Post-Variscan cooling history of the central Western Sudetes (NE Bohemian Massif, Poland) constrained by apatite fission-track and zircon (U-Th)/He thermochronology

Abstract

Apatite fission track (AFT) and zircon (U-Th)/He (ZHe) dating techniques were combined to reveal post-orogenic history of the Rudawy Janowickie Mts. in the West Sudetes (Bohemian Massif). Permian to Jurassic ZHe ages of 271.2±24.8–171.3±11.5Ma obtained for crystalline basement rocks indicate post-orogenic cooling and progressive unroofing of the NE Bohemian Massif. On the other hand, Cretaceous ZHe ages of 130.5±8.8–99.7±6.7Ma prove that the Rudawy Janowickie Mts. region remained under ~190°C during the mid-Cretaceous, suggesting a deep burial. ZHe ages from the Cretaceous sediments located to the east of the Rudawy Janowickie Mts. range between 298.8±16.8 and 181.8±11.9Ma, documenting that the burial did not exceed 6km in the axial part of the Intra-Sudetic Through. AFT ages range from 105.9±6.1 to 51.1±4.3Ma. The Eocene AFT ages revealed by the granite basement and the Cretaceous AFT age revealed by the metamorphic cover suggest the existence of at least two different thermo-tectonic blocks experiencing different post-Variscan cooling and exhumation. AFT results strongly support 3.3–3.5km exhumation for the Rudawy Janowickie Mts. since the Cenomanian, which in combination with ZHe results, clearly contradicts some of the previously proposed evolutionary scenarios for the Sudetes.