Temperature and salinity changes in three high-temperature systems at Reykjanes peninsula, SW-Iceland: Evidence from fluid inclusions

摘要

The Reykjanes peninsula forms the southwest end of the volcanic rift zone in Iceland, where it connects to the Reykjanes ridge. The groundwater systems on the peninsula include a thin freshwater layer overlying a saline one. The fluids in high-temperature systems found in these surroundings show increasing salinities towards the tip of the peninsula. A fluid inclusion study on alteration minerals in three of these systems; Svartsengi, Eldv(o)rp and Reykjanes, show a range of salinities from freshwater to salinities slightly above the respective fluids of the systems. The existence of a freshwater high-temperature system surrounded by saline groundwater ones is puzzling, and has to be explained by freshwater conditions present during glacial times, and a gradual seawater replacement in postglacial time. The homogenization temperatures (Th) of the fluid inclusions also show that the temperature has decreased in the geothermal systems with time.