Aerogeophysical and Ground Followup Studies for Structural Elucidation of the Aladahalli-Nuggihalli Schist Belts and Adjoining Areas, Hassan District, Karnataka and Implications for Future Prospects

摘要

Airborne geophysical data comprising magnetic and electromagnetic data was procured by the GSI Twin Otter Airborne Survey System in the Aladahalli-Nuggihalli area, Hassan district, Karnataka. The magnetic (total field) contour map brought to a plane of 1015 m above mean sea level clearly demarcated the NW-SE trending Aladahalli and Nuggihalli Schist Belts in the centre of the area in the form of a gradient. The northern part of the Archaean Holenarsipur Schist Belt is seen as a prominent magnetic feature in the southwest corner of the area. Two-dimensional modeling of five selected profiles over the Aladahalli Schist Belt indicates a depth of 500 m to the top of body and a width of 1500 m. The magnetic picture also reveals a few isolated plugtype of bodies viz., D1, D2, D3, D4, D5, D6 and D7 (Figure.2). Three dimensional modeling of these bodies indicates an average depth of 700 m and 2600 m to the top and bottom of the bodies of Nuggihalli Schist Belt (D1, D2, D3 and D4) respectively. Anomaly D7 reflects the body magnetised in a different direction, which is confirmed by NRM studies of oriented samples. The airborneectromagnetic (AEM) conductivity map reflects a cluster of anomalies to the north of Shantigrama may be represent a fracture zone associated with the basement. Ground geophysical surveys employing magnetic (TF) and electromagnetic methods conducted over these airborne geophysical anomalies have confirmed these features and warrants detailed geophysical and geological investigation over anomalies D1 to D7 and the AEM anomaly north of Shanthigrama.