Abstract:
Comparative petrological and geochemical characteristics are presented for the rocks from two areas in northern Karelia in the northeastern and southwestern parts of the Belomorian Mobile Belt. Both of the areas were determined to consist of plagioclase and plagioclase-microcline migmatites, plagiogranites, and granites, but the northeastern part is volumetrically dominated by plagioclase migmatites and plagiogranites corresponding to tonalites and trondhjemites in composition. The rocks of the southwestern part of the belt are rich in plagioclase and microcline. Based on the geological relations between the rocks and their petrography and geochemistry, it is demonstrated that the plagioclase migmatites of tonalite and trondhjemite composition were produced by the migmatization of amphibolites and differ from intrusive tonalites and trondhjemites. The rocks examined in both parts of the belt reveal a similar petrochemical and geochemical evolution with similar behaviors of major and some trace elements (except Ba and Sr), which were controlled by migmatization processes. Compared with the rocks of the northeastern part of the belt, those in its southwestern portion are enriched in Ba and Sr, with the differences in the behavior of these elements possibly controlled by variations in the depths at which the rocks were formed in different geodynamic environments. © Pleiades Publishing, Inc. 2006.
