Geological and geothermal mapping in Sveifluháls area, SW-Iceland

Abstract

Geological and surface hydrothermal alteration mapping was carried out in the Sveifluháls area to the north of the active Krýsuvík geothermal field. The upper Pleistocene interglacial and glacial succession is composed of 9 units including hyaloclastite and basaltic lava flows in addition to the historical lava that covers the northwest part of the study area. The study area is crossed by several extensional faults and fractures with a NE-SW general trend. The study area exhibits different grades of hydrothermal alteration, including zeolite-calcite and clay alterations. XRD analysis and petrographic studies showed the presence of different types of zeolite, calcite and clay minerals with different grades of alteration. The field relationships between the hydrothermal alteration and the geological setting of the study area imply that the hydrothermal alterations are quite old and structurally controlled. The geothermal map illustrates the distribution of the alterations. They are concentrated on the western side of the main hyaloclastite ridge in the central and southern parts of the study area, indicating that the centre of geothermal activity lies to the southwest of the study area. That corresponds with resistivity maps of the area. This implies that the geothermal system is cooling down and the activity is moving towards its centre.