Basin structure from gravity and magnetic anomalies in the central part of Cauvery basin, India.

The gravity and magnetic data along three profiles across the central part of Cauvery basin of India have been collected and interpreted with variable density contrast in order to deduce the structure of the sedimentary basin. The first profile is taken from Vridhachalam to Kilyanjiyur covering a distance of 100 km and the second starts from Niddamangalam and ends at Niybankurichchi covering a distance of 120 km and the third is from Pudukottai to Mallipatnam covering a distance of 50 km. The gravity lows and highs have clearly indicated various sub-basins and ridges. The density logs from ONGC, Chennai, show that the density contrast decreases with depth in the sedimentary basin, and hence, the gravity profiles are interpreted using variable density contrast with depth. From the Bouguer gravity anomaly, the residual anomaly is constructed by graphical method correlating with well data and subsurface geology. The residual anomaly profiles are interpreted using polygon and prismatic models. The maximum depths to the granitic gneiss basement are obtained as 6.41km, 8.70 km and 5.20 km for the first, second and third profiles respectively. These studies are useful to refine the subsurface geological studies. The regional anomaly is interpreted as Moho rise towards coast. The aeromagnetic anomaly profiles are also interpreted for charnockite basement below the granitic gneiss group of rocks using prismatic model.