The volcano-sedimentary evolution of a post-Variscan intramontane basin in the Swiss Alps (Glarus Verrucano) as revealed by zircon U–Pb age dating and Hf isotope geochemistry

• Published in: International journal of earth sciences : Geologische Rundschau Vol. 104; no. 1; pp. 123 - 145
• Main Authors: Letsch, Dominik, Winkler, Wilfried, von Quadt, Albrecht, Gallhofer, Daniela
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.01.2015; Springer Nature B.V
• Subjects: Alluvial fans; Basalt; Carboniferous; Earth and Environmental Science; Earth Sciences; Evolution; Geochemistry; Geology; Geophysics/Geodesy; Humid climates; Metamorphic rocks; Mineral Resources; Original Paper; Orogeny; Paleozoic; Permian; Pyrite; Sedimentary geology; Sedimentology; Stratigraphy; Structural Geology; Volcanoes; Detrital zircon ages; Verrucano; Variscan orogeny; Basin analysis; Bimodal volcanism; Red beds; Lower Permian; Swiss Alps
• ISSN: 1437-3254; 1437-3262
• DOI: 10.1007/s00531-014-1055-0

The Late Palaeozoic Glarus Verrucano basin (GVB, Glarus Alps, eastern Switzerland) formed as an intramontane graben in the aftermath of the Variscan orogeny. Its fill, the Glarus Verrucano, consists of immature alluvial fan and playa lake deposits with intercalated bimodal volcanics (basalts and rhyolites). Despite its importance for local and regional geology, no modern sedimentologic or stratigraphic studies on the GVB exist. By means of sedimentologic and geochronologic studies, we reconstruct the volcano-sedimentary evolution of the GVB: it developed at the Carboniferous/Permian boundary and experienced a first (bimodal) volcanic phase around 285 Ma. For the same time, indications for temporarily humid climate in the otherwise rather arid Early Permian are demonstrated (e.g. pyrite-bearing sandstones). During the Middle and Early Late Permian, increasing aridity is indicated by playa deposits, fanglomerates and subaerial ignimbrites, which mark a second (silicic) volcanic phase at 268 Ma. The detrital zircon age spectra are dominated by Late Variscan ages and thus demonstrate that older sedimentary and metamorphic rocks once forming the Variscan nappe edifice were already mostly eroded at that time. Finally, some larger-scale speculations are given which could indicate a causal connection between the widespread tectono-magmatic Mid-Permian Episode and the local development of the Glarus Verrucano basin.