Syllimanit w gnejsach i migmatytach bloku sowiogórskiego
Abstract
Sillimanite in gneisses and migmatites of the Sowie Mts (Central Sudetes)
Abstract
The results of field observations, and the microscopic and chemical analyses of the Sowie Góry rocks containing sillimanite are presented in this paper. Two main modes of the sillimanite occurrences have been distinguished, namely that in 1. fibrolite gneisses, and that, in 2. sillimanite-muscovite-quartz aggregates in gneisses and migmatites. The textures of the fibrolite gneisses are inferred to have originated before the folding associated with migmatitization of the Sowie Góry rocks. The sillimanite present in sillimanite-muscovite-quartz aggregates was formed at a later stage of the metamorphosis, presumably as a result of selective mobilization and partial removal of KaO, Na2O, CaO, FeO, and MgO. The present authors conclude that a high temperature (above 600° C) predominated not only during the time of migmatitization of the Sowie Góry rocks, but also during the latter metamorphic stages (i.e., after partial homogenization of gneisses and migmatites).