Browsing by Author "Abhinay Sharma"

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Arc-related pyroxenites derived from a long-lived neoarchean subduction system at the southwestern margin of the cuddapah basin: Geodynamic implications for the evolution of the eastern dharwar craton, southern india
(University of Chicago Press, 2019) Abhinay Sharma; Rohit Kumar Giri; N.V. Chalapathi Rao; Waliur Rahaman; Dinesh Pandit; Samarendra Sahoo
Mineralogy and bulk-rock geochemistry (including Sr and Nd isotopes) of two ultramafic (pyroxenite) intrusions at Gurramkonda, situated adjacent to the southwestern margin of the Paleo-Mesoproterozoic Cuddapah Basin within the Eastern Dharwar Craton, southern India, are presented. The pyroxenites have a characteristic cumulate texture, with a predominance of pyroxene (augite) and amphibole (hornblende and actinolite), whereas chromite is present mostly as inclusions in pyroxene. Mineral chemistry of these ultramafics is akin to that of arc cumulate rocks, particularly those associated with the Alaskan-type complexes, formed in suprasubduction zones. High Mg#’s (72–74), coupled with high bulk-rock Ni (830–1130 ppm) and Cr (1110–1,360 ppm), strikingly correspond to those of continental arc cumulates. The enrichment of large ion lithophile elements over high field strength elements, conspicuous negative Nb-Ta, Zr-Hf, and Ti anomalies, and chondrite-normalized light rare earth element patterns highlight their arc affinity. Fluid-related modification of the mantle source is apparent from the various trace-element ratios. Negative ɛNd2.15Ga values (20.93 to 22.90) also support contribution of an enriched-mantle reservoir in their genesis. Partial melting of this fertile mantle source has been attributed to the Paleoproterozic lithospheric extension with heat contributions from a mantle plume or convective asthenosphere. Ultramafic intrusions of arc-related geochemical affinity thus constitute rare, but genetically important, occurrences within the Eastern Dharwar Craton. We propose that, together with the recently studied calc-alkaline lamprophyres occurring immediately toward the western margin of the Cuddapah Basin, the Gurramkonda pyroxenites are manifestations of a long-lived and major subduction system of Neoarchean age in the Eastern Dharwar Craton, southern India. © 2019 by The University of Chicago.
Boron measurement in tourmaline from pegmatite veins, Simdega area, Chhotanagpur Gneissic Complex, Eastern India using Electron Probe Microanalysis
(Indian Academy of Sciences, 2019) Deepak Kumar; Dinesh Pandit; Abhinay Sharma; N.V. Chalapathi Rao
Tourmaline group of minerals, the primary source of boron, are cyclosilicates which are widespread in the earth's crust. Earlier studies involving the nomenclature and classification of tourmaline were based on the measurement of its common elements (Al, Mn, Fe, Mg, etc.). In all such studies, boron was assumed to be fixed in the composition and restricted only to the triangular structural site. However, recent discovery of the presence of boron in the tetrahedral structural site as well, necessitates the measurement of boron content. Much of the earlier attempts to measure boron were based on solution methods, and electron microprobe analysis (EPMA) was the least used due to low levels of detection of its analytical crystals. In the present study, we quantify boron - particularly along with fluorine and other major elements - in tourmaline grains using high-sensitivity PC3 analytical crystal. We found that the measured boron content slightly exceeds that of the stoichiometrically calculated boron. Also, the studied tourmalines come under the alkali group in general and belong to the schorl- dravite solid solution series in particular. © 2019 Current Science Association, Bengaluru.
Chrome-diopside Megacryst-bearing Lamprophyre from the Late Cretaceous Mundwara Alkaline Complex, NW India: Petrological and Geodynamic Implications
(Geological Society of India, 2018) Abhinay Sharma; Deepak Kumar; Samarendra Sahoo; Dinesh Pandit; N.V. Chalapathi Rao
The occurrence of a rare mantle-derived chrome-diopside megacryst (∼8 mm), containing inclusions of olivine, in a lamprophyre dyke from the late Cretaceous polychronous (∼100 – 68 Ma) Mundwara alkaline complex of NW India is reported. The olivine inclusions are forsteritic (Fo: 85.23) in composition, and their NiO (0.09 wt%) and CaO (0.13 wt%) contents imply derivation from a peridotitic mantle source. The composition of the chrome diopside (Cr2O3: 0.93 wt) (Wo45.27 En48.47 Fs5.07 and Ac1.18) megacryst is comparable to that occurring in the garnet peridotite xenoliths found in diamondiferous kimberlites from Archaean cratons. Single pyroxene thermobarometry revealed that this chrome diopside megacryst was derived from a depth range of ∼100 km, which is relatively much deeper than that of the chrome-diopside megacrysts (∼40–50 km) reported in spinellherzolite xenoliths from the alkali basalts of Deccan age (ca. 66–67 Ma) from the Kutch, NW India. This study highlights that pre- Deccan lithosphere, below the Mundwara alkaline complex, was at least ∼100 km thick and, likely, similar in composition to that of the cratonic lithosphere. © 2018, Geological Society of India.
Chrome-diopside Xenocrysts Entrained in a Neoproterozoic Lamprophyre Dyke from the Mysuru Area: Their Origin and Implications for Lithospheric Thickness Beneath the Western Dharwar Craton, Southern India
(Springer, 2022) Sneha Raghuvanshi; N.V. Chalapathi Rao; Debojit Talukdar; Abhinay Sharma; Rohit Pandey
In comparison to the eastern Dharwar Craton, the mantle-derived xenocrysts/xenoliths are extremely rare or even unreported from the western Dharwar Craton, southern India. A Neoproterozoic (ca. 800–900 Ma) lamprophyre cropping out in the Mysuru area of southern India contains chrome-diopside xenocrysts (Cr2O3 content varying from 0.2–1.23 wt%) which provide important evidence about the pressure-temperature conditions and lithospheric thickness beneath the western Dharwar Craton. Studied chrome-diopsides show compositional zoning which is lacking in the liquidus phases (amphiboles and feldspars) of the lamprophyre which additionally favors a non-cognate origin of the former. Based on the compositional zoning, all the chrome-diopside xenocrysts can be divided into three groups: (i) Group I- which are euhedral and show reverse zoning with increasing Cr-content from core to rim; (ii) Group II- which are characterized by fractures and resorption textures, show complex reverse zoning and display up to three distinct compositional layers, and (iii) Group III- which evidence the reaction of chrome-diopsides with lamprophyric melt and are marked by alteration phases, such as actinolite and chlorite, together with relicts of some unaltered xenocrysts. High Cr2O3, moderate MgO and low Al2O3 content of all the three varieties of chrome-diopside suggest them to represent disaggregated xenocrysts of mantle-derived garnet peridotite. Temperature-pressure estimates for chrome-diopside xenocrysts ranges from 895–1026 °C (± 30 °C) and 32–38 kbar respectively and correspond to depth range of 106–127 km. The study reveals that lithospheric thickness during the Neoproterozoic beneath the western Dharwar craton was at least ∼115 km and is similar in composition to that of the cratonic lithosphere found in the other cratonic domains. © 2022, Geological Society of India, Bengaluru, India.
Cross-serotype protection against group A Streptococcal infections induced by immunization with SPy_2191
(Nature Research, 2020) Pooja Sanduja; Manish Gupta; Vikas Kumar Somani; Vikas Yadav; Meenakshi Dua; Emanuel Hanski; Abhinay Sharma; Rakesh Bhatnagar; Atul Kumar Johri
Group A Streptococcus (GAS) infection causes a range of diseases, but vaccine development is hampered by the high number of serotypes. Here, using reverse vaccinology the authors identify SPy_2191 as a cross-protective vaccine candidate. From 18 initially identified surface proteins, only SPy_2191 is conserved, surface-exposed and inhibits both GAS adhesion and invasion. SPy_2191 immunization in mice generates bactericidal antibodies resulting in opsonophagocytic killing of prevalent and invasive GAS serotypes of different geographical regions, including M1 and M49 (India), M3.1 (Israel), M1 (UK) and M1 (USA). Resident splenocytes show higher interferon-γ and tumor necrosis factor-α secretion upon antigen re-stimulation, suggesting activation of cell-mediated immunity. SPy_2191 immunization significantly reduces streptococcal load in the organs and confers ~76-92% protection upon challenge with invasive GAS serotypes. Further, it significantly suppresses GAS pharyngeal colonization in mice mucosal infection model. Our findings suggest that SPy_2191 can act as a universal vaccine candidate against GAS infections. © 2020, The Author(s).
Glimmerite and melteigite xenoliths from the Early Cretaceous campto-tinguaite dyke, Nongchram Fault Zone (East Garo Hills), Shillong Plateau, North East India: Evidence for magma mixing and involvement of subducted as well as plume related mantle sources
(The Physiological Society of Japan, 2025) R. B. Ananth; Nittala Venkata Chalapathi Rao; Abhinay Sharma; J. Amal Dev; Tomson J. Kallukalam
We report the occurrence of glimmerite and melteigite xenoliths from a hybrid Early Cretaceous camptonite-tinguaite dyke from the Nongchram Fault Zone, East Garo Hills, Shillong Plateau, North East India. Glimmerite xenolith contains predominantly biotite with subordinate to minor amounts of pyroxene, ferro-dolomite, rutile, and ilmenite. The melteigite xenolith is dominated by pyroxene and contain pseudo-nepheline (altered to analcime) and rutile. The host campto-tinguaite dyke features a distinctive porphyritic-panidiomorphic and a tinguaitic texture with clinopyroxenes as macrocrysts, microcrysts and clots and amphibole as phenocrysts with accessory minerals such as apatite, magnetite, rutile, and ilmenite. In-situ trace element geochemistry of pyroxenes from the xenoliths and the host rock reveals significant enrichment in LILEs such as Ba and Sr, as well as LREEs like La and Ce, suggesting an enriched mantle source. The geothermobarometric data for pyroxenes from the (i) glimmerite and melteigite xenoliths and macrocrysts and (ii) microcrysts and clots from the campto-tinguaite suggest varying crystallization pressures and temperatures, indicating different depths of origin ranging from 23–96 km. The mineral composition, in-situ trace element data of pyroxenes as well as the geothermobarometric study of clinopyroxenes from both the host and the xenoliths, suggest involvement of multiple shallower magma chambers composed of the camptonitic and tinguaitic magmas generated during distinct pulses, thereby forming a complex magmatic plumbing system. The presence of orogenic geochemical signatures in the minerals of xenoliths and anorogenic geochemical signatures in the host campto-tinguaite pyroxenes imply a complex tectono-magmatic setting, with contributions from both the plume and subduction-modified mantle sources. © © 2025 The Geochemical Society of Japan.
Lamprophyres from the Indian shield: A review of their occurrence, petrology, tectonomagmatic significance and relationship with the Kimberlites and related rocks
(International Union of Geological Sciences, 2020) N.V. Chalapathi Rao; Rohit Kumar Giri; Abhinay Sharma; Ashutosh Pandey
Lamprophyres are some of the oldest recognized alkaline rocks and have been studied for almost the last 150 years. Known for hosting economic minerals such as gold, diamond and base metals, they are also significant in our understanding of the deep-mantle processes (viz., mantle metasomatism and mantleplume- lithosphere interactions) as well as large-scale geodynamic processes (viz., subduction-tectonics, supercontinent amalgamation and break-up). The Indian shield is a collage of distinct cratonic blocks margined by the mobile belts and manifested by large igneous provinces (LIPs) such as the Deccan. A plethora of lamprophyres, varying in age from the Archaean to the Eocene, with diverse mineralogical and geochemical compositions, are recorded from the Indian shield and played a key role in clarifying the tectonic processes, especially during the Paleo- and Mesoproterozoic and the Late Cretaceous. A comprehensive review of the occurrence, petrology, geochemistry and origin of the Indian lamprophyres is provided here highlighting their tectonomagmatic significance. The relationship of the lamprophyres to the Kimberlite clan rocks (KCRs), focusing on the Indian examples, is also critically examined. © 2020 International Union of Geological Sciences. All rights reserved.
Mineralogy and petrology of lamprophyre and dolerite dykes from the end-Cretaceous (~ 66 Ma) Phenaimata alkaline igneous complex, north-western India: evidence for open magma chamber fractionation, mafic recharge, and disaggregation of crystal mush zone in a large igneous province
(Springer, 2023) Abhinay Sharma; Rohit Pandey; Nittala V. Chalapathi Rao; Samarendra Sahoo; Boris V. Belyatsky; Prashant Dhote
The end-Cretaceous (ca. 66 Ma) Phenaimata alkaline igneous complex, associated in space and time with the Deccan large igneous province (LIP) in Western India, consists of bimodal (tholeiitic to alkaline) differentiated plutonic to volcanic igneous rocks. Mineralogy and petrology of variably fractionated alkaline lamprophyre and dolerite dykes of the complex are the focus of this study. The two lamprophyre dykes (termed as camptonite-I and camptonite-II) which intrude the host basalt/olivine dolerites and gabbro, differ in their liquidus minerals and crystal size distribution. Their respective rare earth element (REE) and trace element patterns suggest the lamprophyres to be genetically related, with the camptonite-II being relatively more evolved than that of the camptonite-I. Binary mixing model involving trace elements as well as the Sr˗Nd isotopic data in case of the camptonite-I, brings out involvement of crustal contamination in the generation of the lamprophyres. The two dolerites mostly consist of the liquidus phases, with the exception of olivine antecrysts created during early stages of the host gabbro formation but subsequently inherited into their magma. In terms of their trace element composition, the dolerites of this study show a strong similarity with that of the alkali basalts of the complex. The normal compositional zoning of pyroxene and amphibole from the lamprophyres shows that their parental magma initially experienced a closed system fractionation to form a large crystal mush zone and subsequently developed a smaller magmatic chamber where biotites of the camptonite-II first crystallised. Reverse zoning, resorption of crystals, disparity in crystal size distribution and their composition also reveals that a newer batch of magma was introduced from the feeding zone into the initially developed crystal laden magmatic chamber. This replenishment led to the disaggregation of crystals from the mush zone and the resulting magma subsequently evolved to form camptonite-I. Later on, the successive lateral spreading of the newly generated magma increased its buoyancy to rise through the smaller crustal chamber (with biotites) to generate camptonite-II. Our study demonstrates not only the operation of diverse open and closed system processes such as fractionation, replenishment and mush capturing that have occurred within inter-connected plumbing magmatic chambers beneath the alkaline complexes associated with the flood basalt volcanism in large igneous provinces but also their significant role in influencing the ultimate composition of the associated diverse rocks. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.
Petrology and geochemistry of the diamondiferous Jamnidih occurrence, Bastar Craton, Central India: Metabasalt and not a kimberlite
(Elsevier B.V., 2022) Mahendra Kumar Singh; Rohit Pandey; Abhinay Sharma; N.V. Chalapathi Rao
We have re-visited the ‘diamondiferous kimberlite’ from the Jamnidih area of Mahasamund, Bastar Craton, Central India. This study presents detailed field observations, petrographic and geochemical studies of Jamnidih rocks in view of the reported occurrence of diamonds from them. Megascopically, the Jamnidih rocks are fine grained, yellowish green colour and fragile in nature and lack any visible phenocrysts or xenocrysts. Petrography reveals that chloritization and sericitization has altered much of the primary mineralogy. Feldspar and pyroxene are the identifiable major phases with imprints of alteration and development of feeble foliations at places. Lack of inequigranular texture (two generations of olivine) and kimberlitic indicator minerals viz. chromium- and pyrope-rich garnets, chrome-bearing diopsides, and magnesian-ilmenites are characteristic of Jamnidih rocks. This aspect is also reflected in the geochemistry of these rocks which is entirely different from that of the well-established kimberlites (Wajrakarur field, Eastern Dharwar Craton, southern India), orangeites (Behradih orangeites, Bastar Craton, central India) and transitional kimberlites (Tokapal kimberlite, Bastar Craton, central India). Geochemically the Jamnidih rocks display silica-saturated, and alumina-rich nature and depletion of Ba, Co, Ni, V, Nb, Hf and other metasomatically mobilised elements. Petrography (lack of inequigranular macrocrystic texture), mineralogy (paucity of kimberlite typomorphic phases) and bulk-rock geochemistry (extreme impoverishment of high field strength elements and presence of negative Eu anomaly in chondrite-normalized plot) testify them to be meta-basalts and exclude their affinities to the bonafide Group I or II or even transitional varieties of kimberlites. In this context, the reported occurrence of microdiamonds in these rocks is clearly anomalous and assumes significance. © 2021 The Author(s)
Petrology and Nd–Sr isotopic composition of alkaline lamprophyres from the Early to Late Cretaceous Mundwara Alkaline Complex, NW India: evidence of crystal fractionation, accumulation and corrosion in a complex magma chamber plumbing system
(Geological Society of London, 2022) Abhinay Sharma; Samarendra Sahoo; N.V. Chalapathi Rao; Boris Belyatsky; Prashant Dhote; Bernd Lehmann
The Early to Late Cretaceous Mundwara alkaline complex (comprising the Musala, Mer and Toa plugs) displays a broad spectrum of alkaline rocks closely associated in space and time with the Deccan large igneous province in NW India. Petrology and Nd–Sr isotopic data on the two youngest and altogether compositionally different lamprophyre dykes of the Mundwara alkaline complex are presented in this paper to understand their petrogenesis and also to constrain the magmatic processes responsible for generation of the rock spectrum in the complex (pyroxenite, picrite ankaramite, carbonatite, shonkinite, olivine gabbro, feld-spathoidal and foid-free syenite). The two lamprophyre dykes occurring in the Mer and the Musala hills are referred to as basaltic camptonite I and camptonite II, respectively. The basaltic camptonite I is highly porphyritic and contains olivine, clinopyroxene and magnetite macrocrysts embedded within the groundmass of micro-phenocyrsts composed of clinopyroxene, phlogopite, magnetite and feldspar. Camptonite II, however, with a more or less similar texture, contains amphibole, biotite, magnetite and clinopyroxene within the microphenoc-rystic groundmass of amphibole, biotite, apatite and feldspar. Pyroxenes are chemically zoned and display corrosion of the cores, revealing that they are antecrysts developed during the early stages of magma evolution and later on inherited by more evolved magmas. The mineral chemistry and trace element composition of the lamprophyres reveal that fractional crystallization was a dominant process. Early segregation of olivine + Cr-rich clinopyroxene + Cr-spinel from a primary hydrous alkali basalt within a magmatic plumbing system is inferred, which led to the generation of basaltic camptonitic magma (M1) forming the Mer hill lamprophyre. Subsequently, progressive fractionation of pyroxene and Fe–Ti oxides from the basaltic camptonitic (M1) magma generated camptonitic (M2) magma forming the Musala hill lamprophyre. Both lamprophyre dykes on the Sr–Nd isotopic array reflect plume-type asthenospheric derivation, which largely corresponds to the Réunion plume and other alkaline rocks of the Deccan large igneous province. Our study brings out a complex sequence of processes such as crystal fractionation, accumulation and corrosion in the magmatic plumbing system involved in the generation of the Mundwara alkaline complex. © 2021 The Author(s). Published by The Geological Society of London. All rights reserved.
Petrology and Sr-Nd isotope systematics of the Ahobil kimberlite (Pipe-16) from the Wajrakarur field, Eastern Dharwar craton, southern India
(Elsevier B.V., 2019) Abhinay Sharma; Alok Kumar; Praveer Pankaj; Dinesh Pandit; Ramananda Chakrabarti; N.V. Chalapathi Rao
Detailed mineralogical, bulk-rock geochemical and Sr-Nd isotopic data for the recently discovered Ahobil kimberlite (Pipe-16) from the Wajrakarur kimberlite field (WKF), Eastern Dharwar craton (EDC), southern India, are presented. Two generations of compositionally distinct olivine, Ti-poor phlogopite showing orangeitic evolutionary trends, spinel displaying magmatic trend-1, abundant perovskite, Ti-rich hydrogarnet, calcite and serpentine are the various mineral constituents. On the basis of (i) liquidus mineral composition, (ii) bulk-rock chemistry, and (iii) Sr-Nd isotopic composition, we show that Ahobil kimberlite shares several characteristic features of archetypal kimberlites than orangeites and lamproites. Geochemical modelling indicate Ahobil kimberlite magma derivation from small-degree melting of a carbonated peridotite source having higher Gd/Yb and lower La/Sm in contrast to those of orangeites from the Eastern Dharwar and Bastar cratons of Indian shield. The TDM Nd model age (∼2.0 Ga) of the Ahobil kimberlite is (i) significantly older than those (1.5–1.3 Ga) reported for Wajrakarur and Narayanpet kimberlites of EDC, (ii) indistinguishable from those of the Mesoproterozoic EDC lamproites, and (iii) strikingly coincides with the timing of the amalgamation of the Columbia supercontinent. High bulk-rock Fe-Ti contents and wide variation in oxygen fugacity fO2, as inferred from perovskite oxybarometry, suggest non-prospective nature of the Ahobil kimberlite for diamond. © 2018 China University of Geosciences (Beijing) and Peking University