DETRITAL ZIRCON AGES OF DEVONIAN AND EARLY CARBONIFEROUS SEDIMENTS IN THE SOUTHEASTERN RHEINISCHES SCHIEFERGEBIRGE (RHENO-HERCYNIAN ZONE, CENTRAL EUROPEAN VARISCIDES) – A MULTIDISCIPLINARY APPROACH AND PLATE TECTONIC IMPLICATIONS

The Rhenohercynian fold-and-thrust belt is one of the structural units of the European Variscides which have been interpreted by a number of studies as a collage of major and minor plates. These plates were successively accreted during Early Devonian to Late Carboniferous times and finally led to the beginning amalgamation of the supercontinent Pangaea. The Rheinisches Schiefergebirge as a part of the Rhenohercynian belt is a classical region of Devonian research providing a dense database of several thousands of papers published within the last 150 years on structural/tectonic development, palaeogeography, stratigraphy and facies. In the Rheinisches Schiefergebirge east of the river Rhine, several parautochthonous units occur, the latter already recognized by Kossmat (1927) who proposed the nappe tectonic concept for the Rhenohercynian for the first time. In terms of structural geology the southeastern part of the Rheinisches Schiefergebirge can be subdivided in the Lahn syncline (parautochthon) and the Dill syncline which are separated by the Hörre zone (allochthonous). Further to the southeast other allochthonous units occur, such as the Frankenbach imbrication zone and the Giessen nappe.

The cluster of U-Pb ages of detrital zircon grains point to a provenance of the debris from the Saxo-Thuringian zone or rock complexes of the Mid-German Crystalline zone for the allochthonous units. The zircon populations derived from the Saxo-Thuringian Zone are representative for a Gondwanan hinterland. In contrast, a Lower Devonian sandstone sample from the parauthochtonous Dill syncline shows a provenance, which is representative for Laurussia. The debris of this area seems to be derived from Baltica and Avalonia.

The aim of our talk is to present U-Pb LA-SF-ICP-MS ages of detrital zircons derived from Devonian and Lower Carboniferous siliciclastic sediments of autochthonous and allochthonous units of the southeastern Rheinisches Schiefergebirge within the context of comprehensive stratigraphical and geochemical data, sedimentary and tectonic implications. Based on a multi-disciplinary approach a modified plate tectonic concept will be presented.

Kossmat, F., 1927. Gliederung des varistischen Gebirgsbaus. Abhandlungen Sächsisches Geologisches Landesamt 1, 1-39.