Plagioclase Composition in Rocks of PGE-Bearing Layered Series in the Vurechuaivench Massif, Monchegorsk Complex, Kola Region

Abstract

The PGE-bearing Vurechuaivench massif is part of the Paleoproterozoic Monchegorsk Complex, composed of layered rock series: gabbronorite, anorthosite, and norite. Cumulative plagioclase occurs throughout Vurechuaivench massif. According to microprobe analyses, close to the sole and in the middle part of the section, cumulative plagioclase is represented by labradorite and bytownite with an anorthite component varying from An₆₃ to An₇₈. In the upper part of the section, plagioclase corresponds to labradorite An₆₂ to An₆₉. Norite of the neighboring Nud–Poaz massif contains bytownite with an anorthite component varying from An₇₁ to An₈₁. These data corroborate that the Vurechuaivench massif is a tectonic fragment of a larger magmatic body that involved Nud–Poaz massif. The paper presents microprobe data on plagioclase and orthopyroxene. The latter are unique to the Vurechuaivench massif, because relict fragments of pyroxene grains have not been encountered in high-grade metamorphic rocks.