• Dora M L

      Articles written in Journal of Earth System Science

    • Petrography and geochemistry of the Proterozoic sandstones of Somanpalli Group from Pomburna area, Eastern Belt of Pranhita–Godavari Valley, central India: Implications for provenance, weathering and tectonic setting

      Rao N K Dora M L Baswani S R Malpe D B Deshmukh M S

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      In this paper, we, for the first time, report geochemistry of sandstone from Somanpalli Group from Pomburna area in the Eastern Belt of Pranhita–Godavari (PG) Valley, central India and studied to infer their provenance, intensity of paleo-weathering and depositional tectonic setting. Petrographic study of sandstones show QFL modal composition of arenite. Chemical results show high $\rm{SiO_{2}}$ and CIA but lower $\rm{Al_{2}O_{3}}$, $\rm{TiO_{2}}$, Rb, Sr, $\rm{K_{2}O}$ indicating mixed sources. Major elements chemistry parameters such as, $\rm{K_{2}O/Al_{2}O_{3}}$ ratio and positive correlation of Rb with $\rm{K_{2}O}$, reflects a warm and humid climate for study area. The tectonic discrimination plots $\rm{(SiO_{2}/20–K_{2}O+Na_{2}O–TiO_{2}+Fe_{2}O_{3}+MgO}$; $\rm{K_{2}O/Na_{2}O}$ vs. $\rm{SiO_{2}}$; Th–Sc–Zr/20) indicate dominantly passive margin and slight active tectonic setting. Concentrations of Zr, Nb, Y, and Th are higher compared to the UCC values and the trends in Th/Cr, Th/Co, La/Sc and Cr/Zr ratios support a felsic and mafic source for these sandstones and deposition in passive margin basin. Chondrite normalized REE pattern reflects LREE depletion, negative Eu anomaly and flat HREE similar to UCC, felsic components. ICV value (0.95) also supports tectonically quiescent passive margin settings. CIA values (74) indicate high degree of chemical weathering and warm and humid paleoclimatic condition.

    • A new find of calc-alkaline lamprophyres in Thanewasna area, Western Bastar Craton, India

      Meshram R R Dora M L Naik R Shareef M Gopalakrishna G Meshram T Baswani S R Randive K R

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      Lamprophyre dykes within the granitoid and charnockite are reported for the first time from the Western Bastar Craton, Chandrapur district, Maharashtra. It shows porphyritic–panidiomorphic texture under a microscope, characterised by the predominance of biotite phenocrysts with less abundance of amphibole and clinopyroxene microphenocryst. The groundmass is composed more of K-feldspars over plagioclase, amphiboles, clinopyroxene, biotite, chlorite, apatite, sphene and magnetite. The mineral chemistry of biotite and magnesio-hornblende is indicative of minette variety of calc-alkaline lamprophyre (CAL), which is further supported by preliminary major oxides and trace element geochemistry. This unique association of CAL with granitoid provides an opportunity to study the spatio-temporal evolution of the lamprophyric magma in relation to the geodynamic perspective of the Bastar Craton.

    • The first report on the chemical (Th–U–Pb) monazite age of the Mul granite pluton, Western Bastar craton, central India and its metallogenic significance

      Dora M L Yamuna Singh Joshi S Kundu A Suresh G Randive K

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      Petrography and the geochemical attributes of the studied Mul granite pluton reveal mixed characteristics of A-type and I-type within-plate granites consistent with an extensional tectonic environment. The dominance of the primary biotite over the primary muscovite suggests its meta-aluminous nature. The dating of monazite from the Mul granitoid pluton by the in situ Th–U–Pb electron probe micro analyser chemical method indicates the tectonomagmatic event around 1602 $\pm$ 27 Ma in the western Bastar craton, Chandrapur district, Maharashtra. The age data possibly represent the emplacement of large bodies of grey granite and attendant monazite crystallisation at $\sim$1600 Ma. This monazite age implies that Mesoproterozoic magmatism is coeval with the formation of the Pranhita Godavari rift in the eastern flank in Maharashtra and associated with the copper and barite mineralisation in Thanewasna and the adjoining areas.

    • Characterisation and genesis of the chalcedony occurring within the Deccan lava flows of the LIT hill, Nagpur, India

      Kirtikumar Randive Sushma Chaudhary Sneha Dandekar Kavita Deshmukh Dilip Peshve Dora M L Boris Belyatski

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      The Deccan trap basaltic lava flows host a plethora of secondary minerals, notably zeolites, quartz and calcite. These minerals occupy the vesicles and cavities that are formed during the solidification of the lava flows. Much attention has been given to beautifully developed zeolites of the Deccan traps and well-crystallised quartz varieties such as rosy quartz and amethyst. However, a group of minerals consisting of cryptocrystalline and amorphous silica did not receive much attention despite their consistent occurrence in all parts of the Deccan large igneous province. The freshly exposed samples of the chalcedonic silica occurring in the vesicular basalt at the Laxminarayan Institute of Technology (LIT) hill, Nagpur University Campus, were studied, one of which was studied in detail using X-ray diffraction analysis, differential thermal analysis, thermogravimetric analysis, Fourier transform infrared and scanning electron microscope–energy dispersive spectroscopy. The present study has demonstrated that the secondary silica occupying vesicles in the basaltic lava flows was length-fast chalcedony showing fibrous morphology overprinted by grainy morphology. It was concluded that the mother fluid was a hot ($\sim$100–300$^{\circ}$C) aqueous solution, which was acidic in nature and high in sulphur, probably derived from the host Deccan trap basaltic magma itself.

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