First U–Pb LA-ICP-MS zircon ages assessed from a volcano-sedimentary complex of the mid-European Variscides (Pennsylvanian, Flöha Basin, SE Germany)

Abstract

Nine radiometric ages constrained by U–Pb isotopes from magmatic zircon grains are provided for different volcanic rocks from the Floha Basin and its surroundings. For most of them, this is the first reliable data to correlate with the International Chronostratigraphic Chart. Measurements were obtained with LA-ICP-MS and revealed middle Pennsylvanian ages (311–308 Ma) allowing first consistent correlation to other Variscan volcano-sedimentary basins of the Saxo-Thuringian and Tepla Barrandian zones. The Obermuhlbach Volcano, formerly considered to be early Permian in age, is shown to be of middle Pennsylvanian age. In contrast, the dykes from Metzdorf village and Oederan have shown to be not Pennsylvanian, but rather of early Permian age. Biostratigraphic data obtained from the Floha Formation macroflora coincide with the new isotopic evidence which encompasses a likely time span from the middle to late Bolsovian (Westphalian C) up to the Bolsovian–Asturian boundary. The results not only yield a modified picture of the Floha Formation and their intercalated pyroclastics. As new insights challenge previous geological mapping they contribute to the understanding of the complex volcano-tectonic processes in the type area of the Saxo-Thuringian zone of the European Variscides.