Browsing by Author "Prakash D."

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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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    Geochemical and geochronological evolution of the UHT granulites from the Eastern Ghats Mobile Belt, India: implications from F-OH substitution in biotite, thermal events and cooling age
    (Taylor and Francis Ltd., 2024) Singh S.; Prakash D.; Yadav R.; Kumar M.; Mahanta B.; Sol� Vi�as J.
    The thin lenses and bands of ultra-high temperature (UHT) granulites with diagnostic sapphirine and quartz in contact are occasionally found on the western flank of the Eastern Ghats Mobile Belt (EGMB), which inherits the suturing and over-thrusting signatures of the EGMB with the Greater Indian Landmass (GIL). The mineral biotite contains an abnormally high fluorine concentration, as revealed by the geochemical examination of these granulites from the research area (Kothuru), which was caused by the F-OH substitution to withstand extreme thermal metamorphic conditions. The geochemical results from the multi-element spider diagram and the Harker�s variation diagram with primitive-mantle normalization also show an enrichment of light rare earth elements and large-ion lithophile elements over depleted heavy rare earth elements and high-field strength elements. An evolutionary history has been established for the high-grade rocks that were subjected to ultra-high temperature metamorphism, based on the geochemical signatures of the examined granulites. The use of isotopic K-Ar cooling ages and electron microprobe monazite chemical ages of the thermal episodes, which act as useful tools to explain the time and span of the polycyclic metamorphic terrane, is another significant component of the current work. Numerous researchers have attempted to estimate the thermal episodes in various areas of the Eastern Ghats Mobile Belt, but their cooling ages are still poorly understood. Consequently, two thermal episodes that happened at 842 Ma and 637 Ma ago, as well as a cooling age of about 448 Ma that marked the quick exhumation of the high-grade rocks under study, have been recorded in the current investigation. The association between the Greater Indian Landmass and Eastern Antarctica during the existence of the Rodinian supercontinent has been established by recorded geochronological events. � 2023 Informa UK Limited, trading as Taylor & Francis Group.
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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.
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    Reproductive Biology, Genetics, Evolution, and Diversity in Finger Millet (Eleusine coracana (L.) Gaertn.)
    (Springer Nature, 2024) Shamkuwar S.; Srivastava K.; Tirkey A.E.; Prakash D.; Madankar K.; Saha S.
    Finger millet (Eleusine coracana (L.) Gaertn.) is a nutrient-dense climate-resil-ient major grain crop in Asian and African subcontinents. Being future smart food crop, its production will help in improving the livelihood of people by improving nutritional status. Thus, it is essential to understand its floral biology, genetics, origin, evolution, and genetic diversity to achieve the goal of nutritional security in the developing countries. The origin of finger millet traced back to 5000 years, and Africa and India were recognized as the primary and secondary centers of diversity. Finger millet is a highly self-pollinated allotetraploid crop with as low as 1% cross-pollination aided by wind; thus, artificial hybridization techniques can permit its further improvement immensely. Identification of modern emascu-lation techniques like chemically hybridizing agent (ethrel), hot water emascula-tion, cold water, and plastic bag method transformed from traditional to modern production system due to complex architecture and tiny nature of florets of finger millet. Study of genetic diversity for identification of resistance against various biotic and abiotic stresses as well as high calcium, zinc, and iron-containing species helps in classification and improving the overall production aspect of finger millet. Thus, it is vital to preserve the germplasm for the conservation of genetic diversity and understanding the crop in-depth. This chapter discusses the details about finger millet origin, evolution, floral biology, and cytogenetics, and genetic diversity also highlights the germplasm for overall improvement of finger millet. � The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.