Svecofennian accretion, an example of the early Structural Evolution in a Large Hot Orogen (SELHO)

“Svecofennian accretion, an example of the early structural evolution in a large hot orogen (SELHO)” is still in its initial phase and planning for geophysical investigations. The project addresses the controversy regarding mountain building in the Palaeoproterozoic⁠. A preliminary comparison between the Palaeozoic Caledonian and the Palaeoproterozoic Svecofennian (Svecokarelian) orogen indicates a different style of tectonic evolution. Younger orogens typically feature very shallow dipping thrusts on which bedrock has been transported over large distances, mostly juxtaposing rock units of different origin. Studies from the considerably older Svecofennian orogen suggest that major steep dipping shear zones here represent the major boundaries in the remains of the orogen. However, geophysical investigations show that thrusts are also preserved despite deep erosion, indicating a crustal scale extent which has not yet been observed in younger orogens like the Caledonides. Note that a major difficulty in the interpretation of ancient “hot” orogens is the long magmatic and metamorphic activity which, in general, obscures the record of deformation. Recently, three to four levels of major shallow dipping shear zones have been discovered in the Svecofennian orogen of central Sweden. The geochemistry of the magmatic rocks in the area suggests that they, rather than the steep shear zones, represent the major boundaries in this orogen. Similar structures have been observed in the marine BABEL seismic profiles just east of Hornslandet. A drillhole through this, given current knowledge, unique tectonic pile will allow high-resolution investigations of the different tectonic units and their interfaces and result in an improved understanding of orogenic accretionary geometries and processes.

Principal investigators: Håkan Sjöström, Karin Högdahl, Uppsala University.