Evidence of Paleo-Subduction along the Pranhita-Godavari Basin, India: Constraints from the joint interpretation of aeromagnetic and gravity data

Pranhita-Godavari (PG) Basin is an inter-cratonic failed rift basin between the Dharwar and Bastar cratons in the Southern Indian Shield. Previous studies reveal an unusually thick crust beneath it with high surface heat flow, a characteristic uncommon in inter-cratonic failed rift basins. To understand this uncommon phenomena, we carry out the aeromagnetic and Bouguer gravity data interpretation of the PG Basin constrained by seismic and seismological data. The Bouguer gravity anomaly highs on either side of the basin reflect crustal extension of the Karimnagar Granulite Belt (KGB) and Bhopalpatnam Granulite Belt (BGB). The Moho depth map, derived from constrained 3-D gravity inversion, shows depth variations between 35 and 47 km in the region. Additionally, the estimated Curie depths from aeromagnetic anomaly data vary between 22 and 30 km, with shallower depths (∼22–26 km) beneath the basin, and reconcile with the observed higher heat flow in the region. The crustal model reveals: i) a normal crustal thickness below the PG Basin; ii) a high-density lower crustal body (∼3.05 gm/cc) within the basin; iii) high-density, upper-mid crustal bodies interpreted as granulitic rocks (KGB and BGB) exhibit increased magnetisation at the margins of the PG basin. Both the KGB and BGB thicken with depth beneath the PG Basin before rapidly thinning-resembling boudinage beneath the basin depocenter. Both KGB and BGB represent once continuous package of granulite rocks. The thinning of granulite package is related to crustal thinning associated with rift formation and the development of PG Basin.