Gierałtów versus Śnieżnik gneisses – what is the real difference?

Abstract

Structural and petrographic study applied to the gneisses from the eastern part of the Orlica-Śnieżnik Dome, indicate that two different types of gneiss are present. The Śnieżnik gneisses are porphyrithic granites, constricted and sheared into L-S tectonites, most commonly with augens; the Gierałtów gneisses are sheared migmatites, porphyroblastic gneisses and banded gneisses, with two sets of metamorphic foliation, intrafolial folds and lensoid leucosome aggregates or metamorphic porphyroblasts. Both lithologies were later zonally sheared and transformed into more or less deformationally advanced mylonites, difficult to be distinguished from one of the two types. Identification of the Śnieżnik and Gierałtów gneisses is possible only between zones of the late (Variscan) shearing, in which the original, pre-kinematic structures are preserved.