Rola bloków litosfery i ruchy przesuwcze w przedmolasowym rozwoju waryscydów na brzegach Masywu Czeskiego

Józef Oberc

Abstrakt


A ROLE OF LITHOSPHERE BLOCKS AND SHIFTING MOVEMENTS IN THE PREMOLASSE DEVELOPMENT OF THE VARISCIDES ON THE BOHEMIAN MASSIF MARGINS

Summary
In Palaeozoic the Cadomian tectogen divided into blocks separated by two break systems: NE- SE and SW-NE. Sedimentation on the block margins begun and finished in various periods. Its character depended on the rate of vertical movements of the blocks adjacent to geosynclines. The Variscides are a two-branched tectogen. Its intermontane consists of the Middle Germany crystalline zone continued to the metamorphic rocks of the middle Odra. The primary configuration of the lithosphere blocks caused the zone bow-shaped and northward protuberant. The external branch of the Variscides comprises the Rhine Schistic Mountains, the Harz and zones of folds known only from the boreholes in northern Germany, Wielkopolska and the zone of the Kraków folds. The vergency is directed outside the bow.
The internal, more elevated zone comprises numerous SW-NE and NW-SE oriented zones of folds with vergencias that converged at the right angle. Folding proceeded in several phases: old Variscan along the SE border of the Bohemian Massif - Sudetic that gave the Variscides leading features of structure - Asturian best know in the Ruhr Basin and in its SW part as well in the upper Silesia. Some phases comprise separated units: later caledonian phase - the South Karkonosze Mountains, the Żelazne Mountains with the Hlinsko zone and the Kraków folds the pre-upper Devonian phase in the Kłodzko Structure, the Nassau phase - the Świebodzice Structure.
In the Kaczawa and Bardo units apart from the Sudety phase) a strong phase appeared near the Tournai/Visean border with the same structural plan as the Sudety phase. The folding action depended on transversal movements of the complex blocks. They were limited by the deep faults. Bach block consists of individual blocks of the Cadomian rocks and zones of folds composed of the Palaeozoic rocks. There are two systems of the complex blocks. In the first one the transport had the NW- SE direction. It consists of the Rhine Schistic Mountains - Schwartzwald, Moravia - the Harz of which the Żelazne Mountains and the Klin zone, the Drahny block - the middle Elbe, the Silesia- Lusatian and the Kraków- Wielkopolska blocks should be separated.
In the second block system the transport had the NE-SW direction. This block consists of the Orlickie - Sowie Mountains block, the Izerskie Mountains - the Żelazne Mountains block and the Lusatian block. During the Sudety phase the generał direction of the transport was from the north. The faults limiting the complex transversal blocks are of strike-slip character. They developed during several phases changing their character of various sections. Changes in the compression directions of particular tectonic phases caused changes in character of faults. Trying to explain the tectogenesis the author has rejected subduction as unproven and thus a classical version of plate tectonics; he has proposed its subductionless version: an expansion of the Barth being heterogeneous causes removing the lithosphere blocks and introducing geosynclines. On sloping surfaces of astenosphere the lithosphere blocks remove gravitationally on overcoming resistence they fold the content of geosynclines.
This model admits possibilities of removing particular bloc ks and f olding the sedimentary series found on its transport way. During the sudetic phase a depression of the Barth crust base set up bellow the intermontane zone of the Middle Europe Variscides. Towards the direction of the depression the lithosphere blocks removed gravitationally shoving under particular zones of folds. The vergency of folds of the sudetic phase on the both branches is contrary to the directions of block movements.

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