Provenance of Upper Devonian clastic (meta)sediments of the Böllstein Odenwald (Mid-German-Crystalline-Zone, Variscides)

Abstract

Detrital zircons separated from paragneisses of the northern Bollstein Odenwald (Mid-German Crystalline Zone, Variscides) yielded Cambrian to Upper Devonian U–Pb ages. The age of the youngest detrital zircon population (371 ± 3 Ma) and the Lower Carboniferous metamorphic overprint indicate an Upper Devonian depositional age of the paragneiss protolith. The age spectra of detrital zircons suggest the latter to be derived from (1) Ordovician igneous rocks of the Saxothuringian Zone, (2) a late Cadomian magmatic arc (Tepla-Barrandian Unit) and (3) a Silurian-Devonian magmatic arc. Cadomian igneous activity is also documented by Cambrian zircon cores in Lower to Middle Devonian detrital zircons. Meso- and Paleoproterozoic detrital zircons, which are typical for the Old Red Continent and the Rhenohercynian Zone, are entirely lacking. The restricted Palaeozoic detrital zircon age spectrum is attributed to a Silurian-Devonian intra arc or trench setting. Both the lack of Mesoproterozoic detrital zircons and the striking similarity of the U–Pb ages of the detrital zircon obtained from the Bollstein Odenwald with U–Pb ages from crystalline rocks of the Saxothuringian basement, rules out that the Bollstein Odenwald is forming a tectonic window (Rhenohercynian lower plate) inside the Mid-German Crystalline Zone (Saxothuringian upper plate).