Petrography and structural history of the Caledonian rocks north of Haukelisæter, Hardangervidda.

Abstract

The main features of the geology of the Caledonian nappe front north of Haukelisæter are described. The Precambrian basement in this area is overlain by an autochthonous\/parautochthonous sequence in the east and by Caledonian nappes in the west. The rocks above the Precambrian basement are divided into tectono-stratigraphic units; the authochthonous Cambro-Ordovician sequence, the Holmasjø Formation, the Nupsfonn Complex, the Dyrskard Group and the Kvitenut Complex. At least five episodes of deformation may be distinguished (F0-F4), in the area. The F0 structures in the Dyrskard Group and the pre-F1 structures in the Nupsfonn and Kvitenut Complexes are thought to be of Precambrian age, whereas the last four episodes (F1-F4) are of Caledonian age. The F1 folds trend ENEWSW and are most probably related to the main episode of thrusting from the geosyncline southeastwards onto the Baltic Shield. During the F2 episode thrusting occurred towards the NE causing the formation of NW-SE trending structures. F3 is recorded only in the phyllitic quartz schist of the Holmasjø Formation, and the F3 fold axes are subparallel to the F2 fold axes. F4 produced an intense crenulation cleavage within the pelitic rocks during a \"backward\" movement of the nappes towards the north-west.