Metamorphic evolution of mineral assemblages in the layered unit and its host rocks of the eastern part of the Pana Massif, Kola Peninsula

The paper presents data on the mineral assemblages and chemical composition of minerals in rocks from the eastern part of the Pana Massif, Kola Peninsula, and the results obtained by studying the amphibolization of rocks of this massif genetically related to metamorphism. The rocks contain four amphibole populations, which can be used as good indicators for metamorphic facies. The amphiboles show broad compositional variability. Their evaluated P-T crystallization conditions indicate that the prograde stage of the overprinted metamorphic processes occurred at temperatures increasing from 382 to 473 degrees C and pressures from 1.7 to 4.3 kbar. The retrograde stage (biotitization, chloritization, silification, and carbonatization) took place at temperatures of about 370 degrees C and pressures of approximately 1 kbar. The fluid regime of the metamorphic transforms was also controlled by the temperature: the fluids were oxidizing early in the course of the process and gradually became more reducing with decreasing temperature.