imported>Ira Leviton: massivs→massifs - toolforge:typos

2025-06-27T07:49:16Z

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{{No footnotes|date=October 2024}}
{{Geology of the Alps}}

The '''Helvetic zone''', '''Helvetic system''' or the '''Helveticum''' is a [[geology|geologic]] subdivision of the [[Alps]]. The Helvetic zone [[outcrop|crops out]] mainly in [[Switzerland]], hence the name (derived from ''Helveticus'': [[Latin]] for Swiss). Rocks in the Helvetic zone are [[sedimentary rock|sedimentary]] and were originally [[sedimentation|deposited]] at the southern [[continental margin|margin]] of the [[Europe|European plate]]. The Helvetic zone [[correlation|correlates]] with the [[France|French]] '''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 [[tectonics|tectonically]] very different units. The "[[Helvetic nappes]]" are a [[nappe stack]] that was thrust over the [[molasse]] of the [[Molasse basin]] in the Alpine [[Foreland basin|foreland]]. They are composed of [[Mesozoic]] [[Marine (ocean)|marine]] [[limestone]], [[marl]]s and [[shale]]s. The Helvetic nappes are completely [[Decollement|detached]] from their former [[basement (geology)|basement]].

The Helvetic nappes are thrust over the "[[Infrahelvetic complex]]" in eastern Switzerland. The Infrahelvetic complex is composed of [[wiktionary:autochthonous|autochthonous]] Mesozoic sediments on top of [[Hercynian orogeny|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]] and therefore shallower in [[sedimentary facies]]. The Infrahelvetic is internally [[deformation (geology)|deformed]] by thrusting and [[Fold (geology)|fold]]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 massives" were formed, places where the Hercynian basement rock crops out in large [[anticlinorium|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 [[competency (geology)|competent]] [[crystalline rock|crystalline]] rocks of these external massifs form the first of the higher ranges of the Alps. These chains are (from southwest to northeast): the [[Mercantour]], the [[Massif des Écrins]], the [[Belledonne]], the [[Aiguilles Rouges]] and the [[Mont Blanc Massif]], the [[Aarmassif]] and the [[Lepontine Alps|Gotthardmassif]].
[[File:Sigriswiler Rothorn.jpg|thumb|right|200px|Sigriswiler Rothorn in the Emmental Alps]]

==References==
*[https://web.archive.org/web/20051219072231/http://pages.unibas.ch/earth/tecto/Members/Schmid/alps/schmid_html/Text_Schmid.html Geology of the western and central Alps, website of S.M. Schmid]

[[Category:Geology of the Alps]]
[[Category:Structural geology]]
[[Category:Geology of Switzerland]]
[[Category:Geology of Austria]]

[[de:Helvetisches System]]
[[it:Elvetico]]

Helvetic (geology) - Revision history

imported>Ira Leviton: massivs→massifs - toolforge:typos