Aeromagnetic image of a part of peninsular India and its relation to geology and structure

Abstract

The total intensity aeromagnetic image of a part of peninsular India, published recently (GSI, 2000) by the Geological Survey of India, covers the area between the latitudes 8°N to 25° N and the longitudes 74°E and 89°E, exclusive of a major portion of the Deccan Volcanic Province, which is yet to be covered by aeromagnetic surveys. The aeromagnetic coverage over most of the area was at a nominal line spacing of 400 m and at a flight height varying between 1500 m and 2700 m above mean sea level. Over areas such as the Cuddapah Basin and parts of the Singhbhum Craton, drape-flown data with 1000 m and 250 m line spacing were included in the image. Because of the varying flight heights, we continued all the data either upward or downward to a common altitude of 2100 m to produce a consistent contiguous image. As the inclination of the Earth's field varies between 0° and 35°, we produced a Reduced to Pole (RTP) image, which gives a better understanding of the magnetic anomalies, by transforming the total magnetic intensity data by parts and then stitching them together. We also provide the first vertical derivative image of the RTP data, which provides a better insight to near-surface structures. Our interpretation, based on the images of total magnetic intensity, RTP, and first vertical derivative data is presented in this paper. In general, the total magnetic intensity image brought out the regional geology and structure very well. The southern granulite terrain differentiates itself from the rest of the area by means of high amplitude and high frequency anomalies. The boundary between the western and eastern Dharwar Cratons appears to be the eastern boundary of the Chitradurga Schist Belt. The boundary of the Karimnagar Granulite Terrain could be established from the image. Several major lineaments that were previously unknown could be identified from this image. A major lineament, starting from the west coast and extending about 1500 km to Bhuvaneswar in the east, cuts across other major trends and might be of tectonic significance. The image supports the proposition that the Peninsular Shield is an agglomeration of land masses that came together and were sutured in the course of geological time. The image also provides clues to the intracratonic tectonic elements or subdivisions with characteristic cross trends. The Godavari, Mahanadi, and Damodar Rift Systems appear to have been connected together and joined to the Narmada Rift, and this is another new inference from the image.