The Hirnantian glaciation in the Alps - a provenance study in Ordovician to Silurian (meta)-sedimentary successions

Basic data for this project

Description

The Hirnantian glaciation marks a major global perturbation in the late Ordovician at around 445 Ma. Its centre was in northern Africa where a large ice sheet existed as evidenced by widespread glacial deposits. To the north, glaciomarine sediment was deposited on a broad shelf. From the Upper Ordovician to the Silurian, this shelf underwent strong extension and breakoff of various terranes, before collision started in the Devonian in the course of the Variscan orogeny. In the Alps, relics of these terranes are exposed, but were affected by a different style of Variscan and Alpine structural-metamorphic overprint, making a paleogeographic reconstruction difficult. Presently, competing models exist about the initial location of these terranes along the northern Gondwana shelf prior to break-off, and its detailed configuration within the Variscan Belt. In order to elucidate the location, width and structure of the peri-Gondwana shelf but also the post-break-off terrane drift history, sediment profiles from mainland Gondwana to the proto-Alps will be investigated, with a particular focus on sedimentary rocks deposited during the Hirnantian glaciation. New information will be derived by combining results of sediment facies analysis with a multi-proxy provenance study, comprising traditional provenance techniques (petrography, geochemistry, heavy mineral analysis) with in-situ U-Pb-dating of zircon and rutile, Hf isotopy of zircon and trace element analyses of rutile and garnet. The analyses will be carried out on samples taken from non- to medium-grade metamorphic, biostratigraphically well-constrained Ordovician to Silurian sections in the eastern and southern Alps with a major focus on the Carnic Alps, the Greywacke Zone, and the Gurktal Thrust System. Subsequently, these data will be compared with published data and with data from potential source areas in Africa presently studied by the applicants, comprising age-equivalent glacigenic sediment in Ethiopia and on the Arabian Peninsula. The results of this project will place (1) new constraints on the plate tectonic reconstructions of peri-Gondwana of the Alpine crustal segments, and (2) the temporal-spatial relationships of pre-Mesozoic basement exposed in the Alps, with those exposed in the Moldanubian and Saxothuringian zones. Furthermore, they will help us to reach (3) a better understanding of the effects of large continental ice sheets on sedimentation in adjacent marine systems.