Isotope Studies and Chemical Investigations of Tattapani hot Springs in Kotli (Kashmir, NE Pakistan): Implications on Reservoir Origin and Temperature

The present study is focused on the isotopic signatures and geochemical analyses of the geothermal field of Tattapani area in Kotli District of Kashmir (Pakistan) to understand the origin, subsurface history and reservoir temperature. The study area encompasses of complex overlapping thrust tectonics due to its close affinity to the suture zones of relatively younger ongoing collision between Indian and Eurasian plates (<55Ma). The area is located on the apex of active Balakot-Bagh Fault (Kashmir earthquake, 2005), besides other regional thrust faults in the surroundings including Riasi Thrust, Punjal Thrust, Main Boundary Thrust and the Himalaya Frontal Thrust respectively. Field observations revealed that the water discharge of the springs varies from 4.3 to 11.8 liters per second with the surface temperature from 59.2 to 60.7 °C. Samples collected are analyzed for various isotopes (18O, 2H & 3H of water) and water chemistry, which synthesized that the thermal waters are slightly acidic and have low dissolved contents. Sodium and bicarbonate are dominating ions. δ18O and δ2H of all the sampled geothermal manifestations were found to be –6.54 to –6.19‰ and –41 to –37‰ respectively. Source of recharge is meteoric water (rains at higher altitude), whereas thermal waters are of immature nature with a significant component of fresh water mixing and circulation time of about 40 years. On the basis of K–Mg and Na–K–Mg thermometers, the average reservoir temperature is 140 °C. In addition, geothermometer based on dissolved silica showed average reservoir temperature about 105 °C.