3.1 The Early Palaeoproterozoic of Fennoscandia: Geological and Tectonic Settings

Abstract

The Fennoscandian Shield forms part of a large crustal segment sandwiched between the Scandinanvian Caledonian Orogenic Belt and the cover sequences of the Russian platform (Gorbatschev and Bogdanova 1993). Our main area of interest is the eastern part of the shield, which contains a long record of Archaean and Palaeoproterozoic evolution that, excluding minor remnants of c. 3500 Ga gneisses (Mutanen and Huhma 2003), started at c. 3200 Ma (Fig. 3.1, Koistinen et al. 2001). Five main geological subdivisions can be identified, from oldest to youngest: (1) late Archaean granitoid-gneiss basement with relicts of greenstone belts (Fig. 3.2); (2) early Palaeoproterozoic (2500–2000 Ma) volcanic and sedimentary complexes deposited on the Archaean sialic basement (Fig. 3.3); (3) early Palaeoproterozoic (c. 2100–1930 Ma) high-grade sedimentary and volcanic terranes with a major juvenile component (Lapland and Umba granulite belts, e.g. Daly et al. 2006; Fig. 3.3); (4) early Palaeoproterozoic ophiolite complexes forming a discontinuous chain from Outokumpu to central Finnish Lapland (Nuttio) (Fig. 3.3; c. 2015–1950 Ma; Hanski and Huhma 2005; Peltonen 2005); and (5) middle Palaeoproterozoic (1920–1880 Ma, Kähkönen 2005) sedimentary and volcanic rocks accreted together due to microcontinent-island arc collisions during the Svecofennian orogenies (Lahtinen et al. 2009) (Fig. 3.4).