Harstad. Beskrivelse til det berggrunnsgeologiske gradteigskart M 8 - 1:100 000 (med fargetrykt kart)

Abstract

From a structural point of view the bedrocks of the map area can be subdivided into 1. Precambrian basement (autochthonous), and 2. Allochthonous Caledonian units. The Caledonian sequence embraces a) The lowermost over-thrust units, b) The main unit (Harstad Nappe) and c) The upper units (Straumsbotn Nappe and Niingen (?) Nappe). The main unit belongs to the Seve-K\u00CEli Nappe Complex. The bedrock lithoogies within these units are briefly described. Metasediments, metamorphosed igneous intrusive rocks and possible metavolcanics (some amphibolite layers) are met with in the allochthounous sequence together with deformed Precambrian granite. Within the autochthonous Precambrian, granite and granitic gneiss predominate although meta-gabbro covers a large area in the northwestern part. Ore occurrences (magnetic ore, copper etc.) of the \"skarn type\" are connected with inclusions of metasediments (marble, mica schist etc.) in the Precambrian granite. The deformation history of the area can be subdivided into 3 episodes (F1, F2, F3) of which F1 and F2 are the most important ones. F1 resulted in mainly recumbent folds with an axial plane schistosity. This F1 schistosity is the regional schistosity now observed.