The Nasafjället Window in the Seve-Köli Nappe Complex is composite consisting of three minor windows. Each of these is composed of Proterozoic granites overlain by quartzites and phyllites of the Mierkenis Group. The minor windows have been overthrust by the Gargatis Nappe, a tectonic unit composed mainly of Proterozoic acid and intermediate volcanites, granites and basic dykes; the uppermost part of the nappe consists of sediments of the Mierkenis Group. The Mierkenis Group is presumed to be of Late Proterozoic-Ordovician age and is correlated with the ‘Hyolithus-zone’ along the eastern margin of the Swedish Caledonides. The thrust at the base of the Gargatis Nappe is discussed in relation to the décollement-style tectonics of the eastern Caledonian thrust front.