On the new wildflysch-to-flysch, blueschist-rich Lower Visean succession of the Western Sudetes (SW Poland)

Abstract

Dolnowizeńska sukcesja wildfliszowo-fliszowa zawierająca łupki niebieskie (Sudety Zachodnie, SW Polska) Field and laboratory works realized in last years allowed us to redefine one of the lithotectonic units of the western Sudetes, till now considered to be composed of Cambrian to Lower Carboniferous, stratigraphically coherent, volcano-sedimentary succession, as the Lower Carboniferous, probably lower Visean, wildflysch-toflysch succession. This unit forms the westernmost part of the Kaczawa Complex and is situated at the boundary zone between the Kaczawa Mts. (Polish Sudetes) and the Górlitzer Schiefergebirge (Germany) or - at a larger scale - between the Sudetes and Lugian tectonostratigraphic zones of the Variscan orogen. Petrographical studies of rocks sampled from the larger allochthonous bodies (olistolithes and slide-sheets) of the wildflysch sequence have revealed some peculiar features of the lithic composition of this succession. They consist in the presence of: (1) - unmetamorphosed and metamorphosed volcanites with a distinct HP-overprint, characteristic of suprasubduction zones, gabbro-type plutonites, and relatively numerous detrital chromite grains indicating the occurrence of ophiolite ultramafics in the source area; and (2) - large block(s) of rock composed of quartz (almost 100% Si02), previously interpreted as Palaeozoic quartz vein, now documented by the authors to be totally silicified primary evaporites, composed of gypsum (selenite), anhydrite and salt. The last finding would be of special significance as the first strong evidence of evaporites within the Variscan orogenic complex in Europe, if further studies confirm proposed here tectonic position of the silicified evaporites. General lithic composition of the Jędrzychowice/Ludwigsdorf wildflysch detrital material is characterised by the presence of such lithologies, as: black and gray-to-green cherts, black shale mudstones and cherts, (turbidite-) siliciclastics, carbonates (both bioclastic and diagenetic), basic and acid, unmetamorphosed and epi-to- HP-metamorphosed volcanites, and gabbros and ultrabasites (the latter noted only by detrital chromites). Moreover, the siliciclastic material of the olistosthrome matrix discloses the presence of acid magmatic (granites) and high-grade metamorphics of gneiss-to- mica-schist type in the source areas. Such a composition of detrital material clearly reflects a typical tectonic melange as the source terrane for the wildflysch deposit. It would mean that the Jędrzychowice/Ludwigsdorf wildflysch should be considered as the next, strong and unequivocal signal of large-scale tectonic melange stage in a tectonic/geodynamic evolution of the Central European Palaeozoic orogenic system.