Supracrustal and infracrustal rocks in the Gneiss region of the Caledonides west of Breimsvatn.

Abstract

Two rock complexes can be distinguished in the Gneiss region west of Breimsvatn in Sogn & Fjordane, West Norway. The upper complex is composed essentially of original supracrustal rocks: calcareous, psammitic and pelitic schists and biotite-plagioclase gneiss with significant intercalations of gneiss, meta-anorthosite, amphibolite and ultrabasite. An \"eclogite-like rock\" is also recorded. The lower complex is largely composed of migmatite, two-feldspar gneiss and gneiss-granite which has been mechanically transformed into augen gneiss. It is regarded as part of the infracrustal, Precambrian core of the Caledonides in West Norway. The rocks of the upper complex can be arranged in a succession of mappable units, but possible sliding tectonics and recumbent folding make stratigraphical relations still uncertain. The age of the supracrustal rocks is not clear, although it is assumed to be Eocambrian or older corresponding to Precambrian units of the central nappe region. The contact between the supracrustal rocks and their basement is concordant, but strong differential movements shared by both complexes have taken place. Both have experienced two phases of east-west folding, the latest of which is responsible for the pattern of lithological distribution in the investigated area.