A Conceptual Hydrological Model of the Thermal Areas within the Northern Neovolcanic Zone, Iceland using Stable Water Isotopes

Abstract

Iceland is situated on the boundary between the European and American plates. The divergent plate boundary crossing Iceland is generally called the Neovolcanic Zone and is characterized by active volcanism, hydrothermal activity, seismicity and a graben structure. The Northern part of the Neovolcanic zone consists of five NNE-striking left stepping en echelon volcanic systems where a fissure swarm, a central volcano and high temperature hydrothermal areas characterize each system. The isotopic composition of the thermal waters varies considerably both within and between systems and thus reflects the complexity of both inflow and structure of the thermal areas. The origin of the deep thermal fluid in the areas that have been drilled into is precipitation, either local or from far away, and older groundwater with a pre-Holocene component. Observed oxygen shift is also highly variable from less than 1‰ to about 7‰. In the paper the water isotopic characteristics of the thermal areas in the northern part of the Neovolcanic Zone in Iceland will be reviewed and a conceptual hydrological model for the area constructed.