Stosunek waryscydów południowo-zachodniej Polski do kadomskiego podłoża

Józef Oberc

Abstract


ON THE RELATION OF THE VARISCIDES TO CADOMIAN BASEMENT IN SW POLAND

Summary
The Variscides of SW Poland and adjoining parts of CSSR occur in several synclinoria (or tectonic troughs), separated from one another by units of older basement (Fig. 1). Both the onset and end of sedimentation of rock series of individual units were diachroneous in this region (Fig. 2) . In western part of the area, folds were found to display southward vergence (Fig. 3) whereas the time of folding appears more and more delayed in the opposite direction. In the eastern part, the vergence is to the east and delay in time of folding may be traced in the same direction.
Basement of the Variscides is built of the Cadomides. The latter are represented by numerous series of micaceous schists which are varying in age. The schists, formed by alteration of mudstones, are separated by thick plates (packets) of gneisses formed in result of recrystallization of graywackes. The series are arranged in three bunches of folds which surround Moldanubic Sowie Góry Błock: south-western, SE-NW oriented, eastern, SW-NE oriented and with outward vergence, and northern, latitudinal, with southward vergence. The Sowie Góry Block has been squeezed up along deep crustal fractures which was followed by ultramafic intrusions and, subsequently, intrusions of gabbros and diabases. The latter form a garland around the block and at large distances underlay Moldanubic rocks of the Sowie Góry Mts (Mantle diapirism).
The relation of the Variscides to their basement is characterized by: 1) jump in metamorphism between the series, 2) differences in style of original structure (gentle tectonics of Cadomian gneisses and intense or even nappe-type structure of the Variscides), 3) poor paleontological record for Cadomian gneisses and good for Paleozoic rocks, 4) presence of pebbles of mesozonal Cadomian rocks in diagenesed or epimetamorphic Ordovician and younger Paleozoic rocks (indicating two-stage metamorphosis). All the data indicate that Paleozoides are separated from the Cadomides by discordance and stratigraphic gap.
The major problems of the modern tectonics are analysed separately for the Cadomides and Variscides. There is no evidence for presence of oceanic floor nor subduction both in the case of the Cadomides and Variscides. The Sowie Góry Block may be interpreted as a microcontinent. There is growing evidence for phenomena of diapirism in continental crust (acid intrusions) in the Variscan epoch.

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