Crustal structure associated with Gondwana graben across the Narmada-Son lineament in India: An inference from aeromagnetics

Abstract

Aeromagnetic data over an 80-km-wide belt along the ENE-trending Narmada-Son lineament (NSL), starting from Baroda in the west and continuing to the south of Jabalpur in the east, has been studied to understand the structural and tectonic framework of the region. The area is covered by generally E-W-trending steeply dipping and folded Archean phyllites and quartzites as basement, with Bijawars (Upper Precambrian), upper Vindhyans (Upper Proterozoic), and Gondwanas (Upper Carboniferous) overlying them. Overlapping them all are the Deccan trap (Cretaceous-Eocene) flows. Aeromagnetic linements and their disposition and pattern in this region suggest major dislocations in the crust. The region around Hoshangabad, which is the intersection point of the NSL and the northwestern extension of the Godavari lineament, appears to have been intensely disturbed. Spectral analysis of aeromagnetic profiles across the NSL belt brought out a deep magnetic interface within crust at depths varying from 4 km to about 20 km below the surface, perhaps corresponding to the discontinuity characterized by the interface of granitic and basaltic rocks. There is a significant downwarping of this interface under the Hoshangabad region, suggesting that this is perhaps related to the evolution of the Gondwana basin structure in this area. This warping of the magnetic interface may be a reflection of the crustal flexuring and rift faulting. Elsewhere in the world, concentrations of carbonatite complexes and dike swarms are known to occur in areas of crustal flexuring and rift faulting. The occurrence of carbonatite complexes in this region (e.g. at Amba Dongar and Barwaha, and dike swarms in the Dadiapada region) gives credence to the present inferences from the aeromagnetic study.