Paleoproterozoic tectonics of Fennoscandia and the birth of Baltica
Raimo Lahtinen, Juha Köykkä, Johanna Salminen, Mohammad Sayab, Stephen T. Johnston
Abstract
Baltica, in the core of the supercontinent Nuna, comprises Fennoscandia, Sarmatia and Volgo-Uralia. We develop a tectonic model of Paleoproterozoic Fennoscandia based on stratigraphic correlations of 2.5–2.0 Ga cover sequences and a shield-wide recognition of the main 1.93–1.70 Ga D1–D6 deformation events. Rifting of the combined proto-Karelia–Kola continent is recorded by the 2.51–2.49 Ga Mistassini and ca. 2.44 Ga Matachewan LIP systems, and a 2.35–2.15 Ga post-rift epeiric sea stage. The 2.15–1.95 Ga age period encompasses continental breakup along the western margin of Karelia at 2.10–2.05 Ga, between Kola and Karelia at 2.0 Ga, and the 2.0–1.95 Ga opening of a marginal basin. 2.03–1.92 Ga subduction occurred along the western margin of Volgo-Sarmatia and in Fennoscandia followed by collisional, accretionary and oroclinal deformation events. Fennoscandia–Volgo-Sarmatia collision at 1.93–1.92 Ga provided voluminous 2.03–1.96 Ga clastic detritus that collected on the western margin of the Karelia continent and which was multiply recycled at 1.91–1.82 Ga across Fennoscandia. Orogen-perpendicular NE–SW and the orogen-parallel NW–SE shortening events at 1.93–1.70 Ga can be correlated to Laurentia. Paleomagnetic data indicate post-1.76–1.74 Ga 29° clockwise rotation of Sarmatia relative to Fennoscandia. Rotation caused bending of the WNW–ESE trending accretionary belts of southern Fennoscandia and crustal stretching in central Fennoscandia, finalizing the birth of Baltica at ca. 1.70 Ga. Orogen parallel shortening by orocline formation and block rotations played a major role in producing the present complex internal configuration of Baltica and similar processes likely played a role in the formation of other continents.