The Gotthard nappe (German : Gotthard-Decke, in older literature called the Gotthard Massif) 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 (the northern margin of the Alpine Tethys Ocean). As it names suggests, the Gotthard nappe lies in close proximity to the Gotthard Massif.
The Gotthard nappe is found south of its larger neighbour, the Aarmassif. The two crystalline zones are separated by a thin zone of metamorphosed and strongly deformed sedimentary cover rocks of the Tethys sea. In the south, the Simano and Adula nappes lie on top of the Gotthard nappe.
The Gotthard nappe crops out in an elongated strip through the Central Alps. This outcrop begins west of the mountain ridge between the Binntal and the Goms (the valley of the Rhone) east of Brig. It stays south of the Goms and south of the Furka Pass, Andermatt, north of Airolo in the Valle Leventina, south of the Oberalp Pass, Disentis and ends south of the eastern part of the Surselva (the valley of the Vorderrhein).
The outcrop can be divided into three parts or zones: a central core of Ordovician orthogneiss, called the Streifengneis ("striped gneiss"); flanked on both sides by zones of mica schist or paragneiss. The northern paragneiss zone contains lenses of various lithologies, such as calcareous schists, amphibolite, eclogite, peridotite (mostly thoroughly serpentinized) and gabbro. The southern paragneiss zone contains characteristic hornblende-garnet schists called Garbenschiefer, part of the Tremola series. [1]
The crystalline rocks of the Gotthard nappe carry strong traces of at least two older orogenies before the Alpine orogeny. The oldest phase, sometimes (erroneously) called "Caledonian", took place in the Ordovician. The paragneiss of the Gotthard nappe was once oceanic sediment, which was deformed into an accretionary wedge during this orogeny. The gabbros and peridotites, now lenses in the paragneiss, probably represent pieces of oceanic crust underneath these sediments, that were incorporated into the Ordovician accretionary wedge. The eclogite metamorphism has been dated at about 470 Ma (million years ago). [1]
In the late stages of the Ordovician orogenic phase, granitoid magma bodies intruded, especially granite. During the Hercynian orogeny, about 320 Ma, all of these units were strongly deformed. Today, the Ordovician intrusives form the Streifengneis of the central zone. The Hercynian orogeny ended with another phase of granitoid intrusions. Four Hercynian intrusive bodies are found in the current outcrop of the Gotthard nappe: the Rotondo granite north of the Val Bedretto, the Fibbia and Gamsboden granites close to the Gotthard Pass and the Cristallina granite around the Lukmanier Pass. These intrusions have ages between 305 and 290 Ma. [1]
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.
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. The Helvetic zone correlates with the French Dauphinois zone, French geologists often prefer the French name but normally this is considered the same thing.
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.
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.
The Bündner schist or Bündner slate is a collective name for schistose rocks that form a number of geologic formations in the Penninic nappes of the Alps. Bündner schists were originally marine sediments that underwent metamorphism at large depths.
The geology of the Iberian Peninsula consists of the study of the rock formations on the Iberian Peninsula, which includes Spain, Portugal, Andorra, and Gibraltar. The peninsula contains rocks from every geological period from the Ediacaran to the Quaternary, and many types of rock are represented. World-class mineral deposits are also found there.
The Armorican Massif is a geologic massif that covers a large area in the northwest of France, including Brittany, the western part of Normandy and the Pays de la Loire. It is important because it is connected to Dover on the British side of the English Channel and there has been tilting back and forth that has controlled the geography on both sides.
The Saxothuringian Zone, Saxo-Thuringian zone or Saxothuringicum is in geology a structural or tectonic zone in the Hercynian or Variscan orogen of central and western Europe. Because rocks of Hercynian age are in most places covered by younger strata, the zone is not everywhere visible at the surface. Places where it crops out are the northern Bohemian Massif, the Spessart, the Odenwald, the northern parts of the Black Forest and Vosges and the southern part of the Taunus. West of the Vosges terranes on both sides of the English Channel are also seen as part of the zone, for example the Lizard complex in Cornwall or the Léon Zone of the Armorican Massif (Brittany).
The Mid-German Crystalline High is a structural high in the Paleozoic geology of Germany. The high forms a northeast-southwest oriented zone through Germany, but actual rock outcrops are sparse since Paleozoic basement rocks are in most of central Germany overlain by younger sedimentary rocks. The Mid-German Crystalline High crops out in the Odenwald, the Spessart, the northern Vosges and some small other massifs.
The Moldanubian Zone is in the regional geology of Europe a tectonic zone formed during the Variscan or Hercynian Orogeny. The Moldanubian Zone crops out in the Bohemian Massif and the southern part of the Black Forest and Vosges and contains the highest grade metamorphic rocks of Variscan age in Europe.
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.
The Massif Central is one of the two large basement massifs in France, the other being the Armorican Massif. The Massif Central's geological evolution started in the late Neoproterozoic and continues to this day. It has been shaped mainly by the Caledonian orogeny and the Variscan orogeny. The Alpine orogeny has also left its imprints, probably causing the important Cenozoic volcanism. The Massif Central has a very long geological history, underlined by zircon ages dating back into the Archaean 3 billion years ago. Structurally it consists mainly of stacked metamorphic basement nappes.
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