The Harz Mountains (Germany) – Cadomia meets Avalonia and Baltica: U-Pb ages of detrital and magmatic zircon as a key for the decoding of Pangea´s central suture

The nature of Pangea´s internal suture in the Central European Variscides is evaluated on the example of the Harz Mountains (Germany). U-Pb ages of detrital (n = 2273) and magmatic zircon grains (n = 170) were obtained by LA ICP-MS for provenance studies and absolute age dating. Provenance studies point to a docking of East Avalonia onto southern Baltica at c. 430 Ma and to a closure of the Rheic Ocean at c. 430-420 Ma. In the aftermath, the re-opening of a narrow Rhenish Seaway happened in mid-Devonian time. Devonian aged sedimentary rocks of the Harz Mountains were formed at the north-western (Rheno-Hercynian) and on the south-eastern (Saxo-Thuringian) margin of the Rhenish seaway. Deposits formed on the Rheno-Hercynian margin display sedimentary supply from southern Baltica, while most East Avalonian sources were buried and not available for erosion. Siliciclastic shelf deposits of Saxo-Thuringia were derived from Cadomia and its West African hinterland. Provenance studies and spatial arrangement of the tectonostratigraphic units in the Harz Mountains allow to reconstruct the style of obduction of the Harz Mountains onto the southeastern margin of East Avalonia (Rheno-Hercynian Zone). As a result of the closure of the Rhenish Seaway and the collision with the Mid-German Crystalline Zone, the Harz Mountains show a building plan strongly dominated by thin skinned tectonics. Our new data favour a two-plate model for the origin of Pangea´s internal suture in the Central European Variscides, but a re-opening of a narrow oceanic seaway is necessary after closure of the Rheic Ocean.