Articles written in Journal of Earth System Science

    • Rheological thickness and strength of the Indian continental lithosphere

      A Manglik R N Singh

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      The estimates of rheological thickness and total lithospheric strength for the Indian continental lithosphere have been obtained based on the representative rheological properties of upper crust, lower crust and upper mantle, and some of the available heat flow and heat generation data. The rheological thickness, computed at different locations in the Indian shield, shows lateral variation ranging from 79km in the southern part to 65 km in the northern part for a strain rate of 10-14 s-1. The total strength of the continental lithosphere is of the order of 1013 Nm-1 for the same value of strain rate and decreases northward. The computations carried out for a range of strain rates show an increase in the rheological thickness and strength of the lithosphere with increasing strain rate. These results would be important in understanding the flexural response of the Indian continental lithosphere to surface and subsurface loading, and response to tectonic forces acting on it.

    • Characterizing the source of a prominent magnetic anomaly in the southwestern part of the Cuddapah basin


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      The total magnetic intensity anomaly (TMI) map of the Proterozoic intracratonic Cuddapah basin shows the presence of a prominent high–low–high anomaly of about 600 nT amplitude at its southern end. The source of this anomaly is inferred to be a mafic intrusive body due to a thermal plume that might have initiated the basin evolution. Though some quantitative studies have been carried out over this anomaly, the magnetic body remains ambiguous as only a part of this anomaly was modelled along the E–W direction. In present study, we model this anomaly by a 2.5D algorithm and analytical signal of the vertical integral (ASVI) of the TMI approach. A near circular outline of the causative body has been delineated by the analysis of ASVI, which also revealed three characteristic zones of the near surface irregularities. The 2.5D modelling along a SW–NE profile across the anomaly yielded the main body of about 10 km wide top at 3.5 km depth and 40 km wide at 25 km depth. The Curie temperature depth in this region is 30–40 km and this allows the source to be magnetic at this depth. It is inferred from both ASVI and modelling that the main body is bifurcated into two in its south-western part between Parnapalle and Muddanuru while it attains a lopolithic shape over the remaining part. Existing regional aeromagnetic data elucidates shape of the mafic intrusive both laterally and vertically.

    • Magnetotelluric study of an intraplate seismic zone in the Palghar region of the Deccan Volcanic Province, India


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      The Deccan Volcanic Province in the western part of the peninsular India consists of a thick pile of flood basalts resting mainly on the Archaean and Proterozoic rocks forming the basement. This intraplate region experiences moderate seismic activity, the most recent one being a swarm-type activity in the Palghar region, about 120 km north of Mumbai, that started in November 2018 and has produced a few thousand micro-earthquakes and a 4.3 magnitude earthquake since then. We have carried out a magnetotelluric (MT) study along a 35-km long profile across the seismic zone to delineate the subsurface structure to understand the possible cause for the seismic activity. Broadband MT data were acquired at 18 sites with average station spacing of 2 km. Impedance tensors were analyzed for distortion and dimensionality, decomposed into TE- and TM-mode, and inverted by a 2D inversion algorithm. The geoelectric structure yields an assemblage of highly resistive and moderately conductive blocks in the uppermost crust resting on a major listric-type fault, that possibly reaches the surface at the West Coast Fault from a depth of about 15 km beneath the Panvel flexure zone. In conjunction with the regional Bouguer gravity anomaly and the seismicity distribution, we infer that the upper crustal heterogeneities coupled with the basement fault and low rheological strength of the fractured upper-to-middle crust might be leading to triggering of the seismicity in the region.

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