin Gol, Khaychin Gol and Emgentiin Bulag areas from the Ereendavaa terrane and these rocks have been considered to be Precambrian in age. However, new LA–ICP–MS zircon U–Pb dating results indicate that the protolith of the studied metamorphic rocks was formed in two stages: 1) during ~ 296 - 285 Ma, the protolith of mafic, felsic and black schists formed; 2) during ~276 - 271 Ma, the protolith of gneiss and psammitic schists began to deposit. The Early Permian bimodal association composed of low-K basalt and comagmatic high-Na, low-K dacite with high-K calc-alkaline rhyolite, represent protolith of the mafic and felsic schists which were formed in back-arc basin environment. The Middle Permian gneiss, and psammitic schists with sedimentary protolith have geochemical signatures of island arc rocks, such as enrichment of LILE relative to HFSE, and markedly negative Nb, Ta and Ti anomalies, suggesting that they were formed in a continental arc environment. Considering a close spatial relationship of the Ereendavaa terrane with the Mongol-Okhotsk Belt in the north-west, we propose that accompanied with the emplacement of arc magmatic rocks, the arc rifting occurred and formed the Early Permian bimodal volcanic rocks. In the Late Permian, after the formation of the back-arc basin, deposition of the immature deposits as wacke, arkose and litharenite dominated sediments in a continental arc environment started.
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Dolníček, Zdeněk, Rostislav Koutňák, and Jana Ulmanová. "Příspěvek k poznání exotických hornin flyšového pásma Západních Karpat: chloritoidová břidlice z Nového dvora u Kvasic (Chřiby)." Bulletin Mineralogie Petrologie 30, no. 2 (2022): 188–96. http://dx.doi.org/10.46861/bmp.30.188.
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New occurrence of pebbles of chloritoid schists, found in Eocene-to-Oligocene conglomerates of the Zlín Formation, Rača Unit, Magura Flysch, Outer Western Carpathians, Czech Republic, is characterized in this contribution. The rock has very simple mineral composition, including chloritoid, quartz, white mica and trace amount of apatite, rutile, and monazite. Chloritoid contains only very small proportions of magnesiochloritoid (7 - 11 mol. %) and ottrelite (up to 0.4 mol. %) components. The composition of white mica corresponds to muscovite and illite. The significant differences in mineral assemblages of rocks as well as in chemical composition of chloritoid and white mica usually appeared during comparison with those of similar rock types occurring in potential source areas in the Czech Republic, Slovakia, and Austria. The best comparable chemical composition showed only chloritoid in chloritoid schist from Bělá in the Hrubý Jeseník Mts., Silesicum, Czech Republic.
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Mikhalsky, E. V., A. A. Laiba, B. V. Beliatsky, and K. Stüwe. "Geology, age and origin of the Mount Willing area (Prince Charles Mountains, East Antarctica)." Antarctic Science 11, no. 3 (September 1999): 338–52. http://dx.doi.org/10.1017/s0954102099000437.
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Mount Willing in the Prince Charles Mountains (East Antarctica) is part of the Fisher Volcano–plutonic complex which formed as part of the global-scale Grenvillian mobile belt system. Mount Willing is composed of four rock complexes: 1) a metamorphic sequence, 2) gabbro intrusions, 3) deformed felsic intrusives, and 4) abundant post-metamorphic dykes and veins. Three rock types constitute the metamorphic sequence: amphibole–biotite felsic plagiogneiss, mafic to intermediate biotite–amphibole schist, and biotite paragneiss. The bulk composition of the mafic schists classifies them as tholeiitic basalts, and rarely as basaltic andesites or andesites. Index mg ranges widely from 47 to 71. Concentrations of TiO2, P2O5, and high-field strength elements are high in some rocks. These rocks are thought to have been derived from enriched (subcontinental) mantle sources. Sm–Nd and U–Pb isotopic data indicate a series of Mesoproterozoic thermal events between 1100 and 1300 Ma. In particular, these events occurred at 1289 ± 10 Ma (volcanic activity), at 1177 ± 16 Ma (tonalite intrusion), at 1112.7 ± 2.4 and at 1009 ± 54 Ma (amphibolite facies metamorphic events). Rb–Sr systematics also indicates a thermal overprint at 636 ± 13 Ma. Mafic schists show low initial 877Sr/86Sr ratios between 0.7024 and 0.7030. Felsic rocks show higher Sri values between 0.7037 and 0.7061. Basaltic andesite metavolcanic and plutonic rocks form a calc-alkaline evolutionary trend, and probably originated from subduction-modified mantle sources in a convergent plate margin environment. An oceanic basin may have existed in central Prince Charles Mountains about 1300 Ma ago and was closed as a result of continental collision around 1000 to 800 Ma.
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Masquelin, Henri, Hernán Silva Lara, Leda Sánchez Bettucci, Pablo Núñez Demarco, Sofía Pascual, Rossana Muzio, Elena Peel, and Fernando Scaglia. "Lithologies, structure and basement-cover relationships in the schist belt of the Dom Feliciano Belt in Uruguay." Brazilian Journal of Geology 47, no. 1 (January 2017): 21–42. http://dx.doi.org/10.1590/2317-4889201720160119.
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ABSTRACT: This work is the result of a multiyear effort to use field geology to describe lithologies, to establish contact relationships and to create a sketch of the tectonic evolution of the Meso- to Neoproterozoic metasedimentary successions within the Schist Belt of the Dom Feliciano Belt. This low-grade metamorphic cover rests on the high-grade metamorphic basement of the La China and Las Tetas complexes. This basement is Archean-Paleoproterozoic in age. The Schist Belt is overlapped unconformably by the Barriga Negra formation. The Lavalleja complex and the Barriga Negra formation both deformed together during the D2 deformation event (~ 570 -540 Ma), but the Barriga Negra only partially recorded the D2 transpressive event, whereas the Lavalleja complex was affected by both the D1 tangential event and the D2 event. Event D1 would have developed a fold nappe with vergence to the south. This hypothesis is supported by different structures: (i) recumbent and upright folds oriented E-W, (ii) subhorizontal mylonitic foliation in marbles (calc-schists), (iii) stretching lineations plunging towards the SW in metaconglomerates of the Las Tetas Complex, and (iv) a reworking of the subhorizontal foliation parallel to the Sarandí del Yí strike-slip shear zone.
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Mposkos, E., and A. Krone. "NEW EVIDENCES OF THE LOW-P/HIGH-T PRE-ALPINE METAMORPHISM AND MEDIUM-P ALPINE OVERPRINT OF THE PELAGONIAN ZONE DOCUMENTED IN METAPELITES AND ORTHOGNEISSES FROM THE VORAS MASSIF, MACEDONIA, NORTHERN GREECE." Bulletin of the Geological Society of Greece 36, no. 1 (January 1, 2004): 558. http://dx.doi.org/10.12681/bgsg.16753.
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Pelitic rocks of the pre-Alpine "gneiss series" from the Voras Massif record a polymetamorphic history of three metamorphic events; a first HT event indicated by migmatitization phenomena, a subsequent LP-HT event (andalusite-sillimanite series) at 2.5-3 Kbar and 610-640°C, and a third medium-P event at ~11 Kbar and ~550°C. The LP-HT metamorphism is associated with intrusion of Variscan granitoid plutois in a magmatic arc setting. The medium-P metamorphism records an Alpine event (probably Early Cretaceous) indicated by kyanite, chlohtoid, garnet and staurolite formation replacing andalusite and cordierite. The Variscan granitoids and the overlying lithologies of the "schist series" are affected only by the medium-P metamorphism. Granitoids are transformed into phengite orthogneisses having the mineral assemblage phen (Si=3.35-3.47 a.p.f.u.)±Bt-Ab-Kfs- Qtz±Czo±Grt and high-alumina pelites into gamet-chloritoid schists with the mineral assemblage Grt-Ctd-Chl-Ms-Qtz-Rt±llm. The "schist series" which underlies the Late Triassic-Early Jurassic marbles and overlies lithologies of the "gneiss series" and metagranitoids represents protoliths of the Permo-Triassic volcanosedimentary series deposited at the eastern margin of the Pelagonian continental block
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Da Silva Araújo, Paulo Jedean, Vinicius Anselmo Carvalho Lisboa, and José Ramilson Dos Santos Oliveira. "Mapeamento geológico do Pegmatito Alto do Tibiri: aspectos estruturais e mineralógicos." Revista Principia - Divulgação Científica e Tecnológica do IFPB 1, no. 33 (May 16, 2017): 29. http://dx.doi.org/10.18265/1517-03062015v1n33p29-36.
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<p>The Alto Tibiri is a pegmatite body located in the southern region of the Rio Grande do Norte, in Parelhas city, geologically inserted in the Borborema Pegmatite Province and occur intruding the mica schists of the Seridó Formation. Currently, both mica and feldspar are commercially exploited in this pegmatite body. In the field missions, 39 outcrops were described, in each one the main texture and mineralogical aspects of the outcropping rock were described. The geological mapping has allowed us to distinguish two types of schists, based on content and size of the mineral phases. There is a garnet rich schists and other with a relevant cordierite content. The studied region shows narrow pegmatite dykes, composed of quartz, feldspar, muscovite and/or biotite and black tourmaline, these dikes were classified as homogeneous. It’s possible to observe in Alto Tibiri a well- defined mineral zoning, as follows: i) border area, marked by the abundance of muscovite; ii) Zone II, composed of quartz, feldspar and mica, in which the main mineral resources occur (tantalite, spodumene, apatite, etc.) and iii) quartz pockets. The observed mineral zoning is similar to that described as mixed traditional pegmatite bodies.</p>
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Ovchinnikov, R. O., A. A. Sorokin, W. L. Xu, and V. B. Khubanov. "THE FIRST DATA ON THE AGE OF METAMORPHIC ROCKS OF THE SYNCHYGA BLOCK OF THE JIAMUSI CONTINENTAL MASSIF (CENTRAL ASIAN OROGENIC BELT)." Доклады Российской академии наук. Науки о Земле 509, no. 2 (February 1, 2023): 160–64. http://dx.doi.org/10.31857/s2686739722602587.
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The paper presents the results of U–Th–Pb geochronological studies of zircons from metamorphic rocks of the Amur group of the Synchyga Block of the Jiamusi continental massif. It is shown that the garnet-biotite-sericite schists of the Amur group have a primary sedimentary origin. The lower depositional age of the protolith can be determined by the age of the youngest zircons from group with Neoproterozoic ages ~832 Ma. The upper age boundary of protolith, apparently, corresponds to the age of metamorphic zircons ~533 Ma. Thus, the schists of the Amur group of the Synchyga Block are of Neoproterozoic in age rather than Early Precambrian, as was accepted earlier.
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Zapata-García, Gilberto, Gabriel Rodríguez-García, and María Isabel Arango-Mejía. "Petrography, geochemistry and geochronology of metamorphic rocks outcropping in San Francisco Putumayo and the Palermo-San Luis road associated with the La Cocha - River Tellez and Aleluya complexes." Boletín de Ciencias de la Tierra, no. 41 (January 1, 2017): 48–65. http://dx.doi.org/10.15446/rbct.n41.58630.
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The La Cocha – Rio Tellez Migmatitic Complex includes a set of metamorphic rocks, mainly migmatites, schists, gneisses and amphibolites, that lie in faulted contact with the Cuarzomonzonita de Sombrerillo Unit and cretaceous sedimentary rocks. The 163.6±4.7 Ma U-Pb age in zircon is assumed as the age of metamorphism of the La Cocha-Río Tellez Migmatitic Complex, it was obtained in a quartz-feldspar schist that outcrops in the municipality of San Francisco-Putumayo; the ages of 194. 4±2. 0 Ma, 218.8 Ma and Ma 229.8 correspond to inherited ages. The Aleluya Complex encompasses marbles, meta-sandstones, quartzites, and migmatites. U-Pb ages in zircon obtained for two granofels samples collected on the Palermo-San Luis (Huila) road, are separated into three populations of data with ages: 169. 1±2. 7 Ma age of crystallization and inherited ages of 194. 6±3. 2 Ma, 212.5, 218.6 and 235.5 Ma.