Petrogenesis of the post-kinematic magmatism of the central Finland granitoid complex II; Sources and magmatic evolution

The 1.88-1.87 Ga post-kinematic granitoids of the Central Finland Granitoid <LF>Complex (CFGC) provide a key geochemical link to understanding granite formation in Paleoproterozoic orogenic and post-orogenic terrains. Thickness of the crust and intra-crustal differentiation processes played an important role in the formation of three granitoid types that shortly followed the peak of the Svecofennian orogeny. In the eastern CFGC, pyroxene-bearing plutons with C-type geochemical affinities predominate. These were formed from a mixture of low- to moderate-degree partial melts (similar to30%) of mafic mantle-derived (basaltic, similar to49% SiO2) source rocks and partial melts of pre-existing mafic granulite lower crust at depth. In the western CFGC, high-silica, iron-rich, fluorite-bearing plutons with A-ype granite characteristics Predominate. A higher thermal gradient, thinner upper and lower crust, and significantly more shallow Moho depth resulted in higher proportions of crustal melts (0.3-0.4 vs 0.1-0.2 in the eastern CFGC) incorporated into the partial melts Of a mafic mantle-derived source. A geochemical model,focusing on the Jamsa and Honkajoki plutons of the post-kinematic suite is presented, constraining the nature of the source rock(s), the degree of partial melting, Proportions of Partial melts and fractionation processes involved.