The Armorican terrane, Armorican terrane assemblage, or simply Armorica, refers to a microcontinent

Continental fragment

Continental crustal fragments, partially synonymous with microcontinents, are fragments of continents thought to have been broken off from the main continental mass forming distinct islands, possibly several hundred kilometers from their place of origin...

 or group of continental fragments that rift

Rift

In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....

ed away from Gondwana

Gondwana

In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...

 towards the end of the Silurian

Silurian

The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...

 and collided with Laurussia

Euramerica

Euramerica was a minor supercontinent created in the Devonian as the result of a collision between the Laurentian, Baltica, and Avalonia cratons .300 million years ago in the Late Carboniferous tropical rainforests lay over the equator of Euramerica...

 towards the end of the Carboniferous

Carboniferous

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 during the Variscan orogeny

Variscan orogeny

The Variscan orogeny is a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica and Gondwana to form the supercontinent of Pangaea.-Naming:...

. The name is taken from Armorica

Armorica

Armorica or Aremorica is the name given in ancient times to the part of Gaul that includes the Brittany peninsula and the territory between the Seine and Loire rivers, extending inland to an indeterminate point and down the Atlantic coast...

, the Gaulish

Gaulish language

The Gaulish language is an extinct Celtic language that was spoken by the Gauls, a people who inhabited the region known as Gaul from the Iron Age through the Roman period...

 name for a large part of northwestern France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 that includes Brittany

Brittany

Brittany is a cultural and administrative region in the north-west of France. Previously a kingdom and then a duchy, Brittany was united to the Kingdom of France in 1532 as a province. Brittany has also been referred to as Less, Lesser or Little Britain...

, as this matches closely to the present location of the rock units that form the main part of this terrane.

Extent

The main exposures of the Armorican terrane are found throughout Brittany, the Channel Islands

Channel Islands

The Channel Islands are an archipelago of British Crown Dependencies in the English Channel, off the French coast of Normandy. They include two separate bailiwicks: the Bailiwick of Guernsey and the Bailiwick of Jersey...

, parts of Upper Normandy, forming the Armorican Massif

Armorican Massif

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. Its name comes from the old Armorica, a Gaul area between the Loire and the Seine rivers...

. Other fragments thought to have originally formed part of the Armorican terrane assemblage include rock units exposed in the Vosges

Vosges

Vosges is a French department, named after the local mountain range. It contains the hometown of Joan of Arc, Domrémy.-History:The Vosges department is one of the original 83 departments of France, created on February 9, 1790 during the French Revolution. It was made of territories that had been...

, Black Forest

Black Forest

The Black Forest is a wooded mountain range in Baden-Württemberg, southwestern Germany. It is bordered by the Rhine valley to the west and south. The highest peak is the Feldberg with an elevation of 1,493 metres ....

, Bohemian Massif

Bohemian Massif

The Bohemian Massif; or Český masiv; is in the geology of Central Europe a large massif stretching over central Czech republic, eastern Germany, southern Poland and northern Austria...

 and most of the Iberian peninsula

Iberian plate

The microcontinent Iberia encompassed not only the Iberian Peninsula but also Corsica, Sardinia, the Balearic Islands, and the Briançonnais zone of the Penninic nappes of the Alps...

.

History

All of the fragments that make up the Armorican terrane are thought to have originally formed part of the northern margin of Gondawa. Rifting initiated in the Cambrian

Cambrian

The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...

 to Ordovician

Ordovician

The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...

 although the terrane was still close enough to Gondwana to be affected by the Andean-Saharan glaciation during the late Ordovician. Complete separation from Gondwana, across the developing Paleotethys Ocean

Paleo-Tethys Ocean

The Paleo-Tethys Ocean was an ancient Paleozoic ocean. It was located between the paleocontinent Gondwana and the so called Hunic terranes. These are divided into the European Hunic and Asiatic Hunic...

, is thought to have occurred towards the end of the Silurian. At this time Armorica was separated from Laurussia by the Rheic Ocean

Rheic Ocean

The Rheic Ocean was a Paleozoic ocean between the large continent Gondwana to the south and the microcontinents Avalonia and others to the north...

. One possible model includes Armorica as part of the Hun superterrane, while other show it moving separately. The Rheic Ocean closed during the Devonian and early Carboniferous, as the oceanic crust

Oceanic crust

Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...

 was subducted

Subduction

In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

. The Variscan orogeny marks the final closure of the Rheic Ocean as the various continental fragments, including Armorica, collided with Laurussia towards the end of the Carboniferous.