Browsing by Author "Aditya Kharya"

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Metamorphic evolution of the UHT granulites from Mandikota, Eastern Ghats Mobile Belt, India: Constraints from phase equilibria modelling, fluid inclusions and monazite U-Th-total Pb geochronology
(Elsevier B.V., 2023) Saurabh Singh; Divya Prakash; Aditya Kharya; Himanshu K. Sachan
The Eastern Ghats Mobile Belt (EGMB) had been subjected to extreme thermal metamorphic history at various sections of its terrane. One such terrane (Mandikota) located near the western part of the EGMB has been speculated based on asserted reaction textures, conventional geothermobarometry, geochronology, fluid inclusions, and pseudosection modelling. The present integrated study aims to understand the intricacies of the diversified and controversial tectono-metamorphic evolution of these polycyclic granulite terranes. The stable occurrence of sapphirine + quartz in contact is rare in its own and is a diagnostic feature of Ultra-High Temperature (UHT) metamorphism. Conventional geo-thermobarometeric tools applied, suggests an ordered series of reactions for the different stages of metamorphism experienced by the investigated granulites. Also, the P-T estimated by conventional methods lies in sound correlation with the peak P-T condition (in excess of 950 °C at nearly 9 kbar) attained in the constrained pseudosection model. The exhumation trajectory of the examined UHT terrane reflects P-T path responsible for the thrusting mechanism with isothermal decompression of 3 kbar followed by late-stage isobaric cooling. This study also presents the primary report for the systematic fluid inclusion study of the UHT granulites and its correlation with the evolved P-T trajectory. In addition, monazite dating using Electron Micro Probe Analysis (EPMA) is procured to assess the time frame in understanding the P-T-t evolution of the high-grade terrane. The geochronological study further revealed a new age (∼600 Ma) associated with the Visakhapatnam Domain which adheres to the Pan-African orogeny and marks the reworking phase of the widely reported the Grenvillian event in the EGMB province. As such, the results from the studied fluid inclusions displaying monophase inclusions of CO2-rich carbonic fluid, and its corroboration with the P-T pseudosection model interpreting the phase equilibrium conditions prevailing during the Neoproterozoic time (∼900 Ma). © 2023 Elsevier B.V.
Metamorphic P-T conditions and CO2 influx history of medium-grade metapelites from Karakorum, Trans-Himalaya, India
(Elsevier Ltd, 2016) Himanshu K. Sachan; M. Santosh; Divya Prakash; Aditya Kharya; P. Chandra Singh; Santosh K. Rai
The medium grade metapelites of Pangong-Tso area in the trans-Himalayan region underwent sillimanite-grade metamorphism initiated during the Cretaceous, associated with the collision of the Kohistan arc and the Indian plate with Asia. This paper present results from a petrological and fluid inclusion study to understand the metamorphic P-T conditions and fluid history of these rocks. The calculated phase equilibria in the Na2O-CaO-K2O-FeO-MgO-MnO-Al2O3-SiO2-H2O-TiO2 (NCKFMMnASHT) system suggest P-T conditions of 8 kbar and 650 °C for the peak metamorphic event. Primary fluid inclusions occur in staurolite and garnet, whereas quartz carries mostly secondary fluid inclusions. The trapped fluids in primary inclusions show initial melting temperatures in the range of -56.9 to -56.6 °C, suggesting nearly pure CO2 composition. The secondary fluids are of mixed carbonic-aqueous nature. The re-equilibrated inclusions show annular morphology as well as necking phenomena. The CO2 isochores for the primary inclusions indicate pressures of 6.1-6.7 kbar, suggesting that the CO2-rich fluids were trapped during post-peak exhumation of the rocks, or that synmetamorphic carbonic fluids underwent density reversal during isothermal decompression. The secondary CO2-H2O fluids must have been trapped during the late exhumation stage, as their isochores define further lower pressures of 4.8 kbar. The morphology of re-equilibrated fluid inclusions and the rapid decrease in pressure are consistent with a near-isothermal decompression trajectory following the peak metamorphism. The carbonic fluids were probably derived locally from decarbonation reactions of the associated carbonate rocks during metamorphism or from a deep-seated reservoir through Karakorum fault. © 2016 Elsevier Ltd.
Phase equilibria modelling, fluid inclusion study, and U-Pb zircon dating of ultra-high temperature mafic granulites from Rampur domain, Eastern Ghats province: implications for the Indo-Antarctic correlation
(Springer Science and Business Media Deutschland GmbH, 2025) Divya Prakash; Rajeev Kumar Pandey; Saurabh Kumar Singh; Chandrakant Singh; Manish Kumar; Bikash Mahanta; Aditya Kharya; Himanshu Kumar Sachan; Kamesh Sharma
The study area (Rampur domain) is situated to the east of the Eastern Ghats Boundary Shear Zone (EGBSZ) and encompasses portions of the granulite facies rocks of the exhumed Proterozoic Eastern Ghats Province (EGP), India. The EGP is characterized by a diverse array of rock types, featuring a wide variety of mineral parageneses and chemical compositions, including charnockite, mafic granulite, Mg-Al granulite, felsic granulites, amphibolite, khondalite and anorthosite. In this study, we report for the first time evidence of ultra-high temperature (UHT) metamorphism within the mafic granulites of the relatively unexplored Rampur domain of the Eastern Ghats Province, using the two-pyroxene assemblage. The stable mineral assemblage present during peak metamorphism typically includes garnet, orthopyroxene1, clinopyroxene, hornblende1, quartz, and plagioclase1. The consumption of garnet observed in different reaction textures, alongside the formation of striking orthopyroxene2–plagioclase2 and hornblende2–plagioclase2 symplectites, represent the later phases of metamorphism. By applying TWQ calculation procedures to the mineral core compositions, we have determined peak metamorphic conditions of approximately 970 °C at a pressure of 10.5 kbar. Zircon dating results from LA-HR-ICP-MS indicate upper intercept ages of 2509.9 ± 21.7 Ma and 2479.9 ± 21.0 Ma for the protolith, while lower intercept ages of 965.7 ± 40.7 Ma and 979.8 ± 18.1 Ma correspond to the metamorphic age of the analyzed samples E-185 and E-186, respectively. Based on the textural relationship, derived zircon ages, fluid-P-T constraints, and P-T pseudosection model, we propose a decompressional evolutionary P-T-t path that supports the Neo-Proterozoic assembly of the Indo-Antarctic region. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.
Tracing Late-Stage Fluid Sources and Vein Formation within Ophiolitic Mélanges from the Indus Suture Zone, Ladakh Himalaya
(University of Chicago Press, 2021) Aditya Kharya; Himanshu K. Sachan; Christopher J. Spencer; Koushik Sen; Divya Prakash; Shashi Ranjan Rai; Vikash Kumar
Quartz-calcite veins in the Zildat ophiolitic mélange (ZOM) and Shergol ophiolitic mélange (SOM) of the Indus Suture Zone preserve a diversity of fluid activity in the late stages of ophiolitic mélange formation. This article presents fluid-inclusion and isotope geochemistry of these veins to understand their source and evolution in terms of pressure and temperature. The microstructures of quartz and calcite veins indicate deformation temperatures between 2007 and 4007C. The d13 C and d18 O values of calcite veins from the ZOM and SOM are within the mixing hyperbolas of marine and primitive-mantle fields in the mixing model. The Sr and Pb isotopic values of calcite veins from the ZOM suggest a mid-ocean ridge basalt (MORB) fluid source of vein formation that was radiogenically enriched by metasomatism in a suprasubduction zone. For the SOM, fluids may have originated from the enriched-mantle (EM) and the depleted-MORB-mantle rocks. It is inferred that the carbonic fluids were derived from ultramafic lithologies and oceanic crust that formed the ophiolitic mélange rocks, which also host these veins. These source rocks have EM and MORB geochemical signatures that are also obtained in the quartz-calcite veins, as characterized by their C-O-Sr-Pb isotopic ratios. The magmatic saline fluid is inferred to have formed in the early stages of vein formation and to have been subsequently diluted, as exemplified by the presence of low-saline secondary aqueous inclusions. The microthermometry fluid pressure-temperature estimation of veins from the studied sections suggests that the maximum depth of emplacement of veining fluid was about 24.5 MPa (corresponding to ∼2.5 km) at 3367C. The vein-forming fluids (calcareous and siliceous) were introduced into the fractures that developed in the host as a result of deformation. © 2021 The University of Chicago. All rights reserved.