Brittle tectonics and paleostress analysis of the Strzegom – Sobótka granite massif

The Strzegom – Sobótka Massif has been subject of brittle tectonics studies for more than a century. Due to an ongoing extensive mining activity, numerous good exposures occur in a relatively small area, especially in the western part of the massif. A pioneering tectonic model of jointing in granite was established by Cloos (1922) for the study area, in which the NW-SE striking joint set is the dominant one (Q) and the perpendicular set (S), striking NE-SW, is longitudinal to mineral fabric. Also, there are two sets of the so-called diagonal joints, which are supposedly younger and strike N-S and W-E.

The effects of field work conducted in 20 quarries in the Strzegom – Sobótka Massiff are presented in the form of a tectonic map. In addition to direct measurements in the field, photogrammetric models were produced using aerial photographs to allow structural analysis within hardly accessible walls. For inaccessible quarries joint orientations were extracted using orthophoto maps. Several examples of fault related structures were identified and documented during field work in the studied granite quarries. Faults with slickensides and kinematic indicators were scarce but paleostress analyses were conducted whenever possible.

We discuss our field measurements of joint and fault orientations in relation to different petrographic types of granites and their lateral extent to address the effects of petrographic differentiation on the evolution of brittle tectonic structures in granites. We compare our new measurements to the results of previous tectonic studies of the Strzegom – Sobótka Massiff and paleostress analyses conducted for several other parts of the Sudetes. We also discuss our new results in terms of the Alpine reactivation of the Sudetes Mountains.