Geological and geothermal mapping at Nupafjall and Svartsengi, Reykjanes Peninsula, SW-Iceland

Abstract

Geological mapping was done in the Nupafjall area south of Hveragerdi, SW-Iceland. The area is found at the eastern margin of the Reykjanes oblique spreading zone where it runs into the South Iceland seismic zone, of transform character, to the east, and into the Hengill spreading zone, of spreading character, to the northeast. Therefore tectonic activity is high. In the field work a special emphasis was put on the relationships between volcanism and tectonics. The volcanic stratigraphy reveals a lowest succession of lavas and foreset breccias which originated outside the map area. This is followed upwards by a relatively thin succession of simple lava flows also of distant origin, that are found to be more abundant north of the map area. Above these, thick piles of subglacially erupted hyaloclastites that have a local origin are found. The topmost units are late glacial and post-glacial lavas, again erupted outside the map area, within the spreading zone to the northwest. Faults and fractures belonging to N-S, NE-SW and NW-SE directions were found in the older rock units. Large throws were identified generally in N-S trending faults, and two N-S trending graben structures were found in the map area. An analysis on some of the borehole sites in the Olfus region is made, with respect to geologic structures of the region ...