Sydøstligste Helgelands geologi.

Abstract

Geology of the south-eastermost part of Helgeland: Helgeland is the southern part of northern Norway. The present paper is a preliminary report presenting the results of mapping work during the summers 1951-54 by the writer and his assistants. A report based upon this work in 1951-52 has been published earlier (Strand 1953). The rocks in the area can be divided into four main units. The basal massif of Store Børgefjell is built of granitic gneisses, schists and, subordinately, of quartzites. Zones of feldspatiferous porphyroblast schists form a transition between the sedimentary schists and the granitic gneisses and indicate a granitization origin of the latter. On Swedish territory, according to G. Kautsky, the rocks of the Børgefjell amssif are normally overlain by Cambrian sediments of foreland type. This indicates a Pre-Cambrian age of the massif. On Norwegian side no rocks of a corresponding autochtonous or parautochtonous sedimentarty cover have been recognized. The sediments next above the massif have tectonic boundaries and form a tectonic unit composed of four stratigraphic divisions.