Comprehensive view from geophysical signatures over Chitradurga Schist Belt, Karnataka

Abstract

Geology of Chitradurga Schist Belt (CSB) from Gadag to Srirangapatna, as inferred from the gravity and magnetic data analysis and supportive evidences from digitized Airborne Total count map is presented in this paper. Significant inferences have emerged from the integrated geophysical analysis coupled with geological information. Pattern, continuity and intensity of anomalies indicate that CSB can be viewed as three sectors; northern (Gadag), central (Chitdradurga) and southern (Nagamangala). Qualitatively geophysical signatures are diagnostic for the purpose of broad classification of the area into different geological domains such as granite-gneissic (gravity lows, fluctuating magnetic values and moderate radiometric counts), metavolcanic (gravity highs, magnetic highs and radiometric lows), metasedimentary (moderate gravity low, low magnetic values and moderate radiometric values) and granitic (gravity low, magnetic high and radiometric high) regions. Images prepared from gravity, magnetic and radiometric values indicated possibility of an additional arm of the schist belt from Huliyar to Hosdurga between the known Kibbanahalli and Chitradurga arms of CSB. From the gravity image it appears that the eastern margin of CSB may be encompassing Bukkapatna granite in the central sector of CSB. Gravity low closures and gravity high gradient between the granites of Chitradurga and those near Jagalur suggest different nature of geological continuity. Structural features, particularly the sheared contacts of metavolanics with metasedimentaries are demarcated based on gravity gradients. Based on these inferred features coupled with known geological controls of mineralization, a few target areas for gold / base metal exploration are identified. A major structural feature affecting the strike of arms of CSB may be the possible regions for emplacement of ultramafic bodies as observed near Sasival and Ghattishosalli. This in turn is significant for mineral exploration in Chitradurga Schist belt. Gravity and magnetic profiles drawn across CSB for every 15' latitude indicated crustal architecture beneath CSB. Significant rise is noticed in the background gravity field from the arms of CSB to the main schist belt suggesting that the Bababudan volcanics have generated from different depths compared to the Chitradurga volcanics. Further, long wavelength magnetic anomaly coinciding with the eastern margin of schist belt suggests the differences in nature of crust on either side. Frequency analysis of gravity and magnetic anomalies and the modeling indicated the depth persistence of geological units.