Imprints of Gadwal-Raichur Schist Belt Beneath Cuddapah Sediments, Evidences from Gravity and Magnetic Anomalies, Kurnool Area, Andhra Pradesh

摘要

Gravity and magnetic anomalies obtained from systematic geophysical mapping have yielded interesting inferences other than depicting the schist belts in the granite-gneissic terrain of Eastern Dharwar Craton. Extension of Dharwarian trends, as mapped, into the Cuddapah basin reveals the sub-surface geology effectively and makes a case in the utility of geophysical mapping under covered areas. Correlation of gravity anomalies with the signal enhanced magnetic anomalies is striking and together these fields unfold the near surface geology and structures. We present here the results obtained over the western part of Cuddapah basin, covering part of Kurnool Sub-Basin. Lack of physical property contrast amongst various sediments of Kurnool group and the strong regional influence of basement explains the negative relation of the trend of anomalies with the general strike of geological units. The influence of subsurface geological features is so strong that the well-known Gani-Kalva fault is discernible only in the form of termination of anomalies and a shift in the continuation of gravity high zone. Frequency analysis of gravity and magnetic anomalies indicate common depth interfaces coinciding with thickness of the Cuddapah sediments in this part of the area to be of the order of 500 m and the extent of granite-greenstone formations to be about 2 Km. A third interface observed around 6 km could be due to changes in the nature of basement. Modelling of gravity anomalies based on the frequency analysis and the physical properties have depicted the sub surface geological features. Profiles drawn across the general strike of anomalies depict the typical nature of schist belts as bifurcations and merger.