The Composition of Thermal Fluids in Iceland and Geological Features Related to the Thermal Activity

Abstract

Hydrothermal areas in Iceland have been divided into high and low temperature areas. In the drilled high temperature areas underground temperatures are above 200°C in the uppermost 1000 meters but in the low temperature areas underground temperatures are below 150°C at similar depths. Underground temperatures in the hydrothermal areas are rather strongly expressed by their surface thermal manifestations, and undrilled areas are classified as high or low temperature on the basis of the type of these manifestations. It is believed that there is a genetic difference bewteen high and low temperature areas, the former deriving their thermal energy from shallow level intrusions, but the latter by contact with hot rock during a deep convection cycle of the water. The high temperature areas tend to occur within volcanic complexes of basaltic as well as differentiated rocks where intrusive activity is intense. It is postulated that the bulk composition of thermal fluids in Iceland is dominantly governed by three variables. They are temperature, rock type, and influx of sea water into the heat source areas of hydrothermal systems. Juvenile source of sulphur and carbon may also contribute to the bulk composition of the fluids in some of the high temperature areas.