An external massif is, in the

geology of the 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 Alpin ...

, a place where

crystalline rock A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macrosco ...

s of the European plate crop out. Such

massif A massif () is a principal mountain mass, such as a compact portion of a mountain range, containing one or more summits (e.g. France's Massif Central). In mountaineering literature, ''massif'' is frequently used to denote the main mass of an ...

s are found north and west of the Penninic zone (the crystalline "core" of the Alps) as tectonic windows in 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 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 Tethys Ocean ( ; ), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean during much of the Mesozoic Era and early-mid Cenozoic Era. It was the predecessor to the modern Indian Ocean, the Mediterranean Sea, and the Eurasia ...

.Schmid ''et al.'' (2004) The external massifs are the

Argentera Argentera is a ''comune'' (municipality) in the Province of Cuneo in the Italy, Italian region Piedmont, located about southwest of Turin and about west of Cuneo, on the border with France. It consists of a series of sparse hamlets in the upper ...

in the

Alpes Maritimes Alpes-Maritimes (; ; ; ) is a department of France located in the country's southeast corner, on the Italian border and Mediterranean coast. Part of the Provence-Alpes-Côte d'Azur region, it encompasses the French Riviera alongside neighbou ...

, the

Pelvoux massif Pelvoux (; Vivaro-Alpine: ''Pelvós'') is a former commune in the Hautes-Alpes department in the Provence-Alpes-Côte d'Azur region in southeastern France. On 1 January 2017, it was merged into the new commune Vallouise-Pelvoux. Pelvoux bid ...

and the Belledonne range in the

Dauphiné The Dauphiné ( , , ; or ; or ), formerly known in English as Dauphiny, is a former province in southeastern France, whose area roughly corresponded to that of the present departments of Isère, Drôme and Hautes-Alpes. The Dauphiné was ...

part of the French Alps, the

Aiguilles Rouges The Aiguilles Rouges (, "Red Needles") are a crystalline mountainous massif of the French Prealps, opposite the Mont Blanc Massif. The colour of the iron rich gneiss (metamorphique) mountains gives the range its name. The highest summit is the Ai ...

in the

Savoy Savoy (; )  is a cultural-historical region in the Western Alps. Situated on the cultural boundary between Occitania and Piedmont, the area extends from Lake Geneva in the north to the Dauphiné in the south and west and to the Aosta Vall ...

part of the French Alps, the Mont Blanc Massif at the borders between France, Italy and Switzerland and the Aarmassif and Gotthardmassif in the

Central Alps The Alps form a large mountain range dominating Central Europe, including parts of Italy, France, Switzerland, Liechtenstein, Austria, Slovenia, Germany and Hungary. This article describes the delimitation of the Alps as a whole and of subdivi ...

of Switzerland. The massifs are composed of the

basement A basement is any Storey, floor of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the Furnace (house heating), furnace, water heating, ...

of the former margin of the European plate, consisting of

metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

and

igneous rock Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

s of Hercynian age or older. The

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 ...

cover that was originally on top of these rock has mostly been

detached A single-family detached home, also called a single-detached dwelling, single-family residence (SFR) or separate house is a free-standing residential building. It is defined in opposition to a multi-family residential dwelling. Definitions ...

by thin skinned

thrusting 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 syst ...

about 40 to 25 million years ago ( Ma).Pfiffner (2009) At some places along the Aarmassif, the Mesozoic cover is partly still lying conformally on top of the Hercynian basement rock, this Mesozoic is called the

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. The Infrahelvetic complex has been overthrusted by the Helvetic nappes, that part ...

. The uplift that brought the massifs to the surface involved thick skinned thrusting (the style of thrusting in which the basement is itself involved) and took place in a tectonic phase beginning around 19 million years ago.

References

*; 2009: ''Geologie der Alpen'', Haupt Verlag, Berne, . *{{aut, Schmid, S.M.; Fügenschuh, B.; Kissling, E. & Schuster, R.; 2004: ''Tectonic map and overall architecture of the Alpine orogen'', Eclogae Geologicae Helveticae 97, pp 93–117. Geology of the Alps