Massif Armoricain
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The Armorican Massif (, ) is a geologic
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 ...
that covers a large area in the northwest of
France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
, including
Brittany Brittany ( ) is a peninsula, historical country and cultural area in the north-west of modern France, covering the western part of what was known as Armorica in Roman Gaul. It became an Kingdom of Brittany, independent kingdom and then a Duch ...
, the western part of
Normandy Normandy (; or ) is a geographical and cultural region in northwestern Europe, roughly coextensive with the historical Duchy of Normandy. Normandy comprises Normandy (administrative region), mainland Normandy (a part of France) and insular N ...
and the
Pays de la Loire Pays de la Loire (; but can also mean 'Lower Loire') is one of the eighteen administrative regions of France, located on the country's Atlantic Ocean, Atlantic coast. It was created in the 1950s to serve as a zone of influence for its capital an ...
. It is important because it is connected to Dover on the British side of the
English Channel The English Channel, also known as the Channel, is an arm of the Atlantic Ocean that separates Southern England from northern France. It links to the southern part of the North Sea by the Strait of Dover at its northeastern end. It is the busi ...
and there has been tilting back and forth that has controlled the geography on both sides. Its name comes from the old
Armorica In ancient times, Armorica or Aremorica (Gaulish: ; ; ) was a region of Gaul between the Seine and the Loire that includes the Brittany Peninsula, and much of historical Normandy. Name The name ''Armorica'' is a Latinized form of the Gauli ...
, a
Gaul Gaul () was a region of Western Europe first clearly described by the Roman people, Romans, encompassing present-day France, Belgium, Luxembourg, and parts of Switzerland, the Netherlands, Germany, and Northern Italy. It covered an area of . Ac ...
area between the rivers
Loire The Loire ( , , ; ; ; ; ) is the longest river in France and the 171st longest in the world. With a length of , it drains , more than a fifth of France's land, while its average discharge is only half that of the Rhône. It rises in the so ...
and
Seine The Seine ( , ) is a river in northern France. Its drainage basin is in the Paris Basin (a geological relative lowland) covering most of northern France. It rises at Source-Seine, northwest of Dijon in northeastern France in the Langres plat ...
. The massif is composed 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
magmatic 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 m ...
s that were
metamorphosed 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/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 The Bay of Biscay ( ) is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Point Penmarc'h to the Spanish border, and along the northern coast of Spain, extending westward ...
opened during the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...
. The
Cantabrian Mountains The Cantabrian Mountains or Cantabrian Range () are one of the main systems of mountain ranges in Spain. They stretch for over 300 km (180 miles) across northern Spain, from the western limit of the Pyrenees to the Galician Massif ...
and the Armorican Massif were then
rift shoulder In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben ...
s of the Bay of Biscay. The competent old rocks of the Armorican Massif have been eroded to a
plateau In geology and physical geography, a plateau (; ; : plateaus or plateaux), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. ...
like
peneplain In geomorphology and geology, a peneplain is a low-relief plain formed by protracted erosion. This is the definition in the broadest of terms, albeit with frequency the usage of peneplain is meant to imply the representation of a near-final (or ...
. The highest summit, the
Mont des Avaloirs Mont may refer to: Places * Mont., an abbreviation for Montana, a U.S. state * Mont, Belgium (disambiguation), several places in Belgium * Mont, Hautes-Pyrénées, a commune in France * Mont, Pyrénées-Atlantiques, a commune in France * Mont, Saà ...
(
Mayenne Mayenne ( ) is a landlocked department in northwest France named after the river Mayenne. Mayenne is part of the administrative region of Pays de la Loire and is surrounded by the departments of Manche, Orne, Sarthe, Maine-et-Loire, and Il ...
département), is just above sea level. The western part of the Armorican Massif (which covers Brittany) are the
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 The Armorican Massif (, ) is a geologic massif that covers a large area in the northwest of France, in ...
.


Geology

During the
Neoproterozoic The Neoproterozoic Era is the last of the three geologic eras of the Proterozoic geologic eon, eon, spanning from 1 billion to 538.8 million years ago, and is the last era of the Precambrian "supereon". It is preceded by the Mesoproterozoic era an ...
, older parts of the Armorican Massif formed the northern margin of the
paleocontinent A paleocontinent or palaeocontinent is a distinct area of continental crust that existed as a major landmass in the geological past. There have been many different landmasses throughout Earth's time. They range in sizes; some are just a collection ...
Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...
. During the
Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...
era An era is a span of time. Era or ERA may also refer to: * Era (geology), a subdivision of geologic time * Calendar era Education * Academy of European Law (German: '), an international law school * ERA School, in Melbourne, Australia * E ...
, the Armorican Massif was part of the
microcontinent Continental crustal fragments, partly synonymous with microcontinents, are pieces of continents that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin. Caus ...
Armorica In ancient times, Armorica or Aremorica (Gaulish: ; ; ) was a region of Gaul between the Seine and the Loire that includes the Brittany Peninsula, and much of historical Normandy. Name The name ''Armorica'' is a Latinized form of the Gauli ...
, which probably also included
terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its d ...
s found in the
Vosges The Vosges ( , ; ; Franconian and ) is a range of medium mountains in Eastern France, near its border with Germany. Together with the Palatine Forest to the north on the German side of the border, they form a single geomorphological unit and ...
,
Black Forest The Black Forest ( ) is a large forested mountain range in the States of Germany, state of Baden-Württemberg in southwest Germany, bounded by the Rhine Valley to the west and south and close to the borders with France and Switzerland. It is th ...
and
Bohemian Massif The Bohemian Massif ( or ''Český masiv'', or ''Böhmisches Massiv'') is a geomorphological province in Central Europe. It is a large massif stretching over most of the Czech Republic, eastern Germany, southern Poland and northern Austria. Th ...
further east. Armorica rifted off the northern margin of Gondwana somewhere during the
Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...
or
Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...
periods to move northward and collide with
Laurussia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around (Million years ago, Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during ...
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 The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
to
Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
) (meta-)sediments. The whole sequence was deformed, metamorphosed and
intruded Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form ''intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March 27 ...
by
felsic In geology, felsic is a grammatical modifier, modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted ...
magmas during the Hercynian orogeny. The massif is cut in three by two major late Hercynian southeast-northwest striking
shear zone In geology, a shear zone is a thin zone within the Earth's crust or upper mantle that has been strongly deformed, due to the walls of rock on either side of the zone slipping past each other. In the upper crust, where rock is brittle, the shear ...
s (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 The Moldanubian Zone is in the regional geology of Europe a tectonic zone formed during the Variscan or Hercynian Orogeny (400 to 300 million years ago, during the Devonian and Carboniferous periods). The Moldanubian Zone crops out in the Bohemi ...
of southern
Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
and central Europe. Late Hercynian
granitoid A granitoid is a broad term referring to a diverse group of coarse-grained igneous rocks that are widely distributed across the globe, covering a significant portion of the Earth's exposed surface and constituting a large part of the continental ...
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 Leon, Léon (French) or León (Spanish) may refer to: Places Europe * León, Spain, capital city of the Province of León * Province of León, Spain * Kingdom of León, an independent state in the Iberian Peninsula from 910 to 1230 and again fro ...
) forms an exception. During the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
, the Amorican Massif formed an island landmass isolated from the rest of France by shallow seas, and was inhabited by variety of
dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
, including
stegosaurs Stegosauria is a group of Herbivore, herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous Period (geology), periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere (North America, Europe a ...
,
sauropods Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...
, as well as
megalosaurid Megalosauridae is a monophyletic family of carnivorous theropod dinosaurs within the group Megalosauroidea. Appearing in the Middle Jurassic, megalosaurids were among the first major radiation of large theropod dinosaurs. They were a relatively ...
and possibly
metriacanthosaurid Metriacanthosauridae (Greek for "moderately-spined lizards") is an extinct family of allosauroid theropod dinosaurs that lived in Europe and Asia from the Middle Jurassic to the Early Cretaceous. The family is split into two subgroups: Metriacant ...
theropods.


References

{{Authority control Geology of France Hercynian orogeny Geology of Europe Armorica