Articles written in Journal of Earth System Science

    • Appraisal of Veldurti–Kalva–Gani (VKG) fault, Cuddapah Basin, India: Gravity and magnetic approach


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      A ${\sim}$60 km long Veldurti–Kalva–Gani (VKG) fault is one of the identified strike-slip faults extending from Eastern Dharwar Craton (EDC) to Cuddapah basin in South Indian Shield. The recorded recent seismic activity during year 2012–2016 show occurrences of three microseismic events (<$M_{w}$ 2.0) in the vicinity of this fault. Historically, no major seismic events are recorded near this fault except magnitude of 5.0–5.9 (1843) earthquake at about ${\sim}$80 km west of this fault near Bellary. In the present study, analysis of available gravity, aeromagnetic and newly acquired ground gravity and magnetic data in the vicinity of the fault has been carried out to understand subsurface characteristics of this VKG fault and nearby structural features related to recent seismic activity. Analysis of aeromagnetic and gravity data shows shallow origin of the fault and earthquakes are associated with the zone of intersection like cross faults/lineaments which are parallel and perpendicular to the VKG fault. The calculated log normalized radially averaged power spectrum of the available gravity and aeromagnetic data shows four average depths $h_{0}$ (12.7 km), $h_{1}$ (6 km), $h_{2}$ (2.0 km) and $h_{3}$ (0.5 km). These estimated depths are possibly, bottom of the upper crust, thickness of the Cuddapah basin sediments, horizon of the basic sills, flows and the ferruginous quartzites and cumulative stratigraphic thickness of the Tadpatri shales and the Kurnools in the areas, respectively. The jointly inverted 2-D model from the ground gravity and aeromagnetic data along 2.7 km profile across VKG fault shows, faulting between Banganapalli Quartzite and Tadpatri Shales. The estimated average focal depth from the observed microseismic events is around 13 km. It is concluded from the present study that the observed microseismic events in the vicinity of VKG fault are associated with the intersection zones of cross faults/lineaments near the VKG fault and originated at an average depth of 13 km might be bottom of the upper crust. The estimated depths from the present analysis are well corroborated with previous geophysical studies.


      $\bullet$ Mapping of Veldurti–Kalva–Gani fault through gravity, magnetic and aeromagnetic data which is associated with recent seismic activity.

      $\bullet$ Understanding of origin of the seismic activity through spectral analysis.

      $\bullet$ Estimation of depth to the basement, upper crust and thickness of Cuddapah basin sediments in the study region.

      $\bullet$ Estimation of focal depth from seismological data and corroboration with spectral analysis of gravity and aeromagnetic data.

    • Electrical resistivity tomography of Mesoarchaean chromitite bands from Katpal in Sukinda Ultramafic Complex, Odisha


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      Katpal in Mesoarchaean Sukinda Ultramafic Complex (SUC) hosts chromitites within the ultramafic rocks emplaced in the Tomka–Daitari–Mahagiri greenstone belt, Singhbhum Craton. Chromite deposits occur as seams, lenses or pockets in ultramafic–mafic rocks mainly comprising serpentinised dunite, peridotite and gabbro. Chromite deposits at Kalrangi, Kaliapani and its precincts in SUC are currently being exploited by M/s. Odisha Mining Corporation (OMC), whereas their continuity is elusive in the subsurface in the Katpal area, Sukinda, Odisha. High-resolution electrical resistivity tomography (ERT) was carried out in quarry-G of M/s. OMC in Katpal on four profiles each with a profile length 400 m and each of them is separated at an interval of ${\sim}$100 m to capture and visualise a maximum anomaly variation within the host rock. The objectives of this study are to understand the behaviour of chromite seams vis-à-vis with a high-resolution electric potential signal with depths and to evolve a method to discriminate chromitites from the host rock both in horizontal and vertical directions with depths, which can be used to locate the extension of chromite seams around the study area. The interpretation of the ERT models revealed interesting resistivity anomalies, which is inferred as chromite associated with the ultramafic host rock in the area. Exploratory borehole data of the area confirmed the subsurface occurrence of chromitites within 22–40 m depths as lensoidal bodies within the mafic–ultramafic rocks. The chromite ore is mapped as low-resistive zones with a resistivity of ${\sim}$35–200 ${\Omega}$ m and extended up to a depth of 170 m within the high-resistive (${\ge}$500 ${\Omega}$ m) host rocks. Two distinct chromite bands were identified at different depths: 20–40 and 90–110 m based on the specific resistivity contrast and were validated using the existing shallow borehole data. The second band is highly folded whereas the first band resembles sill-like feature within the host rock. The electrical tomography technique can be aptly applied in an unknown area in SUC to establish the extension of the chromite ore body, its resistive signature and their variation with depths within the host rock for future resource prospecting and exploitation in the given geological setting of the area.


      $\bullet$ The chromite ore is mapped as a low-resistivity signature and its extension is delineated as a low-resistivity anomaly of ~35–200 Ω m.

      $\bullet$ The electrical resistivity models indicate low resistivity as chromite and high-resistivity as ultramafic rock (~500–10,000 Ω m) up to a depth of 170 m.

      $\bullet$ The light green up to yellow bands in the inverted resistivity models characterise various grades of mineralisation within the host rock setting.

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