• SANJIT KUMAR PAL

      Articles written in Journal of Earth System Science

    • New evidence for a thin crust and magmatic underplating beneath the Cambay rift basin, Western India through modelling of EIGEN-6C4 gravity data

      AVINASH KUMAR CHOUHAN PALLABEE CHOUDHURY SANJIT KUMAR PAL

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      The Cambay rift basin (CRB) is an intracratonic rift in the western part of India. The basin assumes great importance in petroleum exploration owing to the presence of thick hydrocarbon bearing sedimentary rocks. Previous investigations using deep seismic soundings (DSS), gravity and heat flow data reveal that the CRB is characterised by a thin crust, high heat Cow and high density lower crust. In this study, a detailed crustal structure of the basin is presented by performing a 2.5D density modelling of the EIGEN-6C4 gravity data. Present study attempt to find a plausible explanation for the variation in the Bouguer anomaly (BA) values from +20 to -50 mGal within the basin. It refined the crustal model that is constrained using results from radial average power spectrum (RAPS) analysis of gravity data along with previous seismological and geophysical studies, which reveals that the values of average sedimentary and Deccan Traps thickness are in the order of 4–5 and 1.5–3 km, respectively, along the rift. It also presents possible evidences for a high density underplated layer of thickness 7–15 km along the central part of the CRB. To study the deep-seated features, upward continuation of the BA is carried out at heights of 30, 40 and 50 km. The extension of underplating layer is noticed in the present crustal model and in the upward continued BA in the western part, while it merges with the Moho in eastern part of the CRB. The Moho depths, varying from 31 to 37 km, are found to be shallower inside the CRB than the surroundings. It is inferred that the high BA values in the basin are due to the combined effect of the high density underplated layer in the lower crust and a shallow Moho.

    • Gravity–magnetic appraisal at the interface of Cuddapah Basin and Nellore Schist Belt (NSB) for shallow crustal architecture and tectonic settings

      SHUVA SHANKHA GANGULI SANJIT KUMAR PAL J V RAMA RAO B SUNDER RAJ

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      Cuddapah Basin (CB) is an intracontinental, Proterozoic basin Canked by Eastern Dharwar Craton(EDC) in the west, Nellore Schist Belt (NSB) and Eastern Ghat Mobile Belt (EGMB) in the east,represents second largest Proterozoic basin of India. Gravity and magnetic surveys were carried out at the interface of Cuddapah Basin (CB) and Nellore Schist Belt (NSB) covering $\sim 2880 \rm{km}^{2}$ area. Gravity map has brought out some distinct zones. The thrusted contact of NSB and Cuddapah sediments has been well delineated from the gravity map by NE–SW trending steep gradient of contours. Relatively high gravity values are observed over NSB in the southeastern part, moderately high values are observed over Cumbum Formation, but distinct low is observed over Baironkonda Formation. These gravity highs and lows are mainly the manifestation of basement characteristics and intrusives. The magnetic map shows two distinct domains, viz., moderate to low zone in the southern part, and moderate to high zone in the northern part. Regional gravity map suggests a change in basement characteristics from felsic to mafic from NW to SE. Presence of mafic basement may be representing EGMB group of rocks underneath the Cuddapah sediments at the eastern part of the study area. The joint gravity and magnetic modelling reveal varied nature of sedimentary units in terms of density and susceptibility and change in basement characteristic.

    • Very low frequency electromagnetic (VLF-EM) study over Wajrakarur kimberlite Pipe 6 in Eastern Dharwar Craton, India

      SARVESH KUMAR SANJIT KUMAR PAL ARINDAM GUHA

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      The Wajrakarur kimberlite Pipe 6 in Eastern Dharwar Craton, is hardly explored using latest ground-based geophysical techniques. The present study uses the Very Low Frequency Electromagnetic (VLF-EM) method for understanding the aerial extension, depth and geometry of the kimberlite pipe. The VLF-EM data have been analyzed using Fraser filtering of in-phase component, 3D Euler deconvolution of Fraser filtered in-phase data, radially average power spectrum (RAPS) of VLF data (raw data) and 2D inversion of VLF data (raw data). The Fraser filtered in-phase grid anomaly map has witnessed as an effective tool for mapping extension of the kimberlite pipe. The maxima of Fraser filtered in-phase component has been observed as a key parameter to delineate the conducting bodies.The high apparent current density in Karous–Hjelt (K–H) pseudo section locate relatively conducting body possibly associated with kimberlite pipe. Two depth interfaces at about 15 and 32 m have been delineated using RAPS. 3D Euler solution indicate dyke-like structure associated with kimberlite pipe having depth solutions ranging from 6 to 40 m with mode of depth 17 m in the study area. 2D resistivity sections indicate that causative bodies are in the depth range of 15–50 m. The results of VLF-EM study are well validated using geological borehole data over the study area reported by Geological Survey of India.

    • Rejuvenation of ‘pop-up’ tectonics for Shillong Plateau in NE Himalayan region

      PARTHA SARKAR P N S ROY SANJIT KUMAR PAL

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      Seismicity variation along with crustal heterogeneity using natural source is of prime interest in advance research nowadays. In the global scenario, North-East India is one of the prominent seismicity active zone characterized by its tectonically complex set-up. The seismicity study area encompasses between $\rm{18^{\circ}–32^{\circ}N}$ latitude and $\rm{88^{\circ}–102^{\circ}E}$ longitude, which basically locates the Shillong plateau and its surrounding in north-east part of India. Here, we have attempted to forecast the seismicity pattern as well as the crustal heterogeneity for Shillong plateau in north-east part of India. In this regard, we have used the most basic seismicity parameter like $b$ value and fractal correlation dimension ($D_{c}$) along with focal mechanism characteristic over the entire region of study. The correlation experiment between the lower $D_{c}$ value and $b$ value indicates the possibility of an earthquake of large magnitude in the south central Burma basin and Shillong plateau region. Various dynamic faults and associated seismicity spread over all around the North-East India supports the possible rejuvenation of pop-up structure for Shillong plateau. We have tested our proposed method on real dataset, presented and analysed our experimental results and compared it with other methods and the overall results are found to be satisfactory.

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