{{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 The Alps () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, Sw ...

and part of the

Helvetic zone {{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 for Swiss). Rocks in the Helve ...

. They consist 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 Cretace ...

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 w ...

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, especiall ...

s and

marl Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. Marl makes up the lower part ...

s that were originally deposited on the southern

continental margin 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 margin ...

of the European continent. During the Alpine orogeny they were

thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...

north over a décollement and at the same time were internally deformed by folding and thrusting.

Tectonic location

The Helvetic nappes are thrust over the Infrahelvetic complex and the external massifs of the Alps (like 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 ...

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 indep ...

). In Switzerland, Germany and Austria they are also thrust over the Molasse basin of the Alpine foreland. In turn, the Helvetic nappes were overthrust by the

Penninic nappes The Penninic nappes or the Penninicum, commonly abbreviated as Penninic, are one of three nappe stacks and geological zones in which the Alps can be divided. In the western Alps the Penninic nappes are more obviously present than in the eastern ...

from the south. In Switzerland these have been eroded away at most places but in Germany and Austria they are still covering the Helvetic nappes. Due to this the Helvetic nappes only crop out as a thin band in those countries, which forms the Northern Limestone Alps.

Lithology

The Helvetic nappes consist of Mesozoic

sedimentary rock 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 ...

s deposited on the former southern continental margin of the European plate. A narrow ocean, the Valais Ocean, existed south of Central Europe in the Mesozoic. This later developed into a

convergent plate boundary A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...

where the European plate subducted beneath the

Apulian plate The Adriatic or Apulian Plate is a small tectonic plate carrying primarily continental crust that broke away from the African Plate along a large transform fault in the Cretaceous period. The name Adriatic Plate is usually used when referring ...

. The sedimentary facies of the rocks from this age thus becomes deeper marine when the rocks were deposited further south. Therefore, the rocks of the Helvetic nappes have a shallower marine facies than the contemporary Bündner slates of the Penninic nappes; and a deeper facies than the rocks of the Infrahelvetic complex of Eastern Switzerland or contemporary sediments in the

Jura Mountains The Jura Mountains ( , , , ; french: Massif du Jura; german: Juragebirge; it, Massiccio del Giura, rm, Montagnas da Jura) are a sub-alpine mountain range a short distance north of the Western Alps and mainly demarcate a long part of the Fre ...

north of the Alps.

Tectonic location

Lithology

See also