Gas geothermometry and equilibria in Icelandic geothermal systems

Abstract

The gas geothermometer temperatures and gas equilibria in Icelandic geothermal systems were studied. Around 290 samples of fumarole vapour samples from six geothermal areas in Iceland, Geysir, Hveravellir, Hengill, Reykjanes, Krafla and Torfajökull, were considered. A large range of temperatures was often observed within a given geothermal system with temperatures ranging from <100 to >800°C. Based on the calculated temperatures it can be concluded that factors other than temperature dependent fluid-mineral equilibria must influence fumarole gas composition at surface, for instance magma gas flux, open system boiling and phase separation, vapour condensation, mixing and oxidation at shallow depth. Based on the observations made in this study it is concluded that gas geothermometery temperatures may in many cases not reflect subsurface reservoir fluid temperatures of geothermal system but rather the source(s) of the gases and secondary processes occurring upon fluid ascent to surface