CONTRASTING EOALPINE P-T EVOLUTIONS IN THE SOUTHERN KORALPE, EASTERN ALPS

The Koralpe crystalline complex and the Plankogel unit represent two l ithologically distinct units within the Koralpe region of the southeas ternmost Austroalpine crystalline basement. The Eoalpine P-T evolution of these two units is derived from new petrographical data. The Plank ogel unit and the Koralpe crystalline complex show markedly different P-T evolutions during the early stages of the Eoalpine event. The rock s of the Koralpe crystalline complex experienced eclogite facies condi tions with minimum pressures in the range of 15-16 kbar and temperatur es in excess of 700 degrees C. At the same time the Plankogel unit res ided in a shallower environment at pressures of 10-11 kbar and tempera tures of less than 600 degrees C. The tectonic emplacement of the Plan kogel unit into its present position on top of the Koralpe crystalline complex took place after the eclogite facies event in a relatively sh allow crustal level. After their juxtaposition the Koralpe crystalline complex and the Plankogel unit were affected by a common amphibolite facies metamorphic overprint. The distinctly different P-T evolution d uring the early stages of the Eoalpine event and a common history at l ater stages imply that major tectonic processes were operative in this part of the Austroalpine crystalline basement during the Cretaceous. Such processes may have involved subduction of oceanic and continental lithosphere which may have lead to significant crustal shortening wit hin the Austroalpine basement.