Abstract
Abstract The writer has mapped for the Swedish State Power Board a flatlying intrusion of Jotnian dolerite in the outlet tunnel and canal at the Umluspen power station, Storuman, Swedish Lappland. The dolerite occurs in a veined gneiss probably belonging to the Middle Archean Elvaberg series (G. Kautsky, 1957) and a grey palingenic granite (Revsund granite) which is in part distinctly intrusive. The general strike of the veined gneiss is east-west, with high dips. The direction of the tunnel is north-south. Part of the dolerite intrusion is seen in Fig. 1. Its width varies between 8 and 15 m. Its dip is low, 10–20°W. Apophyses are known. The texture is ophitic to sub-ophitic. The kernel of the intrusion is medium-grained, whereas the marginal parts are dense though plagioclase phenocrysts appear there. The following mafic minerals have been observed (in order of decreasing quantities): titaniferous augite, olivine, titano-magnetite, biotite, and apatite. Similar flat-lying intrusions of Jotnian dolerite have been described from other parts of Sweden (J. Sobral, 1913, S. Hjelmqvist, 1944, and S. Gavelin, 1955).
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