The Isotopic and chemical characteristics of geothermal fluids from the Western Fjords, Iceland and two selected hot spring areas in the Jinanxi province, SE-China

Abstract

Low-temperature geothermal activity is widespread in the Western Fjords, Iceland. The thermal waters are classified either as HCO3 or Cl types. A few of the waters are mature according to a classification based on relative concentrations of HCO3, SO4 and Cl, and three of the waters samples fall within the zone of volcanic water. The Na-K-Mg triangular diagram suggests that some of the thermal waters have reached equilibrium and indicate reservoir temperature below 100°C. Boron and chloride concentrations and the B/Cl ratio suggest that the origin of these elements in the hot springs is, apart from the initial concentration of the precipitation, either leaching from rocks with which the water has reacted or due to seawater mixing. The δ18O and δD (δ2H) are used to trace and determine the origin and movement of groundwater. All the waters follow a local meteoric water line (δD = 6.55 δ18O - 3.5), indicating that the thermal waters are of meteoric origin. Some of the thermal waters are more depleted in δD than any current precipitation on the Peninsula. This may indicate that these waters have an older, 2H depleted component from a colder climate regime. Radiogenic carbon (14CpMC) shows good correlation with water temperature, δ13C and boron concentration. Earlier helium and carbon isotope study suggested that dilution of the mantle helium input occurs by addition of radiogenic helium and isotopically-light carbon from the uppermost crust ...