The Carboniferous/Permian transition from Variscan orogenic collapse to active rifting in Central Europe, established from zircon U-Pb CA-ID-TIMS geochronology and Sr isotope analysis on volcanic rocks of the continental Chemnitz Basin (Germany)

• We present high-precision zircon ages and Sr isotopic data from the Chemnitz Basin. • Volcanism peaked at 301-299 Ma, coinciding with a major volcanic phase in Europe. • Our data likely pinpoint the onset of continental-scale rifting in central Europe. Around the Carboniferous/Permian boundary, central Europe underwent a major tectonic transition from Variscan collision and subsequent orogenic collapse to post-Variscan rifting. The initiation of rifting triggered extensive volcanism in the northern foreland of the Variscan orogen and influenced the development of fault-controlled volcano-sedimentary basins within the orogen itself. The Chemnitz Basin is one such intramontane basin, the evolution of which straddled the Carboniferous/Permian boundary. In addition, the tectonic, volcanic, and sedimentary evolution of the Chemnitz Basin has been described with exceptional detail. In this study, we present new high-precision zircon U-Pb CA-ID-TIMS and apatite 87 Sr/ 86 Sr data from volcanic rocks of the Chemnitz Basin. Our data show that volcanic activity within the basin peaked between 301 and 299 Ma. This main phase of volcanism is associated with a shift toward more primitive magma sources, as indicated by low apatite 87 Sr/ 86 Sr ratios and supported by inherited zircon age spectra. Concurrently, we observe a structural transition from ENE-trending, orogen-parallel faults to NW-trending structures that cut across the Variscan structural fabric. These observations point to a major tectonic reorganization in the region during that interval. Comparison with other fault-controlled continental basins in central Europe reveals that orogen-parallel basins initiated asynchronously during the Late Carboniferous, while basins that are associated with NW-trending structures initiated synchronously between 301 and 299 Ma. This timeframe, within uncertainties, aligns with rifting and widespread volcanism in the Variscan foreland, thereby allowing us to constrain the onset of Late Carboniferous/early Permian rifting in central Europe with exceptional precision.