The Polish Sudetes: Caledonian or Variscan?

Abstract

AbstractThe Polish Sudetes on the NE margin of the Bohemian Massif comprise a complex mosaic of pre-Permian basement units, traditionally included in the Variscides. A hypothesis of significant Caledonian orogenesis in this area originated in the 1920s, was subsequently rejected, and then was recently revived in models which invoked Early Palaeozoic to Early-Mid Devonian subduction and continental collision along a proposed extension of the Tornquist suture zone. We reassess the evidence invoked in support of the Caledonian orogeny, such as supposed regional pre-Upper Devonian unconformity, Ordovician bimodal magmatism and radiometric, palaeontological, palaeomagnetic and structural data, and suggest these are either inconclusive or misinterpreted. On the other hand, the Sudetes record Mid?-Late Devonian blueschist metamorphism followed by an Early Carboniferous regional high temperature event, widespread Late Devonian/Early Carboniferous flysch/molasse sedimentation and abundant granite intrusion in the Carboniferous to Early Permian. We discuss the usage of the term ‘Caledonian’ in a plate tectonic context and suggest it should not be used simply to denote Early to Mid-Palaeozoic tectonic activity. The tectonic evolution of the Sudetes was temporally different from, and resulted from convergence of different crustal domains than that of the British-Scandinavian-Pomeranian Caledonides. The Sudetic Palaeozoic sequences most probably developed on Armorican Neoproterozoic crust and in adjacent oceanic(?) domains and, therefore, the Sudetes form part of the Variscan orogenic belt.