Magnetotelluric (MT) and Resistivity Survey along Belsara-Rasunpur Traverse Delineating Conductivity Structure over Bakreswar Geothermal Region in Birbhum District, West Bengal

Abstract

Magnetotelluric (MT) and resistivity methods have been carried out over the geothermal region of Bakreswar, West Bengal to obtain a preliminary idea about the nature of conductivity structure and to prepare a meaningful conceptual model of the geothermal region. One conductive anomaly zone is mapped along resistivity traverse Bakreswar-Asanshuli at "n" (separation parameter) =10 in between 1200-1500 m station. Bakreswar hot spring lies adjacent to it and geologically it may be the source of it controlled by hidden fault. In resistivity traverse from Chandrapur to Tantipara, the presence of subsurface conductive bodies (50-400 Ohm-m) mapped between stations 1000-1200 m at a pseudo depth of 400-700 m. This may be the structural breaks like shear zones/geothermal region. The high resistive layer below conductive layer is interpreted by MT survey at a depth of 3001-38103 m showing its occurrence at a shallow depth of 3001 m at Rajnagar but a greater depth of 38103 m at Nakrakonda. This steep gradient in between these two stations could possibly be attributed to a fault zone. Similar type of fault is inferred in between Belsara (7484 m) and Nakrakonda (38103 m). The steep gradient observed between stations also may be coincident with the postulated fault plane. One highly conductive zone is observed in MT pseudo-sections, which may be due to the geothermal zone in the area. Some static shift is evident from the vertical elongations of the apparent resistivity contours (zone of weakness) between Idgachha to Rasunpur region which are not reflected in the phase pseudo-sections. This may be due to the presence of faults/lineament/fracture/shear zone. A high conductive feature is inferred beneath Lokpur and Idgachha region extending from shallow surface into the deep crust. The lower crust in the entire study area is rather conductive whereas the upper crust is resistive.