Structural geology of the Kjølhaugan area, eastern Trøndelag-westernmost Jämtland, central Scandinavian Caledonides

Abstract

Abstract The Kjølhaugan area comprises two major tectonic units separated by the Grense Thrust. The upper (western) unit belongs to the eastern part of the Trondheim Nappe Complex and is composed of meta-sedimentary rocks some of which are turbidites. The underlying (eastern) unit, which is part of the Seve-Köli Nappe Complex, contains mica schists and amphibolites. Structures related to five phases of deformation have been distinguished in the investigated part of the Trondheim Nappe Complex. The two earliest phases predate or are simultaneous with the thrusting of that complex onto the Seve-Köli Nappe Complex. The Grense Thrust is due to this thrusting which continued till the end of the second phase of deformation. Minor, post-thrusting structures found in the Trondheim Nappe Complex are almost totally absent in the Seve-Köli Nappe Complex of the Kjølhaugan area. Along the boundary of the Trondheim Nappe Complex, the continuation of the Sylarna-Riksgränsen Antiform forms a major post-thrusting structure. Mineral lineations in the garbenschiefers of the Seve-Köli Nappe Complex have been deformed by the thrusting of the Trondheim Nappe Complex. The schistosities in both nappe complexes predate this thrusting. The earliest recognized structures in the studied eastern, sedimentary part of the Trondheim Nappe Complex probably post-date the early structures of the Gula and Fundsjø Groups to the west of the Kjølhaugan area. They are also younger than the early structures in the Seve Nappes.