• S K BEGUM

      Articles written in Journal of Earth System Science

    • Multistage magmatic intrusion in Narmada–Tapti region, India: Insights from geopotential modelling

      K N D PRASAD A P SINGH P RAMA RAO OM PRAKASH S K BEGUM

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      The present-day crustal structure of tectono-magmatic regions is the product of dynamic interactions of crust and mantle materials. The Narmada–Tapti region is a mosaic of tectono-magmatic signatures and is characterized by active seismicity, deep-seated faults, shear zones, and high heat flow, suggesting it to be a zone of crustal weakness. The availability of ample seismic and magnetotelluric datasets and inherent complexity drew our attention to image the crustal structure in the third dimension using high-resolution gravity data. The derived 3D crustal density model shows that the Deccan trap extends from 200–1700 m partly below the 90–150 m thick Quaternary sediment exposed in some pockets. The sub-trappean Mesozoic sediment is present at a depth of 250–2400 m followed by the basement. Our 3D model further shows that the high gravity values in residual anomalies are due to high-density magmatic intrusions between 1.5 and 9 km depth. The gravity high in regional anomaly is modelled with a broad dome-shaped high-density (3.02 g/cm3) underplated layer between 14 and 38 km depth. The spatial correlation of delineated high-density lower crustal body with the high-velocity and high conductivity zones mapped by earlier workers in this region indicates the possible presence of mantle magma intrusion in the realm of Deccan volcanism. Analysis of isostatic residual anomaly indicates that the region beneath Narmada–Tapti is not in local isostatic equilibrium. Analysis of the isostatic residual anomaly, root depth, and crustal thickness from the 3D model further ascertains the modification of the crust due to the interaction of mantle plume material. The gravity effect of residual geoid up to 50 km corroborates the high-density magmatic material distribution at two different places, i.e., one at Navsari near the west coast and the other is Junapani near Khandwa. The region has signatures of upliftment and together with the crustal-scale basic magmatic intrusion, satisfies both high gravity anomalies and positive residual geoid undulation. The residual geoid undulations are bounded by major tectonic faults and together with the magmatic underplate at the crustal base indicate that these faults were activated during the Deccan magmatism.

      $\bf{Highlights}$

      $\bullet$ Narmada-Tapti region has a weak crustal architecture with crustal and sub-crustal magmatic intrusions, dyke swarms, atypical geophysical signatures, and crustal upliftment.

      $\bullet$ 2½D crustal density modelling along available seismic sections using high-resolution gravity data in Narmada-Tapti region.

      $\bullet$ Three-dimensional crustal-scale density structure with multistage magmatic intrusion in the Narmada-Tapti region, central India.

      $\bullet$ Positive Bouguer and isostatic anomalies and geoid undulation over the Narmada-Tapti region provide extra arguments for densification of the crust through multistage magmatic intrusions caused by the Deccan magmatism.

      $\bullet$ About 250–2400 m thick Mesozoic sediments delineated at a depth of about 500–3000 m illustrates the potential for hydrocarbon exploration in the Narmada-Tapti region.

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