Gravity and magnetic studies in parts of Odisha and Chhattisgarh (India): implications in regional geology

Geophysical mapping using gravity and magnetic (Total Field) surveys were carried out in 3600 km2 with the aim of identifying the regional geological units and shedding light on the associated structures that may have a bearing on possible mineralisation. The Bouguer gravity anomaly deciphered the anomalous bodies trending in a NE-SW direction, characterised by high gravity signature in the order of -45 to -6 mGal and interpreted in terms of Eastern Ghats Supergroup rocks including charnockite, khondalite, and pyroxene granulites. The conspicuous low gravity zone in the order of -84 to -69 mGal represents the cumulative effect of granites and sediments of the Indravathi Supergroup. The NW-SE trending Sileru shear zone reflects the moderate gravity in the order of -69 to -45 mGal, separating the Archaean Bastar Craton in the west and the Eastern Ghats Mobile Belt in the east, is attributed to a major shear/thrust fault and may be a significant feature in view of mineralisation. Northern and central parts are dominated by medium to small amplitude bipolar nature of anomalies ranging between -247 to 352 nT, where the concentration of magnetite is a natural phenomenon along the fault plane. The Sileru shear zone NW-SE trending alignment is mainly dominated by small amplitude anomalies of bipolar nature. The radially averaged power spectrum of gravity data has highlighted three interfaces at depths of around 6.6, 3.5, and 2.0 km, and for magnetic data two interfaces at the depths of 2.2 and 1.5 km respectively. The studies observed a linear clustering of Euler depth solutions, trending in a NE-SW direction towards the eastern part, whereas curvilinear and NW-SE trending linear cluster towards western and north-western part may be inferred as geologic/faulted contacts. The geophysical mapping in the area was thus useful in characterising not only the surface geology but also the nature of the crust, which primarily influenced the gravity and magnetic anomalies.