Specifika architektury hronovsko-poricskeho zlomu

This contribution presents a modern look at the architecture of the Hronov-Poříčí Fault (HPF), a major post-Variscan structure within the Elbe Fault Zone in the NE part of the Bohemian Massif. Geology has been relatively well documented by galleries excavated in the 19th century and by boreholes and test pits in the 1960s, and reviewed by several field trips within the present study.
The main fault plane of the HPF dips NE at 60-80° and has the character of a reverse fault. The hangingwall block exposes Carboniferous sediments (Westphalian to Stephanian) with coal seams, dipping NE at steep to medium angles. The footwall block generally exposes Permian (Autunian, Saxonian) sediments and volcanics. A 2 km broad synclinal structure in the footwall block, known as the Hronov-Poříčí Graben, is elongated parallel to the fault and filled with Upper Permian (Thuringian), Triassic and Upper Cretaceous sediments. Both limbs of this structure show tectonic dips of max. 60-80°.
The fault core is several tens of centimetres, max. a few metres thick, being dominated by tectonic clay and fractured wallrock. The inner part of the fault damage zone has a width of hundreds of metres, but only tens of metres in the SE segment of the fault (Hronov area), showing crushing, mylonitization and brecciation. The outer part of the zone with slickensides and intensive jointing reaches max. 1 km from the main fault. The drag zone is 2 km wide in the footwall block, where reverse drag passes to normal drag in the immediate fault proximity, thereby forming the “Hronov-Poříčí Graben”. In the hangingwall block, reverse drag continues to the SW limb of the Police Syncline (width 10 km).
The complex structure of the HPF and the extreme width of the drag zone suggest that the fault has a polyphase kinematic history controlled by transpression. Its architecture can be most readily described as bulldozer-style deformation resulting from steep reverse faulting combined with subhorizontal compression.

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