K.N.D.Prasad, A.P.Singh*, V.M.Tiwari
A constrained 3D density model of the upper crust along a part of the Deccan Syneclise is carried out based on the complete Bouguer anomaly data. Spectral analysis of the complete Bouguer gravity anomaly map of the study region suggests two major sources; short wavelength anomalies (<100 km) caused primarily due to the density inhomogeneities at shallow crustal level and long wavelength anomalies (>100 km) produced due to the sources deeper than the upper crust. A residual map of the short wavelength anomalies is prepared from the complete Bouguer anomaly using Butterworth high-pass filter (100 km cut-off wavelength). Utilizing the constraints from deep resistivity sounding (DRS), Magnetotellurics (MT), and Deep Seismic Sounding (DSS) studies, 2½D density models have been generated along thirty-nine profiles of this region. The mismatch between the calculated response of the a priori 2½D model with the residual (short wavelength) gravity anomalies is minimized by introducing high-density intrusive bodies (≥2.81 g/cm3) in the basement. With these 2½D density models, the initial geometry of our 3D density model, which includes alluvium, Deccan Trap, Mesozoic sediment and high-density intrusives in the basement up to a depth of 7 km (upper crust), is generated. In the final 3D model, Deccan Trap extends from 200 m to nearly 1700 m below the 90 to 150-meter thick Quaternary sediment. Further down, the sub-trappean Mesozoic sediment is present at a depth range of 600 to 3000 meters followed by the basement. The derived 3D density model also indicates six intrusive bodies of density 2.83 g/cm3 in the basement at an average depth of about 4-7 km that best fits the residual gravity anomaly of the study area.