Austroalpine nappes

Last updated May 01, 2019

Geology of the Alps
The Alps
Tectonic subdivision
Helvetic Zone
Penninic nappes
Austroalpine nappes
Southern Alps
Formations & rocks
Bündner schist \| flysch \| molasse
Geological structures
Aarmassif \| Dent Blanche klippe \| Engadine window \| Flysch zone \| Giudicárie line \| Greywacke zone \| Hohe Tauern window \| Molasse basin \| Penninic thrustfront \| Periadriatic Seam \| Ivrea zone \| Lepontin dome \| Rechnitz window \| Rhône-Simplon line \| Sesia unit The Aarmassif or Aaremassif is a geologic massif in the Swiss Alps. It contains a number of large mountain chains and parts of mountain chains. The greywacke zone is a band of Paleozoic metamorphosed sedimentary rocks that forms an east-west band through the Austrian Alps. The Hohe Tauern window is a geological structure in the Austrian Central Eastern Alps. It is a window in the Austroalpine nappes where high-grade metamorphic rocks of the underlying Penninic nappes crop out. The structure is caused by a large dome-like antiform in the nappe stacks of the Alps. Contents Lithologies Geographic position Traces of the Eo-Alpine orogenic phase References
Paleogeographic terminology
Valais Ocean
Briançonnais zone
Piemont-Liguria Ocean
Apulian or Adriatic plate

The Austroalpine nappes are a geological nappe stack in the European Alps. The Alps contain three such stacks, of which the Austroalpine nappes are structurally on top of the other two (meaning they were thrusted over the other two). The name Austroalpine means Southern Alpine, because these nappes crop out mainly in the Eastern Alps (the Alps east of the line Lake Constance - Chur – Lake Como).

Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, and the processes by which they change over time. Geology can also include the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology significantly overlaps all other earth sciences, including hydrology and the atmospheric sciences, and so is treated as one major aspect of integrated earth system science and planetary science.

In geology, a nappe or thrust sheet is a large sheetlike body of rock that has been moved more than 2 km (1.2 mi) or 5 km (3.1 mi) above a thrust fault from its original position. Nappes form in compressional tectonic settings like continental collision zones or on the overriding plate in active subduction zones. Nappes form when a mass of rock is forced over another rock mass, typically on a low angle fault plane. The resulting structure may include large-scale recumbent folds, shearing along the fault plane, imbricate thrust stacks, fensters and klippe.

The Alps are the highest and most extensive mountain range system that lies entirely in Europe, separating Southern from Central and Western Europe and stretching approximately 1,200 kilometres (750 mi) across eight Alpine countries : France, Switzerland, Italy, Monaco, Liechtenstein, Austria, Germany, and Slovenia. The mountains were formed over tens of millions of years as the African and Eurasian tectonic plates collided. Extreme shortening caused by the event resulted in marine sedimentary rocks rising by thrusting and folding into high mountain peaks such as Mont Blanc and the Matterhorn. Mont Blanc spans the French–Italian border, and at 4,810 m (15,781 ft) is the highest mountain in the Alps. The Alpine region area contains about a hundred peaks higher than 4,000 metres (13,000 ft).

Because the Austroalpine nappes consist of material from the former Apulian or Adriatic plate, that was thrusted over the European plate, they are called allochthon nappes. In comparison with the other nappe stacks, they have experienced lower-grade metamorphism, which distinguishes them clearly from the Penninic nappes on which they rest.

In structural geology, an allochthon, or an allochthonous block, is a large block of rock which has been moved from its original site of formation, usually by low angle thrust faulting. An allochthon which is isolated from the rock that pushed it into position is called a klippe. If an allochthon has a "hole" in it so that one can view the autochthon beneath the allochthon, the hole is called a "window". Etymology: Greek; 'allo' = other, and 'chthon' = earth.

Metamorphic rock Rock which was subjected to heat and pressure causing profound physical or chemical change

Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock (protolith) is subjected to heat and pressure, causing profound physical or chemical change. The protolith may be a sedimentary, igneous, or existing metamorphic rock.

Lithologies

The Austroalpine nappes are fragments of the former continental shelf and continental slope of the Apulian or Adriatic plate. These fragments contain rocks from the continental basement as well as from sedimentary rocks deposited in these environments.

A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water known as a shelf sea. Much of the shelves were exposed during glacial periods and interglacial periods.

Basement (geology) Metamorphic or igneous rocks below a sedimentary platform or cover

In geology, basement and crystalline basement are the rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin. In the same way, the sediments or sedimentary rocks on top of the basement can be called a "cover" or "sedimentary cover".

Sedimentary rocks are types of rock that are formed by the accumulation or deposition of small particles and subsequent cementation of mineral or organic particles on the floor of oceans or other bodies of water at the Earth's surface. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. Before being deposited, the geological detritus was formed by weathering and erosion from the source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.

The basement rocks have experienced metamorphism related to their original depth in the Earth's crust, but in the Austroalpine nappes Alpine metamorphism (i.e. metamorphism related to the formation of the Alps) is fairly low grade to non-existent. The basement rocks can be greenschist facies to amphibolite facies, depending on their original depth. They are Paleozoic schists and (para-)gneisses intruded by granites of Variscan and Tertiary age.

Metamorphism is the change of minerals or geologic texture in pre-existing rocks (protoliths), without the protolith melting into liquid magma. The change occurs primarily due to heat, pressure, and the introduction of chemically active fluids. The chemical components and crystal structures of the minerals making up the rock may change even though the rock remains a solid. Changes at or just beneath Earth's surface due to weathering or diagenesis are not classified as metamorphism. Metamorphism typically occurs between diagenesis, and melting (~850°C).

In geology, the crust is the outermost solid shell of a rocky planet, dwarf planet, or natural satellite. It is usually distinguished from the underlying mantle by its chemical makeup; however, in the case of icy satellites, it may be distinguished based on its phase.

The Alpine orogeny or Alpide orogeny is an orogenic phase in the Late Mesozoic (Eoalpine) and the current Cenozoic that has formed the mountain ranges of the Alpide belt. These mountains include the Atlas, the Rif, the Baetic Cordillera, the Cantabrian Mountains, the Pyrenees, the Alps, the Apennine Mountains, the Dinaric Alps, the Hellenides, the Carpathians, the Balkan Mountains and the Rila-Rhodope massif, the Taurus, the Armenian Highlands, the Caucasus, the Alborz, the Zagros, the Hindu Kush, the Pamir, the Karakoram, and the Himalayas. Sometimes other names occur to describe the formation of separate mountain ranges: for example Carpathian orogeny for the Carpathians, Hellenic orogeny for the Hellenides or the Himalayan orogeny for the Himalayas.

On top of this basement rock, Permian and Mesozoic sedimentary and volcanic rocks were deposited. Shallow marine limestones are abundant, these limestones now form the mountain chains of the northern part of the Eastern Alps, which are therefore together called the Northern Calcareous Alps . Sometimes, the limestone has been turned into dolomite, as in the Austrian region Salzkammergut and the German region Allgäu.

The Permian is a geologic period and system which spans 47 million years from the end of the Carboniferous Period 298.9 million years ago (Mya), to the beginning of the Triassic period 251.902 Mya. It is the last period of the Paleozoic era; the following Triassic period belongs to the Mesozoic era. The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the city of Perm.

The Mesozoic Era is an interval of geological time from about 252 to 66 million years ago. It is also called the Age of Reptiles and the Age of Conifers.

Volcanic rock rocks composing or associated with volcanoes, volcanic activity or volcanism

Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and metamorphic rocks and constitute an important element of some sediments and sedimentary rocks. For these reasons, in geology, volcanics and shallow hypabyssal rocks are not always treated as distinct. In the context of Precambrian shield geology, the term "volcanic" is often applied to what are strictly metavolcanic rocks. Volcanic rocks and sediment that form from magma erupted into the air are called "volcaniclastics," and these are technically sedimentary rocks.

A special unit is the greywacke zone, a band of Paleozoic metamorphosed sedimentary rocks that forms an east-west band through the Austrian Alps. The greywacke zone crops out between the Mesozoic rocks of the Northern Calcareous Alps and the Austroalpine and Penninic basement rocks of the Central Eastern Alps. Stratigraphically, the greywacke zone can be up to 2 kilometres (1.2 mi) thick.

All of these lithologies were folded and thrusted, so that the basement rock can be found on top of the sediments and vice versa.

Geographic position

In Switzerland, the Austroalpine nappes have been eroded away except for a few isolated outcrops called the Sesia unit and the Dent Blanche klippe (the Matterhorn is the most outstanding example of an Austroalpine klippe). These remaining Swiss nappes have a different tectonic and metamorphic history than their counterparts in Austria, which is why they are not always considered a part of the Austroalpine nappes.

On the other hand, in Austria, the Austroalpine nappes cover the largest part of that country, except for a few windows like the Hohe Tauern window and the Engadin window.

Traces of the Eo-Alpine orogenic phase

Before the formation of the Alps in the lower and middle Tertiary period, the Austroalpine rocks experienced another deformation phase: the Eo-Alpine phase of mountain building that took place in the Cretaceous. The metamorphic grade increases to the east-south-east, so in a west-north-western direction, the traces become less severe. In the west of Switzerland, the event cannot be recognized. In Austria, however, Eo-Alpine eclogite lenses occur close to the Hohe Tauern window.

The Eo-Alpine phase is sometimes seen as the earliest phase of the Alpine orogeny. However, after the initial mountain-building, the tectonic plates moved away from each other. The next phase was more than 50 Ma later, so the events are often seen as unrelated.

Related Research Articles

The Alps form part of a Cenozoic orogenic belt of mountain chains, called the Alpide belt, that stretches through southern Europe and Asia from the Atlantic all the way to the Himalayas. This belt of mountain chains was formed during the Alpine orogeny. A gap in these mountain chains in central Europe separates the Alps from the Carpathians to the east. Orogeny took place continuously and tectonic subsidence has produced the gaps in between.

The Central Eastern Alps, also referred to as Austrian Central Alps or just Central Alps comprise the main chain of the Eastern Alps in Austria and the adjacent regions of Switzerland, Liechtenstein, Italy and Slovenia.

The Helvetic zone, Helvetic system or the Helveticum is a geologic subdivision of the Alps. The Helvetic zone crops out mainly in Switzerland, hence the name. Rocks in the Helvetic zone are sedimentary and were originally deposited at the southern margin of the European plate. The Helvetic zone correlates with the French Dauphinois zone, French geologists often prefer the French name but normally this is considered the same thing.

The Penninic nappes or the Penninicum are one of three nappe stacks and geological zones in which the Alps can be divided. In the western Alps the Penninic nappes are more obviously present than in the eastern Alps, where they crop out as a narrow band. The name Penninic is derived from the Pennine Alps, an area in which rocks from the Penninic nappes are abundant.

The Southern Alps are a geological subdivision of Alps that are found south of the Periadriatic Seam, a major geological faultzone across the Alps. The southern Alps contain almost the same area as the Southern Limestone Alps. The rocks of the southern Alps gradually go over in the Dinarides or Dinaric Alps to the south-east. In the south-west they disappear below recent sediments of the Po basin that are lying discordant on top of them.

The Dent Blanche nappe or Dent Blanche klippe is a geologic nappe and klippe that crops out in the Pennine Alps. The nappe is tectonostratigraphically on top of the Penninic nappes and by most researchers seen as Austroalpine.

The Sesia unit or Sesia nappe, also called the Sesia-Dent Blanche unit is a tectonic unit or terrane in the Swiss and Italian Alps. The zone crops out in the Pennine Alps and in the southeastern part of the Aosta Valley. It is widely seen as part of the Austroalpine nappes and correlated with the Dent Blanche nappe that crops out further to the northwest.

The Valais Ocean is a subducted oceanic basin which was situated between the continent Europe and the microcontinent Iberia or so called Briançonnais microcontinent. Remnants of the Valais ocean are found in the western Alps and in tectonic windows of the eastern Alps and are mapped as the so-called "north Penninic" nappes.

The Lepontine dome or Lepontin dome is a region of tectonic uplift in the Swiss part of the Alps. It is located in the Lepontine Alps and Glarus Alps.

The Penninic thrustfront is a major tectonic thrustfront in the French Alps. The thrustfront moves over a developing decollement horizon, and separates the (internal) high grade metamorphic rocks of the Penninic nappes from the (external) sedimentary rocks and crystalline basement of the Helvetic nappes. The last are in France often called zone Dauphiné or Dauphinois.

The Fatra-Tatra Area or the Tatra-Fatra Belt of core mountains is a part of the Inner Western Carpathians, a subprovince of the Western Carpathians. Most of the area lies in Slovakia with small parts reaching into Austria and Poland. The highest summit of the whole Carpathians, the Gerlachovský štít at 2,655 m (8,711 ft), lies in the High Tatras range which belongs to this area.

The Helvetic nappes are a series of nappes in the Northern part of the Alps and part of the Helvetic zone. They consist of Mesozoic limestones, shales and marls that were originally deposited on the southern continental margin of the European continent. During the Alpine orogeny they were thrusted north over a décollement and at the same time were internally deformed by folding and thrusting.

The Zermatt-Saas zone is a tectonic unit in the western part of the Alps. Its lithology is mainly ophiolite but there are some pelitic zones too.

The Western Carpathians are an arc-shaped mountain range, the northern branch of the Alpine-Himalayan fold and thrust system called the Alpide belt, which evolved during the Alpine orogeny. In particular, their pre-Cenozoic evolution is very similar to that of the Eastern Alps, and they constitute a transition between the Eastern Alps and the Eastern Carpathians.

The Pyrenees are a 430-kilometre-long, roughly east–west striking, intracontinental mountain chain that divide France, Spain, and Andorra. The belt has an extended, polycyclic geological evolution dating back to the Precambrian. The chain's present configuration is due to the collision between the microcontinent Iberia and the southwestern promontory of the European Plate. The two continents were approaching each other since the onset of the Upper Cretaceous (Albian/Cenomanian) about 100 million years ago and were consequently colliding during the Paleogene (Eocene/Oligocene) 55 to 25 million years ago. After its uplift, the chain experienced intense erosion and isostatic readjustments. A cross-section through the chain shows an asymmetric flower-like structure with steeper dips on the French side. The Pyrenees are not solely the result of compressional forces, but also show an important sinistral shearing.

The Engadin window or is a tectonic window that exposes penninic units lying below the austroalpine units in the alpine nappe stack. It has a roughly elliptical shape with the long axis striking northwest-southeast and dimensions of 55 x 17 km.

The geology of Austria consists of Precambrian rocks and minerals together with younger marine sedimentary rocks uplifted by the Alpine orogeny.

References

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