Appraisal of geothermal setup using magnetic spectral analysis and 3D gravity inversion for the southern part of Mahanadi geothermal province within Eastern Ghats Mobile Belt, Odisha, India

Abstract

The study aims to establish possible linkages between the occurrence of four hot springs of the Mahanadi geothermal province, lying in the central part of the Eastern Ghats Mobile Belt, and the prevalent structural setup, by deciphering the crustal configuration as well as the thermal regime of the area. The centroid method is used for estimating Curie point depths (CPD) utilizing the EMAG2v3 magnetic anomaly data, thereby to obtain the corresponding geothermal gradient, and heat flow values for the study area. The CPD, geothermal gradient, and heat flow values range from 19.5 km to 32 km, 26.6 K/km to 43.6 K/km, and 66.5 mW/m² to 109.1 mW/m², respectively. The CPD results are shallower than the Moho depth variations obtained from the 3D inversion of global gridded gravity data and the CRUST1.0 model. The surface heat flow due to radiogenic heat production (RHP) of the major rock types within the study area is calculated and compared with that obtained from the CPD estimates. The average heat flow estimates from the CPD calculations (i.e., 77.5 mW/m²) and from the RHP estimates (i.e., 70.2 mW/m²) are both higher than the global mean value, implying a combined influence of radiogenic heat sources of the thin magnetic crust as well as heat from the deeper part. The shallower CPD and higher heat flow around the Mahanadi Shear zone region, indicate its role as the pathway for the thermally heated fluids from both deeper sources and near-surface radioelement-rich areas to the geothermal systems of Deulajhari, Atri, and Tarabalo. The Taptapani hot spring corresponds with a relatively deeper CPD, and lower heat flow values, where thermal water is possibly transported to it from a far-away source by the nearby shear zones and associated fracture/fault systems. Thus, the study suggests that the shear zones and the fault/fracture system around the hot springs play a vital role in developing these geothermal systems, along with the contribution of the radiogenic heat.