Browsing by Author "Singh C.K."

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    Garnet-Staurolite-Mica Schist from Southern Sonbhadra District, U.P.: Constraints from Geothermobarometry and P-T Pseudosection Modelling
    (Geological Society of India, 2024) Singh A.A.; Prakash D.; Singh B.P.; Singh C.K.; Pandey R.K.
    The area around Renukoot town shows the exposure of garnet-staurolite-mica schist belonging to the Chhotanagpur Granite Gneiss Complex (CGGC). The characteristic mineral assemblage present in the rock are garnet�biotite�staurolite�quartz along with minor opaque minerals like rutile, ilmenite and hematite. For the constituent minerals, the calculated XMg value decreases in the order: chlorite>biotite>staurolite>garnet. The metamorphic conditions of the garnet-staurolite-mica schist were determined using the winTWQ and Perple_X programmes, and the peak pressure-temperature conditions for the rock are estimated to be 5.3 kbar and 570�C. The metamorphic episode in the CGGC during Mesoproterozoic time may be attributed to the global level Columbian Super-continental accretionary orogeny. � 2024, Geological Society of India. All rights reserved.
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    Geochemistry, Monazite (U�Pb�Th) Geochronology, and P-T Pseudosection Modelling of Two-Pyroxene Mafic Granulite from Sonapahar, Shillong Meghalaya Gneissic Complex, India: Implication for Tectono-Metamorphic Evolution and Global Pan-African Correlation
    (2024) Bikash Mahanta; Prakash D.; Kumar M.; Singh S.; Pandey R.K.; Singh C.K.; Tewari S.
    Abstract: Granulites exposed in high-grade regional metamorphic belts and exhumed as xenoliths in basaltic pipes are considered as window into the deep crust thus play a key role in constraining models of crustal processes and evolution. Here we present a detailed investigation of the tectono-metamorphic history of the two-pyroxene mafic granulite located in the southern region of the Sonapahar area. This involves conducting monazite chemical dating, analyzing petrological and geochemical characteristics, applying geothermobarometry, performing phase equilibria modeling, and tracing a pressure-temperature (P-T) path. Metamorphic P-T conditions estimated for the mafic granulite using conventional thermobarometer and winTWQ shows temperature in excess of 800�C and pressure of about 8.6 kbar, stand for high temperature granulite facies metamorphism. The metamorphic evolution path obtained from P-T pseudosection suggest a clockwise P-T evolution path, thus signify isothermal decompression and indicate rapid upliftment. Geochemical study of trace and rare earth elements (REE), suggest protolith is of tholeiite basalt in nature that is derived from back arc basin setting near to subduction zone. Additionally, the analyzed rock was examined using primitive mantle-normalized trace element spider diagram. The results indicate an enrichment in large-ion lithophile elements (Th, U, K, Pb) and a depletion in high field-strength elements (Nb, Ta, Ti). The presence of negative anomalies in Nb and Ti, coupled with elevated values of Th, K, and Pb, suggests the possibility of crustal contamination. Monazite chemical data from the studied rock reveals a peak metamorphism age of 521.3 � 4.20 Ma, which corresponds to the Kuunga Orogeny in the later phase of global Pan-African collision. � Pleiades Publishing, Ltd. 2024. ISSN 0016-7029, Geochemistry International, 2024, Vol. 62, No. 6, pp. 574�608. Pleiades Publishing, Ltd., 2024. ISSN 0016-7029, Geochemistry International, 2024. Pleiades Publishing, Ltd., 2024.
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    Metamorphic P-T evolution and tectonic implications of UHT metamorphism from the Shillong Meghalaya Gneissic Complex, India: evidence from phase equilibria modelling, monazite U-Pb-Th geochronology, K-Ar dating and geochemistry
    (Cambridge University Press, 2024) Mahanta B.; Prakash D.; Singh S.; Singh C.K.; Kumar M.; Pandey R.; Tewari S.
    The study area Sonapahar is an integral part of Shillong Meghalaya Gneissic Complex (SMGC), which is located in the Northeastern part of India. This complex mainly comprises metamorphic formations spanning from Upper Amphibolite to Ultra-high temperature granulite, interspersed with various igneous intrusions. In this study, particular attention is directed towards unravelling the metamorphic history of Mg-Al granulite. For the very first time, we establish the pressure�temperature (P-T) trajectory of the Mg-Al granulite from Sonapahar, SMGC. Employing conventional thermobarometry along with winTWQ analysis, the inferred metamorphic conditions for this granulite reveal temperatures exceeding 900�C and pressures of approximately >8 kbar. These conditions firmly indicate the presence of ultra-high-temperature metamorphism. By utilizing the Perple_X software in the MnO-Na2OCaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe2O3 compositional system, we construct a P-T pseudosection. This gives a clockwise P-T path, signifying an episode of cooling (� minor decompression). Such a pattern also suggests rapid cooling of the tectonically-thickened crust. Concurrently, a geochemical exploration of trace and rare earth elements in the rocks offers further insights. These investigations give an idea about the protolith, having a clay-to-sandstone in nature. Additionally, chemical data from monazite within the studied rock provide a weighted mean age of 682 Ma for the peak metamorphic stage. This age aligns with the global Pan-African orogenic events. The biotite K-Ar isotopic geochronology from the symplectite position provides decompression history or cooling age of 442 Ma. This age corresponds to a period after the last peak metamorphic phase that occurred during the Pan-African thermal event. � The Author(s), 2024.
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    Mineral Chemistry and IMA Nomenclature of Amphibole Minerals of Amphibolite Sills from Chhotanagpur Granite Gneiss Complex (CGGC), Southern Sonbhadra, Central India
    (Geological Society of India, 2024) Singh A.A.; Prakash D.; Singh B.P.; Singh C.K.; Yadav M.K.; Pandey R.K.
    In southern part of Sonbhadra District, near the Rihand Dam, low to medium grade amphibolites of Paleoproterozoic age are exposed. The outcrops are in the form of sills that occur at places in the Chhotanagpur Granite Gneiss Complex (CGGC). The essential mineralogical constituents of the amphibolite are amphibole-plagioclase-chlorite-biotite-iron oxides. Based on the mineral chemistry and interpretation as per the international mineralogical association (IMA) nomenclature scheme, amphiboles in the analysed amphibolite rock samples have been identified as magnesio-hornblende, magnesio-ferri-hornblende and edenite. � 2024 Geological Society of India, Bengaluru, India.