Euramerican tonsteins: overview, magmatic origin, and depositional-tectonic implications

摘要: Abstract Carboniferous tonsteins (kaolinized volcanic-ash beds) of wide geographic distribution are known in both Europe and North America. Relict volcanic minerals common these Euramerican quartz (including beta-quartz paramorphs), zircon ilmenite; less magnetite, fayalite, rutile, monazite, xenotime, apatite sanidine. Data for two relatively thick (3–13 cm) widespread (>400 km) European (Erda Sub-Worsley Four-foot) indicate an increase detrital near the top beds which indicates mixing with normal clastic sediments, including introduction heavy (e.g., tourmaline garnet). These show multiple horizontal bedding, graded disturbed centimeter-scale scour surfaces. The Fire Clay tonstein America represents from one to five separate air-fall ash deposits as determined by bedding mineralogical analysis. features several episodes deposition very localized subsequent erosion bioturbation. Electron microprobe data glass inclusions a rhyolitic origin reveal chemical “fingerprints” valuable intra- inter-basinal correlations. However, tectonic framework American was quite different. In Europe, were associated Variscan collisional tectonics, whereas America, Ouachita activity, explosive volcanism Yucatan block, collision between South plates, formation Pangea.