Canaveilles Group
Encyclopedia
The Canaveilles Group is the basal metasediment
ary succession of late Neoproterozoic
and Cambrian
age outcropping in the Pyrenees
.
Canaveilles
, a small town in the French
départment
Pyrénées-Orientales
.
. Further north in the Montagne Noire
, the southernmost promontory of the Massif Central
, a comparable succession occurs, the la Salvetat-Saint-Pons Series. The Upper Alcudian of the Iberia
n peninsula also displays great similarities with the Canaveilles Group. The group's main area of distribution focusses on the type locality and the surroundings of Mount Canigou
. Yet the group can also be encountered in the Cadí nappe on the spanish
side of the Pyrenees.
Canaveilles Group reaches a thickness of 3000 meters, otherwise its thickness varies between 2000 and 4000 meters. On Mount Canigou the group's base overlies leptynitic, so-called “transitional gneiss
es” with underlying augen gneisses. The group's age reaches back to the Ediacarian, to about 580 million years. Essentially the group consists of shale
s (with subordinate black shales) and greywacke
s, intercalated are carbonate
s and rhyodacite
s. In the Cadí nappe archeocyathid-bearing limestone
s occur during the lower Cambrian. With the onset of the middle Cambrian the Canaveilles Group is replaced by the lower metamorphic (greenschist facies conditions, chlorite zone), flysch
oid Jujols Group, to be more specific by its basal formation, the olistostrome
-rich Tregurà Formation.
s and calc schists (from top to bottom):
marbres de base). They include five layers of calcareous marble of sometimes massive habit and a layer of impure marbles that has formed from calcarenites. Within the last layer there are gneissic bands reaching ten centimeters and more in thickness; they are composed of calcsilicates and probably represent marl
y horizons.
. In some layers also clinochlore and phlogopite
appear.
Intercalated between the dolomitic marbles and the overlying calcareous marbles are layers of quartzite
and greywackes.
al origin of the marbles, most likely as bioherms.
-rich marbles. They can take on the character of multicoloured (mainly light and greenish colours), banded hornfels
. They contain the minerals diopside
, tremolite
, clinozoisite
, basic plagioclase
, microcline
and microscopic biotite
.
At the type locality these calcsilicates form sandy calcschists.
s) have been metamorphosed to fine-grained leptynites. Stratigraphically they usually follow after the basal calcareous marbles, but occasionally they can be found somewhat higher above the calcareous marbles. Radiometric age dating on these rhyodacites yielded 581 million years supporting the Ediacarian age of the Canaveilles Group.
. The sediments are of marine origin and probably were left behind on the continental margin. Possible bioherms within the carbonaceous intercalations and the archeocyathid reefs in the Cadí Nappe point at shelf
or shelf edge deposits with some incorporated reefal complexes. The rhyodacites probably were associated with an island arc
, so it is possible that the Canaveilles Group was sedimented in a backarc position. This finds support in the group's close relationship with the Alcudian of central Iberia, a 15 kilometer! thick, strongly subsident Neoproterozoic sedimentary succession formed along a transform fault traversing the active northern margin of Gondwana.
in the Pennsylvanian
about 310 million years ago the sediments of the Canaveilles Group were metamorphosed
under mesozonal conditions (amphibolite facies). The original shales transformed into mica schists of the cordierite, andalusite and sillimanite zone in the lower part of the section, higher up they only converted to greenschist facies phyllite
s of the biotite zone. The carbonaceous intercalations became marbles and calcsilicates. Close to the contact with the “transitional gneiss” first the andalusite
isograd
is reached, followed by the cordierite
isograd. This indicates a magmatic origin of the gneisses formed from intrusive granitoid
s.
s. These dikes form part of the deep-seated Canigou granite. They intrude mainly the basal calcareous marbles and the dolomitic marbles, but can also be found higher up-section. In the lower section diorite
s and quartz diorite
s sometimes occur. All these granitoid intrusions developed after the formation of the nappe structures towards the end of the Variscan orogeny.
. In the Canigou Massif the group's metasediments together with the gneisses and the augengneisses were folded into a gigantic flat-lying isoclinal fold. Due to shearing in the fold limbs two nappe units formed which were later deformed plastically (internal folding) and buckled anticlinally. Upon reaching the brittle regime the continuing shortening led to thrusting and backthrusting (especially along the south side of Mount Canigou).
Since several revisions of the intrusion age of the orthogneisses now all find a lower Ordovician age of 474 million years for the last cristallisation on zircon
s , the concept of a Cadomian
basement has become highly questionable. This also casts doubts on the presumed isoclinal fold structure, yet the nappes and later deformations rest established.
A further consequence of the intrusive character of the orthogneisses resides in the fact, that the underlying paragneisses, once considered to be also of Cadomian age, now have to be attributed to the Canaveilles Group. Most likely these metagreywackes only have undergone a higher degree of metamorphism .
Metasediment
In geology, metasediment is sediment or sedimentary rock that shows evidence of having been subjected to metamorphism. The overall composition of a metasediment can be used to identify the original sedimentary rock, even where they have been subject to high-grade metamorphism and intense...
ary succession of 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 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...
age outcropping in the Pyrenees
Geology of the Pyrenees
The Pyrenees form part of the huge alpine orogenic system. This 430 kilometre long, roughly east-west striking, intracontinental mountain chain divides France, Spain, and Andorra. It has an extended, polycyclic geological evolution dating back to the Precambrian...
.
Etymology
The Canaveilles Group, sometimes also called Canaveilles Series, was named after its type localityType locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....
Canaveilles
Canaveilles
Canaveilles is a commune in the Pyrénées-Orientales department in southern France.-References:*...
, a small town in the French
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...
départment
Department
A department is a part of a larger organization with a specific responsibility. For the division of organizations into departments, see departmentalization.In particular:...
Pyrénées-Orientales
Pyrénées-Orientales
Pyrénées-Orientales is a department of southern France adjacent to the northern Spanish frontier and the Mediterranean Sea. It also surrounds the tiny Spanish enclave of Llívia, and thus has two distinct borders with Spain.- History :...
.
Geographical occurrence
The areal distribution of the Canaveilles Group centers on the eastern PyreneesPyrenees
The Pyrenees is a range of mountains in southwest Europe that forms a natural border between France and Spain...
. Further north in 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...
, the southernmost promontory of the Massif Central
Massif Central (geology)
The Massif Central forms together with the Armorican Massif 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...
, a comparable succession occurs, the la Salvetat-Saint-Pons Series. The Upper Alcudian of the Iberia
Iberia
The name Iberia refers to three historical regions of the old world:* Iberian Peninsula, in Southwest Europe, location of modern-day Portugal and Spain** Prehistoric Iberia...
n peninsula also displays great similarities with the Canaveilles Group. The group's main area of distribution focusses on the type locality and the surroundings of Mount Canigou
Canigou
The Canigou is a mountain located in the Catalan Pyrenees of southern France.Due to its sharp flanks and its dramatic location close to the coast, until the 18th century the Canigou was believed to be the highest mountain in the Pyrenees.-Trekking and sightseeing:Spectacular jeep tracks on the...
. Yet the group can also be encountered in the Cadí nappe on the spanish
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
side of the Pyrenees.
Main sequence
At its type locality the marineMarine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
Canaveilles Group reaches a thickness of 3000 meters, otherwise its thickness varies between 2000 and 4000 meters. On Mount Canigou the group's base overlies leptynitic, so-called “transitional 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” with underlying augen gneisses. The group's age reaches back to the Ediacarian, to about 580 million years. Essentially the group consists of shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
s (with subordinate black shales) and 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, intercalated are carbonate
Carbonate rock
Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite and dolostone, which is composed of the mineral dolomite .Calcite can be either dissolved by groundwater or precipitated by...
s and rhyodacite
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...
s. In the Cadí nappe archeocyathid-bearing limestone
Limestone
Limestone 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....
s occur during the lower Cambrian. With the onset of the middle Cambrian the Canaveilles Group is replaced by the lower metamorphic (greenschist facies conditions, chlorite zone), 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...
oid Jujols Group, to be more specific by its basal formation, the olistostrome
Olistostrome
The term olistostrome is derived from olio - a dish of many ingredients or stew; a mixture of heterogeneous elements; hodgepodge. and stroma - a bed covering...
-rich Tregurà Formation.
Carbonate interlayers
Within its schists the Canaveilles Group contains at its type locality four carbonate interlayers which have been metamorphosed to marbleMarble
Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite.Geologists use the term "marble" to refer to metamorphosed limestone; however stonemasons use the term more broadly to encompass unmetamorphosed limestone.Marble is commonly used for...
s and calc schists (from top to bottom):
- calcsilicates
- calcareous marbles
- dolomiticDolomiteDolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....
marbles - basal calcareous marbles
Basal calcareous marbles
Intercalated at the base of the group are about 150 meters of calcareous marbles (fr.French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
marbres de base). They include five layers of calcareous marble of sometimes massive habit and a layer of impure marbles that has formed from calcarenites. Within the last layer there are gneissic bands reaching ten centimeters and more in thickness; they are composed of calcsilicates and probably represent marl
Marl
Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...
y horizons.
Dolomitic marbles
The fine-grained, grey to cream coloured dolomitic marbles develop the mineral chondroditeChondrodite
Chondrodite is a nesosilicate mineral with formula 522. Although it is a fairly rare mineral, it is the most frequently encountered member of the humite group of minerals. It is formed in hydrothermal deposits from locally metamorphosed dolomite. It is also found associated with skarn and...
. In some layers also clinochlore and phlogopite
Phlogopite
Phlogopite is a yellow, greenish, or reddish-brown member of the mica family of phyllosilicates. It is also known as magnesium mica.Phlogopite is the magnesium endmember of the biotite solid solution series, with the chemical formula KMg3AlSi3O102. Iron substitutes for magnesium in variable amounts...
appear.
Intercalated between the dolomitic marbles and the overlying calcareous marbles are layers of quartzite
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...
and greywackes.
Calcareous marbles
The white, sometimes also greyish calcareous marbles are banded. They display a great variability in thickness. Their normal thickness of about 20 meters can increase in places up to 180 meters. These pronounced variations in thickness indicate a reefReef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
al origin of the marbles, most likely as bioherms.
Calcsilicates
The very fine-grained calcsilicates have a gneissose appearance. They originated from very potassiumPotassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
-rich marbles. They can take on the character of multicoloured (mainly light and greenish colours), banded hornfels
Hornfels
Hornfels is the group designation for a series of contact metamorphic rocks that have been baked and indurated by the heat of intrusive igneous masses and have been rendered...
. They contain the minerals diopside
Diopside
Diopside is a monoclinic pyroxene mineral with composition MgCaSi2O6. It forms complete solid solution series with hedenbergite and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class...
, tremolite
Tremolite
Tremolite is a member of the amphibole group of silicate minerals with composition: Ca2Mg5Si8O222. Tremolite forms by metamorphism of sediments rich in dolomite and quartz. Tremolite forms a series with actinolite and ferro-actinolite. Pure magnesium tremolite is creamy white, but the color grades...
, clinozoisite
Clinozoisite
Clinozoisite is a mineral, a complex sorosilicate of calcium and aluminium and is usually a grey green colour.Its formula is Ca2Al3[O|OH|SiO4|Si2O7]....
, basic plagioclase
Plagioclase
Plagioclase is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series...
, microcline
Microcline
Microcline is an important igneous rock-forming tectosilicate mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium. It is common in granite and pegmatites. Microcline forms during slow cooling of orthoclase; it is more stable at lower temperatures...
and microscopic biotite
Biotite
Biotite is a common phyllosilicate mineral within the mica group, with the approximate chemical formula . More generally, it refers to the dark mica series, primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more aluminous endmembers...
.
At the type locality these calcsilicates form sandy calcschists.
Rhyodacites
The original rhyodacites (or rhyodacitic tuffTuff
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) have been metamorphosed to fine-grained leptynites. Stratigraphically they usually follow after the basal calcareous marbles, but occasionally they can be found somewhat higher above the calcareous marbles. Radiometric age dating on these rhyodacites yielded 581 million years supporting the Ediacarian age of the Canaveilles Group.
Depositional environment
Most likely the Canaveilles Group was deposited during the interval end-Neoproterozoic to lower Cambrian at the northern edge of GondwanaGondwana
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,...
. The sediments are of marine origin and probably were left behind on the continental margin. Possible bioherms within the carbonaceous intercalations and the archeocyathid reefs in the Cadí Nappe point at shelf
Shelf
Shelf may refer to:* Shelf , a flat horizontal surface used for diplay and storage* Shelf , a user interface feature in the NeXTSTEP operating system* Shelf, West Yorkshire, a village in England...
or shelf edge deposits with some incorporated reefal complexes. The rhyodacites probably were associated with an island arc
Island arc
An island arc is a type of archipelago composed of a chain of volcanoes which alignment is arc-shaped, and which are situated parallel and close to a boundary between two converging tectonic plates....
, so it is possible that the Canaveilles Group was sedimented in a backarc position. This finds support in the group's close relationship with the Alcudian of central Iberia, a 15 kilometer! thick, strongly subsident Neoproterozoic sedimentary succession formed along a transform fault traversing the active northern margin of Gondwana.
Metamorphism
During the Variscan orogenyVariscan 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:...
in the Pennsylvanian
Pennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
about 310 million years ago the sediments of the Canaveilles Group were metamorphosed
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...
under mesozonal conditions (amphibolite facies). The original shales transformed into mica schists of the cordierite, andalusite and sillimanite zone in the lower part of the section, higher up they only converted to greenschist facies phyllite
Phyllite
Phyllite is a type of foliated metamorphic rock primarily composed of quartz, sericite mica, and chlorite; the rock represents a gradation in the degree of metamorphism between slate and mica schist. Minute crystals of graphite, sericite, or chlorite impart a silky, sometimes golden sheen to the...
s of the biotite zone. The carbonaceous intercalations became marbles and calcsilicates. Close to the contact with the “transitional gneiss” first the andalusite
Andalusite
Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5.The variety chiastolite commonly contains dark inclusions of carbon or clay which form a checker-board pattern when shown in cross-section....
isograd
Isograd
In geology, an isograd is a plane of constant metamorphic grade in the field; it separates metamorphic zones of different metamorphic index minerals. On geologic maps focusing on metamorphic terranes , the boundaries between rocks of different metamorphic grade are commonly demarcated by isograd...
is reached, followed by the cordierite
Cordierite
Cordierite or iolite is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: 2 to 2...
isograd. This indicates a magmatic origin of the gneisses formed from intrusive 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.
Magmatism
The sedimentary succession of the Canaveilles Group often is crosscut by dikes of two-mica granite and associated pegmatitePegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....
s. These dikes form part of the deep-seated Canigou granite. They intrude mainly the basal calcareous marbles and the dolomitic marbles, but can also be found higher up-section. In the lower section diorite
Diorite
Diorite is a grey to dark grey intermediate intrusive igneous rock composed principally of plagioclase feldspar , biotite, hornblende, and/or pyroxene. It may contain small amounts of quartz, microcline and olivine. Zircon, apatite, sphene, magnetite, ilmenite and sulfides occur as accessory...
s and quartz diorite
Quartz diorite
Quartz diorite is an igneous, plutonic rock, of felsic composition, with phaneritic texture. Feldspar is present as plagioclase with 10% or less potassium feldspar. Quartz is present at between 5 to 20% of the rock. Biotite, amphiboles and pyroxenes are common dark accessory...
s sometimes occur. All these granitoid intrusions developed after the formation of the nappe structures towards the end of the Variscan orogeny.
Structural development
During the Variscan orogeny the Canaveilles Group was not only metamorphosed but also strongly deformedDeformation
In materials science, deformation is a change in the shape or size of an object due to an applied force or a change in temperature...
. In the Canigou Massif the group's metasediments together with the gneisses and the augengneisses were folded into a gigantic flat-lying isoclinal fold. Due to shearing in the fold limbs two nappe units formed which were later deformed plastically (internal folding) and buckled anticlinally. Upon reaching the brittle regime the continuing shortening led to thrusting and backthrusting (especially along the south side of Mount Canigou).
Since several revisions of the intrusion age of the orthogneisses now all find a lower Ordovician age of 474 million years for the last cristallisation on zircon
Zircon
Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...
s , the concept of a Cadomian
Cadomian Orogeny
The Cadomian Orogeny was a tectonic event or series of events in the late Neoproterozoic, about 650-550 Ma, which probably included the formation of mountains. This occurred on the margin of the Gondwana continent, involving one or more collisions of island arcs and accretion of other material at a...
basement has become highly questionable. This also casts doubts on the presumed isoclinal fold structure, yet the nappes and later deformations rest established.
A further consequence of the intrusive character of the orthogneisses resides in the fact, that the underlying paragneisses, once considered to be also of Cadomian age, now have to be attributed to the Canaveilles Group. Most likely these metagreywackes only have undergone a higher degree of metamorphism .
Sources
- Jaffrezo, M. (1977). Pyrénées Orientales Corbières. Guides géologiques régionaux. Masson. ISBN 2-225-47290-4