Characterization of the geothermal zone by remote sensing, hydrochemical, and magnetotellurics data: a case study from Lasundra, Gujarat, India

The westernmost part of India is the junction of three rift basins, namely Kachchh, Cambay, and Narmada. The Cambay rift basin, located in the Gujarat state (west of India), is well known for the presence of several geothermal zones. The Lasundra geothermal zone is located on the eastern flank of the Cambay basin, in proximity to the East Cambay Marginal fault. To characterize this geothermal zone, a combined study of remote sensing, hydrochemical, and magnetotellurics is conducted in the study area (Lasundra geothermal zone). To decipher and map the temperature anomalies associated with the geothermal zone, Advanced Spaceborne Thermal Emission and Reflection Radiometer and Landsat-8 remote sensing data are used. The hydrochemical analysis of the water sample indicates the anomalous (excess) value of salinity, fluoride, TDS, conductivity, etc. To determine the depth and extension of the geothermal zone, an MT survey is carried out near and around the geothermal zone. A total of 18 MT sites with a close interstation spacing of ~ 1–2 km are acquired along two transects. From 2-D inversion of the MT data, a ~ 100-m-thick conductive layer (< 30 Ohm.m) of sediments has been seen at the surface followed by the relatively less conductive layer of Deccan trap (30–150 Ohm.m), where thickness increases towards the NW direction of the profile. The results show the presence of highly conductive zones at the depth of ~ 2.5 km and ~ 4 km, respectively, along two transects. This conductive zone may be inferred as the possible reservoir associated with the Lasundra geothermal zone. The highly resistive features (> 4000 Ohm.m) may represent Granite based on the resistivity values and surrounding geology. These resistive structures are encountered at shallow depths in the SE direction and extend deeper in the NW along the transects. Apart from the presence of fractures, the possibility of some blind fault zones acting as conduits for the upward migration of thermal fluid cannot be ruled out.