Massif Central (geology)
Encyclopedia
The Massif Central
forms together with the Armorican Massif
(Brittany
and Normandy
) one of the two big basement massifs in France
. Its 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
. There is no doubt, that the Massif Central has a very long geological history underlined by zircon ages dating back into the Archaean 3000 million years ago. Structurally it consists mainly of stacked metamorphic
basement nappe
s.
The basement outcrops of the Massif Central have roughly the outline of a triangle standing on its tip. Because of its size – 500 kilometers long and 340 kilometers wide – the Massif Central partakes in several tectono-metamorphic zones formed during the Variscan orogeny. The bulk of the massif belongs to the Ligero-Arvernian Zone, sometimes also called the microcontinent Ligeria. With its northeastern tip, the Morvan
, it reaches into the Morvano-Vosgian Zone which becomes the Moldanubian Zone
farther east. All these zones constitute the interior core of the Variscan orogen in Europe
which is characterized by the following traits:
In the far south the Massif Central forms part of the Montagne Noire Zone. This zone constitutes together with the Pyrenees
the microcontinent Aquitania; it is no longer made up of basement nappes, but contains low-grade Paleozoic
sedimentary nappes having gravitationally slid off to the south from the rising Neoproterozoic basement.
The most important fault line is probably the NNE-SSW-striking Sillon Houiller, a 250 kilometer long normal fault with a strong sinistral wrenching component. The Sillon Houiller separates the nonvolcanic western section from the volcanic central and eastern section. Farther south it becomes the Toulouse fault.
The Oligocene
Limagne graben penetrates nearly 150 kilometers into the Massiv Central from the North and almost manages to cut through towards the Grands Causses.
The narrow central section west of this graben system carries stratovolcano
es like the Cantal
– Europe's highest shield volcano – and the Monts Dore (including the highest elevation in the massif, the Puy de Sancy
), but also maar
and explosion craters of the Chaîne des Puys
farther north.
The eastern section extends from the Morvan
in the Northeast to the Cevennes
in the South. It is bounded in the East by the Bresse graben and its extension into the Bas Dauphiné. The change in altitude towards the grabens is quite drastic. The graben structures along the southeastern edge already form part of the oceanic Liguro-Provençal Basin. The eastern section is further subdivided by the Roanne graben and its southern continuation the Plaine du Forez. It is also cut by the NE-trending Permian
strike-slip basin of Blanzy
– Le Creusot
which separates the Morvan from the main massif.
An important ESE-WNW-striking division is situated near Figeac
and Decazeville
separating the Rouergue
and the Montagne Noire
in the South almost completely from the main basement outcrops.
In general the Massif Central is an asymmetric basement plate elevated at its southern margin by the Pyrenees orogeny and along its eastern margin by the Alpine orogeny. Along these margins it descends very abruptly to the surrounding grabens. These margins also show the highest elevations, the plate being gently inclined to the Northwest where the basement rocks disappear under the Mesozoic cover of the Aquitaine basin and the Paris basin
. This somewhat simplistic model is locally disturbed by fault lines and graben structures – for instance the massif's highest elevation is positioned in the central section (Puy de Sancy culminating at 1886 meters) as already mentioned.
es and metamorphic schist
s) have been divided by M. Chenevoy (1974) into three tectono-metamorphic domains:
The Arverne domain is structurally the lowermost domain with parautochthonous character. It surrounds basement highs like the Saint-Mathieu dome, the Sussac dome or the enormous Plateau de Millevaches
. All these tectonic window
s into the lower basement are situated in the nonvolcanic western section. More continuous outcrops of the Arverne domain can be found in the Auvergne (thence the name), the western Marche
, the northern Morvan
, the Lyonnais
and the Livradois (Haut-Allier).
The now high-grade metamorphic rocks – essentially the amphibolite facies with medium-pressure high-temperature conditions was reached - were originally deposited as flysch
sequences along Gondwana
s northern continental slope. This flysch sequence consisted of monotonous, rhythmically interbedded clayey (pelite
s) and sandy (greywacke
s) deposits reaching the astonishing thickness of 15 kilometers in places. Its middle section contains bimodal volcanic deposits with a thickness of several thousand meters. Material of rhyolitic
composition prevails, but tholeiitic basalt
s, rare peridotite
s and carbonate
lenses do also occur. This Neoproterozoic
sequence originally was estimated to be 650 million years old, its age though has recently been reduced to 600 – 550 million years BP (Ediacaran
).
The sediments of the Arverne domain were metamorphosed mainly during the Acadian phase of the Caledonian orogeny
about 400 – 350 million years ago. Pressures reached 0,6 – 0,8 GPa according to a burial depth of about 20 – 25 kilometers, the temperature gradient being 20 – 25 °C per kilometer. The original sedimentary succession transformed into migmatite
s at its base, followed by gneiss
es, micaschists and finally sericite schists and chlorite schists at the top, the schists at the top only being metamorphosed under greenschist facies conditions. The volcanogenic material was metamorphosed to leptynites and amphibolite
s.
Included in this metamorphic succession are also augengneisses that originated from sheared orthogneisses, which in turn represent porphyric granitoid
s dated around 500 MA BP (Furongian).
and in the western parts of the Cevennes. The once sedimentary succession starts off like in the Arverne domain but comprises also a Paleozoic
sequence at its top. The Paleozoic begins in the Lower Cambrian
with a thick volcanogenic series of rhyolitic composition. This is followed by dated Upper Cambrian, Ordovician
and Silurian
.
In the Limousin the Ruteno-Limousin domain underwent like the Arverne domain solely the Acadian phase metamorphism. In the Rouergue though this was overprinted by hercynian metamorphism that developed under LP/HT conditions.
To summarize: all three domains share the basal Neoproterozoic succession (or at least parts of it). They differ in the Paleozoic part: the Arverne domain for example is completely devoid of Paleozoic rocks. The Arverne domain reaches structurally deepest, its Neoproterozoic goes right down to basal migmatites. The Cevenole domain on the other hand is much more superficial, its Neoproterozoic comprises only structurally higher schists and in the Montagne Noire even a completely nonmetamorphic Paleozoic. The Ruteno-Limousin domain takes on an inetrmediary position.
, the Thiviers-Payzac unit in the Bas Limousin, the Mazerolles Schists in the Haute Charente, the Brévenne Unit in the Lyonnais in the Northeast and the schists of the Albigeois in the South.
The Génis Unit for example shows the following succession (from young to old):
The Thiviers-Payzac Unit consists mainly of rhyodacitic
tuff
s, greywackes and siltstones. Their metamorphic degree can reach the amphibolite facies.
The Mazerolles Schists are aluminous micaschists with interbedded quartzitic
layers. They derive from pelites and siltstones and are probably Cambrian in age.
The Brévenne Unit is an ophiolitic nappe of Upper Devonian age. It comprises pillow basalts, dolerites, gabbro
s, ultramafic rocks, chert
s and massive sulfide
s.
The southern edge of the Montagne Noire possesses a nearly complete sedimentary succession from the Cambrian right up to the Mississippian.
The Cambrian starts with basal rhyolites, followed by the Grès de Marcory, a sandstone formation, by archaeocyathid-bearing limestones, shales and more sandstones. The Ordovician and the Silurian consist mainly of shales, whereas the Devonian is made up exclusively of carbonates in Mediterranean facies.
Along the northern side of the Montagne Noire the series is more incomplete, the entire Upper Ordovician is missing. As a recompense one can study here the gradual changeover of the nonmetamorphic Cambro-Silurian system into the metamorphic equivalents of the Albigeois.
In the Morvan Devonian sediments of the Givetian, Frasnian
and Famennian
stages are exposed. Givetian and Frasnian are developed as reef
al limestones. The Famennian is composed of clymeniid
-bearing shales interbedded with spilite
s.
to just southwest of Montluçon
.
The series starts in the Lower Viséan
with shaly to sandy sediments, followed by greywackes, conglomerate
s and carbonate
s in the Middle Viséan (the Tournaisian
is generally missing in the Massif Central, exceptions being some scattered occurrences in the Morvan). Very important are the transgressing Tufs anthracifères in the Upper Viséan (dated between 335 and 330 MA BP). They consist of pyroclastic tuffs with rhyolitic or dacitic
composition, cover a large area and reach large thicknesses. The name is derived from occasional interbedded anthracite layers that indicate a paralic environment near a shallow sea.
, Bashkirian
and Moscovian
– Sudeten Phase and Asturian Phase) accompanied by extensive granitisation the young orogen underwent late orogenic extension in the Kasimovian
. As a consequence narrow fault-bounded graben-like depressions formed that were filled with lake sediments (conglomerates, sandstones, shales interbedded with layers rich in organic material that later transformed into coal
seams). Sometimes rhyolitic intercalations do occur.
Examples are the relatively small coal-bearing basins near Ahun
, Argentat
, Blanzy
, Decazeville
, Graissessac
, Le Creusot
, Messeix
within the Sillon Houiller, Saint-Étienne
, Sainte-Foy
and Sincey-lès-Rouvray
.
Later during the Saalian Phase the sedimentary infill of these basins was strongly folded due to wrenching movements in the adjacent basement blocks.
and more basins were formed, mainly along the periphery of the Massif. The detrital sedimentary infill consisted mainly of continental red desert sandstones, siltstones and shales.
Examples are the basins near Autun
, Blanzy
, Brive
, Espalion
, Moulins
and Saint-Affrique
.
the Massif Central stayed above sea-level, yet the severe erosional processes attacking it since the end of the Carboniferous continued unabatedly and gradually leveled the former mountain range into a peneplain. Along its edges and especially in the Southeast the Jurassic
sea deposited thick limestone sequences that later became the Causses
.
the Massif Central started to feel the effects of the pyrenean
and the alpine orogeny
, especially along its southern and eastern edges that were uplifted quite drastically. The consequences of these strong stresses on the crust initiated explosive volcanism already during the Paleocene
. The volcanic activities have continued since then practically up to this day.
During the Late Eocene
the so-called Sidérolithique was deposited. This is an iron-rich sediment resembling laterite
s and indicating extensive erosion of the massif (after its renewed uplift) under subtropical climatic conditions.
In the Middle Eocene (Lutetian
) a new distensional period started that reached its climax during the Oligocene
. The stretching of the crust caused extensional grabens to form. Examples are the roughly N-S- to NNW-SSE-striking asymmetric graben structures of the Bresse
, Cher
, Limagne
, Plaine du Forez and the Roanne graben. These depressions were again filled with lake sediments with occasional volcanic intercalations, the so-called peperite
s. The sediments can reach considerable thicknesses e.g. 2500 meter in the Limagne.
Towards the end of the Miocene
the precursors of the great stratovolcanoes Cantal
and Monts Dore started to form. In the eastern Velay thick alkaline basalts extruded and phonolitic
plugs pushed up.
During the Pliocene
a new period of strong uplift began that led to increased erosion and triggered very strong volcanism. In fact the Massif Central experienced its climax in volcanic activities at this time - the Cantal stratovolcano for example started to build up to elevations over 3000 meters.
The last ice age
saw valley glaciers and small ice caps establishing themselves on the Cantal and on the Monts Dore, as is demonstrated by moraine
s and cirque
s.
The last phreatomagmatic explosions happened in the Chaîne des Puys
only 3000 to 4000 years ago.
The northwestern edge of the Massif Central near Rochechouart
was struck close to the Triassic
/Jurassic
boundary (about 210 million years ago) by a large meteorite
, probably of the stony-iron type. The impact excavated a crater with a diameter of 20 kilometers in the peneplained basement rocks. Today the crater structure is almost completely eroded away, yet some suevite
s, several impact breccias, planar deformation features (PDFs), shatter cone
s and many local thrusts in the basement still document this event.
It seems now well established that at the end of the Neoproterozoic
the Massif Central (i.e. the microcontinent Ligeria
) and Armorica
were part of Gondwana
s northern edge. At that time an extremely thick flysch sequence with interbedded bimodal volcanics was laid down in the adjoining ocean to the North. During the Lower Ordovician parts of Gondwanas northern rim started to break off and a sliver carrying Armorica and its eastern continuation - also called the Hun Superterrane – slowly started drifting northward. This opened up the Paleotethys in the wake. As a consequence the Rheic Ocean
and the Rhenohercynian Ocean to the north were more and more constricted and eventually became subducted below Armorica or the Hun Superterrane. This subduction
event corresponds in the Massiv Central to the deformational phase D2. The final continental collision
during the Mississippian between Gondwana and Laurussia welded Ligeria into its actual position in the interior part of the Variscan orogen. The collision event is represented in the Massif Central by the phase D3.
This is only a very sketchy paleogeographical reconstruction. Lots of models have been presented that usually differ in the sense of the subduction(s) and in the arrangements of the microcontinents. The common somewhat simplistic approach of orthogonal opening/closing can only be a first approximation, because the issue becomes a lot more complicated by trying to incorporate the very important dextral shearing motions affecting the Variscan orogen.
As an introduction into this subject see the paper by Stampfli et al. (2002).
A HP/UHP metamorphism caused by subduction at the Silurian/Devonian boundary was followed in the Devonian/Mississippian by polyphase dynamometamorphism due to crustal shortening. The latter developed a cross pattern in the resulting structures – the well known Variscan x. The intensive nappe-stacking during continental collision transported high-grade terranes in a southerly direction over less deformed units creating the impression of an inverted metamorphism – a feature so ubiquitous in the Massif Central. The last two deformational phases in the Pennsylvanian formed under extensional stresses and again produced a cross pattern in the resulting structures. The strong orogenic extension and final collapse triggered decompressional melting which led to pronounced granitisation and associated mineralisation
mainly of the Au
– Sb
- W
- type.
The structural cross pattern can also be found spatially. In the western and central section of the Massif Central NW-SE trending structures largely dominate, whereas in the eastern section a very strong NE-SW organisation prevails.
Of great importance is the diachronous evolution in the Massif Central. Thrusting and exhumation events migrated temporally and spatially. Thrusting for instance started in the North already at 385 MA BP and only reached the South (Montagne Noire) by 325 to 315 MA BP.
Massif Central
The Massif Central is an elevated region in south-central France, consisting of mountains and plateaux....
forms together with 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...
(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...
and Normandy
Normandy
Normandy is a geographical region corresponding to the former Duchy of Normandy. It is in France.The continental territory covers 30,627 km² and forms the preponderant part of Normandy and roughly 5% of the territory of France. It is divided for administrative purposes into two régions:...
) one of the two big basement massifs in 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...
. Its geological evolution started in the late Neoproterozoic
Neoproterozoic
The Neoproterozoic Era is the unit of geologic time from 1,000 to 542.0 ± 1.0 million years ago. The terminal Era of the formal Proterozoic Eon , it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods...
and continues to this day. It has been shaped mainly by the Caledonian orogeny
Caledonian orogeny
The Caledonian orogeny is a mountain building era recorded in the northern parts of the British Isles, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly...
and 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 Alpine orogeny
Alpine orogeny
The Alpine orogeny is an orogenic phase in the Late Mesozoic and Tertiary that formed the mountain ranges of the Alpide belt...
has also left its imprints, probably causing the important Cenozoic
Cenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
volcanism
Volcanism
Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....
. There is no doubt, that the Massif Central has a very long geological history underlined by zircon ages dating back into the Archaean 3000 million years ago. Structurally it consists mainly of stacked metamorphic
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
basement nappe
Nappe
In geology, a nappe is a large sheetlike body of rock that has been moved more than or 5 km from its original position. Nappes form during continental plate collisions, when folds are sheared so much that they fold back over on themselves and break apart. The resulting structure is a...
s.
Introduction
Morvan
The Morvan is a mountainous massif lying just to the west of the Côte d'Or escarpment in Burgundy, France. It is a northerly extension of the Massif Central and is of Variscan age. It is composed of granites and basalts and formed a promontory extending northwards into the Jurassic sea.-Music:The...
, it reaches into the Morvano-Vosgian Zone which becomes the Moldanubian Zone
Moldanubian Zone
The Moldanubian Zone is in the regional geology of Europe a tectonic zone formed during the Variscan or Hercynian Orogeny...
farther east. All these zones constitute the interior core of the Variscan orogen in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
which is characterized by the following traits:
- It contains remnants of oceanic crustOceanic crustOceanic 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...
that were subducted during the SilurianSilurianThe 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 the DevonianDevonianThe Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
. - The approach of GondwanaGondwanaIn 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,...
from the South onto the cadomian microcontinent ArmoricaArmorican terraneThe Armorican terrane, Armorican terrane assemblage, or simply Armorica, refers to 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...
(and farther east onto the Saxothuringian Mid-German Crystalline Rise) induced a continental collision slicing the basement into several large-scale nappes and thrusting them into southerly directions. - After the thrusting the orogen was exhumed diachronously. Exhumation started in the western and northern Massif Central already in the Upper Devonian (FrasnianFrasnianThe Frasnian is one of two faunal stages in the Late Devonian epoch. It lasted from 385.3 ± 2.6 million years ago to 374.5 ± 2.6 million years ago. It was preceded by the Givetian stage and followed by the Famennian stage...
) 380 million years ago whereas the southern part was elevated much later (in the TournaisianTournaisianThe Tournaisian is in the ICS geologic timescale the lowest stage or oldest age of the Mississippian, the oldest subsystem of the Carboniferous. The Tournaisian age lasted from 359.2 ± 2.5 Ma to 345.3 ± 2.1 Ma...
, 350 MA BP). The VosgesVosgesVosges 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...
farther east were raised even later – at the end of the ViséanViséanThe Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from 345.3 ± 2.1 to 328.3 ± 1.6 Ma...
at 330 MA BP.
In the far south the Massif Central forms part of the Montagne Noire Zone. This zone constitutes together with the Pyrenees
Pyrenees
The Pyrenees is a range of mountains in southwest Europe that forms a natural border between France and Spain...
the microcontinent Aquitania; it is no longer made up of basement nappes, but contains low-grade Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
sedimentary nappes having gravitationally slid off to the south from the rising Neoproterozoic basement.
Geography
The Massif Central is crossed by major fault zones dividing it into several spatial domains.The most important fault line is probably the NNE-SSW-striking Sillon Houiller, a 250 kilometer long normal fault with a strong sinistral wrenching component. The Sillon Houiller separates the nonvolcanic western section from the volcanic central and eastern section. Farther south it becomes the Toulouse fault.
The Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
Limagne graben penetrates nearly 150 kilometers into the Massiv Central from the North and almost manages to cut through towards the Grands Causses.
The narrow central section west of this graben system carries stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...
es like the Cantal
Cantal
Cantal is a department in south-central France. It is named after the Cantal mountain range, a group of extinct, eroded volcanic peaks, which covers much of the department. Residents are known as Cantaliens or Cantalous....
– Europe's highest shield volcano – and the Monts Dore (including the highest elevation in the massif, the Puy de Sancy
Puy de Sancy
Puy de Sancy is the highest mountain in the Massif Central and therefore the highest mountain in central France ....
), but also maar
Maar
A maar is a broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption, an explosion caused by groundwater coming into contact with hot lava or magma. A maar characteristically fills with water to form a relatively shallow crater lake. The name comes from the local Moselle...
and explosion craters of the Chaîne des Puys
Chaîne des Puys
The Chaîne des Puys is a north-south oriented chain of cinder cones, lava domes, and maars in the Massif Central of France. The chain is about 40 km long, and the identified volcanic features include 48 cinder cones, eight lava domes, and 15 maars and explosion craters. Its highest point is...
farther north.
The eastern section extends from the Morvan
Morvan
The Morvan is a mountainous massif lying just to the west of the Côte d'Or escarpment in Burgundy, France. It is a northerly extension of the Massif Central and is of Variscan age. It is composed of granites and basalts and formed a promontory extending northwards into the Jurassic sea.-Music:The...
in the Northeast to the Cevennes
Cévennes
The Cévennes are a range of mountains in south-central France, covering parts of the départements of Gard, Lozère, Ardèche, and Haute-Loire.The word Cévennes comes from the Gaulish Cebenna, which was Latinized by Julius Caesar to Cevenna...
in the South. It is bounded in the East by the Bresse graben and its extension into the Bas Dauphiné. The change in altitude towards the grabens is quite drastic. The graben structures along the southeastern edge already form part of the oceanic Liguro-Provençal Basin. The eastern section is further subdivided by the Roanne graben and its southern continuation the Plaine du Forez. It is also cut by the NE-trending Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
strike-slip basin of Blanzy
Blanzy
Blanzy is a commune in the Saône-et-Loire department in the region of Bourgogne in eastern France.-Geography:The Bourbince forms part of the commune's north-eastern border, then flows southwestward through the middle of the commune.-References:*...
– Le Creusot
Le Creusot
Le Creusot is a commune in the Saône-et-Loire department in the region of Bourgogne in eastern France.The inhabitants are known as Creusotins. Formerly a mining town, its economy is now dominated by metallurgical companies such as ArcelorMittal, Schneider Electric, and Alstom.Since the 1990s, the...
which separates the Morvan from the main massif.
An important ESE-WNW-striking division is situated near Figeac
Figeac
Figeac is a commune in the Lot department in south-western France.Figeac is a sub-prefecture of the department.-History:Figeac is on the via Podiensis, a major hiking medieval pilgrimage trail which is part of the Way of St. James...
and Decazeville
Decazeville
Decazeville is a commune in the Aveyron department in the Midi-Pyrénées region in southern France.The commune was created in the 19th century because of the Industrial Revolution and was named after the Duke of Decazes , the founder of the factory that created the town.-History:The town is built...
separating the Rouergue
Rouergue
Rouergue is a former province of France, bounded on the north by Auvergne, on the south and southwest by Languedoc, on the east by Gévaudan and on the west by Quercy...
and the Montagne Noire
Montagne Noire
* Not to be confused with the Montagnes Noires in Brittany.The Montagne Noire is a mountain range in central southern France. It is located at the southwestern end of the Massif Central in the border area of the Tarn, Hérault and Aude departments...
in the South almost completely from the main basement outcrops.
In general the Massif Central is an asymmetric basement plate elevated at its southern margin by the Pyrenees orogeny and along its eastern margin by the Alpine orogeny. Along these margins it descends very abruptly to the surrounding grabens. These margins also show the highest elevations, the plate being gently inclined to the Northwest where the basement rocks disappear under the Mesozoic cover of the Aquitaine basin and the Paris basin
Paris Basin (geology)
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.-Extent:...
. This somewhat simplistic model is locally disturbed by fault lines and graben structures – for instance the massif's highest elevation is positioned in the central section (Puy de Sancy culminating at 1886 meters) as already mentioned.
Tectono-metamorphic domains
The crystalline basement rocks of the Massif Central (mainly gneissGneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
es and metamorphic schist
Schist
The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...
s) have been divided by M. Chenevoy (1974) into three tectono-metamorphic domains:
- the Arverne domain (AuvergneAuvergne (région)Auvergne is one of the 27 administrative regions of France. It comprises the 4 departments of Allier, Puy de Dome, Cantal and Haute Loire.The current administrative region of Auvergne is larger than the historical province of Auvergne, and includes provinces and areas that historically were not...
) - the Ruteno-Limousin domain (RouergueRouergueRouergue is a former province of France, bounded on the north by Auvergne, on the south and southwest by Languedoc, on the east by Gévaudan and on the west by Quercy...
– LimousinLimousin (région)Limousin is one of the 27 regions of France. It is composed of three départements: Corrèze, Creuse and the Haute-Vienne.Situated largely in the Massif Central, as of January 1st 2008, the Limousin comprised 740,743 inhabitants on nearly 17 000 km2, making it the second least populated region of...
) - the Cevenole domain (CevennesCévennesThe Cévennes are a range of mountains in south-central France, covering parts of the départements of Gard, Lozère, Ardèche, and Haute-Loire.The word Cévennes comes from the Gaulish Cebenna, which was Latinized by Julius Caesar to Cevenna...
)
The Arverne domain
Plateau de Millevaches
right|thumb|220px|Plateau de MillevachesThe Plateau de Millevaches is an upland area in the Limousin région of France...
. All these tectonic window
Window
A window is a transparent or translucent opening in a wall or door that allows the passage of light and, if not closed or sealed, air and sound. Windows are usually glazed or covered in some other transparent or translucent material like float glass. Windows are held in place by frames, which...
s into the lower basement are situated in the nonvolcanic western section. More continuous outcrops of the Arverne domain can be found in the Auvergne (thence the name), the western Marche
Marche
The population density in the region is below the national average. In 2008, it was 161.5 inhabitants per km2, compared to the national figure of 198.8. It is highest in the province of Ancona , and lowest in the province of Macerata...
, the northern Morvan
Morvan
The Morvan is a mountainous massif lying just to the west of the Côte d'Or escarpment in Burgundy, France. It is a northerly extension of the Massif Central and is of Variscan age. It is composed of granites and basalts and formed a promontory extending northwards into the Jurassic sea.-Music:The...
, the Lyonnais
Lyonnais
The Lyonnais is a historical province of France which owes its name to the city of Lyon.The geographical area known as the Lyonnais became part of the Kingdom of Burgundy after the division of the Carolingian Empire...
and the Livradois (Haut-Allier).
The now high-grade metamorphic rocks – essentially the amphibolite facies with medium-pressure high-temperature conditions was reached - were originally deposited as flysch
Flysch
Flysch is a sequence of sedimentary rocks that is deposited in a deep marine facies in the foreland basin of a developing orogen. Flysch is typically deposited during an early stage of the orogenesis. When the orogen evolves the foreland basin becomes shallower and molasse is deposited on top of...
sequences along 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,...
s northern continental slope. This flysch sequence consisted of monotonous, rhythmically interbedded clayey (pelite
Pelite
Pelite is old and currently not widely used field terminology for a clayey fine-grained clastic sediment or sedimentary rock, i.e. mud or mudstone. It is equivalent to the Latin-derived term lutite. More commonly, metamorphic geologists currently use pelite for a metamorphosed fine-grained...
s) and sandy (greywacke
Greywacke
Greywacke or Graywacke is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found...
s) deposits reaching the astonishing thickness of 15 kilometers in places. Its middle section contains bimodal volcanic deposits with a thickness of several thousand meters. Material of rhyolitic
Rhyolite
This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...
composition prevails, but tholeiitic basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
s, rare peridotite
Peridotite
A peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron...
s and carbonate
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
lenses do also occur. This Neoproterozoic
Neoproterozoic
The Neoproterozoic Era is the unit of geologic time from 1,000 to 542.0 ± 1.0 million years ago. The terminal Era of the formal Proterozoic Eon , it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods...
sequence originally was estimated to be 650 million years old, its age though has recently been reduced to 600 – 550 million years BP (Ediacaran
Ediacaran
The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...
).
The sediments of the Arverne domain were metamorphosed mainly during the Acadian phase of the Caledonian orogeny
Caledonian orogeny
The Caledonian orogeny is a mountain building era recorded in the northern parts of the British Isles, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly...
about 400 – 350 million years ago. Pressures reached 0,6 – 0,8 GPa according to a burial depth of about 20 – 25 kilometers, the temperature gradient being 20 – 25 °C per kilometer. The original sedimentary succession transformed into migmatite
Migmatite
Migmatite is a rock at the frontier between igneous and metamorphic rocks. They can also be known as diatexite.Migmatites form under extreme temperature conditions during prograde metamorphism, where partial melting occurs in pre-existing rocks. Migmatites are not crystallized from a totally...
s at its base, followed by gneiss
Gneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
es, micaschists and finally sericite schists and chlorite schists at the top, the schists at the top only being metamorphosed under greenschist facies conditions. The volcanogenic material was metamorphosed to leptynites and amphibolite
Amphibolite
Amphibolite is the name given to a rock consisting mainly of hornblende amphibole, the use of the term being restricted, however, to metamorphic rocks. The modern terminology for a holocrystalline plutonic igneous rocks composed primarily of hornblende amphibole is a hornblendite, which are...
s.
Included in this metamorphic succession are also augengneisses that originated from sheared orthogneisses, which in turn represent porphyric granitoid
Granitoid
A granitoid or granitic rock is a variety of coarse grained plutonic rock similar to granite which mineralogically are composed predominately of feldspar and quartz. Examples of granitoid rocks include granite, quartz monzonite, quartz diorite, syenite, granodiorite and trondhjemite. Many are...
s dated around 500 MA BP (Furongian).
Ruteno-Limousin domain
The metamorphic rocks of the Ruteno-Limousin domain are only encountered in the Limousin, the Rouergue, the eastern Marche, the Châtaigneraie, the southern MargerideMargeride
Margeride is a mountainous region of France, situated in the Massif Central, inside the départements of Cantal, Haute-Loire and Lozère.-Location:...
and in the western parts of the Cevennes. The once sedimentary succession starts off like in the Arverne domain but comprises also a Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
sequence at its top. The Paleozoic begins in the Lower 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...
with a thick volcanogenic series of rhyolitic composition. This is followed by dated Upper Cambrian, 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...
and 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...
.
In the Limousin the Ruteno-Limousin domain underwent like the Arverne domain solely the Acadian phase metamorphism. In the Rouergue though this was overprinted by hercynian metamorphism that developed under LP/HT conditions.
Cevenole domain
The Cevenole domain includes the Cevennes, the Montagne Noire, the Monts d'Albi and the Lyonnais. Basal crystalline schists of the Arverne Domain are followed by a well-dated Paleozoic (Cambrian and Ordovician). In the Montagne Noire in the very South this Paleozoic series completely escaped any metamorphic transformations and reaches right up to the Mississippian, but farther north in the Albigeois and in the Cevennes it progressively takes up hercynian metamorphism.To summarize: all three domains share the basal Neoproterozoic succession (or at least parts of it). They differ in the Paleozoic part: the Arverne domain for example is completely devoid of Paleozoic rocks. The Arverne domain reaches structurally deepest, its Neoproterozoic goes right down to basal migmatites. The Cevenole domain on the other hand is much more superficial, its Neoproterozoic comprises only structurally higher schists and in the Montagne Noire even a completely nonmetamorphic Paleozoic. The Ruteno-Limousin domain takes on an inetrmediary position.
Low-grade metamorphic sequences
Low-grade greenschist facies rocks are underrepresented in the Massif Central and mainly occur along the periphery. Examples are the Génis UnitGénis 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 Thiviers-Payzac unit in the Bas Limousin, the Mazerolles Schists in the Haute Charente, the Brévenne Unit in the Lyonnais in the Northeast and the schists of the Albigeois in the South.
The Génis Unit for example shows the following succession (from young to old):
- Génis Greenschist
- Upper Silurian conodontConodontConodonts are extinct chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils now called conodont elements, found in isolation. Knowledge about soft tissues remains relatively sparse to this day...
-bearing limestoneLimestoneLimestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
lenses - Génis Sericite Schist containing Ordovician acritarchAcritarchAcritarchs are small organic fossils, present from approximately to the present. Their diversity reflects major ecological events such as the appearance of predation and the Cambrian explosion.-Definition:In general, any small, non-acid soluble Acritarchs are small organic fossils, present from...
s - silicified arkoseArkoseArkose is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose....
s of Moulin du Guimalet, showing a possible affinity to the Ordovician Grès armoricain from Brittany - Génis Porphyroids, metaignimbritesIgnimbriteAn ignimbrite is the deposit of a pyroclastic density current, or pyroclastic flow, a hot suspension of particles and gases that flows rapidly from a volcano, driven by a greater density than the surrounding atmosphere....
from the Cambrian/Ordovician boundary - Excideuil Sericite Schist, probably Cambrian
The Thiviers-Payzac Unit consists mainly of rhyodacitic
Rhyodacite
Rhyodacite is an extrusive volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of granodiorite. Phenocrysts of sodium rich plagioclase, sanidine, quartz, and biotite or hornblende are typically set in an aphanitic to glassy light to intermediate...
tuff
Tuff
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
s, greywackes and siltstones. Their metamorphic degree can reach the amphibolite facies.
The Mazerolles Schists are aluminous micaschists with interbedded quartzitic
Quartzite
Quartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...
layers. They derive from pelites and siltstones and are probably Cambrian in age.
The Brévenne Unit is an ophiolitic nappe of Upper Devonian age. It comprises pillow basalts, dolerites, gabbro
Gabbro
Gabbro refers to a large group of dark, coarse-grained, intrusive mafic igneous rocks chemically equivalent to basalt. The rocks are plutonic, formed when molten magma is trapped beneath the Earth's surface and cools into a crystalline mass....
s, ultramafic rocks, chert
Chert
Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...
s and massive sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
s.
Sedimentary evolution
Nonmetamorphic sedimentary successions are very important for paleogeographic reconstructions, because they represent the paleoenvironmental settings in an unaltered or only slightly altered fashion. In the Massif central suitable successions are highly underrepresented with their main outcrops occurring along the periphery. This fact explains the difficulty in reconstructing the massif's evolution in a coherent way.Precarboniferous deposits
Precarboniferous nonmetamorphic sequences can be found in two major areas:- in the Montagne Noire at the southern edge of the massif
- in the Morvan in the Northeast
The southern edge of the Montagne Noire possesses a nearly complete sedimentary succession from the Cambrian right up to the Mississippian.
The Cambrian starts with basal rhyolites, followed by the Grès de Marcory, a sandstone formation, by archaeocyathid-bearing limestones, shales and more sandstones. The Ordovician and the Silurian consist mainly of shales, whereas the Devonian is made up exclusively of carbonates in Mediterranean facies.
Along the northern side of the Montagne Noire the series is more incomplete, the entire Upper Ordovician is missing. As a recompense one can study here the gradual changeover of the nonmetamorphic Cambro-Silurian system into the metamorphic equivalents of the Albigeois.
In the Morvan Devonian sediments of the Givetian, Frasnian
Frasnian
The Frasnian is one of two faunal stages in the Late Devonian epoch. It lasted from 385.3 ± 2.6 million years ago to 374.5 ± 2.6 million years ago. It was preceded by the Givetian stage and followed by the Famennian stage...
and Famennian
Famennian
The Famennian is one of two faunal stages in the Late Devonian epoch. It lasted from 374.5 ± 2.6 million years ago to 359.2 ± 2.5 million years ago. It was preceded by the Frasnian stage and followed by the Tournaisian stage and is named after Famenne, a natural region in southern Belgium.It was...
stages are exposed. Givetian and Frasnian are developed as reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
al limestones. The Famennian is composed of clymeniid
Clymenia
Clymenia is a genus in the ammonoid order Clymeniida, restricted to the Upper Devonian, characterized as with all clymeniids by a dorsal siphuncle that runs along the inside of the whorls, unusual for ammonoids....
-bearing shales interbedded with spilite
Spilite
Spilite is a fine-grained igneous rock, resulting particularly from alteration of oceanic basalt.The term was introduced into the geological literature by Alexandre Brongniart in 1827...
s.
Mississippian
Mississippian sediments crop out in a band stretching from the Roannais via the BeaujolaisBeaujolais
Beaujolais is a French Appellation d'Origine Contrôlée wine generally made of the Gamay grape which has a thin skin and is low in tannins. Like most AOC wines they are not labeled varietally. Whites from the region, which make up only 1% of its production, are made mostly with Chardonnay grapes...
to just southwest of Montluçon
Montluçon
Montluçon is a commune in central France. It is the largest commune in the Allier department, although the department's préfecture is located in the smaller town of Moulins. Its inhabitants are known as Montluçonnais...
.
The series starts in the Lower Viséan
Viséan
The Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from 345.3 ± 2.1 to 328.3 ± 1.6 Ma...
with shaly to sandy sediments, followed by greywackes, conglomerate
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
s and carbonate
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
s in the Middle Viséan (the Tournaisian
Tournaisian
The Tournaisian is in the ICS geologic timescale the lowest stage or oldest age of the Mississippian, the oldest subsystem of the Carboniferous. The Tournaisian age lasted from 359.2 ± 2.5 Ma to 345.3 ± 2.1 Ma...
is generally missing in the Massif Central, exceptions being some scattered occurrences in the Morvan). Very important are the transgressing Tufs anthracifères in the Upper Viséan (dated between 335 and 330 MA BP). They consist of pyroclastic tuffs with rhyolitic or dacitic
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...
composition, cover a large area and reach large thicknesses. The name is derived from occasional interbedded anthracite layers that indicate a paralic environment near a shallow sea.
Coal-bearing Pennsylvanian
After the strong tectonic movements during the period 325 – 305 MA BP (SerpukhovianSerpukhovian
The Serpukhovian is in the ICS geologic timescale the uppermost stage or youngest age of the Mississippian, the lower subsystem of the Carboniferous. The Serpukhovian age lasted from 328.3 Ma tot 318.1 Ma...
, Bashkirian
Bashkirian
The Bashkirian is in the ICS geologic timescale the lowest stage or oldest age of the Pennsylvanian, the youngest subsystem of the Carboniferous...
and Moscovian
Moscovian (Carboniferous)
The Moscovian is in the ICS geologic timescale a stage or age in the Pennsylvanian, the youngest subsystem of the Carboniferous. The Moscovian age lasted from 311.7 ± 1.1 to 306.5 ± 1.0 Ma, is preceded by the Bashkirian and is followed by the Kasimovian...
– Sudeten Phase and Asturian Phase) accompanied by extensive granitisation the young orogen underwent late orogenic extension in the Kasimovian
Kasimovian
The Kasimovian is an geochronologic age or chronostratigraphic stage in the ICS geologic timescale. It is the third stage in the Pennsylvanian , lasting from 306.5 ± 1.0 to 303.9 ± 0.9 Ma. The Kasimovian stage follows the Moscovian and is followed by the Gzhelian.-Name and definition:The Kasimovian...
. As a consequence narrow fault-bounded graben-like depressions formed that were filled with lake sediments (conglomerates, sandstones, shales interbedded with layers rich in organic material that later transformed into coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
seams). Sometimes rhyolitic intercalations do occur.
Examples are the relatively small coal-bearing basins near Ahun
Ahun
Ahun is a commune in the Creuse department in the Limousin region in central France.-Geography:A farming area comprising the village and several hamlets situated in the valley of the Creuse River, some southeast of Guéret, at the junction of the D942, D13 and the D18.It was the Roman site of...
, Argentat
Argentat
Argentat is a commune in the Corrèze department in central France.-Geography:Argentat is situated on the Dordogne River, to the south west of Bort-les-Orgues. It is the point where the Maronne, a tributary of the Dordogne, converges with the famous river...
, Blanzy
Blanzy
Blanzy is a commune in the Saône-et-Loire department in the region of Bourgogne in eastern France.-Geography:The Bourbince forms part of the commune's north-eastern border, then flows southwestward through the middle of the commune.-References:*...
, Decazeville
Decazeville
Decazeville is a commune in the Aveyron department in the Midi-Pyrénées region in southern France.The commune was created in the 19th century because of the Industrial Revolution and was named after the Duke of Decazes , the founder of the factory that created the town.-History:The town is built...
, Graissessac
Graissessac
Graissessac is a commune in the Hérault département in Languedoc-Roussillon in southern France.-References:*...
, Le Creusot
Le Creusot
Le Creusot is a commune in the Saône-et-Loire department in the region of Bourgogne in eastern France.The inhabitants are known as Creusotins. Formerly a mining town, its economy is now dominated by metallurgical companies such as ArcelorMittal, Schneider Electric, and Alstom.Since the 1990s, the...
, Messeix
Messeix
Messeix is a commune in the Puy-de-Dôme department in Auvergne in central France.-References:*...
within the Sillon Houiller, Saint-Étienne
Saint-Étienne
Saint-Étienne is a city in eastern central France. It is located in the Massif Central, southwest of Lyon in the Rhône-Alpes region, along the trunk road that connects Toulouse with Lyon...
, Sainte-Foy
Sainte-Foy-Saint-Sulpice
Sainte-Foy-Saint-Sulpice is a commune in the Loire department in central France.-References:*...
and Sincey-lès-Rouvray
Sincey-lès-Rouvray
Sincey-lès-Rouvray is a commune in the Côte-d'Or department in eastern France.-Population:-References:*...
.
Later during the Saalian Phase the sedimentary infill of these basins was strongly folded due to wrenching movements in the adjacent basement blocks.
Permian basins
The orogenic stretching continued also during the PermianPermian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
and more basins were formed, mainly along the periphery of the Massif. The detrital sedimentary infill consisted mainly of continental red desert sandstones, siltstones and shales.
Examples are the basins near Autun
Autun
Autun is a commune in the Saône-et-Loire department in Burgundy in eastern France. It was founded during the early Roman Empire as Augustodunum. Autun marks the easternmost extent of the Umayyad campaign in Europe.-Early history:...
, Blanzy
Blanzy
Blanzy is a commune in the Saône-et-Loire department in the region of Bourgogne in eastern France.-Geography:The Bourbince forms part of the commune's north-eastern border, then flows southwestward through the middle of the commune.-References:*...
, Brive
Brive-la-Gaillarde
Brive-la-Gaillarde is a commune of France. It is a sub-prefecture of the Corrèze department. The population of the urban area was 89,260 as of 1999. Although it is by far the biggest commune in Corrèze, the capital is Tulle.-History:...
, Espalion
Espalion
Espalion is a commune in the Aveyron department in southern France.-Main sights:*Château de Calmont d'Olt*The Pont-Vieux is part of the World Heritage Sites of the Routes of Santiago de Compostela in France....
, Moulins
Moulins, Allier
Moulins is a commune in central France, capital of the Allier department.Among its many tourist attractions are the Maison Mantin the Anne de Beaujeu Museum.-History:...
and Saint-Affrique
Saint-Affrique
Saint-Affrique is a commune in the Aveyron department in southern France.-History:Saint-Affrique grew in the 6th century around the tomb of St. Africain, bishop of Comminges. In the 12th century a fortress was built on the neighboring rock of Caylus. The possession of Saint-Affrique was vigorously...
.
Mesozoic
During the MesozoicMesozoic
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...
the Massif Central stayed above sea-level, yet the severe erosional processes attacking it since the end of the Carboniferous continued unabatedly and gradually leveled the former mountain range into a peneplain. Along its edges and especially in the Southeast the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
sea deposited thick limestone sequences that later became the Causses
Causses
The Causses are a group of limestone plateaus in the Massif Central. They are bordered to the north-west by the Limousin and the Périgord uplands, and to the east by the Aubrac and the Cévennes. Large river gorges cut through the plateaus, such as the Tarn, Dourbie, Jonte, Lot and Aveyron...
.
Cenozoic
At the beginning of the CenozoicCenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
the Massif Central started to feel the effects of the pyrenean
Pyrenees
The Pyrenees is a range of mountains in southwest Europe that forms a natural border between France and Spain...
and the alpine orogeny
Alps
The Alps is one of the great mountain range systems of Europe, stretching from Austria and Slovenia in the east through Italy, Switzerland, Liechtenstein and Germany to France in the west....
, especially along its southern and eastern edges that were uplifted quite drastically. The consequences of these strong stresses on the crust initiated explosive volcanism already during the Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
. The volcanic activities have continued since then practically up to this day.
During the Late Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
the so-called Sidérolithique was deposited. This is an iron-rich sediment resembling laterite
Laterite
Laterites are soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock...
s and indicating extensive erosion of the massif (after its renewed uplift) under subtropical climatic conditions.
In the Middle Eocene (Lutetian
Lutetian
The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between and . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the Middle Eocene subepoch...
) a new distensional period started that reached its climax during the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
. The stretching of the crust caused extensional grabens to form. Examples are the roughly N-S- to NNW-SSE-striking asymmetric graben structures of the Bresse
Bresse
Bresse is a former French province. It is located in the regions of Rhône-Alpes, Bourgogne, and Franche-Comté of eastern France. The geographical term Bresse has two meanings: Bresse bourguignonne , which is situated in the east of the department of Saône-et-Loire, and Bresse, which is located...
, Cher
Cher
Cher is an American recording artist, television personality, actress, director, record producer and philanthropist. Referred to as the Goddess of Pop, she has won an Academy Award, a Grammy Award, an Emmy Award, three Golden Globes and a Cannes Film Festival Award among others for her work in...
, Limagne
Limagne
The Limagne is large plain in the Auvergne region of France in the valley of the Allier river, on the edge of the Massif Central. It lies entirely within the département of Puy de Dôme...
, Plaine du Forez and the Roanne graben. These depressions were again filled with lake sediments with occasional volcanic intercalations, the so-called peperite
Peperite
A Peperite is a sedimentary rock that contains fragments of igneous material and is formed when magma comes into contact with wet sediments. The term was originally used to describe rocks from the Limagne region of France, from the similarity in appearance of the granules of dark basalt in the...
s. The sediments can reach considerable thicknesses e.g. 2500 meter in the Limagne.
Towards the end of the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
the precursors of the great stratovolcanoes Cantal
Cantal
Cantal is a department in south-central France. It is named after the Cantal mountain range, a group of extinct, eroded volcanic peaks, which covers much of the department. Residents are known as Cantaliens or Cantalous....
and Monts Dore started to form. In the eastern Velay thick alkaline basalts extruded and phonolitic
Phonolite
Phonolite is a rare igneous, volcanic rock of intermediate composition, with aphanitic to porphyritic texture....
plugs pushed up.
During the Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
a new period of strong uplift began that led to increased erosion and triggered very strong volcanism. In fact the Massif Central experienced its climax in volcanic activities at this time - the Cantal stratovolcano for example started to build up to elevations over 3000 meters.
The last ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
saw valley glaciers and small ice caps establishing themselves on the Cantal and on the Monts Dore, as is demonstrated by moraine
Moraine
A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...
s and cirque
Cirque
Cirque may refer to:* Cirque, a geological formation* Makhtesh, an erosional landform found in the Negev desert of Israel and Sinai of Egypt*Cirque , an album by Biosphere* Cirque Corporation, a company that makes touchpads...
s.
The last phreatomagmatic explosions happened in the Chaîne des Puys
Chaîne des Puys
The Chaîne des Puys is a north-south oriented chain of cinder cones, lava domes, and maars in the Massif Central of France. The chain is about 40 km long, and the identified volcanic features include 48 cinder cones, eight lava domes, and 15 maars and explosion craters. Its highest point is...
only 3000 to 4000 years ago.
Meteorite impact
Rochechouart
Rochechouart is a commune in the Haute-Vienne department in the Limousin region in west-central France. It is a sub-prefecture of the department....
was struck close to the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
/Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
boundary (about 210 million years ago) by a large meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
, probably of the stony-iron type. The impact excavated a crater with a diameter of 20 kilometers in the peneplained basement rocks. Today the crater structure is almost completely eroded away, yet some suevite
Suevite
Suevite is a rock consisting partly of melted material, typically forming a breccia containing glass and crystal or lithic fragments, formed during an impact event...
s, several impact breccias, planar deformation features (PDFs), shatter cone
Shatter cone
Shatter cones are rare geological features that are only known to form in the bedrock beneath meteorite impact craters or underground nuclear explosions...
s and many local thrusts in the basement still document this event.
Structural organisation
Structurally the Massif Central consists of stacked metamorphic basement nappes that have been overthrust onto their southern foreland (Aquitania). The following structural units can be discerned (from structurally higher to structurally lower):- Low-grade to non-metamorphic units. Usually they overlie the Upper Gneiss Unit with a thrust contact. An exception are the discordantly overlying tufs anthracifères.
- Upper Gneiss Unit(UGU). Carries eclogiteEclogiteEclogite is a mafic metamorphic rock. Eclogite is of special interest for at least two reasons. First, it forms at pressures greater than those typical of the crust of the Earth...
and granuliteGranuliteGranulites are medium to coarse–grained metamorphic rocks that have experienced high temperature metamorphism, composed mainly of feldspars sometimes associated with quartz and anhydrous ferromagnesian minerals, with granoblastic texture and gneissose to massive structure...
remnants at its base, followed by the leptyno-amphibolitic complex and a thick anatexite-bearing paragneiss sequence. This unit has experienced the strongest metamorphism. The Upper Gneiss Unit is separated from the underlying Lower Gneiss Unit by myloniteMyloniteMylonite is a fine-grained, compact rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. It is classified as a metamorphic rock...
s. - Lower Gneiss Unit (LGU). Consists mainly of a succession of metamorphosed greywackes, pelites and rhyolites with interlayered orthogneisses (augengneisses) that originated from alkaline granitoids. The granitoids intruded the country rocks in the interval 540 – 430 MA BP. The Lower Gneiss Unit overthrusts the Parautochthonous Micaschist Unit.
- Parautochthonous Micaschist Unit (PMU). Mainly micaschists, but also minor quartziteQuartziteQuartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...
s, occasional amphibolites and carbonate lenses. The metamorphic grade is greenschist facies to epidote amphibolite facies. The PMU overthrusts the fold and thrust belt to the South. - Paleozoic fold and thrust belt. This unit is very well developed in the Montagne Noire. It shows kilometer-scale isoclinal recumbent folding with thrusting to the South. It comprises a low-grade to non-metamorphic sedimentary sequence ranging from the Lower Cambrian to the Mississippian.
- Foreland basin. This basin reaches from the southeastern Montagne Noire to the Pyrenees and is filled with Viséan and Serpukhovian turbiditeTurbiditeTurbidite geological formations have their origins in turbidity current deposits, which are deposits from a form of underwater avalanche that are responsible for distributing vast amounts of clastic sediment into the deep ocean.-The ideal turbidite sequence:...
s. Its proximal facies in the Montagne Noire carries olistholiths from the fold and thrust belt.
Geodynamic evolution
Geodynamically the Massif Central can be subdivided into six major deformational phases, according to Faure et al. (2008):- Phase D0. Synchronous with end-Silurian HP (high pressure) to UHP metamorphism recorded only in eclogites and granulitic orthogneisses of the Upper Gneiss Unit at about 415 MA BP. This phase can be correlated with the eovariscan (or Caledonian) Ardennian phase. Pressures reached 1.8 – 2.0 GPa equivalent to a burial depth of about 55 to 60 kilometers, temperatures ranged between 650 and 750 °C.
- Phase D1. This corresponds with the already mentioned mediovariscan (or Caledonian) Acadian phase in the Lower Devonian, which left a profound imprint on the Massif Central. Great recumbent isoclinal folds with a pronounced flatlying foliation were produced in this phase. The fold limbs sheared off at the hinges and turned into thrust sheets. The basement was deeply sliced and two major thrust units started to develop: the Upper Gneiss Unit and the Lower Gneiss Unit.
The movement sense of these basement nappes was top to the southwest. As a consequence of the collisional movements anatectic melts were generated between 385 and 380 MA BP and the country rocks were partially migmatisedMigmatiteMigmatite is a rock at the frontier between igneous and metamorphic rocks. They can also be known as diatexite.Migmatites form under extreme temperature conditions during prograde metamorphism, where partial melting occurs in pre-existing rocks. Migmatites are not crystallized from a totally...
. The migmatites sometimes contain eclogite remnants that have been retromorphosed to amphibolites under pressures of 0.7 GPa and temperatures at 700 °C.
In the North the Upper Gneiss Unit is unconformably overlain by undeformed Upper Devonian sediments. This shows that in this part of the Massif Central the tectono-metamorphic evolution had come to an end by 380 MA BP.
- Phase D2. Bretonian phase from 360 to 350 MA BP (end of the Upper Devonian – TournaisianTournaisianThe Tournaisian is in the ICS geologic timescale the lowest stage or oldest age of the Mississippian, the oldest subsystem of the Carboniferous. The Tournaisian age lasted from 359.2 ± 2.5 Ma to 345.3 ± 2.1 Ma...
). This phase caused ductile shearing with a top to the Northwest motion. The metamorphic conditions were MP/MT. - Phase D3. Sudeten phase. This phase was active during the ViséanViséanThe Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from 345.3 ± 2.1 to 328.3 ± 1.6 Ma...
at 345 – 325 MA BP. It initiated thusting in the South of the Massif Central that affected the Parautochthonous Micaschist Unit and the fold and thrust belt. The sense of motion was top to the SSW. Yet in the North it manifested as synorogenic stretching exemplified by the explosive volcanism that deposited the Tufs anthracifères. - Phase D4. Neovariscan crustal extension during the SerpukhovianSerpukhovianThe Serpukhovian is in the ICS geologic timescale the uppermost stage or youngest age of the Mississippian, the lower subsystem of the Carboniferous. The Serpukhovian age lasted from 328.3 Ma tot 318.1 Ma...
, BashkirianBashkirianThe Bashkirian is in the ICS geologic timescale the lowest stage or oldest age of the Pennsylvanian, the youngest subsystem of the Carboniferous...
and MoscovianMoscovian (Carboniferous)The Moscovian is in the ICS geologic timescale a stage or age in the Pennsylvanian, the youngest subsystem of the Carboniferous. The Moscovian age lasted from 311.7 ± 1.1 to 306.5 ± 1.0 Ma, is preceded by the Bashkirian and is followed by the Kasimovian...
at 325 – 305 MA BP. The stretching of the crust in a NW-SE direction caused the extensive emplacement of synkinematic leucograniteLeucograniteIn geology, leucogranites are amongst the youngest intrusions related to anatexis of continental crust anywhere in the world. Leucogranites are commonly found in deformed metapelitic/metagraywacke sequences that have been thrusted over basements during crustal thickening associated with continental...
s and monzogranites. - Phase D5. Asturian phase. Postorogenic collapse at the end of the Carboniferous (KasimovianKasimovianThe Kasimovian is an geochronologic age or chronostratigraphic stage in the ICS geologic timescale. It is the third stage in the Pennsylvanian , lasting from 306.5 ± 1.0 to 303.9 ± 0.9 Ma. The Kasimovian stage follows the Moscovian and is followed by the Gzhelian.-Name and definition:The Kasimovian...
). The stresses causing the stretching acted now in a NNE-SSW direction. They are responsible for the numerous coal-bearing graben structures.
Paleogeography
Neoproterozoic
The Neoproterozoic Era is the unit of geologic time from 1,000 to 542.0 ± 1.0 million years ago. The terminal Era of the formal Proterozoic Eon , it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods...
the Massif Central (i.e. the microcontinent Ligeria
Ligeria
Ligeria is a genus of flies in the family Tachinidae.-Species:*L. angusticornis *L. latigena Wood, 1985*L. rostrata Herting, 1971...
) and 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...
were part of 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,...
s northern edge. At that time an extremely thick flysch sequence with interbedded bimodal volcanics was laid down in the adjoining ocean to the North. During the Lower Ordovician parts of Gondwanas northern rim started to break off and a sliver carrying Armorica and its eastern continuation - also called the Hun Superterrane – slowly started drifting northward. This opened up the Paleotethys in the wake. As a consequence 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...
and the Rhenohercynian Ocean to the north were more and more constricted and eventually became subducted below Armorica or the Hun Superterrane. This subduction
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"...
event corresponds in the Massiv Central to the deformational phase D2. The final continental collision
Continental collision
Continental collision is a phenomenon of the plate tectonics of Earth that occurs at convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroyed, mountains produced, and two continents sutured together...
during the Mississippian between Gondwana and Laurussia welded Ligeria into its actual position in the interior part of the Variscan orogen. The collision event is represented in the Massif Central by the phase D3.
This is only a very sketchy paleogeographical reconstruction. Lots of models have been presented that usually differ in the sense of the subduction(s) and in the arrangements of the microcontinents. The common somewhat simplistic approach of orthogonal opening/closing can only be a first approximation, because the issue becomes a lot more complicated by trying to incorporate the very important dextral shearing motions affecting the Variscan orogen.
As an introduction into this subject see the paper by Stampfli et al. (2002).
Concluding remarks
The Massif Central being a centerpiece of the Variscan orogen has undergone a rather complex geological evolution. Since its (diachronous) exhumation it has experienced very strong erosive peneplanation uncovering the polymetamorphic crystalline basement. Supracrustal sequences of sedimentary origin are strongly underrepresented and mainly occur along the periphery. Obviously this fact seriously hinders the reconstruction of the massif's geodynamic evolution.A HP/UHP metamorphism caused by subduction at the Silurian/Devonian boundary was followed in the Devonian/Mississippian by polyphase dynamometamorphism due to crustal shortening. The latter developed a cross pattern in the resulting structures – the well known Variscan x. The intensive nappe-stacking during continental collision transported high-grade terranes in a southerly direction over less deformed units creating the impression of an inverted metamorphism – a feature so ubiquitous in the Massif Central. The last two deformational phases in the Pennsylvanian formed under extensional stresses and again produced a cross pattern in the resulting structures. The strong orogenic extension and final collapse triggered decompressional melting which led to pronounced granitisation and associated mineralisation
Mineralization (geology)
In geology, mineralization is the hydrothermal deposition of economically important metals in the formation of ore bodies or "lodes".The first scientific studies of this process took place in Cornwall, United Kingdom by J.W.Henwood FRS and later by R.W...
mainly of the Au
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
– Sb
Antimony
Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...
- W
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
- type.
The structural cross pattern can also be found spatially. In the western and central section of the Massif Central NW-SE trending structures largely dominate, whereas in the eastern section a very strong NE-SW organisation prevails.
Of great importance is the diachronous evolution in the Massif Central. Thrusting and exhumation events migrated temporally and spatially. Thrusting for instance started in the North already at 385 MA BP and only reached the South (Montagne Noire) by 325 to 315 MA BP.
Sources
- Éditions BRGM. (1996). Carte géologique de la France au millionième. Service Géologique National.
- Faure, Michel, Lardeaux, Jean-Marc und Ledru, Patrick (2008). A review of the pre-Permian geology of the Variscan French Massif Central. Les grands traits de l’évolution anté-permienne du Massif central français. Comptes Rendus Géoscience, Volume 341, numéro 2-3, pages 202-213 (Février 2009).
- Peterlongo, J. M. (1978). Massif Central. Guides géologiques régionaux. Masson. ISBN 2-225-49753-2