A juvenile arc terrane in the Mid-German Crystalline Zone: constraints from zircon U–Pb–Hf isotope data and implications for pre- to syn-Variscan evolution

Abstract Presently, little is known about the zircon age–Hf isotope record of (meta)sedimentary rocks exposed in the southernmost part of the Mid-German Crystalline Zone and adjacent Rhenohercynian Domain, preventing detailed reconstructions of the geodynamic evolution in Central Europe. In this study, such data are presented from Late Devonian to Viséan greywackes and granite gneisses of the Palatinate Forest (Mid-German Crystalline Zone) and the Harz Mountains (Rhenohercynian). These provide evidence that clastic sedimentary rocks in both realms were sourced from a so far unrecognized, juvenile oceanic arc terrane, which was initially formed at 490–570 Ma (εHf t up to + 13.0), and internally reworked at ca. 500, 400, 370 and 335 Ma (εHf t = + 2.0 to + 8.4), prior to Variscan collision and post-collisional magmatism at 330 Ma. Late Devonian arc reworking is indicated by zircon U–Pb ages of ca. 370 Ma estimated for the Albersweiler granite gneiss (εHf t = + 3.6 to + 7.7) and an amphibolite-facies paragneiss; other reworking events are indicated by the detrital zircon record. The results of data compilation further suggest that the oceanic arc terrane remained widely isolated from continental input within the Prototethys–Rheic oceanic realm until its collision with Avalonia at 335 Ma. The relics of the arc system became widely dispersed within the Saxothuringian, Rhenohercynian, Teplá-Barrandian, and Moldanubian domains during the Variscan collision and collapse. Graphical abstract