Deformacja i metamorfizm serii skalnych na wschód od bloku sowiogórskiego - nowe dane i interpretacje

Stanisław Mazur, Jacek Puziewicz



An important NNE-SSW - trending tectonic boundary, located between the Góry Sowie Gneiss Block to the west and the Strzelin Crystalline Unit to the east (Fig. 1), separates the structures of the West and East Sudetes in the area of the Fore-Sudetic Block. The West Sudetes have been traditionally included into the Saxothuringian and the East Sudetes into the Moravo-Silesian major facies-structural zones of the European Variscan belt. The boundary between the two zones continues further southwestward along the SE margin of the Bohemian Massif into the Moldanubian thrust [45] which separates Moldanubian and Moravian nappe piles. The ductile, NNE-directed, synmetamorphic displacements with a significant dextral, strike-slip component have been documented in this area throughout the entire length of the SE margin of the Bohemian Massif [26, 42, 21]. In contrast, the mylonites of the Niemcza Zone, located immediately to the west of the Western/ Eastern Sudetes boundary (Fig. 1), recorded effects of sinistral strike-slip displacements [28]. Metamorphic rocks cropping out to the east of the Góry Sowie Block are subdivided into three regional units. From west to east these are: the Niemcza Shear Zone, the Niemcza-Kamieniec Metamorphic Unit and the Doboszowice Metamorphic Unit (Fig. 1). The orientation of foliations and lineations in these units are shown in Figures 3, 4 and 7. On the basis of our field data, we established a tentative sequence of three tectonic events in the rock sequences of the study area (Fig. 8). The DJ event was related to E-directed tectonic transport under amphibolite facies conditions. The DJ fabric is preserved in paragneisses comprising the eastern part of the Doboszowice Metamorphic Unit (Fig. 6). The western part of this unit is composed of orthogneiss body (Fig. 6) representing a syntectonic granite intrusion emplaced during the D2 event. The D2 structures, well developed in this orthogneiss body and in coarse-grained mica schists exposed near to Kamieniec Ząbkowicki (Fig. 5) recorded a top-to-NE shearing under amphibolites fades conditions. The D3 event involved sinistral, strike-slip displacement in the Niemcza Shear Zone (Fig. 2) and a top-to-SW shearing in the Niemcza-Kamieniec Unit. The Niemcza Zone (Fig. 2), extending along the eastern edge of the Góry Sowie Block, consists of mylonites derived from the Góry Sowie gneisses during the D3. The mylonites occur as high- and low-temperature varieties produced under the amphibolite and greenschists facies conditions, respectively. The D2 event corresponds to synmetamorphic NNE-directed thrusting recognized along the entire SE margin of the Bohemian Massif. The displacements towards NNE were preceded by a separate stage of E-directed tectonic transport. The sinistral sense of shear in the Niemcza Zone is related to the subsequent D3. It seems to be comparable with late-orogenic, sinistral shearing localized in several NNE-SSW shear zones and ductile to brittle faults in the S and SE part of the Bohemian Massif [10].