Scholarly Publications
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This community showcases the academic contributions of faculty and researchers at Banaras Hindu University (BHU) and provides a year-wise compilation of publications across disciplines. Institutional Repository BHU
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PublicationArticle Petrology of ijolite xenoliths entrained in a nephelinite dyke from the Kamthai area, Late Cretaceous polychronous Sarnu-Dandali alkaline complex, North-West India: Evidence for recurrent magmatic pulses and magma mixing(Elsevier B.V., 2024) Sudipa Bhunia; N.V. Chalapathi Rao; Debojit Talukdar; Rohit Pandey; Bernd LehmannThe Late Cretaceous (89–65 Ma) Sarnu-Dandali alkaline complex is intrusive into the Neoproterozoic (∼750 Ma) Malani Igneous Suite of rocks in North-Western India. This complex represents a polychronous setup owing to the available age groups of varied rock types involving nephelinites, alkali pyroxenites, syenites, phonolites, ijolites, carbonatites and lamprophyres. In this study, we report xenoliths of ijolite up to 2 mm in size, comprising minerals such as aegirine, nepheline, sodalite, apatite, sphene, fluorite, Ti-rich andradite, and perovskite entrained in the host nephelinite from this complex. Pyroxene thermobarometry for both host and xenoliths reveals that the xenoliths crystallized around 876–1114°C; 4.6–18 kbar (Kdcpx−melt ∼0.164), whereas the host magma crystallized around 800–1165°C and 4.5–17.9 kbar (Kdcpx−melt ∼0.44). The redox conditions of the magma are also estimated from Fe-Nb oxy barometry of perovskite and the log oxygen fugacity varies from -2.5 to -3.7 (ΔNNO), showing a resemblance with that of the world-wide kimberlites derived from the cratonic mantle. Furthermore, the composition as well as the barometric study of clinopyroxenes from both the host and the xenoliths, suggest multiple shallower magma chambers composed of ijolite and nephelinite magmas which were activated by different magmatic pulses, thereby forming a complex magmatic plumbing system. © 2023PublicationArticle U-Pb Neoproterozoic age and petrogenesis of a calc-alkaline shoshonitic lamprophyre from Simdega area, Chhotanagpur Gneissic Complex (Eastern India): Implication for the evolution of the Central Indian Tectonic Zone and Rodinia tectonics(Elsevier B.V., 2023) Deepak Kumar; N.V. Chalapathi Rao; Aparajita Tripathi; B. Belyatsky; Priyesh Prabhat; Waliur Rahaman; M. SatyanarayananThe age of emplacement and geochemistry of the lamprophyres are of tectonic significance as they have potential to unravel global scale geodynamic processes. We present petrology, U-Pb SHRIMP apatite and titanite ages and bulk-rock Sr-Nd isotope data for an unmetamorphosed and undeformed lamprophyre dyke from the Simdega area of the Chhotanagpur Gneissic Complex (CGC) which is a component of the E-W trending Central Indian Tectonic Zone (CITZ), India. The CITZ is a major intercontinental suture which separates the northern Indian and the southern Indian blocks whose polarity of their subduction is a contentious issue. The lamprophyre exhibits a strong porphyritic-panidiomorphic texture imparted by the megacrysts/phenocrysts of mica and amphibole with feldspar, apatite, titanite, zircon and opaques confined to the groundmass. Based on combined mineralogy and geochemistry, the lamprophyre is classified to be of calc-alkaline variety (minette) with shoshonitic affinities. Mg# (70.7–78.2) contents highlight the primitive melt character whereas incompatible trace element ratios exclude crustal contamination and are indistinguishable from those of the subduction-related global as well as Eastern Dharwar craton (southern India) calc-alkaline lamprophyres. U-Pb dating of apatite gave an emplacement age of 944 ± 82 Ma which is indistinguishable, within the error limits, from the U-Pb titanite age of 942.1 ± 5 Ma demonstrating a Neoproterozoic magmatic emplacement age of the lamprophyre synchronous with the Rodinia assembly. Bulk-rock 87Sr/86Srinitial (0.707239 and 0.708910) and ɛNdinitial (-8.9 to -8.3) highlights the involvement of an enriched mantle source. Calculated Paleoproterozoic model ages (Nd depleted mantle) of 2.1 Ga of the lamprophyre are indistinguishable from those of the co-spatial amphibolite dykes. Petrogenetic modeling involving rare earth elements reveals that the derivation of the lamprophyre magma from 2 to 3% partial melting of a mixed garnet (70%) and spinel (30%) lherzolitic mantle source with minor phlogopite. Our study highlights that the western part of the CGC was less affected, relative to the eastern part, by the M3 regional amphibolite grade metamorphic event (ca. 920-880 Ma) and also supports the geodynamic models involving northward-directed subduction of the Southern Indian block under the Northern Indian block.- © 2023 Elsevier B.V.PublicationArticle Petrology, U-Pb titanite dating and Sr-Nd isotope geochemistry of a shoshonitic lamprophyre dyke near the Western Dharwar Craton-Southern Granulite Terrane contact, southern India: Implications for long-lived enriched mantle, widespread Tonian-Cryogenian rifting, and Rodinia configuration(Elsevier B.V., 2023) Sneha Raghuvanshi; N.V. Chalapathi Rao; D. Talukdar; B. Belyatsky; P. Prabhat; Waliur Rahaman; B. Lehmann; J.G. MeertWe present petrology, U-Pb titanite geochronology, bulk-rock and Sr-Nd geochemistry of an undeformed and unmetamorphosed shoshonitic lamprophyre (spessartite) from the Mysuru area (Halaguru- Harohalli alkaline province) located approximately 80 km north of the tectonic contact between the Western Dharwar Craton and the Southern Granulite Terrane, southern India, to understand its origin and to evaluate its geodynamic significance. The lamprophyre shows a typical porphyritic-panidiomorphic texture with amphibole phenocrysts. Clinopyroxene occurs only as xenocrysts with feldspar, apatite, titanite and titano-magnetite confined to the groundmass. Amphibole mineral composition classifies them as pargasite and tremolite, and the groundmass is essentially constituted of alkali feldspar. High whole-rock Mg# (56–65), Ni + Cr (245 to 730 ppm), a lack of correlation between SiO2 and Rb/Sr as well as ɛNd(i) indicates that crustal contamination experienced by the lamprophyre magma is limited. U-Pb titanite (n = 18) SHRIMP-II dating yielded a Neoproterozoic Tera-Wasserburg concordia age of 820 ± 15 Ma (MSWD = 5.9). Whole-rock derived 87Sr/86Sr(i) (0.70425–0.70530) and ɛNd(i) (-6.3 to −4.3) suggest origin of the lamprophyre from an enriched lithospheric mantle source. Paleoproterozoic depleted-mantle model ages of ca. 1.8 Ga suggest the existence of a long-lived enriched mantle which correspond to the timing (ca.1.9–1.7 Ga) of widespread mafic dyke swarms’ emplacement in the Dharmapuri-Agali-Tiruvannamalai domain in the Salem block at the northernmost portion of the Southern Granulite Terrane. The Tonian emplacement age of the studied lamprophyre is synchronous with several co-spatial Neoproterozoic (i) alkaline complexes ± carbonatite ± lamprophyre from the northern part of the Southern Granulite Terrane, and (ii) other mafic alkaline dykes of the Halaguru-Harohalli alkaline province from the southern part of the Eastern Dharwar Craton. Our results highlight the importance of this lamprophyre dyke, present close to the'Fermor Line’ as well as near the boundary between Eastern and Western Dharwar Cratons, which provides a rare opportunity to understand its spatio-temporal link with alkaline dykes of the Southern Granulite Terrain. Our findings also help understand the role of repeated large-scale rifting, associated with the Rodinia break-up, leading to the generation of a wide spectrum of Tonian-Cryogenian alkaline magmas in southern Indian Shield. The new age data also have implications for the configuration of India's paleoposition during the Neoproterozoic and support the idea that South China Block-India were located on the periphery of Rodinia or were already detached from the supercontinent. © 2023 Elsevier B.V.PublicationArticle 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 RaoWe 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)PublicationArticle Petrochemistry and Sr-Nd isotopes of post-collisional Neoproterozoic (ca. 950 Ma) amphibolite dykes of continental flood basalt affinity from the Simdega area: Implications for the geodynamic evolution of the Chhotanagpur Gneissic Complex, Eastern India(Elsevier B.V., 2022) Deepak Kumar; N.V. Chalapathi Rao; Priyesh Prabhat; Amitava Chatterjee; Waliur RahamanMetamorphosed mafic dykes are significant stratigraphic markers which also represent a shift from extensional to compressional geodynamic processes. We present petrology, bulk-rock geochemistry, and Sr-Nd isotope data on nineteen E-W to ENE-WSW trending mafic dykes metamorphosed under amphibolite facies in the Simdega area in the south western domain of the Chhotanagpur Gneissic Complex (CGC). The CGC is widely regarded as an eastern extension of the Central Indian Tectonic Zone (CITZ) which separates the Northern Indian and the Southern Indian blocks. Calcic amphiboles and plagioclases are the dominant minerals whereas clinopyroxene (diopside), biotite, chlorite, quartz, apatite, titanite, ilmenite and magnetite are present in minor amounts. Relict igneous textures are also present in some of the samples. Conventional thermobarometry and pseudosection modelling gave consistent peak temperatures (619 ± 13 °C) and pressures (5.8 ± 0.1 kbar) corresponding to the amphibolite facies. Major oxide geochemistry of the studied samples show differentiation trends and display arc-tholeiitic, high Fe-tholeiitic, high Mg-tholeiitic and calc-alkaline characters. Based on the LREE and HREE fractionation (LaN/YbN, LaN/SmN and GdN/YbN) the studied samples can be classified into two broad groups: Group-I and Group II. In terms of the 87Sr/86Srinitial and 143Nd/144Ndinitial contents, both the Group I and II samples are confined to an array of continental flood basalts and EM-1 and EM-2 reservoirs. The TDM (depleted mantle) model age of ca. 1.9 Ga suggest the source enrichment of the dykes during the Paleoproterozoic. Trace element ratios of both groups of the amphibolite dykes reveal that the (i) crustal contamination to be minimum, (ii) subduction-related fluid enrichment influenced their source regions, and (iii) mixed arc-, OIB-, and oceanic plateau- type geochemical signatures to be their characteristic features. Petrogenetic modelling involving REE suggest variable degrees of partial melting ranging from 5 to 10% for most of the samples of G-I and 1–3% for G-II dykes from a mixed source comprising predominantly of spinel lherzolite and minor amounts of garnet lherzolite. A three-stage model is proposed for the evolution of the CGC amphibolite dykes which involves: (i) sub-continental lithopheric mantle (SCLM) source enrichment due to the fluids derived from the subduction zone prior to ca. 1.9 Ga, (ii) emplacement of the mafic dykes in a post-collisional intra-continental extensional tectonic setting due interaction between the mantle plume and SCLM during the Tonian period at ca. 0.95 Ga and (iii) subsequent amphibolite facies thermal event at 0.92–0.88 Ga, associated with the amalgamation of the Rodinia supercontinent, that metamorphosed the mafic dykes as well as the much of the south-western part of CGC. Our findings support models proposing a northward subduction of the southern Indian block beneath the northern Indian block along the CITZ as well as bring out the role of a mantle plume in the generation of the Precambrian mafic dykes in the CGC. © 2022 Elsevier B.V.PublicationArticle Kimberlites, lamproites and lamprophyres from the indian shield: Highlights of researches during 2016-2019(Indian National Science Academy, 2020) N.V. Chalapathi Rao; Rohit K. Giri; Ashutosh PandeyHighlights of researches on kimberlites, lamproites and lamprophyres (and their entrained xenoliths) during 2016-2019 from the Indian context are presented. A few previously unknown occurrences have been brought to light, and a wealth of petrological, geochemical and isotopic data on these rocks became available. All these studies provided new insights into the nomenclatural as well as geodynamic aspects such as subduction-tectonics, mantle metasomatism, lithospheric thickness, supercontinent amalgamation, and break-up and nature of the sub-continental lithospheric mantle from the Indian shield. © 2020 Indian National Science Academy. All rights reserved.PublicationReview Supercontinent transition as a trigger for ~1.1 Gyr diamondiferous kimberlites and related magmatism in India(Elsevier B.V., 2020) Ashutosh Pandey; N.V. Chalapathi RaoKimberlites are volatile-rich deep mantle-derived rocks that often contain diamonds. Numerous Grenvillian (ca. 1.1 Gyr) diamondiferous kimberlites, ultramafic lamprophyres, and lamproites are exposed in the Eastern Dharwar Craton and the Bastar Craton, India, and are aligned almost parallel to the Eastern Ghats (granulite) Mobile Belt (EGMB). The trigger for these kimberlite and related magmatic events still remains an open question. We review the available geochronological and radiogenic isotopic data for the ~1.1 Gyr kimberlites, lamproites, and ultramafic lamprophyres from the Eastern Dharwar Craton and the Bastar Craton of the Indian shield. We show that kimberlites and associated magmas were emplaced for a longer duration (ca. 130 Myr) in the Indian shield during the Mesoproterozoic and sampled distinct mantle source regions. The kimberlites and ultramafic lamprophyre are characterized by slightly depleted to chondritic Nd isotopic ratios revealing their origin at deeper sub-lithospheric regions, whereas the lamproites essentially show an enriched Nd isotopic signature suggesting their derivation from enriched sub-continental lithospheric mantle. We argue that the absence of linear age progression, prolonged magmatic activity compared to the time span of coeval large igneous provinces (the Umkondo, the Keweenawan, and the Warakurna) and a cooler ambient mantle as revealed from the entrained xenoliths, constitute important limitations for a plume model earlier proposed for the genesis of these kimberlites and related magmas. These observations together with a geographical and temporal (Grenvillian) link to the EGMB points towards edge-driven convection as a trigger for kimberlite magmatism- similar to the model proposed for the Mid-Cretaceous kimberlite corridor in North America. However, this model can't explain the coeval formation of sub-continental lithospheric mantle-derived lamproites. As the timing of kimberlite and related magmatism coincides with that of the Grenvillian orogeny and succeeded a magmatic lull of ~360 Myr in the Dharwar Craton during the Mesoproterozoic, we instead, propose that small scale partial melting of heterogeneous mantle caused by plate reorganization during Columbia to Rodinia supercontinent extroversion served as a trigger for this ca. 1.1 Gyr magmatism in the southeastern Indian shield. © 2020 Elsevier B.V.PublicationArticle A new analytical protocol for high precision U–Th–Pb chemical dating of xenotime from the TTG gneisses of the Bundelkhand Craton, central India, using CAMECA SXFive Electron Probe Micro Analyzer(Springer, 2020) Hiredya Chauhan; Aparajita Tripathi; Dinesh Pandit; N.V. Chalapathi Rao; Talat AhmadAbstract: Xenotime is a significant accessory mineral which is being extensively used for precise U–Th–Pb geochronology by Electron Microprobe Analysis (EPMA). This paper presents a protocol for high analytical precision (<3% uncertainties on the measured ages) developed for the accurate estimation of U–Th and Pb content in xenotime using SXFive EPMA at the Department of Geology, Banaras Hindu University, by deploying five spectrometers attached with TAP, LIF, LPET, LTAP and PET crystals. The protocol is applied to the xenotime grains of tonalite-trondhjemite-granodiorite-gneiss (TTG) rocks from the geochronologically well-constrained terrain of the Bundelkhand Craton, central India. The obtained xenotime age 2929±23 Ma of TTGs is in agreement with the earlier published Neoarchaen 2697±3 Ma Pb–Pb zircon ages from the same area which validates the authenticity of the analytical method developed at the BHU-EPMA facility. Highlights: Analytical protocol for high precision U–Th–Pb chemical dating of xenotime by EPMA.High precision ages from TTG gneiss of the Bundelkhand Craton, Central India.Ages distinguishable from earlier reported ages from other techniques and samples.Validates the authenticity of the analytical method developed at the BHU-EPMA facility. © 2020, Indian Academy of Sciences.PublicationArticle 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 RaoDetailed 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 UniversityPublicationArticle Petrogenesis of an alkaline lamprophyre (camptonite) with ocean island basalt (OIB)-affinity at the NW margin of the Cuddapah basin, eastern Dharwar craton, southern India(E. Schweizerbart'sche Verlagsbuchhandlung, 2019) Rohit Kumar Giri; Praveer Pankaj; N.V. Chalapathi Rao; Ramananda Chakrabarti; Dinesh PanditWe report petrology and geochemistry (including Sr and Nd isotopes) of a fresh lamprophyre at Ankiraopalli area at the north-western margin of Paleo-Mesoproterozoic Cuddapah basin, eastern Dharwar craton, southern India. Ankiraopalli samples possess a typical lamprophyre porphyritic-panidiomorphic texture with phenocrysts of kaersutite and diopside set in a plagioclase dominant groundmass. Combined mineralogy and geochemistry classify it as alkaline lamprophyre in general and camptonite in particular. Contrary to the calc-alkaline and/or shoshonitic orogenic nature portrayed by lamprophyres occurring towards the western margin of the Cuddapah basin, the Ankiraopalli samples display trace element composition revealing striking similarity with those of ocean island basalts, Italian alkaline lamprophyres and highlights an anorogenic character. However, the 87Sr/86Srinitial (0.710316 to 0.720016) and Ndinitial (-9.54 to -9.61) of the Ankiraopalli lamprophyre show derivation from an ‘enriched’ mantle source showing long term enrichment of incompatible trace elements and contrast from those of (i) OIB, and (ii) nearby Mahbubnagar alkaline mafic dykes of OIB affinity. Combining results of this study and recent advances made, multiple mantle domains are identified in the Eastern Dharwar craton which generated distinct Mesoproterozoic lamprophyre varieties. These include (i) Domain I, involving sub-continental lithospheric mantle source essentially metasomatized by subduction-derived melts/fluids (represented by orogenic calcalkaline and/or shoshonitic lamprophyres at the Mudigubba, the Udiripikonda and the Kadiri); (ii) Domain II, comprising a mixed sub-continental lithospheric and asthenospheric source (represented by orogenic-anorogenic, alkaline to calc-alkaline transitional lamprophyres at the Korakkodu), and (iii) Domain III, representing a sub-continental lithospheric source with a dominant overprint of an asthenospheric (plume) component (represented by essentially alkaline lamprophyres at the Ankiraopalli). Our study highlights the varied mantle source heterogeneities and complexity of geodynamic processes involved in the Neoarchean-Paleo/Mesoproterozoic evolution of the Eastern Dharwar craton. © 2019 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany.