Bündnerschiefer accretion in the western Eastern Alps

The Bündnerschiefer exposed in the Alps represent an accretionary wedge orginating from the accretion and subduction of the Penninic oceans and microcontinents. This accretionary wedge is exposed in the Prättigau- Halfwindow, the Engadine Window and the Tauern Window in different stages of metamorphic and structural overprint . A multidisciplinary approach will be used to reconstruct the geodynamic evolution of this accretionary wedge. Geochronological methods (Ar/Ar-, Rb/Sr- and Fission track-dating) in combination with lithostratigraphic, structural and petrological investigations should help to understand the evolution of the oceans from their rift-stage to the nappe stack existing today. The investigations will be concentrated on the central Engadine Window which represents an ideal cross-section through this accretionary wedge. Here all three main tectonic units of the Pennine realm are exposed in a short distance, allowing a deep insight in the structure of the Eastern Alps. Despite of blueschist and greenschist facies metamorphic overprint, sedimentological and locally even biostratigraphic observations are possible. However, the metamorphic overprint is sufficient to date metamorphic and partly structural events with geochronological methods. For regional comparisons limited investigations will be performed in the Prättigau area in the West, where the structure is simple, and in the East in the western Tauern Window, where the structural / metamorphic evolution of the Bündnerschiefer below the overriding Austroalpine thrust sheet becomes rather complex. The proposed systematic investigations shall yield further important arguments to solve the controversial problems - being debated since decades - if the main Bündnerschiefer unit of the Tauern Window (Glockner Nappe) has to be correlated with the southern (Ligurian) or northern ( Valais) Penninic trough. Finally the results of the various methods will contribute to reconstruct the evolutionary history of the Penninic realm from the rifting stage to the accretion, overthrusting and exhumation stages, including also the high pressure rocks. The results of the project will therefore also of importance for the various aspects of correlation between the Swiss Central Alps and the western Eastern Alps.