{{Geology of the Alps 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 (derived from ''Helveticus'':

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power ...

for Swiss). Rocks in the Helvetic zone are

sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

and were originally deposited at the southern margin of the European plate. The Helvetic zone correlates with the

French French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...

Dauphinois zone, French geologists often prefer the French name but normally this is considered the same thing.

Occurrence

In Switzerland the Helvetic zone is found in outcrops on the northern side of the Alpine mountain ranges. The French Alps consist mainly of Helvetic (Dauphinois) material. In Germany and Austria the Helvetic nappes crop out as a narrow band.

Subdivision

The Helvetic zone consists of a number of tectonically very different units. The "

Helvetic nappes {{Unreferenced, date=June 2019, bot=noref (GreenC bot) The Helvetic nappes (german: Helvetische Decken) 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 ...

" are a nappe stack that was thrust over the molasse of the

Molasse basin The Molasse basin (or North Alpine foreland basin) is a foreland basin north of the Alps which formed during the Oligocene and Miocene epochs. The basin formed as a result of the flexure of the European plate under the weight of the orogenic wedge ...

in the Alpine foreland. They are composed of

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Creta ...

marine

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms wh ...

, marls and

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

s. The Helvetic nappes are completely detached from their former

basement A basement or cellar is one or more Storey, floors of a building that are completely or partly below the storey, ground floor. It generally is used as a utility space for a building, where such items as the Furnace (house heating), furnace, ...

. The Helvetic nappes are thrust over the "

Infrahelvetic complex The Infrahelvetic complex is a tectonic unit in the Swiss Alps. It consists of autochthonous rocks of the former southern continental margin of the European Plate. The Infrahelvetic complex has been overthrusted by the Helvetic nappes, that partl ...

" in eastern Switzerland. The Infrahelvetic complex is composed of autochthonous Mesozoic sediments on top of Hercynian basement rock. The Mesozoic of this unit is contemporary with that of the Helvetic nappes, but deposited further north on the former

continental slope A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental marg ...

and therefore shallower in sedimentary facies. The Infrahelvetic is internally deformed by thrusting and

fold Fold, folding or foldable may refer to: Arts, entertainment, and media * ''Fold'' (album), the debut release by Australian rock band Epicure *Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot *Above ...

ing that continues into the Hercynian basement. Because basement and "cover" were not detached, geologists do not call the Infrahelvetic units "nappes". At places throughout the Alps the European basement was, after being detached of its cover rocks, tectonically uplifted in a late stage of the orogeny. Thus the "external massivs" were formed, places where the Hercynian basement rock crops out in large anticlinoria at the southern (or in France eastern) side of the Helvetic zone. Seen from the north (or in France from the west) the hard

competent Competence may refer to: *Competence (geology), the resistance of a rock against deformation or plastic flow. *Competence (human resources), a standardized requirement for an individual to properly perform a specific job *Competence (law), the me ...

crystalline A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

rocks of these external massivs form the first of the higher ranges of the Alps. These chains are (from southwest to northeast): the Mercantour, the

Massif des Écrins The mountains of the Massif des Écrins (; Écrins Massif) form the core of Écrins National Park in Hautes-Alpes and Isère in the French Alps.Belledonne Belledonne (french: link=no, La chaine de Belledonne, ) is a mountain range (french: link=no, massif) in the Dauphiné Alps (part of the French Alps) in southeast France. The southern end of the range forms the eastern wall of the mountains th ...

, the

Aiguilles Rouges The Aiguilles Rouges ("Red Needles") are a crystalline mountainous massif of the French Prealps, opposite the Mont Blanc Massif. The colour of the iron rich gneiss (metamorphique) mountains gives the range its name. The highest summit is the Aig ...

and the

Mont Blanc Massif The Mont Blanc massif (french: Massif du Mont-Blanc; it, Massiccio del Monte Bianco) is a mountain range in the Alps, located mostly in France and Italy, but also straddling Switzerland at its northeastern end. It contains eleven major indepen ...

, the

Aarmassif The Aarmassif or Aaremassif (German: ''Aarmassiv'') is a geologic massif in the Swiss Alps. It contains a number of large mountain chains and parts of mountain chains. Name The massif is named after the Aar, a river that has its source in the A ...

and the Gotthardmassif. Sigriswiler Rothorn

References

Geology of the western and central Alps, website of S.M. Schmid
Geology of the Alps Structural geology Geology of Switzerland Geology of Austria de:Helvetisches System it:Elvetico