Origin and subsurface history of geothermal water of Murtazabad area, Pakistan - an isotopic evidence

The Murtazabad area represents one of the major geothermal fields in Pakist an, with seven hot springs lying along the Main Karakoram Thrust. Discharge of the springs is 50-12001 per minute with the surface temperature from 40 to 94 degreesC. Environmental isotopes and chemical concentrations have be en used to investigate the origin and subsurface history of thermal water. Four sets of water samples were collected and analyzed for various isotopes including O-18, H-2 and H-3 of water; S-34 and O-18 of dissolved sulphates and chemical contents. Isotopic and chemical data show that the origin of thermal water is meteoric water. On the delta -diagram, delta O-18 and delt a H-2 data plotting below the local meteoric water line with a slope around 12.3 show that the original thermal water receives recharge from precipita tion at higher altitude (3000m) and undergoes delta O-18 shift of about 1% due to exchange with rocks. Different correlations between isotopes, temper ature and Cl indicate that the observed isotopic compositions have evolved due to mixing of different proportions of shallow water at different spring paths during movement of thermal water towards the surface. It is also inf erred from the tritium data along with delta O-18 and delta H-2 that the ci rculation time is long and is estimated to be more than 50 years. (C) 2001 Elsevier Science Ltd. All rights reserved.