Tektoniczna analiza dynamiki uskoków z niektórych obszarów struktury bardzkiej (Sudety)

Zbigniew Cymerman, Anna Krzyż




Eight areas located within the Late Paleozoic Bardo Structure (Sudeten) were selected for the first dynamic analysis of paleostress in the Lower Silesia (SW Poland). 658 faults were examined and fault strike and dip, slickenside dip and sense of a shear were measured in each fault. Axes of main stress (σ1>σ2>σ3), R value (shape of stress ellipsoid), F value (fluctuation) and diagrams of pressuretension axes) were determined for each area. A characteristic feature is almost horizontal orientation of the axes of main stress σ1 and σ2 except of the area III (Zdanów-Wilcza environs). Directions of axis σ1 are usually close to meridional, and in the southern part are close to the NE-SW orientation while in the western part the axes are running along the west-east direction (Fig. 3). The orientation of intermediate axis of main stress σ2 is usually running along the west-east or NW-SE directions. The axis of minimum main stress 0"3 is almost vertical with an exception of the area III where it is almost horizontal (Table I). The R values are quite differentiated. The smallest value (R = 0.315) is related to the central part of the Bardo Structure and the greatest value (R = 0.849) to its southern part. Besides, in the southern part of the Bardo Structure the greatest value F = 280 was recorded, and this indicates the greater heterogeneity of fault population in that part of the Bardo Structure. This conclusion is supported by the analysis of P-T axis (Table I). The results of paleostress analysis of the Bardo Structure to a large extent are in accordance with the earlier tectonic investigation of the structure. Many synclines and anticlines as well as overthrusts and imbrications originated during the post-Visean transpression of the NNE-SSW axis of the maximum main stress σ1. The most complicated is the picture of paleostresses of the area III as the area coincides with the Wilcza tectonic loop. Approximately one third of the analysed faults originated during the Permian extension and young Alpine deformations.