Petrogenesis of the post-kinematic magmatism of the Central Finland Granitoid Complex I; Radiogenic isotope constraints and implications for crustal evolution

Post-kinematic granitoids of the Central Finland Granitoid Complex (CFGC) w ere emplaced into the Palaeoproterozoic crust of central Finland shortly af ter the similar to1.89 Ga peak of the Svecofennian orogeny. They are found as discordant, generally non-foliated plutons with A- and C-type granite ch aracteristics and a bimodal (mafic-felsic) magmatic association. Convention al and ion microprobe U-Pb data show that the post-kinematic magmatism comm enced in the northeastern CFGC at similar to1.885 Ga and gradually moved to the west, where the plutons are dated at similar to1.870 Ga. Radiogenic is otope (Nd, Sr, Pb) composition of the post-kinematic plutons indicates homo geneous initial ratios: epsilon (Nd) (at 1.875 Ga) similar to0, Sr-87/Sr-86 similar to0.703, and Stacey & Kramers-type Pb with low long-term Th/U (sim ilar to2). These help to constrain the protolith history of the post-kinema tic magmatism. Nd and Pb isotopic data for Palaeoproterozoic granitoids, Pb isotopic data for associated sulphides, and Nd and Pb isotopic composition of the classic similar to1.6 Ga Finnish rapakivi granites reveal several d istinct crustal domains in the Finnish Svecofennian orogen, and indicate th at the central part of the Svecofennian orogen consists of several terranes (microcontinents) that were amalgamated in Palaeoproterozoic times. The CF GC region is the oldest (similar to2.0 Ga) among these terranes.