Eastern Alps

from Wikipedia, the free encyclopedia
Simplified geological map of the Alps: In the northeast of the Alpine arc, predominantly eastern ( ) units bite out. 

The Ostalpin , also called Austroalpin in international scientific parlance , is originally the second southernmost and tectonically highest nappe pile in the Alps . It owes its name to its occurrence in the Eastern Alps and Austria , while it has already been almost completely eroded in the more prominent and deeply eroded Western Alps . Geographically, the Eastern Alps are divided into the Northern Limestone Alps , the Central Eastern Alps and the northern part of the Southern Limestone Alps .

tectonics

The Lungau and the Steirische Kalkspitze in the Niedere Tauern belong to the carbonate Central Eastern Alpine Mesozoic Era, which was actually superimposed on the crystalline, but here it is locally rolled up (inverse) and erosively exposed under the hanging basement. In the background the Upper Eastern Alpine Dachstein massif .

Palaeogeographic considers the Eastern Alps heard as the Southern Alps to the Adriatic plate , which in the Mesozoic an Africa upstream microplate was. In the course of the alpine mountain formation , the Eastern Alpine was sheared off from its lower crust, stacked and folded and also pushed horizontally far (estimated 100 km to 200 km) to the north over the southern edge of the old European plate ( Penninic , Helvetic ).

During the alpine thrust over the north upstream and subducted Penninic, the Eastern Alpine was divided into several partial ceilings, which in turn were stacked on top of each other like roof tiles. The originally southernmost area, the Oberostalpin , pushed over the Unterostalpin to the north. In turn, today's Northern Limestone Alps (Oberostalpin) and the Grauwackenzone , which were originally located in the most southerly position, pushed over the Lower Central Eastern Alpine, which is also sometimes referred to as the Upper Eastern Alpine Basement , Central Alpine Upper Eastern Alpine or Middle Eastern Alpine - some of the structural models are still the subject of ongoing research over the decades Further developments.

The Upper Eastern Alpine Northern Limestone Alps and the Greywacke Zone were completely pushed over the Penninic and Lower Central Eastern Alpine and are now north of both, whereby they themselves were intricately folded and stacked on top of each other as partial ceilings (Bajuvarikum, Tirolikum, Juvavikum).

During this thrust, not only the Penninic, but also the Lower Eastern Alps and the Lower Central Eastern Alps were sunk to greater depths and metamorphically overprinted under high pressure and temperature, so that Permomesozoic Central Eastern Alpine sediments now also appear as quartzites , marbles and shale (equivalents of the Lunz Formation, for example near chapels ). Well-known occurrences are in the western Ortler Alps , the Radstädter Tauern or in the Semmering region .

The Northern Limestone Alps, on the other hand, show at most a weak degree of metamorphosis (especially at their base). However, the Drauzug (also known as the Upper Central Eastern Alpine), which was "left behind" in the south of the Upper Eastern Alps, has a weak to locally medium degree of metamorphosis.

The overturned Penninic is almost completely covered by the Eastern Alps, it was only vaulted in tectonic windows and exposed by erosion: Lower Engadine windows , Tauern windows , Rechnitz windows .

The following table compares the different tectonic models:

Tollmann (1977) Penninic including Matreier Zone Unterostalpin excl. Matreier Zone Deepest Oberostalpin (Bajuvarikum), Mittelostalpin Higher Oberostalpin (Tirolikum, Juvavikum) incl. Drauzug, Grauwackenzone and Gurktaler Paleozoic, the highest crystalline in the Middle East
Froitzheim / Janák (2004) Penninic Lower Eastern Alps Lower Central Eastern Alps Upper Central Eastern Alps
Schmid et al. (2004) Penninic Lower Eastern Alps Deepest Northern Limestone Alp cover (Bajuvarikum), Upper East Alpine basement cover incl. Permomesozoic cover Higher Northern Limestone Alps and Grauwackenzone; highest proportion of the Upper Eastern Alpine basement blankets and their Permomesozoic cover

Rock content

The Eastern Alpine nappes consist at the very bottom of a pre-Alpine base of highly metamorphic rocks, especially gneiss and mica schists , which were formed in the Paleozoic , predominantly in the Variscan and Caledonian mountain formation (polymetamorphic basement). Today they make up the majority of the Central Eastern Alps, but can also still be found as relics in southern Switzerland (for example Matterhorn ).

Above this, at least in the eastern Alpine nappes that were originally furthest to the south, follows a weakly metamorphic sequence of slates , greywackes , phyllites , limestones and rocks of volcanic origin from the Variscan and Caledonian mountain formation; today, for example, they are in the greywacke zone , in Styria and north-eastern Carinthia to find.

The uppermost and youngest units are sediments predominantly from the Permomesozoic. Above all, carbonate rocks from the Triassic , Jura and Chalk (limestone and dolomite stones ) should be mentioned here, which were deposited in a tropical shallow sea on the Paleozoic subsurface and which today form, for example, the Northern Limestone Alps and the Drauzug (large part of the Gailtal Alps and northeastern part of the Karawanken ). In the lower Upper Triassic, a prominent layer of sandstones and shale clays that can be traced from afar is switched on ( Lunz Formation ), which covered the reefs until lime production began again. It can also be found in the tectonically independent southern Alps as a Raibl formation . The thickness of the Triassic sediments is greatest in the southernmost deposit areas (today the Northern Limestone Alps) , while it is more important in the northernmost (today Lower Eastern Alps) in the Jura (comparable to the Penninic to the north).

At the base of the carbonates, sometimes showing a clear transgression limit to the lying Paleozoic, a sequence of Upper Permian to Lower Triassic conglomerates (e.g. Präbichl Formation , Alpine Verrucano ) and sandstones ( Werfen Formation ) can be observed, which go upwards in the Middle Triassic Limes.

The very youngest parts of the Permomesozoic are sediments from the Upper Cretaceous to the early Paleogene (formerly known as the Old Tertiary ), which are deposited in sea gullies and basins during the already beginning Alpine unfolding ("Old Alpine" or "Eoalpine" mountain formation) and called the Gosau Group . The layers of the Gosau group show a clear angular discordance compared to the Triassic to Lower Cretaceous layers , which were already folded in the Cretaceous , but were then further deformed in the course of the Jungalpid mountain formation (higher Paleogene, deeper Neogene ), included in the ceiling structure and sometimes wedged between older ceilings and sheds.

Occurrence

The occurrences of the various stratigraphic and tectonic levels can be shown in the following table:

Lower Eastern Alpine ceilings Upper Eastern Alpine: Lower Central Eastern Alpine Ceilings Oberostalpin: Upper Central Eastern Alps
Permomesozoic Eastern Grisons (eg. Piz Ela ), southern Tux Alps ( Tarn Valley ceiling ), Radstädter Tauern , change window , Wiesmather window;
Schmid also considered the permomesozoic cover of the Upper Eastern Alpine basement blankets: Mürz Valley - Semmering , western edge of Leithagebirge and Hundsheimer Berge (already convey to the Little Carpathians ) 		deepest nappes of the Northern Limestone Alps (Bajuvarikum), Hoch Ducan , Sesvenna Group , western Ortler Alps , southern edge of the Rätikon , Brenner Mesozoic ( Kalkkögel , Serles chain, Tribulaune ), narrow deposits in the Nockberge ( Stangalm Mesozoic ) and Murbergen , Eastern edge of the Seckauer Tauern (Alpine Verrucano) higher nappes in the Northern Limestone Alps (Tirolikum, Juvavikum) including the Gosau basin , Blaser ceiling (above the Brenner Mesozoic), narrow deposits in the Nockberge (rolled up and overturned on the Pfannock), Kainach -Gosau, Gosau sandwiched under the Graz Paleozoic - Shed, Krappfeld , Sankt Paul im Lavanttal , Drauzug with the northeastern Karawanken ( Hochobir , Petzen ) and the main ridge of the Gailtal Alps ( Dobratsch , Reisskofel group , Lienz Dolomites)
weakly metamorphic Paleozoic (is missing) (is missing) Steinacher blanket - Sattelberg , Grauwackenzone , Eisenkappel , Gurktaler blanket (eastern Nockberge ) - Murau Paleozoic, Grazer Paleozoic , Sausal , Possruck , small island-like occurrences in southern Burgenland
polymetamorphic basement Sesia zone / Dent-Blanche blanket of ( Matterhorn ), eastern Graubünden ( Piz d'Err , Piz Bernina ), change window , Wiesmather window;
Schmid also considered the upper eastern alpine basement blankets: Tux Alps (Innsbruck quartz phyllite), Mürz Valley ( Stuhleck ), Bucklige Welt , Ödenburger Gebirge , Leithagebirge , eastern edge of the Hundsheimer Berge (already convey to the Little Carpathians ) 		Silvretta , Ötztal and Stubai Alps , eastern Ortler Alps , southern edge of the Venediger group ( Lasörling ), Schober group , Bundschuh - western Nock Mountains , Niedere Tauern , Seetal Alps , Saualpe , Bacher Mountains , Poßruck , Koralpe , Pack and Stubalpe , Gleinalpe , Troiseck - Floning -Train classic Oberostalpin (Tollmann): individual small miners at the base of the Grauwackenzone (crystalline from Anger , Kaintalegg , Traidersberg );
Upper Central Eastern Alps : also Villgraten Mountains , Kreuzeck Group , base of the Gailtal Alps , Eisenkappel

literature

Individual evidence

  1. ↑ Schmid et al., 2004, p. 105
  2. ↑ Froitzheim
  3. ↑ Christof Kuhn: Excursion suggestions in Austria and the surrounding area: Präbichl - Eisenerz (Styria): Transgression Polsterkalk - Präbichlschichten , accessed on November 22, 2018
  4. ↑ Schmid et al., 2004
  5. ↑ Froitzheim
  6. ↑ Christof Kuhn: Selected chapters on the Alps: Triaskalke des Oberostalpin in the Nockberge , accessed on November 22, 2018
  7. ↑ Schmid et al., 2004
  8. ↑ Froitzheim