Tectonics of the Caledonides of part of Nordland, Norway

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Abstract
The tectonic pattern of an area approximately 100km by 40 km in the interior of the Caledonides in Nordland is described. Detailed studies of a part of the area by a number of workers are used to provide a provisional tectonic interpretation of the whole. The region is shown to consist of two ‘internal’ basement complexes separated by a tectonic depression in which higher structural units are preserved. The basement complexes show nappe tectonics and the Pre-Cambrian gneisses in the nappe cores have been completely ‘Caledonized’. The main nappes recognized belong to the second period of deformation (F 2 ) and their movement was directed towards the main tectonic depression from both sides. The basement areas are shown to be essentially anticlinal and some of the major synforms in the area are shown to be the ‘drooping’ closures of anticlinal nappes de recouvrement. An earlier period of deformation (F 1 ) is revealed by some major isoclinal folds that have east-west trending axes like the F 2 nappes. The F l deformation appears to have been largely conjunctive (i.e., to have preserved the major stratigraphical relationship), but one major disjunctive F 1 nappe complex has been recognized. This upper nappe-complex may be equivalent to the Rödingsfjåll nappe in Sweden. The base of this complex is made up of granitized schists and gneisses, which are succeeded by rock groups stratigraphically equivalent to those in the lower nappe-complex. The main tectonic depression between the basement complexes is regarded as a continuation of the Sulitjelma tectonic depression, which lies between the ‘external’ basement complexes on the Swedish-Norwegian frontier zone. The relation of the region to the Swedish thrust-zone is briefly discussed and comparisons are made between the structures recognized and those recently described from the Scottish Highlands.

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