Synmetamorphic penetrative mylonitization in orthogneisses of the Bystrzyca Mts, Sudetes

Abstract

Medium and coarse-grained granitegneisses of the Bystrzyca Mts, western part of the Kłodzko-Orlica dome, Middle Sudetes, are characterized by a strong stretching lineation. The stretching fabric was associated with the grainsize reduction and ductile mylonitization of originally granitic rocks. Mylonitic foliation of the resultant granitegneisses was due to contrasting ductility of quartz, K-feldspar, and plagioclase during the deformation. The deformation was overlapped and severe recrystallization of the minerals once ground down, in particular K-feldspar, which obliterated partly the earlier farbic, and to local increase in grainsize. Blastomylonitization of the primary granitic masses, emplaced into metasedimentary schistose rocks, was related to pervasive shearing and an easterly directed Variscan thrusting as well as napping that all took place toward the end of the main N-S oriented folding in the region. The direction of stretching ubiquitously conforms with that of the main folds and the mineral lineation in the schistose Stronie formation, hence it likely represents the Y axis of strain ellipsoid.