TSK 11 Göttingen 2006 Kühn et al.
 Oligocene emplacement of
 the Eclogite Zone of the cen-
 tral Tauern Window, Eastern
 Alps, Austria Poster
 Alexander Kühn1 Johannes Glodny2
 Uwe Ring3
 The EZ is an approximately 20 km long
 and 2–3 km wide coherent unit of the
 Tauern Window in the Eastern Alps. It
 is sandwiched between the Venediger-
 and the Glockner Nappe. While rocks
 in the EZ experienced HP metamor-
 phic conditions (24 kbar/650°C), rocks
 from the underlying Venediger Nappe
 and the overlying Glockner Nappe only
 record lower alpine metamorphic condi-
 tions with peak pressures not exceeding
 10 and 8 kbar, respectively. While meta-
 morphism in the EZ is well dated with
 an average age of 31.5±0.7Ma (Glodny
 et al. 2005) the final emplacement of
 these different nappes is still under de-
 bate.
 Thrusting of the EZ on top of the
 underlying Venediger Nappe is docu-
 mented by top-N shear-sense indicators
 in carbonaceous mica schists and my-
 lonites from the Dorfertal. The inter-
 nal structure of the EZ is characterized
 by N-vergent folds at the 100m to km
 scale. Fold axial planes are moderately
 to steeply dipping. The upper boundary
 of the EZ at its contact with the Glock-
 ner Nappe is characterized by blueschist
 to greenschist facies carbonate bearing
 mylonites. Stretching lineations in the
 ENE-striking mylonites dip on average
 20° to the ENE indicating sinistral shear
 1 Institut für Geowissenschaften, Becher-
 weg 21, Universität Mainz, D-55099 Mainz,
 Germany 2 GeoForschungsZentrum Pots-
 dam, Telegrafenberg C2, D-14473 Potsdam,
 Germany 3 Department of Geological Sci-
 ences, University of Canterbury, Christchurch
 8004, New Zealand
 with a slight extensional component.
 Two carbonate mylonites from the Dor-
 fertal, (samples EIS 14a and 14b; cal-
 cite, dolomite, muscovite, paragonite,
 tourmaline and rare garnet) yielded
 Rb/Sr mineral isochron ages between
 30.5 ± 0.8Ma and 29.1 ± 0.5Ma, in-
 terpreted to date the final thrust em-
 placement of the EZ above the Venedi-
 ger Nappe. The youngest ages are ob-
 tained from the most fine-grained mus-
 covites in these mylonites, which are fur-
 ther characterised by particularly high
 Sr concentrations. This may be due
 to a change of the Sr partition coeffi-
 cient between carbonate and muscovite
 during progressive deformation and co-
 eval decompression, related to the arag-
 onite to calcite phase transition. A
 Rb/Sr mineral isochron age of 31.4 ±
 0.4Ma from a mafic schist from the base
 of the Glockner Nappe (Seekopfscharte,
 sample EIS11) directly above the EZ
 dates blueschist facies metamorphism
 and sinistral shearing within the Glock-
 ner Nappe. Rb/Sr data from carbonate-
 dominated mylonites (sample EIS 6; cal-
 cite, dolomite, muscovite, rare amphi-
 bole and epidote), marking the upper
 boundary of the EZ in the Timmeltal
 provide a deformation age of 31.2 ±
 0.7Ma.
 Our data indicate that top-N thrust-
 ing at the base and large-scale fold-
 ing of the EZ was coeval with sinistral
 strike-slip faulting at its upper bound-
 ary and eclogite-facies metamorphism
 in the EZ. The data also indicate that
 today’s nappe architecture must have
 been established in less than 2Ma af-
 ter the eclogite facies metamorphism in
 the EZ. Very fast exhumation of the EZ
 was accomplished in a transpressional
 setting, which might explain why the ex-
 posed EZ is such a small unit.
 1
Kühn et al. TSK 11 Göttingen 2006
 References
 Glodny J, Ring U, Kühn A, Gleissner P &
 Franz G (2005) Crystallization and very
 rapid exhumation of the youngest Alpine
 eclogites (Tauern Window, Eastern Alps)
 from Rb/Sr mineral assemblage analysis.
 Contributions to Mineralogy and Petrology
 149, 699–712
 2