Abstract:
Ground magnetic surveys were conducted over the Mahanadi basin covering an area of 21.000 km'. Both total field and vertical field data were collected at 5 km interval, mainly to study the deeper regional features. Total field anomaly map prepared after correcting for the IGRF and external field variations, shows a combination of NE-SW, E-W, and NW-SE trends. To identify magnetic sources related to different depths, various transformations have been applied to the total field anomaly map. The second vertical derivative and downward continued map showed that the NE-SW and E-W trends are related to ridges and depressions of the coastal basin; implying that these are shallow features. The deeper features evidenced from upward continuation showed NW-SE trends. Thus, the Mahanadi delta is composed of two structural units associated with different tectonic events. These NW-SE trends may possibly be associated with the extension of Mahanadi graben underneath the coastal basin. The study reveals that the shallow NE-SW to E-W trends are superposed on the deeper NW-SE trends formed prior to the break-up of Gondwanaland, and the former trends resulted due to the dismemberment of Gondwanaland. A comparison with DSS studies conducted over Mahanadi delta and Lambert graben of East Antarctica showed that the. deeper features can be correlated with an intracrustal layer related to a velocity of 6.4 km/s-6.6 km/s at an average depth of 6.5 km. seen in both the areas. Analysis of aeromagnetic data over Lambert graben of East Antarctica will help reconfirm our observation.
