The Helvetic zone, Helvetic system or the Helveticum is a geologic

Geology

Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

 subdivision of the Alps. The Helvetic zone crops out

Outcrop

An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. -Features:Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be...

 mainly in Switzerland

Switzerland

Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....

, hence the name (derived from Helveticus: Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 for Swiss). Rocks in the Helvetic zone are sedimentary

Sedimentary rock

Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

 and were originally deposited

Sedimentation

Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...

 at the southern margin

Continental margin

The continental margin is the zone of the ocean floor that separates the thin oceanic crust from thick continental crust. Continental margins constitute about 28% of the oceanic area....

 of the European plate

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

. The Helvetic zone correlates

Correlation

In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....

 with the French

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 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

Tectonics

Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...

 very different units. The "Helvetic nappes

Helvetic nappes

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...

" are a nappe stack that was thrusted over the molasse

Molasse

The term "molasse" refers to the sandstones, shales and conglomerates formed as terrestrial or shallow marine deposits in front of rising mountain chains. The molasse is deposited in a foreland basin, especially on top of flysch, for example that left from the rising Alps, or erosion in the Himalaya...

 of the Molasse basin

Molasse basin

The Molasse basin is a foreland basin north of the Alps, that formed during the Oligocene and Miocene epochs. The basin formed due to the flexure of the European plate under the weight of the orogenic wedge of the Alps that was forming to the south....

 in the Alpine foreland

Foreland

Foreland is the easternmost point of the Isle of Wight. It is located three miles east of the town of Brading, and due south of the city of Portsmouth on the British mainland. It is characterised by a pub called the Crab and Lobster and various beach huts plus a beach cafe and a coast guard...

. They are composed of Mesozoic

Mesozoic

The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...

 marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

, marl

Marl

Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...

s and shale

Shale

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

s. The Helvetic nappes are completely detached

Decollement

Décollement is a gliding plane between two rock masses. In French, "décoller" means "to detach from" or "to rip off" and was first used by geologists studying the structure of the Swiss Jura Mountains, but is also known as a detachment zone. This is a structure of strata owing to deformation,...

 from their former basement

Basement (geology)

In geology, the terms basement and crystalline basement are used to define 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...

.

The Helvetic nappes are thrusted over the "Infrahelvetic complex

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....

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

Fold (geology)

The term fold is used in geology when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in...

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 crystalline 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

Massif des Écrins

The mountains of the Massif des Écrins form the core of the Écrins National Park in France.-Mountains:*Barre des Écrins 4102 m*La Meije 3983 m*Ailefroide 3954 m*Mont Pelvoux 3946 m*Pic Sans Nom 3913 m*Pic Gaspard 3883 m*Le Râteau 3809 m...

, the Belledonne

Belledonne

Belledonne is a mountain range in the Dauphiné Alps in southeast France. The southern end of the range forms the eastern wall of the mountains that surround the city of Grenoble....

, the Aiguilles Rouges

Aiguilles Rouges

The Aiguilles Rouges are a crystalline mountainous massif of the French Prealps, opposite the Mont Blanc massif. The color of the iron rich gneiss mountains gives the range its name. The highest summit is the Aiguille du Belvédère at...

 and the Mont Blanc Massif

Mont Blanc Massif

The Mont Blanc massif is a mountain range in the western Alps. It is named after Mont Blanc, at 4,810.45 m the highest summit of the Alps. It is located in France , Italy , and Switzerland...

, the Aarmassif

Aarmassif

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.-Geography:...

 and the Gotthardmassif

Lepontine Alps

The Lepontine Alps are a mountain range in the central part of the Alps. They are located in Switzerland and Italy .On the north the upper Rhône valley separate them from the Bernese Alps and the Furka Pass and the upper Reuss valley separates them from the Urner Alps; on the west the Simplon Pass...

.