• Subba Rao D V

      Articles written in Journal of Earth System Science

    • The geological site characterisation of the Mandla region, Eastern Deccan Volcanic Province, Central India

      Srinivas K N S S S Pavan Kishore P Subba Rao D V

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      Detailed geological studies were carried out on the basaltic sequences along the Jabalpur–Niwas, Jabalpur–Chutka and Jabalpur–Mandla traverses covering an area of about 12 km $\times$ 15 km to characterise various basaltic lava flows and their behaviour on seismotectonics and geodynamic setting of their formation in the Mandla region of the Eastern Deccan Volcanic Province (EDVP). The studies involve an analysis of the satellite images for the identification of lineaments/faults and field geological studies consisting of geological controls such as ground check, thickness of fractures and orientation along the acknowledged lineaments/faults. The results of the present research comprising 65 lineaments/faults mainly belonging to two geometric groups, minor and major dominantly in the NW–SE and the NE–SW and altered strata varying lithology (weathered to compact basalts) are recognised in the study area. Based on their extent, 57 lineaments have been classified as minor (<100 km) trends in three different orientations, i.e., NNE–SSW, ESE–WNW and ENE–WSW, whereas 8 lineaments were classified as intermediate (300–100 km) trends in NNE–SSW. No major (>300 km) lineaments are noticed in the study region. The field geological investigations have facilitated the recognition of 10 flows with different characteristic features and a variety of volcanic structures such as columnar, vesicular, amygdaloidal, inflated pahoehoe lava flows and red bole interflow horizons have been documented. Basement rocks of these Deccan basalt lavas are represented by Tirodi Biotite gneisses, quartzite, quartz–mica schists and crystalline limestone in the SE part of the study area of the Mandla region. The present study will help evaluate the localised site characterisation for urban planning and setting up major civil structures.

    • Alteration of primary Cr-spinel mineral composition from the Suru Valley ophiolitic peridotites, Ladakh Himalaya: Their low-temperature metamorphic implications

      Bhat I M Ahmad T Subba Rao D V

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      The present study focuses on the chemical modification of a Cr-spinel from the Suru Valley ophiolitic peridotites exposed near Trespone Village of Kargil district, Ladakh Himalaya. The Suru Valley peridotite is partially serpentinised with the preservation of the spinel and relics of olivine and pyroxene. These peridotites contain characteristic red-brown spinel grains of corroded grain boundaries. While analysing these grains for mineral chemistry, compositional variation was observed with Cr-rich cores rimmed by Cr-poor compositions. Secondary spinel compositions, i.e., ferritchromite and magnetite were observed along the margins and cracks of primary Cr-spinel grains. The primary Cr-spinel cores are identified as Cr-rich and are characterised by higher values of Cr$^{3+}$# (0.5–0.6) and lower values of Al$^{3+}$# (0.42–0.54). From primary spinel cores to altered rims it was observed that Cr$^{3+}$# and Fe$^{3+}$# increase while Mg$^{2+}$# decreases due to Mg$^{2+}$–Fe$^{2+}$ and Al$^{3+}$–Fe$^{3+}$ exchange with surrounding silicates of host peridotite during alteration. On the basis of present spinel mineral chemistry, metamorphic alteration conditions were transitional between greenschist and lower amphibolite similar to most of the Neo-Tethyan ophiolite peridotites.

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