Pre-Variscan volcanic-sedimentary succession of the central southern Góry Kaczawskie, SW Poland: Outline geology

Abstract

Przedwaryscyjska sukcesja wulkaniczno-osadowa centralnej części południowych Gór Kaczawskich: zarys geologii A revised geological map of the central southern Góry Kaczawskie (Kaczawa Mountains) in the Western Sudetes, at the NE edge of the Bohemian Massif, based on the authors’ detailed survey of volcanic rocks within a Lower Palaeozoic low-grade metamorphic succession, provides the basis for modified tectonic and stratigraphie subdivisions. In contrast to previous tectonic models, the Radzimowice slates are interpreted as a separate tcctonic unit, referred to as the Radzimowice unit. It lies between two other tectonic units, the Świerzawa unit in the north, and the Bolków unit in the south, both comprising similar volcanic-sedimentary sequences. The existing lithostratigraphic subdivisions of the volcanic rocks into a "suite of greenstones" and a "suite of volcanics and volcaniclastics" are considered unsatisfactory and a new working stratigraphie scheme is proposed. It distinguishes (1) units in inferred sequential order: Podgórki volcanic complex, Wojcieszów limestones, Oselka rhyodacites, Gackowa sandstones (these four grouped into the Milek succession), grey slates, Lubrza trachytes, black slates & cherts and siliceous slates; and (2) units of unknown position: Chmielarz slates, Dobków slates, Radzimowice slates, and melanges. The position of the Radzimowice slates and melanges is uncertain, though they are thought to be younger than most of the sequence. The tectonic units are interpreted as thrust sheets. The main southern outcrop o f the Świerzawa unit is considered to define the overturned limb of a south verging anticline. In the Bolków unit, particular subunits probably represent different parts of the sequence which arc arranged into south and SW - verging folds. Lithological units within the Świerzawa and Bolków tectonic units are correlated. Parts of the Milek succession in the lower part, and the Lubrza trachytes in the upper part of the sequence, are found in most sections in both tectonic units. Differences probably reflect primary lateral or vertical changes in the sedimentary and volcanic environment, though some may partly have a tectonic origin.