An external massif is, in the geology of the Alps

Geology of the Alps

The Alps form part of a Tertiary 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...

, a place where crystalline rocks of the European plate crop out

Outcrop

An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. -Features:Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be...

. Such massif

Massif

In geology, a massif is a section of a planet's crust that is demarcated by faults or flexures. In the movement of the crust, a massif tends to retain its internal structure while being displaced as a whole...

s are found north and west of the Penninic zone (the crystalline "core" of the Alps) as tectonic windows

Window (geology)

thumb|right|350px|Schematic overview of a thrust system. The [[fault |hanging wall block]] is called a [[nappe]]. If an [[erosion]]al hole is created in the nappe that is called a window. A [[klippe]] is a solitary outcrop of the nappe in the middle of autochthonous material.A tectonic window...

 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

Tethys Ocean

The Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.-Modern theory:...

.

The external massifs are the Argentera in the Alpes Maritimes, the Pelvoux Massif and the Belledonne

Belledonne

Belledonne is a mountain range in the Dauphiné Alps in southeast France. The southern end of the range forms the eastern wall of the mountains that surround the city of Grenoble....

 in the Savoyan part of the French Alps, the Mont Blanc Massif

Mont Blanc Massif

The Mont Blanc massif is a mountain range in the western Alps. It is named after Mont Blanc, at 4,810.45 m the highest summit of the Alps. It is located in France , Italy , and Switzerland...

 at the borders between France, Italy and Switzerland and the Aarmassif and Gotthardmassif

Gotthard nappe

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 lower crust of the southern margin of the European continent .-Position and outcrops:The Gotthard nappe is found...

 in the Central Alps of Switzerland.

The massifs are composed of the basement

Basement (geology)

In geology, the terms basement and crystalline basement are used to define the rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin...

 of the former margin of the European plate, consisting of metamorphic

Metamorphic rock

Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...

 and igneous rock

Igneous rock

Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava...

s of Hercynian age or older. The Mesozoic

Mesozoic

The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...

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

Decollement

Décollement is a gliding plane between two rock masses. In French, "décoller" means "to detach from" or "to rip off" and was first used by geologists studying the structure of the Swiss Jura Mountains, but is also known as a detachment zone. This is a structure of strata owing to deformation,...

 by thin skinned thrusting

Thrust fault

A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...

 about 40 to 25 million years ago (Ma). At some places along the Aarmassif, the Mesozoic cover is partly still lying conformally

Conformity

Conformity is the process by which an individual's attitudes, beliefs, and behaviors are influenced by other people.Conformity may also refer to:*Conformity: A Tale, a novel by Charlotte Elizabeth Tonna...

 on top of the Hercynian basement rock, this Mesozoic is called the Infrahelvetic complex

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 uplift

Tectonic uplift

Tectonic uplift is a geological process most often caused by plate tectonics which increases elevation. The opposite of uplift is subsidence, which results in a decrease in elevation. Uplift may be orogenic or isostatic.-Orogenic 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.