Current Science

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The total magnetic intensity (TMI) image of the southernmost part of the Indian peninsular shield exhibits a conspicuous NW–SE trending mega lineament of 200 km, associated with Achankovil Suture Zone (AKSZ) across the Southern Granulite Terrain (SGT) that evolved during East African Orogeny. This crustal scale anomaly of 200 nT amplitude, is significant to understand the regional tectonics and the possible linkage between AKSZ and Ranotsara Shear Zone (RSZ) of Madagascar. The structural trends are inferred from magnetic data surrounding AKSZ and RSZ to reconstruct the Gondwana fragments of the SGT and south Madagascar. The aeromagnetic images of conjugate rifted fragments of this part of India and Madagascar are connected well on both sides: the Madurai block with Antananarivo domain and Trivandrum block with Anosyan domain, north and south of AKSZ–RSZ respectively. Magnetic modelling across AKSZ reveals a hidden subsurface basic body suggesting a deep geofracture. We infer the sequence of tectonic development of the AKSZ as: (i) the subduction–accretion process in amalgamation of continental fragments to form Gondwana supercontinent during the Late Neoproterozoic and (ii) Pan-African exhumation of anomalous sub-crustal material.

Keywords

Aeromagnetic Data, Lithological Units, Magnetic Anomaly, Suture Zones, Tectonic Restoration.
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