Browsing by Author "Swapnil Kumar Rai"

Now showing 1 - 4 of 4

Decompression textures in garnet-cordierite gneiss from Kosavankovilpatti, Southern India: Constraints from reaction textures and phase equilibria modelling
(The Earth Science Institute of SAS, 2021) Roopali Yadav; Divya Prakash; Swapnil Kumar Rai; Manoj K. Yadav; Pradip Kumar Singh; Srishti Jaiswal
The Kosavankovilpatti area consists mainly of granulite facies rocks and is part of the Madurai block in the Southern Granulite Terrane, India. The garnet-cordierite gneiss collected at this location exhibits well-preserved metamorphic reaction textures and is used to infer the metamorphic history of the study area. Garnet resorption at the expense of orthopyroxene-cordierite and spinel-cordierite symplectites characterize the retrograde stages of metamorphism. Phase relationships for bulk rock composition in the MnO-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 (MnNCKFMASHT) system, as well as the application of multi equilibrium calculations for the peak metamorphic assemblages, yield maximum temperature (T) and pressure (P) conditions of 900 °C and 9 kbar, respectively. These estimated results are lower compared to those reported for the sapphirine-bearing granulites from the Madurai block that characterize UHT metamorphism. The post-peak P-T path, constructed for garnet-cordierite gneiss based on observed microstructural relationships and thermobarometry results, is characterized by a decompressive P-T segment ending at 810 °C and 5.5 kbar. The geochronological results of SHRIMP U-Pb give an age of 521 ± 30 Ma for the decompression metamorphic overprint that was superimposed on the protolith formation of the garnet-cordierite gneiss at 2561 ± 72 Ma. The proposed P-T path implies that the granulites in the Kosavankovilpatti section probably resulted from denudation of the thickened continental crust. In this way, the present study allows us to understand how this part of the lower continental crust could have evolved during prolonged heating without actually attaining UHT conditions. © 2021 Sciendo. All rights reserved.
Metamorphic P–T evolution of Hercynite-quartz-bearing granulites from the Diwani Hill, North East Gujarat (NW India)
(Elsevier B.V., 2021) Divya Prakash; Manish Kumar; Swapnil Kumar Rai; Chandra Kant Singh; Saurabh Singh; Roopali Yadav; Srishti Jaiswal; Vedika Srivastava; Manoj Kumar Yadav; Sourav Bhattacharjee; Pradip Kumar Singh
Diwani Hill granulites occurring on the southern tip of the South Delhi Terrane (SDT) of Aravalli Mobile Belt (AMB), comprises rocks of granulite facies and represent the deeper level of the crust. The SDT represents an admixture of charnockites, granites, calc-granulites and hercynite-quartz-bearing pelitic granulites. The symplectite and corona textures recorded in the hercynite-quartz-bearing granulites from a part of SDT provides a wide spectrum of P-T sensors in support of the petrological evolution. P-T evolution of these hercynite-quartz-bearing granulites has been constrained through the use of THERMOCALC program, conventional thermobarometry, and pseudosection modelling in the NCKFMASHTO model system using Perple_X software. The unification of these three calculations, demonstrates that the hercynite-quartz-bearing granulites experienced peak pressure and temperature at 6.7 kbar and 750 °C, respectively. The textural imprints, multistage reaction textures, P-T pseudosections as well as the application of multi-equilibrium calculation give evidence for decompressive history related to their exhumation. SHRIMP U-Pb chronological results yield ages between 780 and 680 Ma as a time of metamorphic overprint, and the ages between 1591 and 1216 Ma corresponding with detritus derived from magmatic source for hercynite-quartz-bearing granulites. Zircon ages reflect that continental crust in the SDT resulted from the Mesoproterozoic protolith of an igneous origin whereas sedimentary succession was deposited between 1216 and 780 Ma. The present study envisages that the South Delhi basin would have been a remnant of the proto-Mozambique Ocean in NW India which was closed due to subduction. This subduction metamorphosed the sediments of the basin to granulite facies and the rocks were subsequently, uplifted because of the thrust sheet tectonics during the Neoproterozoic times. © 2020 Elsevier B.V.
New Finding of Silica-deficient Sapphirine-bearing Granulites from NNE of Suranganar Village, Southern Madurai Block, India
(Springer, 2021) Swapnil Kumar Rai; Divya Prakash; Roopali Yadav; Srishti Jaiswal; R.S. Kumar; Chandra Kant Singh
An infrequent occurrence of sapphirine from metapelite rocks of the Cardamom hills of South India has been reported. This report of sapphirine may not be the first from the Southern Granulite Terrane (SGT) but is essentially from a new locality. The studied metapelites are silica-undersaturated devoid of garnet and the sapphirine symplectites. The symplectites of orthopyroxene + cordierite, orthopyroxene + K-feldspar + cordierite, orthopyroxene + sapphirine + cordierite ± K-feldspar ± biotite, orthopyroxene + biotite + cordierite + K-feldspar are discernible. The textural patterns show partial to complete pseudomorphism of the initially formed orthopyroxene and sapphirine and their succeeding decomposition to present stage. The relative XMg calculated for the key minerals show the trend as: Crd > Spr > Bt > Opx. The pseudosection modelling and the calculated P-T diagram drawn from the average bulk composition of the studied metapelite connote isothermal decompression with peak pressure and temperature conditions stable at ∼10 Kbar and ∼985 °C respectively. The assemblage reported in this study has an important bearing on the crustal evolution of the high-grade metamorphism exhumed from a deeper level of the crust. © 2021, Geol. Soc. India.
Ultrahigh-temperature decompression of sapphirine-granulites from the southern Madurai block (South India): Insights from geothermobarometry, pseudosection modelling and U-Pb geochronology
(Elsevier Ltd, 2021) Roopali Yadav; Divya Prakash; Swapnil Kumar Rai; Manoj Kumar Yadav; Srishti Jaiswal; Saurabh Singh; Pradip Kumar Singh; Manish Kumar; Chandra Kant Singh
Madurai block in South India stands as an excellent example of ultrahigh temperature metamorphic terranes being studied globally to understand the extreme thermal capacities of crustal rocks and the processes that cause these extreme thermal environments. The granulites of the Madurai block were subjected to extreme crustal metamorphism during the Late Neoproterozoic, as evidenced by the texture of the sapphirine + quartz association registered as peak metamorphic assemblage. The metamorphic zircon from sapphirine-granulites produces a U-Pb age of 546.5 ± 7.8 Ma which is interpreted as a global Pan-African crustal evolution event and the dominant zircon population indicates multiple sources of Neoarchean to Paleoproterozoic age in the southern Madurai block. Decompression textures other than orthopyroxene-cordierite ± sapphirine symplectites are indicative of retrograde / exhumation in the granulites metamorphic cycle. P–T pseudosections have been constructed for sapphirine-granulites in relation to the NCKFMASHTO system (Na2O-CaO-K2O-FeO-MgO-Al2O3–SiO2-H2O-TiO2-O2) using Perple_X software (version 6). The limitations in the interpretation of mineral reactions and the metamorphic history provided by pseudosection modelling for mineral proportions suggest that the peak metamorphic temperature is ~960 °C and pressure is ~9.2 kbar. © 2021 Elsevier Ltd