Helvetic (geology)

Last updated

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 Helvetic zone are sedimentary and were originally deposited at the southern margin of the European plate. The Helvetic zone correlates with the French Dauphinois zone, French geologists often prefer the French name but normally this is considered the same thing.

Contents

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 very different units. The "Helvetic nappes" are a nappe stack that was thrust over the molasse of the Molasse basin in the Alpine foreland. They are composed of Mesozoic marine limestone, marls and shales. The Helvetic nappes are completely detached from their former basement.

The Helvetic nappes are thrust over the "Infrahelvetic complex" 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 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 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, the Belledonne, the Aiguilles Rouges and the Mont Blanc Massif, the Aarmassif and the Gotthardmassif.

Sigriswiler Rothorn in the Emmental Alps Sigriswiler Rothorn.jpg
Sigriswiler Rothorn in the Emmental Alps

Related Research Articles

<span class="mw-page-title-main">Geology of the Alps</span> The formation and structure of the European Alps

The Alps form part of a Cenozoic orogenic belt of mountain chains, called the Alpide belt, that stretches through southern Europe and Asia from the Atlantic all the way to the Himalayas. This belt of mountain chains was formed during the Alpine orogeny. A gap in these mountain chains in central Europe separates the Alps from the Carpathians to the east. Orogeny took place continuously and tectonic subsidence has produced the gaps in between.

<span class="mw-page-title-main">Penninic</span> Geological formation in the Alps

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 Alps, where they crop out as a narrow band. The name Penninic is derived from the Pennine Alps, an area in which rocks from the Penninic nappes are abundant.

<span class="mw-page-title-main">Austroalpine nappes</span> Geological formation in the European Alps

The Austroalpine nappes are a geological nappe stack in the European Alps. The Alps contain three such stacks, of which the Austroalpine nappes are structurally on top of the other two. The name Austroalpine means Southern Alpine, because these nappes crop out mainly in the Eastern Alps.

<span class="mw-page-title-main">Aarmassif</span> Geologic massif in the Swiss Alps

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.

<span class="mw-page-title-main">Molasse basin</span> Foreland basin north of the Alps

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

<span class="mw-page-title-main">Penninic thrustfront</span>

The Penninic thrustfront is a major tectonic thrustfront in the French Alps. The thrustfront moves over a developing decollement horizon, and separates the (internal) high grade metamorphic rocks of the Penninic nappes from the (external) sedimentary rocks and crystalline basement of the Helvetic nappes. The last are in France often called zone Dauphiné or Dauphinois.

<span class="mw-page-title-main">Fatra-Tatra Area</span>

The Fatra-Tatra Area or the Tatra-Fatra Belt of core mountains is a part of the Inner Western Carpathians, a subprovince of the Western Carpathians. Most of the area lies in Slovakia with small parts reaching into Austria and Poland. The highest summit of the whole Carpathians, the Gerlachovský štít at 2,655 m (8,711 ft), lies in the High Tatras range which belongs to this area.

The Helvetic nappes are a series of nappes in the Northern part of the Alps and part of the Helvetic zone. They consist of Mesozoic limestones, shales and marls that were originally deposited on the southern continental margin of the European continent. During the Alpine orogeny they were thrust north over a décollement and at the same time were internally deformed by folding and thrusting.

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.

<span class="mw-page-title-main">Glarus thrust</span> UNESCO World Heritage Site in Switzerland

The Glarus thrust is a major thrust fault in the Alps of eastern Switzerland. Along the thrust the Helvetic nappes were thrust more than 100 km to the north over the external Aarmassif and Infrahelvetic complex. The thrust forms the contact between older (Helvetic) Permo-Triassic rock layers of the Verrucano group and younger (external) Jurassic and Cretaceous limestones and Paleogene flysch and molasse.

<span class="mw-page-title-main">Rhenohercynian Zone</span> Fold belt of west and central Europe, formed during the Hercynian orogeny

The Rhenohercynian Zone or Rheno-Hercynian zone in structural geology describes a fold belt of west and central Europe, formed during the Hercynian orogeny. The zone consists of folded and thrust Devonian and early Carboniferous sedimentary rocks that were deposited in a back-arc basin along the southern margin of the then existing paleocontinent Laurussia.

<span class="mw-page-title-main">Geology of the Western Carpathians</span>

The Western Carpathians are an arc-shaped mountain range, the northern branch of the Alpine-Himalayan fold and thrust system called the Alpide belt, which evolved during the Alpine orogeny. In particular, their pre-Cenozoic evolution is very similar to that of the Eastern Alps, and they constitute a transition between the Eastern Alps and the Eastern Carpathians.

<span class="mw-page-title-main">External massif</span>

An external massif is, in the geology of the Alps, a place where crystalline rocks of the European plate crop out. Such massifs are found north and west of the Penninic zone as tectonic windows in the Helvetic Zone. They differ from the crystalline nappes in that they were originally part of the European plate, while the Penninic nappes were part of the crust below various domains in the Tethys Ocean.

The Gotthard nappe is, in the geology of the Alps a nappe in the Helvetic zone of Switzerland. It consists of crystalline rocks that were, before the formation of the Alps, part of the upper crust of the southern margin of the European continent. As it names suggests, the Gotthard nappe lies in close proximity to the Gotthard Massif.

<span class="mw-page-title-main">Geology of the Pyrenees</span> European regional geology

The Pyrenees are a 430-kilometre-long, roughly east–west striking, intracontinental mountain chain that divide France, Spain, and Andorra. The belt has an extended, polycyclic geological evolution dating back to the Precambrian. The chain's present configuration is due to the collision between the microcontinent Iberia and the southwestern promontory of the European Plate. The two continents were approaching each other since the onset of the Upper Cretaceous (Albian/Cenomanian) about 100 million years ago and were consequently colliding during the Paleogene (Eocene/Oligocene) 55 to 25 million years ago. After its uplift, the chain experienced intense erosion and isostatic readjustments. A cross-section through the chain shows an asymmetric flower-like structure with steeper dips on the French side. The Pyrenees are not solely the result of compressional forces, but also show an important sinistral shearing.

<span class="mw-page-title-main">Carpathian Flysch Belt</span> Tectonic zone in the Carpathian Mountains

The Carpathian Flysch Belt is an arcuate tectonic zone included in the megastructural elevation of the Carpathians on the external periphery of the mountain chain. Geomorphologically it is a portion of the Outer Carpathians. Geologically it is a thin-skinned thrust belt or accretionary wedge, formed by rootless nappes consisting of so-called flysch – alternating marine deposits of claystones, shales and sandstones which were detached from their substratum and moved tens of kilometers to the north (generally). The Flysch Belt is together with Neogene volcanic complexes the only extant tectonic zone along the whole Carpathian arc.

<span class="mw-page-title-main">Geology of France</span> Overview of the geology of France

The regional geology of France is commonly divided into the Paris Basin, the Armorican Massif, the Massif Central, the Aquitaine Basin, the Pyrenees, the Alps, the Côte languedocienne, the Sillon rhodanien, the Massif des Vosges, the Massif Ardennais, the Alsace graben and Flanders Basin.

<span class="mw-page-title-main">Geology of Germany</span> Overview of the geology of Germany

The geology of Germany is heavily influenced by several phases of orogeny in the Paleozoic and the Cenozoic, by sedimentation in shelf seas and epicontinental seas and on plains in the Permian and Mesozoic as well as by the Quaternary glaciations.

The geology of Austria consists of Precambrian rocks and minerals together with younger marine sedimentary rocks uplifted by the Alpine orogeny.

The geology of Greece is highly structurally complex due to its position at the junction between the European and African tectonic plates.

References