The Helvetic nappes ({{langx, de, Helvetische Decken) are a series of

nappe In geology, a nappe or thrust sheet is a large sheetlike body of rock that has been moved more than or above a thrust fault from its original position. Nappes form in compressional tectonic settings like continental collision zones or on the ...

s in the Northern part of the

Alps The Alps () are some of the highest and most extensive mountain ranges in Europe, stretching approximately across eight Alpine countries (from west to east): Monaco, France, Switzerland, Italy, Liechtenstein, Germany, Austria and Slovenia. ...

and part of the Helvetic zone. They consist of

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

s and

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

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 marg ...

of the European continent. During the

Alpine orogeny The Alpine orogeny, sometimes referred to as the Alpide orogeny, is an orogenic phase in the Late Mesozoic and the current Cenozoic which has formed the mountain ranges of the Alpide belt. Cause The Alpine orogeny was caused by the African c ...

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 Décollement () is a gliding plane between two rock masses, also known as a basal detachment fault. Décollements are a Deformation (geology), deformational structure, resulting in independent styles of deformation in the rocks above and below t ...

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 or Mont Blanc Massif). 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 from the south. In Switzerland these have been

eroded Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust and then transports it to another location where it is deposited. Erosion is disti ...

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 The Northern Limestone Alps (), also called the Northern Calcareous Alps, are the ranges of the Eastern Alps north of the Central Eastern Alps located in Austria and the adjacent Bavarian lands of southeastern Germany. The distinction from the ...

Lithology

The Helvetic nappes consist of Mesozoic

sedimentary rock Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...

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 where the European plate subducted beneath the

Apulian plate The Adriatic or Apulian plate is a small list of tectonic plates, 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 usu ...

. 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 ( ) are a sub-alpine mountain range a short distance north of the Western Alps and mainly demarcate a long part of the French–Swiss border. While the Jura range proper (" folded Jura", ) is located in France and Switzerla ...

north of the Alps.

Tectonic location

Lithology

See also