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PublicationArticle A Late Cretaceous (ca. 90 Ma) kimberlite event in southern India: Implication for sub-continental lithospheric mantle evolution and diamond exploration(Elsevier Inc., 2016) N.V. Chalapathi Rao; A. Dongre; Fu-Yuan Wu; B. LehmannWe report groundmass perovskite U-Pb (SIMS) ages, perovskite Nd isotopic (LA-ICPMS) composition and bulk-rock geochemical data of the Timmasamudram diamondiferous kimberlite cluster, Wajrakarur kimberlite field, in the Eastern Dharwar craton of southern India. The kimberlite pipes gaver similar Mesoproterozoic ages of 1086 ± 19 Ma (TK-1, microcrystic variant) and 1119 ± 12 Ma (TK-3). However, a perovskite population sampled from the macrocrystic variant of TK-1 gave a much younger Late Cretaceous age of ca. 90 Ma. This macrocrystic kimberlite phase intrudes the Mesoproterozoic microcrystic phase and has a distinct bulk-rock geochemistry. The Nd-isotope composition of the ~1100 Ma perovskites in the cluster show depleted εNd(T) values of 2.1 ± 0.6 to 6.7 ± 0.3 whereas the ~90 Ma perovskites have enriched εNd(T) values of -6.3 ± 1.3. The depleted-mantle (DM) model age of the Cretaceous perovskites is 1.2 Ga, whereas the DM model age of the Proterozoic perovskites is 1.2 to 1.5 Ga. Bulk-rock incompatible trace element ratios (La/Sm, Gd/Lu, La/Nb and Th/Nb) of all Timmasamudram kimberlites show strong affinity with those from the Cretaceous Group II kimberlites from the Bastar craton (India) and Kaapvaal craton (southern Africa). As the Late Cretaceous age of the younger perovskites from the TK-1 kimberlite is indistinguishable from that of the Marion hotspot-linked extrusive and intrusive igneous rocks from Madagascar and India, we infer that all may be part of a single Madagascar Large Igneous Province. Our finding constitutes the first report of Cretaceous kimberlite activity from southern India and has significant implications for its sub-continental lithospheric mantle evolution and diamond exploration programs. © 2015 International Association for Gondwana Research.PublicationLetter An alternate perspective on the opening and closing of the intracratonic Purana basins in peninsular India(Geological Society of India, 2015) N.V. Chalapathi Rao; A.N. Dongre; Vivek S. Kale[No abstract available]PublicationArticle Petrology and petrogenesis of Mesoproterozoic lamproites from the Ramadugu field, NW margin of the Cuddapah basin, Eastern Dharwar craton, southern India(Elsevier, 2014) N.V. Chalapathi Rao; Alok Kumar; Samarendra Sahoo; A.N. Dongre; Debojit TalukdarPetrography, mineral chemistry, and major and trace element data are presented for the newly discovered Mesoproterozoic (1.33-1.43. Ga) lamproites from the Ramadugu field (RLF), at the NW margin of the Paleo-Mesoproterozoic Cuddapah basin, in the Eastern Dharwar craton (EDC), southern India. RLF lamproites are emplaced as dykes, have a NW-SE trend and their petrography reveal the effects of low-temperature alteration. However, their textural features, mineralogy and geochemistry are closely similar to other well-characterised lamproites worldwide, including examples from the Eastern Dharwar craton, Leucite Hills, West Kimberley, Smoky Butte and Labrador. The RLF magmas have undergone varying degrees of olivine. +. clinopyroxene fractionation; yet their compatible and incompatible trace element concentrations are sufficiently high to signal a primitive character. Incompatible element ratios suggest limited contamination by continental crust. Geochemical evidence indicates the derivation of RLF magmas from metasomatised harzburgite within the garnet stability field. Rare earth element inversion modelling further highlights substantial involvement of the sub-continental lithospheric mantle in their genesis. The RLF lamproites are geochemically similar to the well-known extension-related ultrapotassic lavas from eastern Virunga and western Anatolia, and exclude an affinity with orogenic lamproites, such as those from the Mediterranean region. Bulk-rock geochemical models, recently developed to infer diamond potential, reveals that RLF lamproites are non-prospective. Lamproites of the RLF, together with those from the Krishna lamproite field and Cuddapah basin are interpreted as an expression of extensional events in the Eastern Dharwar craton possibly related to the break-up of the supercontinent of Columbia between 1.5 and 1.3. Ga. © 2014 Elsevier B.V.PublicationArticle Mantle transition zone-derived eclogite xenolith entrained in a diamondiferous Mesoproterozoic (∼1.1 Ga) kimberlite from the Eastern Dharwar Craton, India: evidence from a coesite, K-omphacite, and majoritic garnet assemblage(Cambridge University Press, 2023) Amitava Chatterjee; N.V. Chalapathi Rao; Rohit Pandey; Ashutosh PandeySubduction-related kimberlite-borne eclogite xenoliths of the Precambrian age may provide significant information about the evolution and recycling of a subducting crust as exhumed/orogenic eclogites of the pre-Mesoproterozoic time-frame are globally rare. In this paper, we report a kimberlite-borne eclogite xenolith from the diamondiferous Kalyandurg kimberlite cluster of the Eastern Dharwar Craton, India, which contains a plethora of ultra-high-pressure minerals such as coesite, majoritic garnet, and supersilicic K-rich omphacite. The presence of these ultra-high-pressure minerals is confirmed by in situ X-ray diffractometry, laser Raman spectra and electron probe microanalysis. The presence of coesite undisputedly pinpoints a subduction origin for the eclogite at ∼2.8 GPa pressure, which corresponds to ∼100 km depth. The geothermobarometric estimations involving garnet-omphacite-kyanite-coesite reveal that such an eclogitic assemblage equilibrated at ∼5-8 GPa (∼175-280 km) pressure during ultra-deep subduction. The textural relationship between omphacite, coarse-grained garnet and majoritic garnet coupled with the laser Raman spectra and geobarometric estimations obtained from the majoritic garnet demonstrate that the majoritic garnet formed at ∼8-19 GPa (∼280-660 km) owing to disassociation of omphacite and coarse-grained garnet to majoritic garnet during increment of pressure up to the mantle transition zone. Thus, the mineralogical and geothermobarometric data suggest that the studied eclogite possibly travelled down to the mantle transition zone before it was rapidly carried up by a pre-Mesoproterozoic mantle plume, and subsequently entrained as a xenolith by the Mesoproterozoic (∼1.1 Ga) kimberlite. © The Author(s), 2023. Published by Cambridge University Press.PublicationArticle Glimmeritic enclave in a lamprophyre from the Settupalle alkaline pluton, Eastern Ghats mobile belt(2010) N.V. Chalapathi RaoA rare occurrence of glimmeritic (mica-rich) enclave - composed of abundant modal biotite, subordinate proportions of clinopyroxene and apatite, minor amounts of feldspar, carbonate and sphene - is reported from the lamprophyre of Settupalle alkaline pluton, Eastern Ghats mobile belt (EGMB), India. The enclave displays very coarse grained equigranular texture (mica laths up to 5 mm and clinopyroxene grains up to 4 mm). In comparison, the host lamprophyre exhibits a marked porphyritic-panidiomorphic texture comprising phenocrysts of clinopyroxene; other phases such as biotite and potash- and plagioclase-feldspar are restricted to the groundmass. A tight closeness in mineral chemistry of the glimmerite and lamprophyre imply a possible genetic relationship between their parent magmas. Glimmeritic enclave is construed to be an autolith of the proto-lamprophyre magma, which failed to reach the surface, and lined the wall-rock along the conduit of the lamprophyric intrusion. Glimmerite enclave provides a direct evidence for the multi-stage modification of the lithospheric mantle due to the infiltration of the potassium-rich hydrous melts such as lamprophyres. Mineralogy of the glimmeritic enclave is also similar to that of a vein component of the hydrous, mafic and potassic-ultrapotassic veined lithosphere in the EGMB. © GEOL. SOC. INDIA.PublicationArticle Alkali feldspar syenites with shoshonitic affinities from Chhotaudepur area: Implication for mantle metasomatism in the Deccan large igneous province(Elsevier, 2014) K.R. Hari; N.V. Chalapathi Rao; Vikas Swarnkar; Guiting HouTwo petrologically distinct alkali feldspar syenite bodies (AFS-1 and AFS-2) from Chhotaudepur area, Deccan Large Igneous Province are reported in the present work. AFS-1 is characterized by hypidiomorphic texture and consists of feldspar (Or55Ab43to Or25Ab71), ferro-pargasite/ferro-pargasite hornblende, hastingsite, pyroxene (Wo47, En5, Fs46), magnetite and biotite. AFS-2 exhibits panidiomorphic texture with euhedral pyroxene (Wo47-50, En22-39, Fs12-31) set in a groundmass matrix of alkali feldspar (Or99Ab0.77to Or1.33Ab98), titanite and magnetite. In comparison to AFS-1, higher elemental concentrations of Ba, Sr and ΣREE are observed in AFS-2. The average peralkaline index of the alkali feldspar syenites is ∼1 indicating their alkaline nature. Variation discrimination diagrams involving major and trace elements and their ratios demonstrate that these alkali feldspar syenites have a shoshonite affinity but emplaced in a within-plate and rifting environment. No evidence of crustal contamination is perceptible in the multi-element primitive mantle normalized diagram as well as in terms of trace elemental ratios. The enrichment of incompatible elements in the alkali feldspar syenites suggests the involvement of mantle metasomatism in their genesis.PublicationArticle Petrology, geochemistry and tectonic significance of Palaeoproterozoic alkaline lamprophyres from the Jungel Valley, Mahakoshal supracrustal belt, Central India(Springer Wien, 2007) Rajesh K. Srivastava; N.V. Chalapathi RaoPalaeoproterozoic (∼1.6 Ga) lamprophyres occur as dykes, plugs and lava flows within the Mahakoshal supracrustal belt of the Jungel Valley, Central India. Although metamorphosed under greenschist facies conditions, the lamprophyres still retain remnants of the diagnostic igneous textures viz., porphyritic-panidiomorphic habit of mafic phenocrysts, leucocratic (carbonate-rich) ocelli and volatile-rich mineralogy. The studied lamprophyres are mineralogically uniform but texturally variable (porphyritic to aphanitic). Chemically they are silica undersaturated, ultrabasic, dominantly alkaline (some of them have normative nepheline) through mildly alkaline to sub-alkaline, sodic to mildly potassic and their magmas are primitive as well as evolved. The lamprophyres are characterized by Ni and Cr abundances and MgO sufficiently high to indicate a mantle source. The chondrite-normalized REE patterns confirm crystallization from a LREE enriched magma. Combined petrological and geochemical studies classify them as belonging to alkaline lamprophyre category in general and camptonites in particular. Geochemistry also suggests that their magmas are not affected by any crustal contamination. This study establishes the occurrence of lamprophyres in the Jungel area and brings to end the speculations about their mistaken identity. The presence of a wide spectrum of undersaturated alkaline magmatism comprising lamprophyres, syenites, tinguites, and possibly kimberlties, highly carbonated rocks and ultrabasic rocks as intrusives in the Mahakoshal supracrustal belt undoubtedly highlights the presence of a carbonate-rich palaeo- to early Proterozoic alkaline province. The occurrence of greenschist facies metamorphosed lamprophyres of Palaeoproteorozoic age in the eastern central Indian shield is also significant in the context of re-construction of ancient continental fits as similar rocks of comparable age have been reported from the Yilgarn and Pilbara cratons of Western Australia. © Springer-Verlag 2006.PublicationArticle Diamond-facies chrome spinel from the Tokapal kimberlite, Indrāvati basin, central India and its petrological significance(Springer-Verlag Wien, 2012) N.V. Chalapathi Rao; B. Lehmann; D. Mainkar; B.K. PanwarWidespread and abundant spinel is the only primary mineral of petrogenetic significance preserved in the hydrothermally altered, crater-facies, Neoproterozoic (≥620 Ma) Tokapal kimberlite pipe that intruded the Indrāvati basin, Bastar craton, Central India. Two distinct spinel populations occur: (i) finer-grained (<50 μm) microcrysts which are zoned from titaniferous magnesiochromite-chromite to magnetite; and (ii) larger macrocrysts (>400 μm) with cores having distinctly chromium-rich (Cr2O3 up to 63. 67 wt%), and TiO2-poor (<0.68 wt%) compositions. Based on their morphology and chemical composition the macrocrysts are inferred to be disaggregated mantle xenocrysts and their compositional range extends well into the diamond stability field. However, the reported absence of diamond and other indicator minerals (such as pyrope garnet, chrome diopside and magnesian ilmenite) in the Tokapal pipe is intriguing since diamondiferous cratonic roots are indeed preserved in the Bastar craton, and also the kimberlite itself was derived from a similar source region(s) as that of the well-known diamondiferous Mesoproterozoic (ca. 1,100 Ma) kimberlites from Wajrakarur, Dharwar craton, southern India. Given the large areal extent (>550 ha) of kimberlite, there is a possibility that it contains diamonds but they were not recovered during the sampling. Alternately, highly oxidising conditions imparted by the metasomatic fluids/melts derived from (i) asthenosphere-lithosphere interaction, or (ii) the kimberlite itself might have played an important role in the destruction of diamond, and other indicator minerals. © 2012 Springer-Verlag.PublicationArticle The Late Cretaceous diamondiferous pyroclastic kimberlites from the Fort à la Corne (FALC) field, Saskatchewan craton, Canada: Petrology, geochemistry and genesis(Elsevier Inc., 2017) N.V. Chalapathi Rao; B. Lehmann; B. Belyatsky; J.M. WarnslohThe Late Cretaceous (ca. 100 Ma) diamondiferous Fort à la Corne (FALC) kimberlite field in the Saskatchewan (Sask) craton, Canada, is one of the largest known kimberlite fields on Earth comprising essentially pyroclastic kimberlites. Despite its discovery more than two decades ago, petrological, geochemical and petrogenetic aspects of the kimberlites in this field are largely unknown. We present here the first detailed petrological and geochemical data combined with reconnaissance Nd isotope data on drill-hole samples of five major kimberlite bodies. Petrography of the studied samples reveals that they are loosely packed, clast-supported and variably sorted, and characterised by the presence of juvenile lapilli, crystals of olivine, xenocrystal garnet (peridotitic as well as eclogitic paragenesis) and Mg-ilmenite. Interclast material is made of serpentine, phlogopite, spinel, carbonate, perovskite and rutile. The mineral compositions, whole-rock geochemistry and Nd isotopic composition (Nd: + 0.62 to − 0.37) are indistinguishable from those known from archetypal hypabyssal kimberlites. Appreciably lower bulk-rock CaO (mostly < 5 wt%) and higher La/Sm ratios (12–15; resembling those of orangeites) are a characteristic feature of these rocks. Their geochemical composition excludes any effects of significant crustal and mantle contamination/assimilation. The fractionation trends displayed suggest a primary kimberlite melt composition indistinguishable from global estimates of primary kimberlite melt, and highlight the dominance of a kimberlite magma component in the pyroclastic variants. The lack of Nb-Ta-Ti anomalies precludes any significant role of subduction-related melts/fluids in the metasomatism of the FALC kimberlite mantle source region. Their incompatible trace elements (e.g., Nb/U) have OIB-type affinities whereas the Nd isotope composition indicates a near-chondritic to slightly depleted Nd isotope composition. The Neoproterozoic (~ 0.6–0.7 Ga) depleted mantle (TDM) Nd model ages coincide with the emplacement age (ca. 673 Ma) of the Amon kimberlite sills (Baffin Island, Rae craton, Canada) and have been related to upwelling protokimberlite melts during the break-up of the Rodinia supercontinent and its separation from Laurentia (North American cratonic shield). REE inversion modelling for the FALC kimberlites as well as for the Jericho (ca. 173 Ma) and Snap Lake (ca. 537 Ma) kimberlites from the neighbouring Slave craton, Canada, indicate all of their source regions to have been extensively depleted (~ 24%) before being subjected to metasomatic enrichment (1.3–2.2%) and subsequent small-degree partial melting. These findings are similar to those previously obtained on Mesozoic kimberlites (Kaapvaal craton, southern Africa) and Mesoproterozoic kimberlites (Dharwar craton, southern India). The striking similarity in the genesis of kimberlites emplaced over broad geological time and across different supercontinents of Laurentia, Gondwanaland and Rodinia, highlights the dominant petrogenetic role of the sub-continental lithosphere. The emplacement of the FALC kimberlites can be explained both by the extensive subduction system in western North America that was established at ca. 150 Ma as well as by far-field effects of the opening of the North Atlantic ocean during the Late Cretaceous. © 2017 International Association for Gondwana ResearchPublicationArticle Thin lithosphere-asthenosphere boundary beneath Eastern Indian craton(2014) Shalivahan; Bimalendu B. Bhattacharya; N.V. Chalapathi Rao; V.P. MauryaThe lithosphere-asthenosphere boundary (LAB) separates the hard and rigid outer layer of the earth (lithosphere) and the weaker, hotter, and deeper part of the upper mantle (asthenosphere) and plays a pivotal role in plate tectonics. However, its definitive detection, especially beneath the cratons, is proving elusive. One of the geophysical tools used to map the LAB beneath the cratons is through magnetotelluric (MT) observations. The resistivity at boundary falls in the range of 5-25. Ω-m and can be explained by the presence of a small amount of water in the asthenosphere, possibly inducing partial melt. Here, we report thickness of the LAB in one of the oldest dated ancient cratons of India-Eastern Indian Craton (EIC) of ~. 3.3. Gyr, from MT studies. The two prominent phase-sensitive strike directions, one each for crust and mantle, and the presence of resistive continental lower crust act as a window to mantle in resolving deeper electrical conductivity structures beneath EIC. Our results show that the LAB beneath the EIC is at 95. km. The region is interesting as the electrical properties of the crust and mantle and the Moho depth are similar to those of the Slave Craton, Canada (~. 4.0. Gyr) but the depth of the LAB beneath the EIC is half that of the Slave craton. As cratonic signatures, depicted by ultrapotassic rocks from Gondwana coal fields close to EIC, are preserved at least till early Cretaceous (117. Ma) it is likely that Himalayan orogeny could have played a major role in delamination of the lithospheric roots of the EIC in addition to attendant seismicity. © 2013 Elsevier B.V.