Browsing by Author "Boris V. Belyatsky"

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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.
Multi-stage enrichment in the mantle source region of cratonic lamproites: Geochemical and Sr-Nd-Hf-Os isotopic insights from the Mesoproterozoic lamproites of Bastar Craton, India
(Elsevier B.V., 2025) Rohit Pandey; Mahendra Kumar Singh; Ashutosh Pandey; Nittala V. Chalapathi Rao; Boris V. Belyatsky
Deep cratonic mantle-derived magmatic rocks such as lamproites provide significant insights into the composition and evolution of the sub-continental and sub-lithospheric mantle. This study presents SHRIMP U-Pb geochronology of rutile and bulk-rock geochemistry including Sr-Nd-Hf-Os isotopes on lamproite dykes from the diamondiferous Nuapada Lamproite Field (NLF) at the tectonic contact between Bastar Craton and Eastern Ghat Mobile Belt, India. The lamproites sampled from the Darlimunda cluster of NLF exhibit inequigranular-porphyritic texture with phenocrysts of olivine pseudomorphs in a groundmass rich in phlogopite. The abundance of low-temperature secondary phases such as vermiculite, chlorite, and carbonates in these rocks indicate significant post-magmatic alteration. The presence of quartz crystals and micro-veins along with zircon megacrysts indicate crustal assimilation to some extent but a strong enrichment in high-field strength elements buffers against significant crustal contamination. Rutile U-Pb geochronology reveals an emplacement age of 1009 ± 121 Ma, which is consistent with the (i) previously reported whole-rock 40Ar/39Ar age of lamproites from the NLF, and (ii) widespread ∼1.05 Gyr lamproite, kimberlite, and ultramafic lamprophyre magmatism in the Eastern Dharwar and Bastar Cratons, India. Moderate initial 87Sr/86Sr (0.703–0.706) and unradiogenic initial Nd-Hf isotopic (ƐNd of −5.96 to −8.08 and ƐHf of −7.25 to −9.02) composition is similar to the global cratonic lamproites and enriched mantle (EM I type) mantle reservoir. Moderately radiogenic and restricted initial 187Os/188Os (0.189–0.257) with low Os content, unlike that of the kimberlites and sub-continental lithospheric peridotites, show similarity to the Carboniferous orogenic Variscan lamproites from Bohemian massif and Neogene to Quaternary orogenic ultrapotassic mafic rocks from Italian peninsula. Based on the Sr-Nd-Hf-Os isotopic results, we propose that the cratonic lithospheric mantle source of these rocks record the evidence of a long-term enrichment in lithophile elements as a result of an ancient recycled crustal component. Elevated high-field strength elements in the lamproites and kamafugites of the NLF, similar to those of the global cratonic lamproites and ocean island basalts, represent an overprinting of ancient subduction-related metasomatized deep sub-continental lithospheric mantle sources by small-scale carbonatitic melts derived from the convecting sub-lithospheric mantle prior to their melting. Vein-plus-wall-rock mantle as a result of multi-stage mantle enrichment appears to play an important role in the origin of cratonic lamproites. © 2025 Elsevier B.V.