• D SESHU

      Articles written in Journal of Earth System Science

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

      D SESHU M PRASANTHI LAKSHMI S PARVEEN BEGUM A MANGLIK

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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.

    • Magnetic characteristics of a part of Closepet Granite, Eastern Dharwar Craton

      S PARVEEN BEGUM M PRASANTHI LAKSHMI D SESHU RAMA RAO CH

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      The exposed granite gneissic complex to the west of Cuddapah basin in Eastern Dharwar Craton (EDC) is studied to understand the magnetic character of various plutons in this region with more emphasis on a part of Closepet Granite (CG). The NW–SE trending plutons in this region show gradual decrease in magnetic intensities from southwest to northeast; CG in the southwest corner of the study area have high mafic content, and there onwards show a depletion in mantle enrichment towards NE. Parts of the CG namely, the main mass and northern intrusions separated by a gap zone are differentiated based on magnetic character deduced by processing the aeromagnetic data. Reduced to the pole (RTP) and its upward continued maps revealed NNW trending eastward convex anomaly highs inferring the magnetic nature of CG due to Porphyritic Monzogranite (PMG). Gap zone is identified to be structurally significant, bounded by deep ENE faults and inferred to be associated with PMG at relatively deeper levels. 2.5D modelling of magnetic anomaly profile substantiated our qualitative analysis of magnetic anomalies over CG, inferring magnetic and non-magnetic units of CG. Known shear zones running north–south are identified with a few inferred shears revealed from magnetic data interpretation within CG.

      $\bf{Highlights}$

      $\bullet$ Understanding the magnetic character of various plutons in the regions using aeromagnetic data with a detailed study over a part of Closepet Granite.

      $\bullet$ The NW–SE trending plutons in this region show gradual decrease in magnetic intensities from southwest to northeast.

      $\bullet$ Parts of the CG namely, the main mass and northern intrusions separated by a gap zone are differentiated based on magnetic character deduced by processing the aeromagnetic data, reduced to the pole (RTP) and its upward continued maps.

      $\bullet$ Gap zone is identified to be structurally significant, bounded by deep ENE faults and inferred to be associated with PMG at relatively deeper levels.

      $\bullet$ 2.5D modelling of magnetic anomaly profile substantiated our qualitative analysis of magnetic anomalies over CG, inferring magnetic and non-magnetic units of CG.

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