Neotectonic Fold-Faulted Morphostructures in the Surroundings of the Town of Brno

Abstract

A characteristic relief feature of the SE margin of the Česká vysočina (Bohemian Highlands) in the surroundings of the town of Brno are neotectonic forms designated by the authors as fold-faulted morphostructures. These morphostructures established by a detailed morphostructural analysis developed by Post Upper Miocene vertical movements. Together with horst and grabens they form a complicated monocline of the SE margin of the Bohemian Highlands. A part of the monocline is covered by Miocene deposits of the Carpathian Foredeep. In the territory investigated involving parts of the Českomoravská vrchovina (Highland), the Brněnská vrchovina (Highland) and the Drahanská vrchovina (Highland) five fold-faulted morphostructures were established (Encl. 1). The fold-faulted morphostructures have an irregular shape in their groundplan controlled by the course of faults. They are further characterized by inner faulting of various intensity (Figs. 1, 2). Their longer axes are as much as 18 km long and run in substance perpendicularly to the margin of the Bohemian Highlands. The summits of the fold-faulted morphostructures are situated in altitudes between 460 to 560 m. They do not occur in the centre of the fold-faulted morphostructures but rather in the interior of the Bohemian Highlands (Fig. 2). Along supposed longer axes of fold-faulted morphostructures deformed remnants of planation surface with monadnocks and outliers usually kept best preserved. Differences in heights between the uppermost and lowermost spots of fold-faulted morphostructures range between 200 and 300 m. A radial valley pattern is characteristic of fold-faulted morphostructures. But in details several smaller river basins have a rectangular valley pattern. Some river basins have a very atypical valley pattern, for instance with tributaries only from one side (a fan-like shape, Fig. 3). Numerous valleys exhibit a distinct height assymetry of slopes. The individual valleys are either rectilinear (valleys on fault and dislocation zones) or curved (on fissures developed due to tensile stress in the course of up-doming). Simultaneously with the development of fold-faulted morphostructures satellite blocks developed at their margins. The territory between neighbouring described fold-faulted morphostructures consists either of grabens of various widths (often with Miocene deposits) or deep incised valleys on dislocation zones. The morphostructural investigations carried out so far in the territory of the Outer Carpathian Depressions adjacent to the part of the Bohemian Highlands under study have shown that fold-faulted morphostructures developed even here. Since the surface of this territory is built predominantly of less resistant Miocene sediments the establishment of deformations is very difficult. More detailed investigations of these morphostructures bave not been carried out so far. The establishment of fold-faulted morphostructures is of considerable significance for understanding of the geomorphological development and neotectonic movements of the marginal parts of the Bohemian Highlands in Upper Tertiary and Quaternary. The results of research can be applied in the delimitation of geomorphological units of lower taxonomic levels and in mineral prospecting.