Browsing by Author "Suparna Tewari"

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Barrovian metamorphism of the metapelites in NE Sikkim (Eastern Himalaya): Constraints from chemographic projection and geothermobarometry
(Elsevier Ltd, 2021) Suparna Tewari; Divya Prakash; Manoj Kumar Yadav; Vedika Srivastava
The Sikkim Himalaya is mostly constituted of Proterozoic metapelites and metavolcanics of the Daling Group and high-grade gneisses and metasediments of the Darjeeling Group. Metapelitic schists and gneisses of the Sikkim Himalaya show an inverted sequence of metamorphic rocks ranging from lower greenschist facies (chlorite zone) to upper amphibolite facies (sillimanite + K-feldspar zone). The relative XMg in the minerals varies as: garnet > staurolite > biotite > muscovite. The P-T evolution of the study area has been constrained through the use of an internally consistent winTWQ programme and Perple_X software in the MnNCKFMASHTO model system. The combination of these two approaches demonstrates that the schists and gneisses have experienced a range of pressure and temperature with increasing grade. Constraints on the interpretation of mineral reactions and metamorphic history provided by pseudosection modelling for mineral proportions suggest the peak metamorphic temperature as ~750 °C and pressure ~7.5 kbar. The proposed prograde P-T path implies that the rocks from the study area may have resulted from a single metamorphic event with continuous changes in pressure and temperature. The conclusions made on the basis of the study of metamorphic event in the area and the regeneration of the reaction history adheres to classical Barrovian type metamorphism. The tectonic implication of such a metamorphic evolution is also discussed in the present work. Finally, we conclude that the possible explanation for the exhumation in this section of Himalaya may most likely be explained with the help of the channel flow model. © 2021 Elsevier Ltd
Garnet-sillimanite bearing gneisses from Darjeeling, eastern Himalaya: Textural relationship and P–T conditions
(Indian Academy of Sciences, 2015) Divya Prakash; Suparna Tewari
The area around Darjeeling consists of medium grade metamorphic rocks and provides a classic example of inverted Himalayan metamorphism. The area under investigation shows upper amphibolite faciesmetamorphism (sillimanite-muscovite subfacies), rocks are intimately associated with the migmatites and granites. The presence of quartzite, calc-silicate rocks, graphitic schist and abundance of aluminous minerals like kyanite or sillimanite in these rocks indicate their metasedimentary character. Granetsillimanite bearing gneisses occupy most of the area of Darjeeling but not persistent throughout. Textural relationship suggests sequential growth of progressively higher-grade metamorphic minerals during D1 and D2 deformation. The relative XMg in the minerals varies in the order: biotite>staurolite>garnet, and the XMn decreases in the order: garnet>staurolite>biotite. The P–T evolution of these garnetsillimanite gneiss has been constrained through the use of conventional geothermobarometry, internally consistent TWEEQU programme and Perple_X software in the KFMASH model system, the combination of these three approaches demonstrates that the Darjeeling gneisses experienced peak pressure and temperature at 7.0 ± 0.3 kbar and 700 ± 30°C. The observation in this study has important bearing on the inverted metamorphism in the Himalayan metamorphic belt. © Indian Academy of Sciences.
Garnet-staurolite-mica schist from Rangli Rangliot, Eastern Himalaya: Constraints from phase equilibria and Thermobarometry
(Geological Society of India, 2016) Divya Prakash; Suparna Tewari
Rangli Rangliot is an integral part of lesser Himalaya. The area around Rangli Rangliot consists of garnetstaurolite-mica schist and it is characterized by mineral assemblage garnet-biotite-muscovite-staurolite-quartz± plagioclase. Different reaction textures are of particular interest as they reflect discontinuous or continuous reactions under changing physical conditions. The relative XMg in the minerals varies in the order: muscovite> biotite> staurolite> garnet, and the XMn decreases in the order: garnet>staurolite>biotite>muscovite. The P-T evolution of the garnet-staurolite-mica schist has been constrained through the use of internally consistent TWEEQU programme and Perple_X software in the KFMASH model system. The combination of these two approaches demonstrates that the garnet-staurolite-mica schist experienced peak pressure and temperature at 5.8 kbar and 590 °C. The proposed clockwise P-T path implies that rocks from the study area could have resulted from thickened continental crust undergoing decompression. © 2016, Geological Society of India.
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; Divya Prakash; Manish Kumar; Saurabh Singh; Rajeev Kumar Pandey; Chandra Kant Singh; Suparna Tewari
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.
Geothermobarometry and barrovian metamorphism of Darjeeling-Mangpu region, eastern Himalaya
(Capital Publishing Company, 2014) Suparna Tewari; Divya Prakash
Along the Darjeeling-Mangpu region, polyphase deformation and barrovian metamorphism has been delineated in relation to the Main Central Thrust (MCT). The different parageneses of pelitic rocks containing chlorite, muscovite, biotite, garnet, staurolite, kyanite, sillimanite, k-feldspar and plagioclase show various texture resulting by the continuous and discontinuous reactions in the different zones. From the Microprobe data of the coexisting minerals show that XMg varies in order garnet
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) Bikash Mahanta; Divya Prakash; Saurabh Singh; C.K. Singh; Manish Kumar; Rajeev Pandey; Suparna Tewari
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 (þ 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.
Metamorphic zonal sequences of pelitic schists and gneisses from the area around Kandra (Jharkhand): Constraints from field and textural relationship
(Geological Society of India, 2017) Divya Prakash; Dhananjay Kumar Patel; Suparna Tewari; Manoj Kumar Yadav; Roopali Yadav
The pelitic schists of the area around Kandra, Singhbhum district, Jharkhand belong to the Chaibasa Formation of the Singhbhum Group, which constitute a part of the youngest Precambrian orogenic cycle of the Singhbhum region. Structurally, the area represents the Singhbhum anticlinorium and is overlain by Dalma traps which form the synclinorium towards the north of the area around Kandra. This area mainly consists of medium to high grade rocks belonging to greenschist and amphibolite facies. These rocks are folded in the E-W trending doubly plunging folds (F1) overturned towards the south with low plunges and superposed by cross-folds (F2). The spatial distribution of the index minerals in the pelitic schists of the area shows Barrovian type of metamorphism. Four isograds, viz. biotite, garnet, staurolite and sillimanite have been delineated by the first appearance of the index minerals and also by isograd reactions. The textural relation suggests that sillimanite is formed from staurolite consumption reaction instead of kyanite consumption. © 2017, Geological Society of India.
Reaction textures and metamorphic evolution of sapphirine-spinel-bearing and associated granulites from Diguva Sonaba, Eastern Ghats Mobile Belt, India
(Cambridge University Press, 2015) Divya Prakash; Praveen Chandra Singh; Chandra Kant Singh; Suparna Tewari; Makoto Arima; Hartwig E. Frimmel
The Diguva Sonaba area (Vishakhapatnam district, Andhra Pradesh, South India) represents part of the granulite-facies terrain of the Eastern Ghats Mobile Belt. The Precambrian metamorphic rocks of the area predominantly consist of mafic granulite (±garnet), khondalite, leptynite (±garnet, biotite), charnockite, enderbite, calc-granulite, migmatic gneisses and sapphirine-spinel-bearing granulite. The latter rock type occurs as lenticular bodies in khondalite, leptynite and calc-granulite. Textural relations, such as corroded inclusions of biotite within garnet and orthopyroxene, resorbed hornblende within pyroxenes, and coarse-grained laths of sillimanite, presumably pseudomorphs after kyanite, provide evidence of either an earlier episode of upper-amphibolite-facies metamorphism or they represent relics of the prograde path that led to granulite-facies metamorphism. In the sapphirine-spinel-bearing granulite, osumilite was stable in addition to sapphirine, spinel and quartz during the thermal peak of granulite-facies metamorphism but the assemblage was later replaced by Crd-Opx-Qtz-Kfs-symplectite and a variety of reaction coronas during retrograde overprint. Variable amounts of biotite or biotite+quartz symplectite replaced orthopyroxene, cordierite and Opx-Crd-Kfs-Qtz-symplectite at an even later retrograde stage. Peak metamorphic conditions of c. 1000°C and c. 12 kbar were computed by isopleths of XMg in garnet and XAl in orthopyroxene. The sequence of reactions as deduced from the corona and symplectite assemblages, together with petrogenetic grid and pseudosection modelling, records a clockwise P-T evolution. The P-T path is characteristically T-convex suggesting an isothermal decompression path and reflects rapid uplift followed by cooling of a tectonically thickened crust. © 2014 Cambridge University Press.
Reaction textures and metamorphic evolution of sapphirine-spinel-bearing and associated granulites from Diguva Sonaba, Eastern Ghats Mobile Belt, India
(Cambridge University Press, 2014) Divya Prakash; Deepak; Praveen Chandra Singh; Chandra Kant Singh; Suparna Tewari; Makoto Arima; Hartwig E. Frimmel
The Diguva Sonaba area (Vishakhapatnam district, Andhra Pradesh, South India) represents part of the granulite-facies terrain of the Eastern Ghats Mobile Belt. The Precambrian metamorphic rocks of the area predominantly consist of mafic granulite (±garnet), khondalite, leptynite (±garnet, biotite), charnockite, enderbite, calc-granulite, migmatic gneisses and sapphirine-spinel-bearing granulite. The latter rock type occurs as lenticular bodies in khondalite, leptynite and calc-granulite. Textural relations, such as corroded inclusions of biotite within garnet and orthopyroxene, resorbed hornblende within pyroxenes, and coarse-grained laths of sillimanite, presumably pseudomorphs after kyanite, provide evidence of either an earlier episode of upper-amphibolite-facies metamorphism or they represent relics of the prograde path that led to granulite-facies metamorphism. In the sapphirine-spinel-bearing granulite, osumilite was stable in addition to sapphirine, spinel and quartz during the thermal peak of granulite-facies metamorphism but the assemblage was later replaced by Crd-Opx-Qtz-Kfs-symplectite and a variety of reaction coronas during retrograde overprint. Variable amounts of biotite or biotite+quartz symplectite replaced orthopyroxene, cordierite and Opx-Crd-Kfs-Qtz-symplectite at an even later retrograde stage. Peak metamorphic conditions of c. 1000°C and c. 12 kbar were computed by isopleths of XMg in garnet and XAl in orthopyroxene. The sequence of reactions as deduced from the corona and symplectite assemblages, together with petrogenetic grid and pseudosection modelling, records a clockwise P-T evolution. The P-T path is characteristically T-convex suggesting an isothermal decompression path and reflects rapid uplift followed by cooling of a tectonically thickened crust. Copyright © Cambridge University Press 2014.