Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)

Nappe tectonics in the Staré Město Group, North Moravia


Mojmír Opletal

Geoscience Research Reports 36, 2003 (GRR for 2002), pages 32–34
Map sheets: Králíky (14-23)

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Geological mapping to the 1 : 25 000 scale of the sheets Hanušovice and Šumperk was carried out since 1997 and finished in the year 1999. The area between Hanušovice, Branná and Staré Město pod Sněžníkem was finished in the year 1996. The last area western of Staré Město pod Sněžníkem was mapped in the year 2002. The surveyed area covered the geological units along the contact of Lugicum (the eastern part of the Orlice-Snieźnik Unit, the Staré Město Group) and Silesicum (mainly Branná Group). The recent mapping, tectonic and petrological studies, support the idea that the contact between Lugicum and Silesicum lies along the Ramzová tectonic line ('thrust') representing i strike-slip fault steeply inclined to W with left-lateral movement. This boundary could previously have the thrust character (probably as the Moldanubian thrust) and later it was transformed to strike-slip fault, but without lenses of ultrabasic rocks. The Ramzová fault is accompanied by cataclastic zone, comprising locally dolomite, ankerite, and rarely chalcopyrite. An important metamorphic jump exists along this fault - staurolite zone in the Staré Město Group vs. biotite zone in the upper part of the Branná Group. The mapping showed that the contact between tht orthogneisses of the Orlica-Snieźnik Unit and the rocks of the Staré Město Group has the character of a thrust fault with local occurrences of serpentinites. The structure of the Staré Město Group is typical for nappe tectonics, six individual scales are separated by longitudinal faults. The thrust faults are emphasized by lenticular bodies of ultrabasic rocks and they are locally transformed to low-angle faults typical for the extension regime.