Koller, Friedrich

English

Koller Friedrich

Schuster Ralf

Hoeck Volker

Hoinkes Georg

Bousquet R.

University of Szeged

Acta Mineralogica-Petrographica, Abstract Series 5, Szeged, 2006 www.sci.u-szeged.hu/asvanytan/acta.htm 56 METAMORPHIC EVOLUTION OF THE EASTERN ALPS  KOLLER, F.1, SCHUSTER, R.2, HOECK, V.3, HOINKES, G.4 & BOUSQUET, R.5 1 Department of Geological Sciences, University of Vienna, Geozentrum, Althanstr. 14, A-1090 Vienna, Austria E-mail: friedrich.koller@univie.ac.at 2 Geological Survey, Rasumofskygasse, A-1030 Vienna, Austria 3 Department of Geography, Geology and Mineralogy, University of Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg, Austria 4 University of Graz, 2 Universitätsplatz, A-8010 Graz, Austria 5 University of Basel, 30 Bernoulli Str., CH-4036 Basel, Switzerland   The Eastern Alps are the product of two orogenies, a Cre-taceous orogeny followed by a Cenozoic one (FROITZHEIM et al., 1996). The former is related to the closure of an em-bayment of the Neotethys ocean into Apulia (Meliata Ocean), the latter is due to the closure of the Alpine Tethys oceans between Apulia and Europe. The result of the orogenic movement is a complex nappe stack, which is built up from north to south and from bottom to the top by the following units (Plate 1 in SCHMID et al., 2004): The proximal parts of the Jurassic to Cretaceous European margin built up the northern Alpine foreland and the Helvetic nappes, whereas the distal margin is represented by the Subpenninic nappes. The Penninic nappes comprise the Piemont-Ligurian and Valais Ocean (Alpine Tethys) and the Briançonnais Terrain. Apulia consists of the northern Austroalpine nappes and the Southern Alpine unit (STAMPFLI & MOSAR, 1999). Rem-nants of the Neotethys embayment occur as slices within the eastern part of the Austroalpine nappe stack. Both orogenic events are accompanied by regional metamorphism of vari-able extent and P-T conditions. The Cretaceous (Eo-Alpine) metamorphism affects mainly the Austroalpine Nappes, the Penninic domain by the Cenozoic metamorphism, some units of the Lower Austroalpine Nappes show signs of both events. The distribution of the metamorphic facies zones in the Eastern Alps is mainly controlled by the northwards transport of the Austroalpine nappes. They show a Cretaceous meta-morphism and are thrusted over the Penninic domains with Tertiary metamorphism. The latter are exposed in the Eastern Alps only as tectonic windows.  The eo-Alpine (Cretaceous) metamorphic event is widespread within and restricted to the Austroalpine unit. It is related to the continental collision following the closure of an embayment of the Tethys Ocean during late Jurassic to Cre-taceous times. Recent investigations indicate that the northern part of the Austroalpine unit forms the tectonic lower plate. The southern parts and the north-eastern margin of the Southalpine unit acted as the tectonic upper plate during the continental collision following the disappearance of the oce-anic embayment (SCHMID et al., 2004). The peak of the eo-Alpine metamorphic event was reached at about 100 Ma, the youngest cooling ages are recorded at 65 Ma (THÖNI, 1999). The eo-Alpine metamorphism starts at the base of the lower plate with greenschist facies and increases structurally up-wards the nappe piles until eclogite facies is reached. It de-creases again in the uppermost nappes to sub greenschist facies. The whole section represents a transported metamor-phism. An overprint of the Variscan crystalline of the lower plate, prior to the eo-Alpine metamorphic event, controlled by a thermal Permian event is widespread. The Tertiary Alpine metamorphic event is due to the closure of the Jurassic to early Cenozoic Briançonnais and Valais oceans (Alpine Tethys). According to WAGREICH (2001) the re-arrangement of the Penninic-Austroalpine bor-der zone from a passive to an active continental margin starts at about 120 Ma. From that time on the oceanic lithosphere and slices from the northern margin of the Austroalpine unit (Lower Austroalpine units) were subducted towards the south below (Upper) Austroalpine units. The Tertiary event reaches blueschist facies conditions in some Mesozoic parts of Penninic windows and some units of the Lower Austroalpine (Tarntal nappe). Eclogite facies conditions followed by a blueschist event occur only in a narrow zone of the Tauern Window. The thermal peak ranges from greenschist to am-phibolite facies, the latter was only reached in the central part of the Tauern Window. After the thermal peak at about 30 Ma (BLANKENBURG et al., 1989) uplift and cooling is recorded by K-Ar and Ar-Ar ages on white micas and fission track ages on zircon and apatite (GRUNDMANN & MORTEANI, 1985; FÜGENSCHUH et al., 1998). In the lower nappes of the Lower Austroalpine units the Tertiary Alpine metamorphism overprints the Cretaceous metamor-phic event.  References BLANKENBURG, F. v., VILLA, I.M., BAUR, H., MORTEANI, G. & STEIGER, R.H. (1989): Contribu-tions to Mineralogy and Petrology, 101: 1–11. FROITZHEIM, N., SCHMID, S.M. & FREY, M. (1996): Eclogae Geologicae Helvetiae, 89(1): 81. FÜGENSCHUH, B., SEWARD, D. & MANCKTELOW, N. (1998): Terra Nova, 9: 213–217. GRUNDMANN, G. & MORTEANI, G. (1985): Jahrbuch der Geologischen Bundesanstalt Wien, 128: 197–216. SCHMID, S.M., FÜGENSCHUH, B., KISSLING, E. & SCHUSTER, R. (2004): Eclogae Geologicae Helvetiae, 97: 93–117. STAMPFLI, G.M. & MOSAR, J. (1999): Memorie di Scienze Geologiche, 51(1): 141–154. THÖNI, M. (1999): Schweizerische Mineralogische und Petrographische Mitteilungen, 79: 209–230. WAGREICH, M. (2001): Terra Nova, 13: 401–406.  brought to you by COREView metadata, citation and similar papers at core.ac.ukprovided by University of Szeged

Metamorphic evolution of the Eastern Alps

http://acta.bibl.u-szeged.hu/31710/1/mineralogica_as_005_056.pdf

Metamorphic evolution of the Eastern Alps

Abstract

Similar works

Full text

Available Versions

University of Szeged