Record of Alpine tectonic activity of the Železné hory Fault expressed by brittle deformation within its southeastern segment

Geoscience Research Reports 52, 2019, pages 141–146

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Published online: November 30, 2019

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Abstract

The Železné hory Fault represents one of the major tectonic structures of the Bohemian Massif which were proved to be reactivated as reverse faults during the Alpine orogeny. However, the architecture and kinematic history of the fault are known only incompletely due to the fact that the trace of the fault is covered by extensive Quaternary sediments. Three sites in the SE segment of the fault were revised and characterized: they provide exposures of the fault core and brittle-deformed ambient rocks for a direct structural study. At the first site at the Sloupno village near Chotěboř, the fault core is exposed in a gorge of a brook. The second site is the nearby active quarry, which reveals the damage zone cutting crystalline rocks. The study of the fault core and its damage zone at the third site of Horní Studenec near Ždírec nad Doubravou would necessitate its re-opening by minor excavations.
Parameters of four stress events were estimated by the paleostress analysis of first few fault-slip datasets. The results were compared with previously known styles of brittle deformation of the Upper Cretaceous sediments. The oldest, probably dominant NE compression reactivated the Železné hory Fault as an oblique reverse fault. It was responsible for transpressional brittle and ductile deformations of rocks in its surroundings. The succeeding compression, of similar orientation, reactivated most faults in the area as strike-slips. The subsequent two events, characterized by NNW and WNW extension, are probably the relatively youngest ones. They were responsible for reactivation of the faults as oblique normal faults. Fault movements during the three younger deformation events resulted in frequent transverse segmentation of the structure of the Železné hory Fault.
Recognition of the sites and the first results of paleostress analysis demonstrated its possibilities and marked the trends in further study, including the adaptation of some of these sites as educational sites for the public.

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