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.

    • Spatial variations in the geochemical characteristics of basalts from the Deccan Volcanic Province, India: Role of mixing and assimilation fractional crystallisation


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      In the present study, we have demarcated five zones within the Deccan Volcanic Province (DVP): (1) Kutch, (2) Western Ghats, (3) Central Son–Narmada, (4) Eastern Son–Narmada and (5) South- Eastern Deccan (SE DVP) to evaluate spatial geochemical variations within the DVP possibly controlled by different eruption loci. True OIB-type unmixed trace element and isotopic signatures are demon strated by both alkali and tholeiitic basalts from Kutch and a small proportion from Western Ghats. However, large number of tholeiitic basaltic samples from both the zones and Central Son–Narmada zone illustrate sub-continental lithosphere mantle (SCLM) signatures. The Eastern Son–Narmada and SE DVP zones of the DVP show evolved compositions, but are dominantly derived from sub-lithospheric sources. The plume–lithosphere interaction is represented by mixing and/or assimilation and fractional crystallisation (AFC) of plume-derived melts with the sub-continental lithospheric mantle (SCLM)- derived melts, sediments preserved in the SCLM, lower crustal (TTG-type) and upper crustal (granitic) components. We argue that melts from the Archaean sediments preserved in the SCLM, represented by calc-alkaline lamprophyres, are the most suited components that interacted with the plume-derived as well as SCLM peridotite-derived melts. Few Kutch zone basalts require granitic components, while some proportion of Western Ghats zone basalts require TTG-type assimilate to explain their isotopic characteristics. Mixing and/or AFC between the plume-derived and sediment-derived melts and SCLM peridotite-derived and sediment-derived melts played fundamental roles in the observed geochemical heterogeneity of the Deccan basalts. We demonstrate that original sub-lithosphere melts may display apparent SCLM signatures by ${\sim}$10% mixing and/or ${\sim}$20% AFC of lamprophyre source melts and entire Deccan data considered in the present study can be explained by 20% mixing and/or 50% AFC of plumederived melts with calc-alkaline lamprophyre as an assimilate.


      $\bullet$ The melts generated from the Archaean sediments preserved in the SCLM, represented by calc-alkaline lamprophyres, are most likely the components that interacted with the plume-derived as well as SCLM-derived partial melts during the formation of DVP.

      $\bullet$ Mixing and/or AFC of calc-alkaline lamprophyres, TTGs and granites by plume-derived melts and SCLM peridotite-derived melts explain total geochemical spread of the Deccan basalts.

      $\bullet$ Approximately, 10% mixing and/or ~20% AFC of Archean calc-alkaline lamprophyre melts can make original sub-lithosphere melts display apparent SCLM signatures.

      $\bullet$ The basalts from the western side of DVP have undergone higher levels of assimilation compared to those from the eastern side.

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