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The Helvetic zone, Helvetic system or the Helveticum is a geology subdivision of the Alps. The Helvetic zone outcrop mainly in Switzerland, hence the name (derived from Helveticus: Latin for Swiss). Rocks in the Helvetic zone are sedimentary rock and were originally sedimentation at the southern margin of the Europe. The Helvetic zone correlation with the France Dauphinois zone, French geologists often prefer the French name but normally this is considered the same thing.
The Helvetic nappes are thrust over the "Infrahelvetic complex" in eastern Switzerland. The Infrahelvetic complex is composed of 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 and therefore shallower in sedimentary facies. The Infrahelvetic is internally deformed by thrusting and folding 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 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 crystalline rock 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.
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