• Malpe D B

      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.

    • Petrology and geochemistry of a boninite dyke from the western Bastar craton of central India

      Biswajit Hazarika Malpe D B Ashish Dongre

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      The Dongargarh Supergroup along with the basal Amgaon Gneissic Complex constitutes the northwestern part of the central Indian Bastar craton. In the present study, we report a new finding of a boninite dyke intruded in the Amgaon gneisses of this area. The dyke composed of mainly pyroxenes, amphiboles and subordinate amount of plagioclase. The higher contents of SiO$_{2}$ (51–54 wt.%), MgO (12–14 wt.%), Ni (375–473 ppm), Cr (1416–1580 ppm) and very low TiO$_{2}$ (0.2–0.4 wt.%) are consistent with the boninite nature of the dyke as well as the unevolved primary nature of the source magma. The extraordinarily high CaO content (15.97–17.7 wt.%) with higher CaO/Al$_{2}$O$_{3}$ (3.13–3.96) ratios classifies it as high-Ca boninite. The trace element ratios including Zr/Ti, Ti/V, Ti/Sc and Ti/Yb further show its geochemical similarity with the Archaean boninite. The dyke also shows negative high-field strength element (Nb, Ta and Ti) anomalies which are the characteristics of the boninite rocks reported elsewhere and along with the enriched light rare earth element pattern, it shows more affinity particularly with the northern Bastar boninite dyke. The mineralogical and geochemical similarities of the boninite dykes from the Bastar craton indicate a widespread boninitic event during the Palaeoproterozoic having a similar origin. These boninite dykes indicate the preservation of subduction-related signatures in the lithospheric mantle beneath the Bastar craton at the time of its evolution or may be during the convergence of the Bastar and Bundelkhand cratons.

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