Basement structure of the Cuddapah Basin from gravity anomalies

Abstract

An attempt has been made to understand the complex nature of gravity anomalies over the Cuddapah Basin and their relationship with geology, structure and tectonics. The gravity anomalies could delineate the approximate boundaries of the basin, which is characterized by a steep gravity gradient on its eastern margin and gentle gradients on all its other sides. Prominent gravity lineaments, which probably represent faults, separate sub-basins within the main basin. Previous studies have indicated that the southwestern gravity high is related to a basic body and that the Macherla high is thought to be due to a greenstone belt. The gravity high near Kurnool also appears to be due to a greenstone belt, which might extend into the basin beneath the sedimentary rocks. With the exception of these highs, the gravity picture of the Cuddapah basin is a broad low of about 35 mGal in amplitude. Regression analysis between residual gravity and basement depths inferred from aeromagnetic interpretation and deep seismic sounding (DSS) data suggest a probable density contrast of about − 0.07 g/cm 3 between the basement and the Cuddapah rocks. P wave velocities from DSS data support this view, with a negative density contrast of about 0.05–0.10 g/cm 3 between the basement and the sedimentary rocks. From the residual gravity, the basement structure map of the Cuddapah Basin has been prepared by using an effective density contrast of − 0.07 g/cm 3. The results indicate that the thickest pile of sedimentary rocks (about 10 km) occurs in the Nallamalai sub-basin. At many locations, the basement depths obtained in the present analysis corraborate those obtained from the analysis of other data.