Magmato-sedimentary Carboniferous to Jurassic evolution of the western Tauern window, Eastern Alps (constraints from U-Pb zircon dating and geochemistry)

Abstract

New geochronological U-Pb (LA-ICP-MS) zircon data and geochemical analyses from the Variscan orthogneisses and metavolcanic rocks in the western Tauern window are presented and used to reconstruct the pre-Alpine evolution of this area. The late-and post-Variscan stage in the Tauern window was characterised by distinct magmatic pulses accompanied by the formation of volcano-sedimentary basins. The magmatic activity started in the Visean (335.4 ± 1.5 Ma) with the intrusion of a K-rich, durbachitic biotite-granite (protolith of the Ahorn gneiss). Following a period of exhumation and erosion, Westfalian-Stefanian volcanics were deposited (Grierkar meta-rhyodacite: 309.8 ± 1.5 Ma; Venntal meta-rhyolite: 304.0 ± 3.0 Ma). A renewed magmatic pulse occurred in the Early Permian, producing large volumes of tonalites and granodiorites (Tux meta-granodiorite: 292.1 ± 1.9 Ma). The youngest magmatism is characterised by pyroclastic and tuffitic deposits (Pfitsch meta-rhyolite: 280.5 ± 2.6 Ma; Schönach valley meta-andesite: 279.0 ± 4.8 Ma). This volcanism was probably related to crustal extensional faulting within an intra-continental graben and horst setting, asthenospheric upwelling and heat flow increase due to the onset of the Permian rifting. The Permo-Triassic peneplanation and subsidence is documented by shallow marine and evaporitic deposits. Probably in the Middle Jurassic times, the area was flooded and in the Late Jurassic the whole area was covered by limestones, representing post-rift sediments on the southern European continental margin.

Pre-Mesozoic Alpine basements—Their place in the European Paleozoic framework

“…330-340 Ma age is characterized by high K and Mg contents (Bussy et al, 2000) with a partial source in the metasomatized lithospheric mantle. Com parable Mg-K magmatites are documented in the entire external domain (Debon et al, 1998;von Raumer and Bussy, 2004;von Raumer et al, 2012), including the basement of the Tauern Window (Lammerer, 1986;Veselá et al, 2011).…”

Geothermal drilling in an Alpine karst aquifer and its impact on downstream springs – A case study from Finkenberg, Tyrol, Austria

“…1), the northern limb is represented by several nappes (from S to N: Ahorn Nappe, Wolfendorn Nappe, Seidlwinkl-Modereck Nappe, Glockner Nappe and Matrei Zone, Innsbruck Quartz Phyllite Nappe). The Ahorn Nappe consists of variably deformed orthogneisses (mainly augen gneiss) with an emplacement age of 335 ± 1.5 Ma (U-Pb zircon, Veselá et al 2011). In the hanging wall of the orthogneisses the Jurassic Hochstegen Formation is exposed.…”