Mechanisms of lateral extrusion and exhumation during orogenic indentation of the Eastern Alps

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1 Mechanisms of lateral extrusion and exhumation during orogenic indentation of the Eastern Alps Andreas Scharf, Silvia Favaro, Audrey Bertrand 1, Susanne Schneider, Mark Handy, Konrad Hammerschmidt, Sebastian Garcia, Claudio Rosenberg 2, Stefan Schmid 3 and colleagues at other institutions (see below). 1 Now at the Université Cergy-Pontoise, Cergy-Pontoise, France 2 Now at the Université Paul et Marie Curie, Paris, France 3 Now at ETH-Zürich, Switzerland The Tauern Window is the most prominent tectonic window of the Eastern Alps. It is also one of the few places in the Alps where one can see the entire history of Adria-Europe convergence, from subduction (84-45 Ma) through collision (40-23 Ma) to indentation of the Adriatic microplate (23 Ma - Present). The excellent exposure and vertical relief (c m) in the Tauern Window make this a good place to study such processes. The beautiful scenery makes the area even more attractive. We want to find out how folding and extensional exhumation were linked to orogenparallel motion. This is key to determining how Alpine-type mountain belts grow, both vertically and laterally, during plate indentation. Were the Eastern Alps pulled to the east during roll-back subduction in the Carpathians, or were they pushed to the east during indentation of the Adriatic microplate? So far, we have found that eastward motion of this part of the Alps during indentation of the Adriatic microplate involved increasing amounts of extensional exhumation going from the central part of the Tauern Window to its eastern margin. There, the entire window is bounded by a SE-dipping, low-angle extensional shear zone, the Katschberg mylonite belt. A similar low-angle extensional shear zone, the Brenner mylonite belt, dips to the west along the western boundary of the Tauern Window. The Katschberg belt was part of a system of stretching faults (in the sense of Means 1989) that was active during km-scale upright folding and doming. Our radiometric dating so far indicates that this coeval doming and lateral stretching occurred in Miocene time, primarily between 23 and 17 Ma in the eastern part of the Tauern Window, and between 23 and 11 Ma in the western part. One of the vexing problems still remaining is to reconcile the motions in the Tauern Window with the kinematics of Miocene-to-Recent subduction at the junction of the Eastern Alps, Carpathians and Dinarides. Do the structure in the orogenic crust mirror this subduction, or were the crust and mantle decoupled during indentation? We are pursuing these questions in an interdisciplinary fashion with a host of colleagues, including Roland Oberhänsli, Martin Ziemann (University of Potsdam), Ralf Schuster, Gerhard Pestal (Geological Survey of Austria), Bernhard Fügenschuh (University of

2 Innsbruck), and Stefan Schmid (ETH-Zürich). Our work is supported by grants from the German Science Foundation (Ha 2403/10, RO 2177/4, 2177/5). Fig.1: Tectonic overview of the project area after Schmid et al. in prep. Boxes indicate views in Figs.2 and 3.

3 Fig.2: View to SE of the southeastern part of the Tauern Window,. parallel to the Möll Valley. Locality is shown in Fig.1.

4 Fig.3: Type locality of the Katschberg Shear Zone at the Katschberg ski-resort (indicated in Fig. 1). View to the NNE shows European plate in the foowalll and Adriatic plate in the hangingwall of this shear zone. Fig.3: Group picture in the Mölltal area shows from left to the right: Mark Handy, Silvia Favaro, Andreas Scharf, Peter Gipper and Friedrich Hawemann. Abstracts 1. Favaro S., Handy M. R., Scharf A., Schuster R., and Pestal G., Exhumation structures in the Tauern Window and their relation to present-day crust-mantle structure in the Eastern Alps. Vol. 14, EGU , Vienna, Austria. 2. Favaro S., Schuster R., Handy M.R., Scharf A., and Pestal G., The Mallnitz synform and its relation to the Mölltal fault (Tauern Window, Eastern Alps, Austria). Vol. 14, EGU , Vienna, Austria. 3. Scharf A., Ziemann M. & Handy M.R., Peak-Temperature (Tp) estimates with Raman micro-spectroscopy on carbonaceous material (RSCM) as a tool for distinguishing tectonometamorphic regimes in the Tauern Window (Eastern Alps, Austria). EGU , Vienna, Austria.

5 4. Scharf A., Favaro S., Handy M.R. & Schmid S.M., Did Adriatic indentation or Carpathian roll-back subduction trigger rapid exhumation and lateral escape in the Eastern Alps? AGU 2011-T53D-06, San Francisco, U.S.A. 5. Schneider S. & Hammerschmidt, K., Dating ductile deformation, its onset, duration and termination: Examples from the western Tauern Window, Eastern Alps, Freiberg Colloquium 2012, Freiberg. 6. Bertrand A., Rosemberg C. & Garcia S., Fault slip analysis and late exhumation of the Tauern Window, Eastern Alps. Colloque en hommage à Jacques Angelier, Jussieu, Paris. 7. Favaro S., Hawemann F., Scharf A., Gipper P., Handy M.R. & Schmid, S.M., Tectonics of the eastern Tauern Window - Austria. GSA , Munich, Germany. 8. Scharf A., Favaro S., Handy M.R. & Schmid, S., Exhumation-related structures at the eastern margin of the Tauern Window (Eastern Alps). GSA , Munich, Germany. 9. Bertrand A., Rosemberg C., Garcia S., Gueydan F. & Fugenschuh B., Cooling Pattern, Fault-slip Analysis, and 2D Thermal Modelling in the Tauern Window. 10th Alpine Workshop CorseAlp2011, San Florant, Corse. 10. Favaro S., Hawemann F., Gipper P., Scharf A., Handy M.R., Schmid S.M., Stucture and Kinematics in the Sonnblick Area (Eastern Tauern Window - Austria). 10th Alpine Workshop CorseAlp2011, San Florant, Corse. 11. Scharf A., Favaro S., Handy M.R. & Schmid S.M., Exhumation-Related Structures at the Eastern Margin of the Tauern Window (Eastern Alps, Austria). 10th Alpine Workshop CorseAlp2011, San Florant, Corse. 12. Schneider S., Bertrand A. S., Favaro S., Garcia S., Hammerschmidt K., Handy M. R., Rosenberg C. L., Scharf A. and Schmid S. M., Erosive Denudation vs. Extensional Unroofing; A Discussion on Exhumation of the Tauern Window. 10 th Alpine Workshop CorseAlp2011, San Florant, Corse. 13. Bertrand A., Rosemberg C. & Garcia S., Fission track ages and Exhumation mechanisms of the Tauern Window, Eastern Alps. Vol. 12, EGU2010, Vienna, Austria. 14. Bertrand A., Rosemberg C. & Garcia S., Brittle deformation and exhumation mechanisms in the core of the Eastern Alps, the Tauern Window. Vol. 12, EGU2010, Vienna, Austria. 15. Scharf A., Schmid S.M. & Handy M.R., Coeval folding, extension and strike-slip faulting at the eastern end of an axial culmination in the Tauern Window (Eastern Alps). EGU , Vienna, Austria.

6 16. Schneider S., Rosenberg, C. L. & Hammerschmidt K., The Western Tauern Window (Eastern Alps): Timing and Interplay of Folds and Sinistral Shear Zones as Result of South-Alpine Indentation. Vol. 12, EGU , Vienna, Austria. 17. Schneider S., Hammerschmidt K. & Rosenberg C. L., Dating the Duration and Termination of Sinistral Shear in the Western Tauern Window: Implications for Indentation and Exhumation in the Eastern Alps. Vol. 12, EGU , Vienna, Austria. 18. Schneider S., Bertrand, A. S. & Rosenberg C. L., The Jaufen Fault: a Kinematic Link between the Tauern Window and South-Alpine Indentation. Vol. 12, EGU , Vienna, Austria. 19. Schneider S. & Hammerschmidt, K., Dating Deformation Using In-situ Techniques: Application of Rb-Sr and Ar-Ar Geochronology. Freiberg Colloquium. 20. Schneider S., Bungies N., Frütsch F., Kitzig C., Rosenberg C.L., Spanka M., von Nicolai C. & Wanner, M., Extent and Significance of Sinistral Shear along the South Western Border of the Tauern Window, Eastern Alps (Italy/Austria). Vol. 11, EGU , Vienna, Austria. 21. Schneider S. & Hammerschmidt, K., K-Ar Dating of Sinistral Deformation in the Upper Schieferhülle, South-Western Tauern Window (Eastern Alps). Vol. 11, EGU , Vienna, Austria. 22. Bertrand A., Rosemberg C. & Garcia S., Exhumation mechanisms of the Tauern window, Eastern-Alps. «AlpShop 2009», Cogne, Italy. 23. Scharf A., Handy M.R.,Hammerschmidt K., Rosenberg C.L & Oberhänsli R., Kinematics, Conditions and Timing of the Katschberg Normal Fault at the eastern end of the Tauern Window (Austria). «AlpShop 2009», Cogne, Italy. 24. Schneider S., Rosenberg, C. L. & Hammerschmidt K., Dating the Duration and Termination of Strike-Slip Displacements in the Tauern Window, Eastern Alps. «AlpShop 2009», Cogne, Italy. 25. Schneider S., Rosenberg, C. L. & Hammerschmidt K., In-situ Rb-Sr Dating of the SEMP Mylonites, Western Tauern Window, Eastern Alps. Vol. 9, EGU2007-A-09136, Vienna, Austria. 26. Schneider S. & Rosenberg, C. L., Kinematics of the SEMP-Fault in the Western Tauern Window (Stillupp Valley). 11 th TSK, Göttingen, Germany. Publications Rosenberg, C. L. & Schneider, S. 2008, The western termination of the SEMP fault (Eastern Alps) and its bearing on the exhumation of the Tauern Window. In: S. Siegesmund, B. Fügenschuh, and N. Froitzheim (eds.), Tectonic aspects of

7 the Alpine-Carpathian-Dinaride System, Geological Society of London, spec. publ., 298,

Changing patterns of exhumation and denudation in front of an advancing crustal indenter, Tauern Window (Eastern Alps)

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