Armorican Massif

The Armorican Massif (French: Massif armoricain, pronounced [masif aʁmɔʁikɛ̃]) 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 Armorica, a Gaul area between the Loire and the Seine rivers. The massif is composed of metamorphic and magmatic rocks that were metamorphosed and/or deformed during the Hercynian or Variscan orogeny (400 to 280 million years ago) and the earlier Cadomian orogeny (650 to 550 million years ago). The region was uplifted when the Bay of Biscay opened during the Cretaceous period. The Cantabrian Mountains and the Armorican Massif were then rift shoulders of the Bay of Biscay.

The competent old rocks of the Armorican Massif have been eroded to a plateaulike peneplain. 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.

French Hercynian massifs EN
Location of the Armorican Massif on a structural map of the north of France. Hercynian massifs are olive coloured.
Geologic map Armorican Massif EN
Geologic map of the Armorican Massif and surrounding areas.

Geology

During the Neoproterozoic, older parts of the Armorican Massif formed the northern margin of the paleocontinent Gondwana. During the Paleozoic era, the Armorican Massif was part of the microcontinent Armorica, which probably also included terranes found in the Vosges, Black Forest and Bohemian Massif further east. Armorica rifted off the northern margin of Gondwana somewhere during the Ordovician or Silurian periods to move northward and collide with Laurussia during the Hercynian orogeny.

The oldest rocks of the massif are Neoproterozoic sediments of the Brioverian Supergroup which were deformed and metamorphosed during the Cadomian orogeny. These are overlain by lower Paleozoic (Cambrian to Devonian) (meta-)sediments. The whole sequence was deformed, metamorphosed and intruded by felsic magmas during the Hercynian orogeny.

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) forms an exception.

FranceNormandieStPhilbertSurOrneRocheDOetre
The site of the "Roche d'Oëtre".

References

  1. ^ King, William Bernard Robinson (1954). "The Geological History of the English Channel". Quarterly Journal of the Geological Society. 110 (1–4): 77–101. doi:10.1144/gsl.jgs.1954.110.01-04.06. Retrieved 15 March 2015.

Coordinates: 48°N 3°W / 48°N 3°W

Armorican terrane

The Armorican terrane, Armorican terrane assemblage, or simply Armorica, was a microcontinent or group of continental fragments that rifted away from Gondwana towards the end of the Silurian and collided with Laurussia towards the end of the Carboniferous during the Variscan orogeny. The name is taken from Armorica, the Gaulish name for a large part of northwestern France that includes Brittany, as this matches closely to the present location of the rock units that form the main part of this terrane.

Asteropyge

Asteropyge is an extinct genus of trilobite. It lived from the end of the Lower Devonian (upper Emsian) into the Middle Devonian (lower and upper Eifelian), in what are today France (Armorican Massif), and Germany (Eifel area).

Cadomian Orogeny

The Cadomian Orogeny was a tectonic event or series of events in the late Neoproterozoic, about 650–550 Ma, which probably included the formation of mountains. This occurred on the margin of the Gondwana continent, involving one or more collisions of island arcs and accretion of other material at a subduction zone. The precise events, and geographical position, are uncertain, but are thought to involve the terranes of Avalonia, Armorica and Iberia. Rocks deformed in the orogeny are found in several areas of Europe, including northern France, the English Midlands, southern Germany, Bohemia, southern Poland and the southwest Iberian Peninsula. The name comes from Cadomus, the Latin name for Caen, northern France. L Bertrand gave the orogeny its name in 1921, naming it after Cadomus the Gaulish name for Caen in Normandy. He defined the end as being marked by Lower Palaeozoic red beds.

The interpretation is that the belt was formed as oceanic crust subducted below the Armorica land mass in a similar way to the Andes. Sediments deposited on the continental margin were pushed up onto the continent, at the same time as intrusions of calc-alkaline magmas occurred.

Conservatoire botanique national de Brest

The Conservatoire botanique national de Brest (32 hectares) is a notable botanical garden located at 52 Allée du Bot, Brest, Finistère, in the region of Brittany, France. It is open daily without charge.

The conservatory site was formerly a quarry and rubbish dump, purchased in 1971 by the municipality to create open space. The conservatory itself was founded in 1977 with a primary mission of preserving endangered species from the Armorican Massif (including parts of Brittany, Basse-Normandie and Pays de la Loire), France, Europe, and islands around the world, but also including plants from China, Japan, the Americas, Australia, and New Zealand. Since 1990 it has been designated a National Botanical Conservation Center to protect endangered and protected plants of the Armorican Massif.

Today the conservatory contains a remarkable collection of endangered plants, totaling about 1700 species, of which 20 species have been preserved in large part by the conservatory's actions. These very rare plants include Brighamia insignis, Centaurium favargeri, Cheirolophus massonianus, Cylindrocline lorencei, Dombeya cacuminum, Hibiscus insularis, Hibiscus liliiflorus, Impatiens thomassetii, Limonium humile, Normania triphylla, Ruizia cordata, and Trochetia boutoniana.

Additional specimens of interest include Amorphophallus titanum, Asparagus fallax, Astrophytum myriostigma, Angraecum sesquipedale, Commelina rupicola, Geranium maderense, Hibiscus storckii (H. rosa-sinensis), Lavandula pinnata, Limonium dendroides, Monizia edulis, Pachypodium rosulatum, Pelargonium cotyledonis, Tolpis glabrescens, Tournefortia bojeri, and Turbina inopinata.

The conservatory includes greenhouses (1000 m² total area), containing over 200 taxa of which 95% are endangered, which are subdivided into four sections: tropical mountains, dry tropics, humid tropical forests, and subtropical ocean islands. It also contains a herbarium (about 5,000 specimens) and cold storage rooms for packs of seeds.

Cotentin Peninsula

The Cotentin Peninsula (French pronunciation: ​[kɔtɑ̃tɛ̃]), also known as the Cherbourg Peninsula, is a peninsula in Normandy that forms part of the northwest coast of France. It extends north-westward into the English Channel, towards Great Britain. To its west lie the Channel Islands and to the southwest lies the Brittany Peninsula.

The peninsula lies wholly within the department of Manche, in the region of Normandy.

Geology of Alderney

The geology of Alderney includes similarities in its rock to the neighbouring Normandy and Guernsey. Although Alderney is only five kilometers long, it has a geological history spanning half of the life of the earth. It is part of the Armorican Massif.

Geology of France

The regional geology of France is commonly divided into the Paris Basin, the Armorican Massif, the Massif Central, the Aquitaine Basin, the Pyrenees, the Alps, the Côte languedocienne, the Sillon rhodanien, the Massif des Vosges, the Massif Ardennais, the Alsace graben (Rhine graben) and Flanders Basin.

Geology of the Massif Central

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.

Génis Unit

The Génis Unit is a Paleozoic metasedimentary succession of the southern Limousin and belongs geologically to the Variscan basement of the French Massif Central. The unit covers the age range Cambrian/Ordovician till Devonian.

Mayenne

Mayenne (French pronunciation: ​[majɛn]) is a department in northwest France named after the Mayenne River. Mayenne is part of the current region of Pays de la Loire and is surrounded by the departments of Manche, Orne, Sarthe, Maine-et-Loire, and Ille-et-Vilaine.

Mayenne is one of the original 83 departments created during the French Revolution on March 4, 1790. The northern two thirds correspond to the western part of the former province of Maine. The southern third of Mayenne corresponds to the northern portion of the old province of Anjou. The inhabitants of the department are called Mayennais.

Monts d'Arrée

The Monts d'Arrée, or Menezioù Are in Breton, are an ancient mountain range in western Brittany which forms part of the Armorican massif. Historically it marked the border of the regions of Cornouaille and Léon.

The mounts constitute rocks dramatically emerging from the land, running in a north-eastern line across the landscape.

Norman Switzerland

Norman Switzerland (French: Suisse Normande) is a part of Normandy, France, in the border region of the departments Calvados and Orne. Its name comes from its rugged and verdant relief resembling the Swiss Alps, with gorges carved by the river Orne and its tributaries, and by erosion in the Armorican Massif between Putanges-Pont-Écrepin and Thury-Harcourt. The river has created a rugged landscape.

In the hills, small steep fields are often bordered by thick hedges or granite dry stone walls and have dense vegetation. Mont Pinçon, at 345 metres (1,132 ft) in elevation, is the highest point in Norman Switzerland. Churches, houses and farm buildings have a style closer to what is found across the English Channel in the United Kingdom (i.e., stone buildings with slate roofs), rather than the timber structures of the Pays d'Auge.

The main towns are Athis-de-l'Orne, Clécy, Condé-sur-Noireau, Flers-de-l'Orne, Pont-d'Ouilly, Putanges-Pont-Écrepin and Thury-Harcourt. Some 34 communes are grouped into the Communauté de Communes de la Suisse Normande.

There are many outdoor tourist activities: canoeing, horse riding, rock climbing, hang gliding, kayaking, paragliding and mountain biking.

Thury-Harcourt hosted the European Canoe Polo Championship in 2007.

Parc botanique de Cornouaille

The Parc botanique de Cornouaille (4 hectares) is a botanical garden located in Kerlever, Combrit, Finistère, Brittany, France. It is open daily in the warmer months; an admission fee is charged.

The garden was established by Jean-Pierre Gueguen in 1981. Today it contains about 3500 plant varieties, with good collections of camellias (550 varieties), rhododendrons (400), magnolias (85), azaleas (80), and hortensias (60). Plantings of interest include Acer trautvetteri, Camellia caudata, Cleyera japonica, Corylus jacquemontii, Distylium racemosum, Embothrium coccineum, Enkianthus perulatus, Magnolia rostrata, and Rhododendron campylocarpum, as well as an aquatic garden (7,000 square metres or 75,300 square feet). The park also contains a mineral museum displaying 1200 specimens from the Armorican Massif and elsewhere.

Paris Basin

The Paris Basin is one of the major geological regions of France having developed since the Triassic on a basement formed by the Variscan orogeny. The sedimentary basin is a large sag in the craton, bordered by the Armorican Massif to the west, the Ardennes-Brabant axis to the north, the Massif des Vosges to the east, and the Massif Central to the south.

Roc'h Trevezel

Roc'h Trevezel is the second peak of the Breton part of the Armorican Massif in the Monts d'Arrée.

Just like the Signal of Toussaines, it reaches 384 metres (1,260 ft) in altitude.

It is located in the commune of Plounéour-Ménez, near Roc'h Ruz, the highest point of the Monts d'Arrée in Brittany.

Roc'h Trevezel is the highest peak on the Paris–Brest–Paris bicycle route.

Rock of Oëtre

The Rock of Oëtre (French: Roche d'Oëtre pronounced [rɔʃ dwatʁ]) is situated in the middle of Norman Switzerland, in the commune of Saint-Philbert-sur-Orne, not far from the border between the départements of Calvados and Orne, and almost equidistant from Thury-Harcourt and Écouché. It is one of the most prestigious lookouts in the west of France.

Sarthe

Sarthe (French pronunciation: ​[saʁt]) is a department of Pays de la Loire situated in the Grand-Ouest of the country. It is named after the River Sarthe, which flows from east of Le Mans to just north of Angers.

Saxothuringian Zone

The Saxothuringian Zone, Saxo-Thuringian zone or Saxothuringicum is in geology a structural or tectonic zone in the Hercynian or Variscan orogen (380-270 million years old) 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).

Sineruga

Sineruga insolita is a fossil ostracod species which existed in what is now France during the Silurian period. It was described by Vincent Perrier in 2012, and is the only species in the genus Sineruga. It has been found at four sites in the Armorican massif of northwestern France.

Mountain ranges of France

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