Bouguer anomaly of the Godavari basin, India and magnetic characteristics of rocks along its coastal margin and continental shelf

Abstract

The Bouguer anomaly map of the Godavari basin has delineated several transverse and median ridges that have divided this basin into several sub-basins. Modelling of a gravity profile in the central part of the basin suggests 5.0 km of Gondwana sediments and high density rocks along the shoulders which may represent upthrusted lower crustal rocks related to the Eastern Ghats orogeny. The total intensity magnetic map of the coastal part of the Godavari basin shows a well-defined magnetic anomaly of approximately 200 nT along the coast which coincides with the Kaza basement ridge. The modelling of this magnetic anomaly indicates 2–2.5 km of sediments over the Kaza ridge and 5.5–6 km thick sediments in the depressions towards the west of this ridge which are constrained from the basement configuration based on seismic sections in the surrounding region. The Kaza ridge, with a susceptibility of 10 −4 SI units, appears to be composed of basic rocks which may be part of the exposed Eastern Ghats towards the west. This magnetic map also shows several high amplitude short wavelength anomalies which are caused by sub-surface basic rocks. These basic rocks are related to the Rajahmundry trap, equivalent to the Deccan traps of late Cretaceous age, and are exposed nearby by. Modelling of the magnetic anomaly across the continental shelf, off the coast of the Godavari basin, suggests an almost 45° inclined contact away from shore at a depth of 2.5 km and having a thickness of 3.5 km. However, this magnetic anomaly could be matched only with a remanent magnetization with declination 310° and inclination −67° which corresponds to the direction of magnetization reported for the Rajmahal traps.