Vestiges of Saxothuringian crust in the central Sudetes, Bohemian massif: Zircon evidence of a recycled subducted slab provenance

Abstract

Four detrital zircon concentrates from the metasediments and metavolcanics of the Central Sudetes, Bohemian Massif, have been dated using SHRIMP II. The Wyszki paragneiss yielded Precambrian age spectra similar to those characteristic of the Cadomian terranes: (1) Archaean and Palaeoproterozoic zircons are scattered between 2830 and 1867 Ma, and (2) there are abundant Neoproterozoic zircons dated at 803-577 Ma. The estimated maximum sedimentation age for this rock is 566 ± 4 Ma. The Klodzko Fortress pyroclastic metarhyodacite gave an igneous emplacement age of 536 ± 2 Ma. The magmatic precursor to the subvolcanic Gniewoszów metarhyolite was dated at 501 ± 3 Ma. Finally, the Scinawica subvolcanic rhyolite yielded an igneous emplacement age of 338 ± 3 Ma and a large population of inherited zircons dated at: Palaeoproterozoic, Neoproterozoic, Cambro-Ordovician and Late Devonian-early Carboniferous. The dated samples come from two adjacent suspect terranes -the Orlica-Snieznik dome and the Klodzko massif in the Central Sudetes that are characterised by contrasting timing of metamorphism and exhumation. Despite this difference, the results obtained show, in conjunction with earlier data, a similar provenance of the studied units and their common affinity to the Saxo-Thuringian terrane. Since the Central Sudetes are separated from Saxo-Thuringia by a collisional suture, the pre-Variscan rocks must represent the deformed and metamorphosed, allochthonous equivalents to Saxo-Thuringian lithologies. They were probably subducted together with the Saxo-Thuringian passive margin during a Variscan collision and then exhumed within an accretionary wedge in front of Brunia/East Avalonia. The Central Sudetic suspected terranes must have been derived from a dismembered single accretionary complex and were then juxtaposed by strike-slip faults.