Eoalpine tectonics of the Eastern Alps: implications from the evolution of monometamorphic Austroalpine units (Schneeberg and Radenthein Complex)

Abstract

Monometamorphic metasediments of Paleozoic or Mesozoic age constituting Schneeberg and Radenthein Complex experienced coherent deformation and metamorphism during Late Cretaceous times. Both complexes are part of the Eoalpine high-pressure wedge that formed an intracontinental suture and occur between the polymetamorphosed Ö tztal-Bundschuh nappe system on top and the Texel-Millstatt Complex below. During Eoalpine orogeny Schneeberg and Radenthein Complexes were south-dipping and they experienced a common tectonometamorphic history from ca. 115 Ma onwards until unroofing of the Tauern Window in Miocene times. This evolution is subdivided into four distinct tectonometamorphic phases. Deformation stage D1 is characterized by WNW-directed shearing at high temperature conditions (550-600°C) and related to the initial exhumation of the high-pressure wedge. D2 and D3 are largely coaxial and evolved during high-to mediumtemperature conditions (ca. 450 to C550°C). These stages are related to advanced exhumation and associated with large-scale folding of the high-pressure wedge including the Ö tztal-Bundschuh nappe system above and the TexelMillstatt Complex below. For the area west of the Tauern Window, F2/F3 fold interference results in the formation of large-scale sheath-folds in the frontal part of the nappe stack (formerly called ''Schlingentektonik'' by previous authors). Earlier thrusts were reactivated during Late Cretaceous normal faulting at the base of the Ö tztal-Bundschuh nappe system and its cover. Deformation stage D4 is of OligoMiocene age and accounted for tilting of individual basement blocks along large-scale strike-slip shear zones. This tilting phase resulted from indentation of the Southern Alps accompanied by the formation of the Tauern Window.

The western end of the Eoalpine High‐Pressure Belt (Texel unit, South Tyrol / Italy)

“…Kozur et al ., ; Schweigl and Neubauer, ; Faupl and Wagreich, ; Janák et al ., ; Handy et al ., ; Stüwe and Schuster, ; Zanchetta et al ., ); however, its westernmost end is generally interpreted to represent an intracontinental HP shear zone (e.g. Schmid et al ., ; Sölva et al ., ; Krenn et al ., ). The various PT‐conditions for the eclogite facies overprinted rocks of the EHB published by different authors are listed in Table .…”

“…Due to the complex polyphase tectonometamorphic history of the (Eastern) Alps, hints of such geological processes are rare and often heavily overprinted, making it difficult to recognise, quantify and attribute them unequivocally. Recently published models for the high‐pressure Texel unit include Sölva et al ., ; Habler et al ., ; Zanchetta, ; Krenn et al ., ; Zanchetta et al ., , . Yet none of them fully answer the large‐scale, key aspects such a model has to account for: apparently opposing Eoalpine ‘subduction’ directions east and west of the Tauern Window; contradicting kinematics of Eoalpine thrusting and later normal faulting in the wider Ötztal area; the significance of the Eoalpine metamorphic pattern in the Ötztal‐Stubai nappe. …”

The Tauern Window (Eastern Alps, Austria): a new tectonic map, with cross-sections and a tectonometamorphic synthesis

“…90 Ma) eclogitic parageneses (Hoinkes and Thöni 1987;Habler et al 2006;Thöni 2006). It is southerly adjacent to the Schneeberg Unit that forms the part of the Schneeberg-Radenthein Unit (9) located west of the Tauern Window, a unit consisting of amphibolite grade sequences of meta-pelites of Late Palaeozoic age that only suffered Alpine metamorphism (Krenn et al 2011). The Schneeberg Unit, sandwiched between the northerly adjacent and structurally higher Ö tztal Nappe and the southerly adjacent Texel Unit, was formerly interpreted as a N-dipping normal fault zone (Sölva et al 2005).…”

“…The eclogite-facies Millstatt Unit is overlain by the amphibolite-grade Radenthein Unit of the Koralpe-Wölz Nappe system (Krenn et al 2011). This configuration is analogous to that found west of the Tauern Window, which suggests that these configurations were adjacent to each other before orogen-parallel extension contemporaneous with the formation of the Tauern Window tore them apart (Frisch et al 1998).…”

An den Grenzen des Waldes und der menschlichen Siedlung

“…Abb. 10A-C stellt die tektonische Entwicklung dieses Teils der Ostalpen ab der Oberkreide schematisch dar und basiert auf dem Modell von Krenn et al (2011). Der SC befindet sich heute in einer Position zwischen dem ÖC im Hangenden und dem TC im Liegenden (Sölva et al 2005).…”