Austroalpine Basement

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Alpenseminar by Georg Löwe


 On the 14h of  May we had a very interesting talk by Georg Löwe on the evolution of the Austroalpine Basement. This talk particularly particularly focused on Metamorphism, Geochronology and the Geodynamics of these basement sequences. These basement sequences outcrop at certain locations, which is highlighted on the figure below:
Overview of Austroalpine Basement units, after Thöni, 2006


In general, the Austroalpine Basement Units comprises a Nappe pile that is composed of several different sequences. This includes: pre-Variscan sediments and intrusions of various ages, including pre-Variscan, Permo-Triassic and Tertiary magmatism.

These units were exposed to various metamorphic events during the Variscan times, Permo-Triassic and during the Eo-Alpine orogeny. These are summarised on the following diagrams: 



Various metamorphic conditions experienced by the Austro-Alpine sequences, after Schuster et al., 2001


And, a more regional view, after Bousquet et al., 2008


We may now consider a cross-section to view the Metamorphic facies distribution and related magmatism and volcanism during the different stages of the geodynamic evolution:


Cross-section view, after Bousquet et al., 2008


To end, we can summarise the various metamorphic events as follows:

1. Variscan Metamorphism:

This is linked to the closure of Rheic Ocean and subsequent collision of Laurussia and Avalonia/Gondwana. MORB-type eclogites related to this process includes the c. 347 Ma Ötztal, the c. 350 Ma East Silvretta and the c. 336 Ma Ulten High crystalline units. 

2. Permo -Triassic Metamorphism 

This closely follows the break-up of Pangea and the opening and eventual closure of the Meliata Ocean. Peak metamorphism occurred c. 260 Ma and this can be associated with the Saualpe-Koralpe Complex.

3. Eo -Alpine Metamorphism 

This is linked to the opening and eventual closure of the Penninic Ocean. During this event the Austroalpine underwent a subduction polarity change from being the lower plate in Cretaceous times and the closure of the Meliata Ocean, to being the upper plate during the closure of the Penninic Ocean. Peak metamorphism occurred c. 100 Ma.


 Overview of the Austro-Alpine basement units, after Schuster and Stüwe, 2008 



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