Литосфера (Jan 2016)
Mineral associations in the rocks and metamorphism conditions of the Kandalaksha gabbro-anorthosite massif (Kola Peninsula)
Abstract
The composition of mineral associations was studied in the main varieties of the rocks within the metamorphosed Kandalaksha gabbro-anorthosite massif in the southern part of the Kola Peninsula. In terms of composition, clinopyroxene corresponds to diopside, less often to fassaite, and orthopyroxene to bronzite and hypersthene. Garnet developed in the form of reaction rims at the pyroxene-plagioclase boundary belongs to pyralspite group Alm-Prp-Grs composition. Plagioclase corresponds to andesine and labradore. Relict clinopyroxene grains, according to microprobe profiling, are characterized by homogeneous composition. For garnet from reaction rims developed between clinopyroxene and plagioclase, increasing CaO contents and lower MgO contents were identified when approaching the border of plagioclase. Large relict grains of plagioclase among the granular matrix are characterized by weak deanortization of the marginal parts. Calculations for garnet-clinopyroxene thermometers and barometers for most of the samples showed temperatures values of mineral equilibria at a level 830-910°C and a pressure of about 10 kbar, which correspond to the isobaric conditions of the granulite facies metamorphism developed nearly 1.9 Ga during the collision process of the Kandalaksha-Kolvitsa granulite zone.
