The Archaean-Proterozoic boundary beneath the Caledonides of northern Norway and Sweden: U-Pb, Rb-Sr, and isotope data from the Rombak-Tysfjord

Abstract

The Baltic Shield includes an Archaean craton in northeastern Finland. Early Proterozoic accretions to this Archaean craton comprise of (1) the Svecofen- nian domain, which consists of island arc volcanic and sedimentary rocks that formed at 1.94 - 1.85 Ga and that between 1.83 and 1.78 Ga became inten- sely intruded by post-orogenic granites and (2) the Transscandinavian Granite Porphyry Belt (TGPB), which represents a 1.80 - 1.70 Ga magmatic arc at the western and southwestern margin of the Svecofennian domain. The TGPB granites extend across the boundary between the Archaean and Svecofennian crustal blocks. This boundary is in Finland a dextral strike-slip fault zone (Raahe- Ladoga zone) that to the west (Sweden and Norway) widens to a ca. 250 km wide heterogeneous zone.