Geology and structure of the Bjøllånes area, Rana, Nordland.

Abstract

The field relationships of rock groups of three tectonic units from the area west of the Lønsdalen basal massif are outlined and the lithologies and mineral assemblages are described. Chemical analyses of marbles and amphibolites are presented and discussed in relation to analytical data from neighbouring areas of the Caledonides. Most of the amphibolites are shown to be of igneous origin and sub-alkaline, but their precise nature is uncertain. The structure recorded suggest four phases of Caledonian deformation. The F1 phase probably had axes orientated roughly E-W which is also the axial trend of the F2 phase. The first deformation produced minor isoclinal folds, the main foliation and one possible thrust zone. The second phase gave rise to relatively tight mesoscopic and macroscopic folds. The F3 phase, approximately N-S oriented, deforms the earlier structures and is responsible for the main lithological outcrop pattern. The thrusting of the middle and the upper unit is thought to be connected with this deformation phase. Possible correlations of the Bjøllåsen rocks with those from neighbouring aeras of the Caledonides in Norway and Sweden are proposed. There would seem to be good evidence that the R\u00F6dingsfj\u00E4ll Nappe is situated at a tectonically higher level than the Gasak Nappe which previously was suppossed to be in an identical tectonic position.