Petrogenesis of the Post-kinematic Magmatism of the Central Finland Granitoid Complex II; Sources and Magmatic Evolution |
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| Authors: | ELLIOTT BRENT A |
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| Institution: | DEPARTMENT OF PHYSICS AND EARTH SCIENCE, UNIVERSITY OF NORTH ALABAMA, FLORENCE, AL 35632-0001, USA |
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| Abstract: | The 1·88–1·87 Ga post-kinematic granitoidsof the Central Finland Granitoid Complex (CFGC) provide a keygeochemical link to understanding granite formation in Paleoproterozoicorogenic and post-orogenic terrains. Thickness of the crustand intra-crustal differentiation processes played an importantrole in the formation of three granitoid types that shortlyfollowed the peak of the Svecofennian orogeny. In the easternCFGC, pyroxene-bearing plutons with C-type geochemical affinitiespredominate. These were formed from a mixture of low- to moderate-degreepartial melts ( 30%) of mafic mantle-derived (basaltic, 49% SiO2)source rocks and partial melts of pre-existing mafic granulitelower crust at depth. In the western CFGC, high-silica, iron-rich,fluorite-bearing plutons with A-type granite characteristicspredominate. A higher thermal gradient, thinner upper and lowercrust, and significantly more shallow Moho depth resulted inhigher proportions of crustal melts (0·3–0·4vs 0·1–0·2 in the eastern CFGC) incorporatedinto the partial melts of a mafic mantle-derived source. A geochemicalmodel focusing on the Jämsä and Honkajoki plutonsof the post-kinematic suite is presented, constraining the natureof the source rock(s), the degree of partial melting, proportionsof partial melts and fractionation processes involved. KEY WORDS: magmatic evolution; geochemistry; Proterozoic; granite; Finland |
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