Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

D. Atchuta Rao ¹, Ch. Rama Rao ¹, D. S. Bhaskara Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad-500007, IN

Abstract

Interpretation of the total intensity aeromagnetic anomaly data and the residual gravity data of the pericratonic Mahanadi coastal basin, situated in the east coast of India has brought out NW-SE trending dislocations cutting across these basins and extending into the shelf area. This structure may be inferred as the possible extension of the NW-SE trending intracratonic Mahanadi rift. Depth estimates on the regional aeromagnetic anomalies have brought out a deep-seated sub-basement magnetic marker horizon at depths of 5-6 km in the inferred rift zone and it rises to around 2 km on either side in the onshore region. The trends in the residual gravity map around Cuttack suggests a tectonic environment possibly related to the location of triple junction at this point. This zone lies between shot points SF60 and SP70 of the Konark-Mukundpur DSS profile where it is reported that the energy has been heavily attenuated (at near distances) leading to large jumps in travel time. This zone of anomalous behaviour coincides with the inferred triple junction and calls for further detailed studies.

Keywords

Geophysics, Aeromagnetics and Gravity, Mahanadi Rift, Lambert Rift, East Antarctica.

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D. S. Bhaskara Rao ¹, Ch. Rama Rao ¹, D. Atchuta Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

The statistical structure of the aeromagnetic anomaly field over an area of approximately 30,000 sq. km of parts of eastern Dharwar craton and the western parts of Cuddapah basin has been studied. The distribution of statistical moments of aeromagnetic field showed two magnetically different zones, viz., one towards north of 14°45'N Lat., and the other to the south of it. Directional filtering operations over the exposed granite-greenstone terrain and the adjoining intracratonic Cuddapah basin has clearly brought out an ENE to E-W trending long linear possibly related to a deep seated tectonic feature. This mega lineament separates this part of the crust into two zones of different magnetic character. Filtering operation over the aeromagnetic data applying sequential trend suppression in E-W, NW-SE and ENE-WSW directions has clearly brought out magnetic trends striking nearly N-S. These nearly N-S trends may reflect the structures that controlled the development of greenstone belts or the structures resulted during the E-W compressional event.

Keywords

Aeromagnetics, Structure, Granite-Greenstone Terrain, Cuddapah Basin, Eastern Dharwar Craton.

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D. Atchuta Rao ¹, H. V. Ram Babu ¹, Ch. Rama Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

The discovery of a hemispherical shaped Maha Stupa, the largest known in South India belonging to the 2nd to 6th century A.D., Buddhist monastic order at Nelakondapally (Khammam district, Andhra Pradesh), has marked the area for further exploration for cultural sites and objects. The Department of Archaeology and Museums, Government of A.P., has been actively pursuing exploration in this area using conventional methods and brought to light some important archaeological findings indicating the importance of the area for elucidating the full structural details of the dwelling complexes and other cultural objects. With a view towards creating awareness among the archaeologists on the use of geophysics in archaeology, an experimental geophysical survey has been carried out using magnetic, electrical and electromagnetic methods, in an area near Nelakondapally. These surveys have brought out geophysical anomalies resulting in the discovery of sites and objects of archaeological interest. This paper describes the survey and the results which led to the discoveries.

Keywords

Geoarchaeology, Geophysical Surveys, Nelakondapally. Andhra Pradesh.

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D. Atchuta Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad, IN

Abstract

The basement configuration of the eastern part of the Proterozoic Vindhyan basin has been deduced by re-processing of the aeromagnetic data. The depths to the magnetic basement vary from 2 to 6 km. The basement in this part appears to consist of basement 'highs' (culminations) and 'lows' (depressions) elongated in a general ENE-WSW to EW direction. This configuration has divided the eastern Vindhyan basin into sub-basins. The large thickness of sediments in the sub-basins may be of interest in exploration for oil industry.

Keywords

Geophysics, Aeromagnetics, Oil Exploration, Vindhyan Basin.

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D. Atchuta Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad- 500 007, IN

Abstract

Kimberlites, in addition to being the principal source of industrial and precious diamonds, also serve as windows into the earth's mantle. Therefore, their discovery has academic and economic importance. Power spectral analysis of the aeromagnetic data of a part of the Eastern Dharwar Craton, comprising the western part of the Cuddapah basin and the adjoining crystallines, has brought out upwarping (anticlise) and downwarping (syneclise) of intra-crustal magnetic interface. The known kimberlite diatremes at Wajrakarur and Chigicherla are principally concentrated in zones overlying the domal upwarps of the magnetic interface and these zones perhaps delineate two distinct kimberlite fields. Exploration in such zones (zones overlying upwarp of magnetic interface) is recommended for verifying the validity of the relationship and location of additional kimberlites.

Keywords

Acromagnetics, Gravity, Kimberlite, Eastern Dharwar Craton.

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