Geologic massif that covers a large area in the northwest of France
Location of the Armorican Massif on a structural map of the north of France. Hercynian massifs are olive coloured.Geologic map of the Armorican Massif and surrounding areas.
The Armorican Massif (French: Massif armoricain, pronounced[masifaʁmɔʁikɛ̃]) 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.[1]
Its name comes from the old
rift shoulders
of the Bay of Biscay.
The competent old rocks of the Armorican Massif have been eroded to a plateaulikepeneplain. The highest summit, the Mont des Avaloirs (Mayenne département), is just 417 m (1,368 ft) above sea level. The western part of the Armorican Massif (which covers Brittany) are the Monts d'Arrée.
Geology
During the
Laurussia
during the Hercynian orogeny.
The oldest rocks of the massif are Neoproterozoic sediments of the
The massif is cut in three by two major late Hercynian southeast-northwest
striking shear zones (the North and South Armorican Shear Zones). The divisions are simply called the North, Central and South Armorican Zones. Generally the north was less deformed during the Hercynian orogeny than the south. The South Armorican Zone is considered part of the core of the Hercynian orogeny, comparable to the Moldanubian Zone of southern Germany and central Europe. Late Hercynian granitoid bodies were intruded along the South Armorican Shear Zone. The northern parts of the Armorican Massif have less intrusive rocks, although a small zone in the northwest of Brittany (Léon Zone
