Provenance analysis of the Rhenohercynian Basin and its southern collision zone: transition from a Silurian volcanic arc to the Rhenohercynian shelf (Central European Variscides)

There are numerous contradictory models concerning the reconstruction of the Palaeozoic palaeogeography of the Central European Variscides. A key region is the suture zone, the Northern Phyllite Zone, between the southern continent Gondwana including Armorica and the northern continent Laurussia including the continents Avalonia and Baltica. The Northern Phyllite Zone hosts the Silurian volcanic arc of the Rheic Ocean. This volcanic arc has been interpreted as an island arc that was accreted together with the northern part of Armorica against Laurussia in the Lower Devonian. Our results of U–Pb age dating of detrital and magmatic zircon grains give constraints on the provenance of metasedimentary rocks and the extrusion age of the volcanic rocks of the Rhenish Massif and adjacent Northern Phyllite Zone of the Central European Variscides. These help to validate the geodynamic models. U–Pb data of zircon grains indicate that the Silurian arc of the Northern Phyllite Zone is a continental arc. It received detritus from the East Avalonian basement that points to a position at the southern plate boundary of Laurussia. This Silurian arc cannot be correlated with the Silurian to Devonian magmatic arc of the Mid-German Crystalline Zone, because the host rocks of the Silurian plutons received detritus from Armorica or Baltica. The volcanic rocks of the Northern Phyllite Zone are dated with the U–Pb zircon method from 442 to 431 Ma. During the latest Silurian (Pridolian), the volcanism vanished and Devonian shelf sediments accumulated on top of the continental arc. At the same time, numerous Devonian plutons intruded into the magmatic arc of the Mid-German Crystalline Zone. Palaeogeographic reconstructions suggest that the Brabant High, the eastern most part of Avalonia, is the most obvious source area for the Devonian sediments of the Rhenohercynian Basin. The U–Pb data of the detrital zircon grains of the Rhenohercynian Basin do not fit the Avalonian age spectrum of the Brabant High, which is characterized by a high proportion of Ediacaran zircon grains. The detritus of the Rhenohercynian Basin is dominated by Mesoproterozoic zircon grains. Ediacaran zircon grains are absent. This limits the possible source area of the Rhenohercynian Basin to West Baltica and to the early Palaeozoic sediments of South Norway, Sweden and Denmark. Our data, along with published results, indicate that there was no collision between the northern part of Armorica and Laurussia during the Lower Devonian in the German part of the Rhenohercynian Zone.