Valais Ocean

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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

Paleogeographic terminology

Valais Ocean

Briançonnais zone
Piemont-Liguria Ocean
Apulian or Adriatic plate

The Valais Ocean is a subducted oceanic basin which was situated between the continent Europe and the microcontinent Iberia or so called Briançonnais microcontinent. Remants of the Valais ocean are found in the western Alps and in tectonic winodows of the eastern Alps and are mapped as the so-called "north Penninic" nappes.[1]

Tectonic history[edit]

After the breakup of Pangaea in the early Mesozoic age the continents Africa, South America, Europe and North America began to move away from each other. The breaking up or rifting was not a process that happened along one clear line. At the southern edge of the European plate the microcontinent Iberia began also to break away from Europe. In the western part of the rift that separated the two landmasses oceanic crust was formed in what is at present the Gulf of Biscay, while in the eastern part the Valais Ocean was formed.

When in the Cretaceous period Africa began to move towards Europe again the Valais Ocean was sandwiched between the two continents. To the east the Valais oceanic crust, together with a piece of Iberian continental crust (called the Briançonnais terrane) subducted beneath the Apulian plate, a part of the African tectonic plate that had begun to move independently. This process eventually lead to the formation of the Alps. To the west no subduction took place, but the Iberian plate moved along and against the European plate along a large transform fault, which lead to the formation of the Pyrenees.

Fragments of Valais oceanic crust have been obducted and can be found as ophiolites in the Penninic nappes of the Alps.

Name[edit]

The Valais Ocean has been named after the Swiss canton Valais.

Occurrences[edit]

In the eastern Alps remnants of the Valais are confined to tectonic windows and the northern margin of the Alps. They include oceanic sediments (e.g. radiolarites, turbidites) and oceanic crust (e.g. basalt, pillow lava). The windows in the overlying Austroalpine nappes reveal the underlying Penninic nappes. In the Engadin window remnants are found in the Pfundser zone. In the Tauern window the "Obere Schieferhülle". At the northern margin of the Alps the remnants are called Rhennodanubic flysch.[1]

In the western Alps remnants of the Vailais crop out in many areas of Switzerland and France. This includes the Cheval noir unit, the Versoyen unit, the Sion-Courmayeur Zone, the Niesen nappe, the Schlieren flysch, the Antrona unit, the Wägital flysch and the Prätigau Bündnerschiefer.[2]

References[edit]

  1. ^ a b Schmid, Stefan M.; Fügenschuh, Bernhard; Kissling, Eduard; Schuster, Ralf (30 April 2004). "Tectonic map and overall architecture of the Alpine orogen". Eclogae Geologicae Helvetiae 97 (1): 93–117. doi:10.1007/s00015-004-1113-x. Retrieved 23 February 2013. 
  2. ^ Bousquet, Romain. "Metamorphic structure of the Alps - Revised version". Retrieved 23 February 2013. 

See also[edit]