Tauern window

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Geological map of the Tauern Window

Tauern window is the geological name of a region in the central Alps in Austria , in which window-like Penninic ceilings and possibly also Helvetic ceilings , framed by rocks from the Eastern Alps , emerge. The tectonically deepest components of the Tauern window are the central gneiss cores surrounded by rocks of the so-called slate envelope. The smaller Engadine window located further to the west as well as the Gargellen window in Vorarlberg and the Rechnitz window at the eastern end of the Alps are of similar origin and geological position .

location

Simplified geological map of the Alps. The Tauern window is clearly visible in the right half of the picture as a larger exclave of Penninic units marked in purple in the middle of the Eastern Alpine units shown in blue.

The Tauern window is located in the Austrian federal states of Tyrol , Salzburg and Carinthia between the Brenner Pass in the west and the Schladming - Mauterndorf line in the east, its most south-westerly corner is in South Tyrol and therefore already in Italy . It has a length of about 176 km from the southwest corner south of the Brenner to Schladming in the northeast and a north-south extension of about 30 km between Mittersill and Matrei . At its widest point between Sankt Johann im Pongau and Spittal , it measures almost 54 km. Its rocks essentially make up the Zillertal Alps and the eponymous Hohe Tauern .

Emergence

Shown in simplified form the basis of the period made Malm to Lower Cretaceous existing former Piedmont Ocean , the original rock of today Tauernfenster disrupted rocks.

In the course of the formation of the Alps , the ocean closed, and in the Cretaceous and Tertiary times its rocks were pushed over like a blanket by the rock formations of the Eastern Alps and in this way (geologically) sunk relatively quickly into the depths. From the metamorphic (“ crystalline ”) rocks in the Tauern window, a former cover thickness of more than 10 km can be derived. The rocks were subject to several metamorphoses , changed their mineral content accordingly and became the crystalline rocks that are pending today. For example, an early, retrograde, eclogite facial metamorphosis (with pressures of 1.9 to 2.2 GPa and temperatures of 600 to 630 ° C) can be followed by a later blue schist facial metamorphosis (with pressures of 0.9 to 1.0 GPa and temperatures from 400 to 450 ° C) can be distinguished; Both metamorphoses belong to the high-pressure-low temperature (HP / LT) type, which is characteristic of subduction zones . After the sinking, the rocks were excavated geologically just as quickly.

Towards the end of the Oligocene , rocks from the Tauern Window were exposed to a greater extent on the surface of the earth for the first time, as can be seen from the appearance of characteristic heavy minerals in the sediments of the Alpine Molasse zone . The uplift of the Alps - and with it the Tauern Window - continues today. The active processes are weathering and erosion, so that the Tauern window slowly increases in the course of time to the extent that the formerly covering rocks of the Eastern Alps are eroded.

The Tauern window as a Pennin-Helvetian double window

Some geologists describe the Tauern window as a double window in which not only Penninic but also Helvetic units appear. The lower slate shell and the central gneiss are assigned to the Helvetic system. The reason for this assumption are studies which have shown that the sequence of layers in the Tauern window partially corresponds to the European continental margin in the Helvetian facies. The Malmian high- rise marbles can be compared with the Quintner limestone in the Helvetian area.

Otto Thiele spoke of a Helvetic facies room in the Tauern window for the first time in 1970. Bernd Lammerer called for a tectonic allocation to the Helvetic area and thus the definition of the Tauern window as a Pennin-Helvetic double window in 1986.

This view can also be found in more recent publications. The working group around Stefan M. Schmid is of the opinion that the lower slate shell of the Tauern Window, like the central gneiss, belongs to the Sub-Penninic, which contains tectonically strongly deformed remnants of the European continental margin, i.e. does not come from the actual Pennine Ocean. Likewise, in his Geology of the Alps , published in 2009, Othmar Adrian Pfiffner is in favor of assigning certain parts of the layer sequence of the Tauern Window to the Helvetic.

Scientific importance

The existence of the Tauern Window was an important milestone in the history of geological exploration of the Alps in understanding mountain engineering. Early mapping work was undertaken in 1853 by Marko Vincenc Lipold and his assistants Dionýs Štúr and Carl Ferdinand Peters , which were continued by other geologists over the next few years of the second half of the 19th century.

In the subsequent work of the first half of the 20th century, the Alps were thoroughly geologically investigated and the subdivision of the major units of the southern , eastern, Penninic and Helvetic units, which is still valid today , was established. The Tauern window was assigned to the Penninic and its geological structure was explored in the main features. Numerous works on geochemistry and isotope geology appeared from the beginning of the 1970s, and since around 1980 the processes of the Alpid mountain formation have been interpreted in terms of plate tectonics .

In 1903, Pierre-Marie Termier put forward the theory that the Western Alps in Eastern Switzerland disappear under the Eastern Alps and reappear in a tectonic window in the Hohe Tauern. This statement sparked a decade-long geological dispute between fixists and mobilists . Today it is clear that Termier's theory is true: the rocks of the Eastern Alps were pushed at least 150 km over the entire area of ​​the Tauern window.

literature

  • Harald Rost: On the geology, petrography and tectonics of the Pennine, the Matreier Zone and the old crystalline . Erlangen 1989 (diploma thesis, University of Erlangen, pdf version ).
  • SM Schmid, B. Fügenschuh, E. Kissling and R. Schuster: Tectonic map and overtall architecture of the Alpine orogen . In: Eclogae geologicae Helvetiae . tape 97 . Birkhäuser Verlag, 2004, ISSN  0012-9402 , p. 93–117 ( pdf version ).
  • Reinhard Schönenberg, Joachim Neugebauer: Introduction to the geology of Europe . 4th edition. Verlag Rombach, Freiburg 1981, ISBN 3-7930-0914-9 .
  • Alexander Tollmann: Eastern Alps Synthesis . Deuticke, Vienna 1963.
  • Karl Krainer: Hohe Tauern National Park GEOLOGY - Scientific writings . 2nd Edition. Carinthia University Press, Klagenfurt 2005, ISBN 3-85378-585-9 , p. 23-75 .

Individual evidence

  1. ^ G. Hoschek: Thermobarometry of metasediments and metabasites from the Eclogite zone of the Hohe Tauern, Eastern Alps, Austria . In: Lithos . tape 59 , 2001, p. 127-150 .
  2. ^ R. Zimmermann et al .: Eocene high pressure metamorphism in the Penninic units of the Tauern Window (Eastern Alps): evidence from Ar / Ar dating and petrological investigations . In: Contrib. Mineral. Petrol. tape 117 , 1994, pp. 175-186 .
  3. ↑ Otto Thiele: On the stratigraphy and tectonics of the slate shell of the western Hohe Tauern . In: Negotiations of the Federal Geological Institute . Vienna 1970, p. 230–244 ( digital version [PDF; 584 kB ; accessed on August 19, 2018]).
  4. ↑ Bernd Lammerer: The autochthon in the western Tauern window . In: Yearbook of the Federal Geological Institute . tape 129 . Vienna 1986, p. 51-67 ( PDF file ).
  5. ↑ Schmid et al. 2004, p. 108
  6. ^ O. Adrian Pfiffner: Geology of the Alps . Haupt-Verlag, Bern 2009, ISBN 978-3-8252-8416-9 , p. 47 .
  7. ↑ Harald Rost: Part B: History of Research. In: On the geology, petrography and tectonics of the Pennine, the Matreier Zone and the Altkristalline between Pürschbach and Grossklausenbach (Durreck Group, Ahrntal, South Tyrol). 1989, accessed December 1, 2009 .

Coordinates: 47 ° 0 '  N , 12 ° 30'  E