Seismic images of Paleoproterozoic microplate boundaries in the Fennoscandian Shield
Published:January 01, 2008
Annakaisa Korja, Pekka J Heikkinen, 2008. "Seismic images of Paleoproterozoic microplate boundaries in the Fennoscandian Shield", When Did Plate Tectonics Begin on Planet Earth?, Kent C. Condie, Victoria Pease
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Deep seismic-reflection data from the BABEL and FIRE profiles across the Fennoscandian Shield image Svecofennian crust that is made up of a collage of terranes. The data suggest sequential accretion of island arcs and microcontinents to the Karelian craton (1.9–1.8 Ga). These accretionary events may have caused temporary changes to arc geometries, accretionary episodes or collisional phases, and westward growth of the continent. The accreted terranes experienced gravitational collapse that stabilized the crust and exhumed the medium- to high-grade rocks to their present positions. The structures froze after isostatic balance was achieved and thus have been protected from later tectonic deformation. The accretionary growth period was terminated by continent-continent collision, after which it was possible for the Wilson cycle to operate at the margin of the newly formed continent.
As in modern accretionary systems, several tectonic environments are found. These include paleosubduction, obduction, continental transforms, collision of hot and cold terranes, and collapse of hot and cold collisions, which are all supportive of plate tectonics operating in the Paleoproterozoic. From the different collision zones, the following tectonic units can be recognized: hinterland-foreland fold-and-thrust belts, metamorphic cores, accreted arcs and basins, and foreland fold-and-thrust belts. The metamorphic cores are associated with granitoid complexes and/or core complexes. The platetectonic theory together with gravitational balancing is a viable model to explain the evolution of the Svecofennian orogen.