Tectonic and metamorphic events in the Polish part of the Orlickie Mts.

Abstract

Brief petrographical characteristic of rocks belonging to the Stronie formation and the Nove Mesto formation as well as gneisses of the Śnieżnik type is given. Three major stages and within them six deformational phases (F1-F6) were recorded in these rocks. The two oldest phases (F1 and F2) stimulated and were followed by metamorphic events (M1 and M2) taking place at the time of kinematic calm. F1 and F2 folds are tight and roughly co-axial. They have NW - SE or NE - SW trending (because of subsequent rotations), generally northwesterly or westerly dipping axial planes and plunge at different angles to NW or at very small angles to NE. Folds of these both sets were accomplished at first by flexure mechanism and later on by superimposed shearing. The shear gliding in F2 + M2 phase was parallel to the planes of axial foliation referred to as S2 and perpendicular to F2 axial directions. This shearing exerted considerable influence on the mode of transformations of rock fabric involved as well as arrangement of rock-forming minerals. F1 + M1 and F2 + M2 phase gave rise to independent mineral indexes and sets of fabric characteristic of each of the phases. Features of these two sets of fabric were recognized well and studied in the hinge regions of F2 folds occurring in every lithological variety. Original sedimentary rocks (perhaps of Proterozoic age) were regionally metamorphosed and metamorphically differentiated under conditions of greenschist facies (M1 phase) and next under those of amphibolite facies (M2 phase). The main folds of the investigated region were developed during F2 + M2 phase, probably at the Caledonian-Variscan turn. They display tight or isoclinal geometry. The fourth deformational movements referred to as F4 resulted in diagonal (transversal refolding of the earlier structures on the southwesterly dipping axial planes (S4) and about westerly plunging axes. F4 folds were accomplished by flexure mechanism and are characterized by persistently northern asymmetry. Brittle structures started to develop in the F4 phase. F4 and F6 folds are responsible for the reorientat