Geology of the Pyrenees

The geology of the Pyrenees is determined by the fact that the approximately 430 kilometers long , polycyclic mountain range separating France and Spain is part of the huge Alpidic mountain system . The Pyrenees chain ( strike 110 °) running from east to west was created as a result of the continental collision between the microcontinent Iberia and the southwestern extension of the Eurasian plate (southern France). The rapprochement between the two continents took place from the beginning of the Upper Cretaceous ( Albium / Cenomanian ) around 100 million years ago and during the Paleogene ( Eocene / Oligocene ) between 55 and 25 million years led to the elevation of the orogen . Since then, the rock has been subject to isostatic compensatory movements, mainly to strong erosion . The profile of the Pyrenees has an asymmetrical fan structure with steeper angles of incidence on the French north side. The mountain range is not only of compressive origin , but also has a significant sinistral shear component .

Geographical framework

The intra-continental mountain range of the Pyrenees is the most north-westerly branch of the approximately 12,000 kilometers long Alpine mountain system . In a narrower sense , the Pyrenees extend over 430 kilometers in a west-northwest-east-southeast direction (N 110) from the Biscay in the west to the Golfe du Lion and the Golf de Roses in the east, the width varies between 65 and 150 kilometers. Its northern boundary is formed by the Northern Pyrenees Front ( French: Front nord-pyrénéen ), a thrust front along which ceiling units from the Northern Pyrenees zone were transported north over their foreland - the Aquitaine Basin . The southern limit is the southern Pyrenees front ; here the Sierras Marginales and equivalent ceiling units push over the Ebro basin , its southern foreland.

In a broader sense , however, the Pyrenees continue geologically to the west in the Basque and Cantabrian Pyrenees (in the so-called Basko-Cantabrian chain ). You then dive along the continental margin of Asturias . In the east, too, they do not end directly in the Golfe du Lion, like the geographic unit, but rather, using the ceiling units of the Corbières , they move into the Bas Languedoc and into southern Provence . At its eastern end in Provence, typical Pyrenean folds are superimposed with Alpidic structures, only to be completely cut off from the western Alpine arc . The Pyrenees in the broader sense are around 1000 kilometers long.

Structural structure of the orogen

The Pyrenees in the narrower sense show a fan-shaped structure in profile. The fan has a strong asymmetry with a narrow, steep French north side and a much wider and flatter Spanish south side.

Within the orogen, the following tectonic zones can be distinguished, which can be separated from each other by significant faults or thrusts (from north to south):

• the northern foreland - Aquitaine Basin
• the Sub-Pyrenees zone (or the Sub-Pyrenees basin )
• the northern Pyrenees zone
• the primary axis zone
• the South Pyrenees
• the Sierras Marginales
• the southern foreland - Ebro basin .

Northern foreland

See also: Aquitaine basin

Sub-Pyrenees zone

Geologically , the Sub-Pyrenees already belongs to the Aquitaine Basin , the northern foreland of the Pyrenees. It was folded in the course of the Eocene and pushed over by the northern Pyrenees along the staggered North Pyrenees front. The thrusts take on a pronounced ceiling character in the west with the ceiling of the Bas Adour and in the east with the ceiling of the Corbières . The continuation of these thrusts further east takes place by means of the folds and scales at Saint-Chinian and the folds near Montpellier , in order to finally pass into the southern Provencal thrust (for example near Sainte-Baume ); the latter then roots sideways south of Brignoles .

In the area of ​​the Pyrenees in the narrower sense, the Sub-Pyrenees zone is built up on the surface from sediments from the Upper Cretaceous and a very powerful Palaeogene . The sediments show a very simple fold structure with WNW-OSO-trending axes. However, the subsoil is much more complicated due to Triassic diapirs and internal North Vergent thrusts. Under more than 6000 meters thick cover layers there should be more than 6000 meters of Paleozoic basement. The Mesozoic Era consists of a more than 1500 meters thick Triassic, 500 meters thick Jura and 3000 meters thick chalk .

The detritic Lower Triassic ( red sandstone ) reaches 500 meters and consists of conglomerates , breccias , brown sandstones , claystones , shale and siltstones . The Middle Triassic ( Muschelkalk ) can be up to 400 meters thick, it contains silty shale clays, evaporites and dolomitic micrites . The growing to over 500 meters Keuper consists of carbonate-rich sediments, saline rocks and siltstones together shows but also insertions of Ophite diabase or olivinführenden dolerites . The lower Lia has transgressive character and contains up to 200 meters is not marine sandstones, marine limestones of the littoral and evaporites. The middle and upper lias consist of 230 meters of shallow marine shelf sediments (bioclastic, clayey and micritic limestone). During the Great Dane , which is mainly composed of clay-rich micrites, an oolithic barrier reef divides the sedimentation space into an outer and an inner shelf. The Upper Jurassic ( Malm ) consists mainly of shale and carbonates, towards its end the sedimentation area narrows and dolomitic micrites, ligament limes and evaporites develop. The Lower Cretaceous begins in the Neokom with sandstones, shale, limestone and calcareous breccias. In the Barremium , marls and limes follow , which in the detritic lower aptium change into sandstones, slate clays, sandy marls and limes. During the upper Aptium and the Albium , mainly marl and limestone are again sedimented. The Upper Cretaceous begins in the Turonian as littoral facies with sandstones and sandy limestone. With the beginning of the Senon ( Campanium ) a deep, elongated sedimentary basin had formed (the South Pyrenees Basin), into which a very powerful flysch series was now poured. The turbiditic flysch rocks of the Campanium and the Maastrichtian are 2000 to 3000 meters thick; they represent a rhythmic alternation of fine-grained (marl, calcareous shale and claystones) with coarse-grained sediments (conglomerates, sandstones and greywacke ). When the Cretaceous / Tertiary boundary was reached, continental red sediments of the Garumian facies were deposited in the Sub-Pyrenees basin, in which eggs were even occasionally deposited found by dinosaurs . At this point the Sub-Pyrenees Basin was folded for the first time and weakly metamorphic overprinted.

Above the Albium and before the beginning of the Campanium, volcanic rocks occur, including basaltic lavas , spilites and diabase, but also pyroclastic rocks such as tuffs , lapillite tuffs , volcanic breccias and agglomerates . The volcanic rocks are occasionally broken through by lamprophyte dikes.

North exit of the Mas d'Azil cave . The cave was washed out by the Arize from flat-lying calcareous sediments of the Lower Thanetium of the eastern Sub-Pyrenees zone.

In the Paleocene / Eocene, the sea transgressed from the Atlantic into the Sub-Pyrenees Basin, which sank under the load of the Pyrenees advancing from the south. During this period, a very powerful 2000 to 3000 meter series was deposited in the Sub-Pyrenees basin, which is made up of very fine-grain, detritic or calcareous sediments. At the end of the Eocene, sedimentation then came to a standstill due to very severe constriction (main phase of the Pyrenees).

In the area of ​​the left-shifting Muret fault , an extension of the Toulouse fault , the sub-pyrenees zone is split into two differently structured halves. The eastern half can again be divided into three between Garonne and Aude :

• In a narrow, but quite powerful, steep flysch band from Upper Cretaceous in the south. The northern Pyrenees front immediately to the south overturned the flysch band by being dragged to the north and created an asymmetrical syncline in front of it .
• In a 10 kilometer wide, folded zone with northern boundary in the Petites Pyrénées , which are due to a displacement hidden in the subsoil. The folded zone runs out again before the Aude is reached. In the upper area it consists of a covering layer of mighty Upper Cretaceous flysch, below it follows the Jura with internal thrusts and, at the bottom, the gypsum-containing Triassic.
• In a northern foreland.

In the western half only the northern foreland is developed. It consists of only moderately folded, but strongly fissured, epicontinental sediments of the Mesozoic Era , which are covered by the Miocene molasses. The fold construction shows interference between east and south-east strike directions and is interspersed with northeast-trending fractures. Triassic diapirs appear in the deeper subsurface.

In the eastern half of the Aude immersed in the northern foothills east the Paleozoic basic mountain massif of Mouthoumet on (to the south tilted Horst ), which is overlaid right here of continental Eocene.

In Bas Languedoc, the folds of the Sub-Pyrenees zone interfere with the northeast-southwest-trending Cevennes fault , a sinistral lateral shift .

Northern Pyrenees Zone

The northern Pyrenees zone, which is usually only 10 kilometers wide and sometimes grows to 40 kilometers, is very heavily folded internally. Along its northern boundary - the North Pyrenees Front - it pushes itself in a northerly direction over the Sub-Pyrenees zone and compresses it into saddles and hollows. The Northern Pyrenees, in turn, is pushed over by the Primary Axial Zone in the south along the Northern Pyrenees Fault. The North Pyrenees Fault contains tectonically highly stressed mylonites . The surrounding rocks bear horizontal linear lines and underline the laterally shifting character of the North Pyrenees Fault. In the rest of the North Pyrenees, the degree of deformation was also very high, but the elongation linear here is steep.

The sediment package of the Northern Pyrenees, which is more than 6000 meters thick, consists of Jurassic and Cretan cover layers that have slid northward above the Triassic evaporites. In contrast to the Sub-Pyrenees zone, the North Pyrenees zone contains almost no paleogene. Upper Triassic shales and evaporites can have local deposits of dolomitic rocks, tuffs and diabases (ophites). These Keup layers have a very high plasticity and usually form a tectonic mélange , with internal contact surfaces often acting as decollement (shearing). Jura and Lower Cretaceous are limestone sediments of a tectonically undisturbed, shallow shelf sea. During the middle Albium there was a drastic restructuring of the sedimentation area towards deep marine deposit conditions. The 400-kilometer-long North Pyrenees Basin was now formed , which was created as a pull-apart basin due to distensive shear movements between the continental blocks and was filled with a discordant turbiditic flysch series during the Upper Cretaceous . In the upper Albium, the basin split into two parts - an internal basin in the immediate vicinity of the North Pyrenees fault, which was filled by the flysch ardoisier , and an external basin further north with the flysch noir as a sediment filling . The external basin received the flysch à fucoides , a very powerful alternation of calcareous claystones / marls and sandy calcarenites in the course of the Turonian and Coniacian . This flysch is followed in the Maastrichtian by a regressive series consisting of quite thick marls ( Marnes de Plagne ), shelf limes ( Calcaires nankins ), as well as lagoon and lacustrian sediments. Overall, the deposits of the Coniacium-Maastrichtian period reach a thickness of 3000 meters.

The Paleozoic basement occasionally pierces the surface layers at almond-shaped, clump-like eruptions . Examples of this are the so-called massifs satellites nord-pyrénéens (northern Pyrenees satellite massifs - massifs of the Agly , the Arize , the Barousse , the Bessède , the Castillon, the Milhas , the Plantach , the Saint-Barthélémy , the Salvezines and the Trois Seigneurs) between Lourdes and Perpignan and the massifs in the northern Basque Country. These are sinistral shear bodies tilted to the north with a simultaneous vertical shear component, which were very probably already created in the Variscan orogeny. Their size varies between 1 and 300 square kilometers.

A narrow, less than 5 kilometers wide, but more than 200 kilometers long strip along the North Pyrenees Fault was covered by a dynamic and thermal metamorphosis (high temperature / low pressure HT / LP) during the Albian / Cenomanian . Isolated occurrences north of the satellite massifs (in Bigorre, in the southern Corbières) have also been metamorphosed. The metamorphosis took place without the supply of new substances (isochemical). It only affected the Mesozoic surface layers, which were transformed into Marmore and Hornfelse . The anhydrous Paleozoic basement was spared from it.

Lherzolite from the northern Pyrenees from L'Étang de Lers, Ariège

In the metamorphic strip there are isolated occurrences of Lherzolite (with the type locality at Lers ), which penetrated from the Upper Mantle by means of very deep faults . The lherzolites are crossed by pyroxenites and amphibolites . Also amphibolführende peridotites may occur. The mantle rock deposits are arranged like swarms and are no larger than 3 square kilometers (occurrence of Moncaup ). They extend from the Béarn to the southeastern Aude . Their ascent is not completely clear, but the following factors should be taken into account:

• the Jurassic and Sub-Cretaceous marbles of the metamorphic band
• the granulites of the nearby satellite massifs
• the migmatic kinzigite
• the relative proximity to the North Pyrenees Fault a little further south.
• Lherzolite clasts are embedded in the marbles of the metamorphic band, so the Lherzolite was created before the metamorphosis.

Smaller, scattered rock deposits of volcanic origin also occur in the Northern Pyrenees. They can be found in the sediments of the Lias and the Upper Cretaceous ( Aptium to Campanium ), mainly in the western section (near Tarbes , Orthez and in the Basque Country), but also in the Corbières. These are spilites , picrites and nepheline syenites that are undersaturated with silica . Lamprophyres ( Camptonite and Monchiquite ) occur on gangue rocks .

Also worth mentioning are post-metamorphic breccias of various forms .

In broad terms, the North Pyrenees can be divided into three on the basis of significant fracture zones:

• In a northern area with the surface layers that have slipped off the satellite massifs. It contains chalk flysch.
• In a central section in which the satellite massifs come to light.
• To a southern area that was affected by the Pyrenees metamorphosis.

The northern Pyrenees gradually merge to the west into the Basque belt of folds due to north-northeast-south-southwest trending sinistral lateral shifts. After a sharp bend in the area of ​​the Corbières, it continues to the east into southern Provence. At its eastern end, this now Pyrenean-Provencal zone is then interrupted and cut off by northwest-southeast trending, Miocene folds of the external western Alps .

Primary axis zone

Granodiorite massif of the Maladeta in the primary axial zone with glacier and paleozoic shell sediments (front right)

The primary axis zone is a large bulge of Precambrian and Paleozoic ( "primary") bedrock , which already during the variscan mountain formation metamorphosed and was verfaltet. Late Orogenic granitoids then appeared towards the end of the Variscan orogeny process . In the axis zone are the highest Pyrenean peaks such as the Pico de Aneto , hence the name axis .

Among the granitoids are found predominantly granodiorite ( Maladeta , Massif Bassiès ) biotitführende Granite ( Canigou , Massif Quérigut ) and two-mica granites ( Massif Caillaouas ). Most of the intrusives are very shallow epizonal rocks, with mesozonal and catazonal granitoids as well.

The great heights of the axial zone (mostly over 3000 meters) are isostatically compensated for by a thickening of the continental crust ; For example, a root zone has formed below the Maladeta , so that the Moho is found here at a depth of 50 kilometers. Because of this, a negative gravity anomaly can also be measured over a large part of the axial zone , which however gradually disappears again towards the east.

The basement is criss- crossed by large, late-cynical , more or less east-west trending fracture zones that were reactivated during the Alpine Pyrenees cycle. The fracture zones in the eastern part of the axial zone are generally steep, such as the Mérens fault . In the western part, the fracture zones are mostly shallow (more) to the north and are designed as thrusts advancing southwards, staggered from northwest to southeast, in which the basement runs over Mesozoic sediments. Examples of this are the escarpments of the Eaux-Chaudes , Gavarnie and Bénasque - Las Nogueras (area of ​​the upper reaches of the Noguera Pallaresa and Noguera Ribagorzana rivers ). The ceiling complexes associated foliations , the basement concern as well as the Hüllsedimente and are therefore alpine origin. All of these fracture zones are the result of crust narrowing, the amount of which is estimated at 10 to 20 kilometers. The axial zone was thus narrowed by around 20%. As a consequence, it was (Engl. In an anti-mold ceiling stack anti formal stack ) saddle-shaped arched.

From the Haut Béarn towards the west, the primary axial zone gradually descends like a pericline beneath the upper Cretaceous layers, only to reappear in the basement massif of Aldudes - Quinto Réal , the southernmost of the Basque massifs. In the east, the Axial Zone collapses under the Neogene and Quaternary rift systems of northern Catalonia more and more, before finally being completely covered by the Mediterranean Sea .

The central and eastern section of the Axial Zone is bounded in the north by the North Pyrenees Fault, a system of N 110-trending, very steep faults. The North Pyrenees fault is noticeably disappearing in the western section; obviously it is near the Basque Massive by a lateral displacement and, after the South will come possibly on Spanish territory south of the Basque Marble Ceiling and south of the Basque Faltenbogen continued. The fault eventually follows the Atlantic coast in the province of Santander . The southern border of the Axial Zone lies entirely on Spanish territory. This is a south-verging, Alpidic displacement along which the post-Variscan sediments of the southern Pyrenees are crossed by the axial zone; in the eastern section, the axial zone meets the sediments of the Sierras Marginales.

South Pyrenees Zone

The Monte Perdido , an internal sedimentary cover within the northern southern Pyrenees zone

The southern Pyrenees zone is built up from a Mesozoic-Eocene sediment sequence that has slid southwards from the primary axial zone at the level of the Middle and Upper Triassic; the substratum is not open anywhere. Their southerly movement was so to speak “channeled” by two conjugate faults, in the west by the northwest-southeast trending fault zone at the Cinca (thrusts and the anticline trains of Boltaña and Mediano) and in the east by the staggered, northeast-southwest trending lateral shifts on the Segre . These lateral shifts have created very complicated structures on the eastern edge of the nappe (back thrusts, fan-like interlocking of the ascending nappe units), which arose in the late Eocene and early Oligocene. The constriction forced the sediment skin to push itself over several times. This naturally led to a sharp increase in the thicknesses. Examples of this are the ceiling of Monte Perdido , the ceiling of the Cotiella or the more centrally located Bóixols ceiling and the Upper Pedreforca ceiling in an equivalent position further to the east . The Bóixols Nappe shows back thrust and at its front end it passes over the Montsec Nappe, which is further south . The sediment sequence of the Bóixols Nappe, for example, reaches a thickness of 5000 meters and consists mainly of chalk sediments. The Montsec Nappe, which can be correlated with the Lower Pedraforca Nappe, is 2000 meters thick and is composed of Upper Cretaceous limestone and syntectonic conglomerates, sandstones and shale clays from the Lower and Middle Eocene.

The South Pyrenees finally pushes along the South Pyrenees crossing over the Sierras Marginales.

The movements took place during the Eocene. They created interlocking partial ceilings with piggyback-like sedimentary basins . However, the amount of shift (to the south) is controversial. Some authors see it as relatively small, while others consider amounts between 30 and 50 kilometers.

Sierras Marginales

The Sierras Marginales (Sierras Aragoneses and Sierras Catalanes), like the South Pyrenees, also consist of a Mesozoic-Eocene sediment sequence, which is, however, much thinner with a thickness of 900 meters. The sedimentary sequence includes Keuper, Jura, discordant Lower Cretaceous bauxites , Paleocene in Garumian facies and Lower Eocene. The units of the Sierras Marginales underlay the sedimentary sequences of the Ebro basin and were then discordantly covered by its Oligocene and Miocene . Further to the west, the Sierras Marginales are replaced by the Jaca-Pamplona Nappe, which consists of Upper Ocene and Oligocene sediments. In this ceiling to the west of simplifying Gallego structures: so the sediment cover in the Basque and Cantabrian Pyrenees is recognized only by elongated and relatively open folds trains that occasionally salt risers of the Keuper be penetrated. To the east, the Sierras Marginales are represented by the Port del Comte Nappe and the Cadí Nappe , which are essentially Eocene.

The Sierras Marginales are pushed over in the north by the Montsec Nappe, which is part of the Süpyrenäzone.

The end of the ceiling movements was diachronous and slowly migrated from east to west. The movements in the Cadí Nappe ended 34 million years ago at the turn of the Eocene / Oligocene, while in the Jaca-Pamplona Nappe it wasn't until around 23 million years ago at the turn of the Oligocene / Miocene.

Southern foreland

The southern foreland of the Pyrenees is the Ebro Basin , sometimes referred to as the Ebro Foreland Basin . In its north-eastern section in Catalonia it has been compressed and folded by the approaching Pyrenees ceilings (Sierras Marginales and eastern equivalents), otherwise its layers lie flat or dip only slightly to the north. The intensity of the formation of folds decreases more and more towards the south, to finally merge into the undisturbed strata of the Ebro basin. The fold axes more or less follow the Pyrenees or the respective frontal direction of the ceiling, but turn into the northeast-southwest direction near the Segre (the Oliana anticline may serve as an example ).

The rock sequence in the Ebro Basin begins with the Paleozoic, followed by Upper Cretaceous / Paleocene Red sediments, Eocene marine limestone and marl as well as Upper Oceo evaporites ( Cardona salt ). The lower Oligocene consists of conglomerates that merge to the south in evaporites and lake sediments. In the folded area, folded paleogene is discordantly covered by flat, non-marine layers from the Miocene / Pliocene of the Ebro Basin.

The Ebro Basin deepens in the direction of the South Pyrenees front and has 3000 meters of sediment cover there. However, this is reduced to 1500 meters near the Sierras Marginales. The deepest point of the Ebro basin with 5000 meters of sediment is near Logroño at the northwest end.

Development of the Pyrenees Orange

Because of its polycyclicity, the Pyrenees orogen can be divided into two large sections:

• In a pre-alpine development cycle.
• In an alpine development cycle.

Pre-Alpine development cycle

Precambrian

Tectonic and petrological investigations were able to detect remnants of Precambrian in metamorphic rocks from the Primary Axial Zone and from the Northern Pyrenees Zone . For example, in the massif of the Canigou and the massif of the Agly, the remains of an ancient basement were discovered (recognizable by radiometric dating of granitoids and other tectonic structures), which was later incorporated into the Variscan orogen through deformations and metamorphosis.

Note: These original dates could not be confirmed in more recent investigations using the SHRIMP method (only age values ​​between 477 and 471 million years were found). The idea of ​​a Cadomian basement is therefore questionable.

Neoproterozoic and Paleozoic Era

The metamorphic rocks of the Kambro Ordovician include migmatites from the upper amphibolite facies , mica schist with andalusite , cordierite and staurolite from the lower amphibolite facies as well as green slate facies phyllites .

The epicontinental sedimentary rocks of the Neoproterozoic and the Lower Paleozoic consist largely of detritic, clayey-sandy sequences that are essentially fossilized. They were mostly influenced later by the Variscan orogeny. In the detritic sequences, carbonate formations intervene mainly in the lower section .

The sediment sequence begins with the 2000 to 3000 meter thick Canaveilles group in the Ediacarian around 580 million years ago. It mainly carries slate and greywacke with rhyodacite and carbonate interferences. Archaeocyathid limestone also occurs in the area of ​​the Cadí Nappe in the Lower Cambrian . The Canaveilles group on the border with the Central Cambrian is replaced by the flyschoid Jujols group , a 2000 meter thick series of slates , shales and siltstones with calcareous and quartzitic intermediate layers . The Jujols group shows a slightly lower degree of metamorphosis than the mesozonal Canaveilles group. Their sedimentation probably lasted into the lowest Ordovician .

After a longer gap in the shift, up to 100 meters of conglomerates of the Caradocs (5th / 6th stage of the Ordovician), the Rabassa conglomerate, follow discordantly . The cava formation , which was up to 500 meters thick, was then deposited, alternating greywacke and slate clays with volcanic intermediate layers. The overlying, approximately 200 meters thick Estana Formation consists of limestone and calcareous shale clays. The limestones contain a benthic fauna ( brachiopods , bryozoa , cystoids ) and conodonts and come from the late Ordovician. The conclusion is formed by the poorly stratified Ansobell Formation (20 to 300 meters), dark slate with micro-conglomerates that indicate glaciomarine influences. The Ansobell Formation can occasionally reach down discordantly to the Cava Formation.

The volcanic rocks and the conglomerates of the Ordovician suggest restless tectonic processes, which are very likely to be attributed to the early Caledonian cycle ( Taconic phase ).

In the Silurian , up to 20 meters of quartzites ( bar quartzite ) and then 50 to 250 meters of dark graptolite schist were sedimented in the Rhuddanium . The thickness of the graptolite schist can grow to 850 meters in the west. They cover almost the entire Silurian region ( Aeronium to Pridoli), documented by means of the graptolites. In their upper section ( Ludlow and Pridoli) they lead fossil-containing calcareous horizons and calcareous tubers (with conodonts, nautiloids , bivalvia , crinoids and ostracods ). In the vicinity of the Basque massifs, the calcareous facies merge into a detritic facies made of alternating layers of sand and siltstone. The graptolite slates were later metamorphosed into sub-amphibolite facials, strongly tectonized and form a preferred shear horizon (décollement).

The Devonian is marine and rich in fossils ( spiriferids and trilobites such as Phacops ). It has six sedimentation areas (and a myriad of formations), some of which have very different sedimentary developments (especially the Basque Pyrenees). In general, shallow marine deposits predominate in the western section, while hemipelagic facies with isolated high areas to the east. The sequence of layers (100 to 600 meters, up to 1400 meters in the Basque Pyrenees) of the Devonian, which is subject to strong fluctuations in thickness, consists of very different types of facies such as greywacke , reef limestone and sandstone . Pink to red, blue or green ligamentous and tuber limestone, the so-called griottes of the Lower Famennium, are particularly striking . Calcareous slate clays and black slate also occur.

The Lochkovium consists mostly of black schist and black limestone and is very rich in conodonts. During the pragium , a siliciclastic fan formed, the San Silvestre quartzite from the Basibé formation . There were very strong lithological differences between the Upper Givetian and Frasnian periods, with significantly increased sedimentation rates beyond that. Reef complexes then formed in the lower frasnium, and at the same time siliciclastic beds penetrated the central, western and Basque Pyrenees. With the beginning of the Middle Famennium , the sedimentation over the entire Pyrenees was unified again and until the end of the Devonian monotonous, condensed cephalopod limestones (griotte and gray to pink, bulbous supra-griotte limestone) were deposited. Towards the end of the famennium, the first shift gaps appear and then give way to a complete emergence of the western Pyrenees area at the beginning of the Mississippium . This discordance, which only developed in the western Pyrenees, corresponds to an early deformation stage of the Variscan orogeny ( Breton phase ).

The Lower Carboniferous (Mississippian) begins in the western Pyrenees with a transgression discordance (quartz pebbles). In the rest of the sedimentation area, the Supra-Griotte Limestone is followed by concordant pre-orogenic sediments, which begin with the Lower Kieselschist of the Tournaisium . The lower silica schist consists of 50 meters of black silica schist containing phosphate tubers and intermediate layers of black schist. After intermediate gray, bulbous goniatites- bearing limestone, the upper silica slate is deposited in the viséum - gray or green silica slate, which can contain pyroclastic layers. The series finally ends with gray tuber limestone.

The lower Carboniferous then merges into the detritic sediments of the synorogenic Kulm facies , up to 1000 meters thick ; The western Pyrenees are an exception, in which dark gray, laminated limestone is sedimented in the course of the Serpukhovian before the cave sediments set in. The diachronic Kulm facies consists of alternating layers of sandstones with dark shale clays and is designed like a flysch ( Turbidite ) - a harbinger of the Variscan mountain formation. Hemipelagic limestone layers, conglomerate banks, carbonate breccias and olistolites also occur in it. It begins in the east at the turn of the Viseum / Serpukhovium ( Namurium ), west of the Gállego, however, only in the Pennsylvania , in the Lower Westphal ( Bashkirium ). Their sedimentation continues in the Basque Pyrenees as far as the Moskowium . The Kulm facies were deposited in a fore-depth of the Variscan orogen migrating to the south-west; facially, this is sediments that were deposited in canyons of the continental slope and as submarine alluvial fans.

Variscan orogenesis

The Variscan orogeny is expressed in the sediments as a significant discordance , which is placed above the Lower Westphal (Bashkirium) and below the Stephans (Moskowium), sometimes also below the Upper Westphalian. The tectonic movements therefore took place around 310 million years ago, dated using fossil plant material.

The conglomerate Upper Westphal shows a significant discordance at its base, the Moskowium then consists of blue-black shale. The so-called gray unit of the Kasimovium (Stephan B) and the transition layers of the Gzhelium (Stephan C and Autunium) follow the Moskowium . These sediments are not or only weakly metamorphic, whereas the underlying consequences completely registered the Variscan metamorphosis.

The profound effects of the Variscan orogeny affected the Pyrenees in many ways. First of all, the tectonically induced constrictions that folded the Paleozoic sediments should be mentioned. Several generations of folds were often created, some of which overlap. With the folds created foliations . In addition, the Paleozoic and its Precambrian substratum were metamorphosed under high-temperature-low pressure conditions ( HT / LP ) . In places there was even anatexis ; Occasionally, Precambrian gneisses of the pre-Variscan basement together with their overlying mica slate skin were melted. A much more far-reaching consequence, however, was the late orogenic plutonism , which allowed numerous granitoids, mostly acidic, but also more basic, to penetrate. Including catazonal, relatively deep-seated , diffuse intrusives associated with migmatites ; but also epizonal, well-defined, classic plutons, some of which rose very high and spread out in the anticlines of the Variscan fold structure. Plutonism persisted from 310 to 270 million years (the cooling ages from the late Pennsylvania and Lower Permian). A typical example would be the 280 million year old Maladeta granodiorite .

Another significant effect was the formation of fractional tectonic structures , which had probably already been sketched out during the Paleozoic. The fracture structures largely follow the WNW-OSE direction of the Pyrenees , the best example of which is the North Pyrenees fault. These fracture structures will then play a decisive role in the further development of the orogen.

Alpine development cycle

Compare also: Aquitaine Basin - Sedimentary Development

Pennsylvania, Permian, and Lower Triassic

The Pic du Midi d'Ossau , remains of a former volcanic caldera from the Permian

The sediments deposited after the Asturian phase in the Upper Westphalian (Moskowian) up to the Lower Triassic can be regarded as late Orogenic molasses of the Variscican. In half-trenches in the outgoing Pennsylvania and in the Permian, 2500 meters of non-marine sediments with intermediate andesites and basalts collected . Detritic formations of limnic character with coal seams in the Stephan (Kasimovium and Gzhelium) followed by red sandstones with isolated plant remains in the Permian are the typical weathering products of the variscides that have not yet come to rest.

The gray unit of the Kasimovium is a sequence with grain size decrease towards the hanging wall. It begins with breccias and conglomerates at the base and then turns into sandstones and shale clays with coal seams (anthracite deposits near Campo de la Troya ). It also contains andesitic layers, which can be very important in places. The transition layers of the Gzhelium, like the gray unit, also form a cycle with grain size decrease towards the hanging wall (conglomerates, sandstones and claystones with coal seams). On volcanic rocks, however, they have tuffs and rhyodacite lavas. They close with lacustrian calcareous sediments containing stromatolites , charophytes and ostracods.

The continental red sediments of the Permian lie discordantly on the transitional layers. They show strong fluctuations in thickness and can reach up to 800 or 1000 meters. Its main distribution area is the Basque Pyrenees and the Axial Zone. Like the sediments of St. Stephen, they were also deposited as alluvial (in alluvial fans and draining rivers) and as limnic sediments in transient basins within the Variscan orogen.

The already mentioned fracture structures play an important role in the facial distribution of these sediments. At the same time, however, they also influenced the distribution of successive volcanic eruptions, such as the calcareous volcanic series on the Pic du Midi d'Ossau (andesitic storages and lacolites ) or the basalt series of the Basque Country (basalt lavas from La Rhune ). The triggers for the volcanism are probably the first sideways movements of Iberia in relation to the Eurasian plate.

The Permian can be divided into three sequences in the axial zone (from hanging wall to lying):

• Episode of la Peña de Marcanton . It reaches a thickness of 500 meters and is predominantly fine-grained.
• Follow the Pic Baralet . Grows up to 300 meters thick and contains polygenic conglomerates with fragments of Paleozoic limestone embedded in red sandstone. It is partly discordant on the sequence of the Somport.
• Follow the Somport . A generally fine-grained sequence that can be up to 300 meters thick and consists of red to purple clay stones. It follows the transitional layers discordantly.

The detritic Lower Triassic ( red sandstone ) is very similar in its formation to the consequences of the Permian. It is 400 to 500 meters thick and is made up of coarse conglomerates, sandstones, psammites with plant prints ( Equisetites , Coniferomyelon ), as well as green and red to purple clay stones. At this point in time, the leveling of the Variscan orogen is already well advanced and the sedimentation areas are widening.

Middle Triassic to Upper Jura

The sediment sequences on the north and south sides of the Pyrenees are very similar from the Middle Triassic to the Upper Jura .

In coquina a marine advance, but only affects the North Pyrenean Zone and the Basque Country already done again. It leaves 20 to 100 meters of dolomitic cell limestone, gray fossil limestone and wave limestone. In the Upper Triassic ( Keuper ) the sedimentation extends to the entire Pyrenees area. In lagoons to settle evaporites - colorful, gypsum leading iron-rich clays, gypsum, anhydrite , dolomite marl, dolomite, rock salt , and potash and magnesium salts occur. At the turn of the Upper Triassic / Hettangian , doleritic tholeiites ( ophites ) are formed in the Pyrenees and in the southern Aquitaine Basin, indicating renewed movements in the fracture structures (submarine fissure eruptions and storage channels in as yet unconsolidated Keuper sediments).

The further course of sedimentation in the Jura is characterized by the growth of a carbonate shelf. The sediments consist of epicontinental deposits of the littoral followed mainly by limestone, marl and dolomites with marine or littoral fauna. The sedimentation area of ​​that time was subject to distant forces that created elongated troughs with different subsidence along the Variscan fracture structures , interrupted by threshold regions .

The Lias begins with a transgression that is more significant than the sea advances in Muschelkalk and Keuper. Its overall thickness varies between 150 and 400 meters. When the sea level rises, fossil-bearing limestone sediments in the hettangium, which is replaced by evaporites (rock salt and anhydrite with isolated layers of carbonate) with the onset of regression. At the edge of the basin and in the eastern Pyrenees, clayey limestone and ribbon dolomites with anhydrite layers are deposited, which are converted into monogenic breccias by dissolving the anhydrite. During the Lower Sinemurian, the sea retreat continues, intra- and supratidal ligament limestone and dolomite are deposited. With a renewed rise in sea level in the Upper Sinemurium (Lotharingium), more open marine conditions are established, fossil limes appear in deeper areas and oolite limes on thresholds. The Middle Lias ( Pliensbachian ) also begins transgressively with fine-detritic, calcareous-marly sediments (iron-containing oolites, fossil limestone and marl), which then turn into marl. In the east, under poorly ventilated conditions, pyrite-containing clay stones form with a very rich ammonite fauna in the south-east; the Atlantic ammonite fauna, on the other hand, is relatively monotonous. During the Upper Lias ( Toarcium ) the fine detritic sedimentation continues at high level. Pelagic, black marls ( marnes noires and schistes esquilleux ) are deposited . Towards the end of the Upper Lias, regressive tendencies are again noticeable.

The sea retreat that began at the end of the Lias continues in the Dogger . In the vicinity of Pau an oolite barrier grows up to Poitiers , which divides the sedimentation space into two halves. The bar remains in place up to the Upper Malm. On the deeper half, which is open to the Atlantic, infratidal shelf sediments are sedimented (black to bluish, clayey limestone rich in benthic organisms, microfilaments and ammonites); on the closed east side, a huge intertidal arises in which various carbonate facies such as pseudooolites and ligament dolomites as well as evaporative dolomites (Anhydrite) are deposited. The intertidal sediments are subject to a simultaneous onset of strong dolomitization. Towards the end of the Dogger there is a further drop in sea level.

Upper Jurassic and Lower Cretaceous

With the Upper Jura ( Tithonium ) and the Lower Cretaceous there was a drastic change in the situation. At the same time, the Iberian spreading movement begins and the Bay of Biscay slowly begins to open (with the formation of oceanic crust during the period from the middle Albian to the end of the Coniacian).

In the Malm , which reaches a total thickness of 600 to 750 meters, sedimentation only begins again in the Upper Oxfordium , the Lower Oxfordium is hardly represented. The 100 to 150 meter thick Oxfordium consists to the west of the oolite bar of infratidal shelf sediments (clayey, sandy and pyrite limestone), the eastern area is still subject to dolomitization. The 300 to 400 meter thick Kimmeridgium experienced a strong unification of the entire sedimentation area with noticeable flattening of the western area. Solid, very fine-grained, black lithographic limestones and fine-grained plate limestones are deposited. During the Tithonian, which reaches 200 meters in thickness, strong regressive tendencies become noticeable, which end in a complete retreat of the sea (in the Basque Country the retreat took place at the end of the Kimmeridgian). In the course of the regression, evaporitic and dolomitic, but also lagunar and lacustrine facies are left behind.

After a sea advance from the southeast through a narrow sea strait east of Pau in the Berriasium , which leaves a maximum of 100 meters of intertidal to subtidal limestone with sandy to clayey marginal facies, emersion occurs in the neocom. During the Valanginian and Hauterivian , bauxites are formed on the sills that have emerged at the expense of clayey marls under ferallitic climatic conditions , which are fossilized by later transgressions. In the trough aggregations, after a further sea incursion in the Barremium from the east , 200 to 300 meters of marine shelf carbonates are deposited, such as dolomites, algae limestone , foraminiferous limestone and rudist limestone - sediments of the Urgon facies that can occur as far as the Albium (Corbières, southern Pyrenees zone ). Under the sinking sea level in the Upper Barremium, black, pyrite-containing claystones and lagoon limestone rich in ostracods and characeae sediment.

From the turn of the Barremium / Aptium , marked by a renewed high level, there are four more sea level oscillations during the Aptium and Albium, which lead to significant sediment accumulation (up to 3000 meters in places!). Due to the sinking of the Atlantic rift zones, the water masses of the Atlantic and the Tethys are now mixed for the first time. The sediments of the Aptium / Albium period are characterized by a competitive interplay of fine-grain terrigenic and organogenic deposits. The latter are responsible for the formation of flat shelf platforms, built by rudists, hexacorals and algae. In the Upper Albium, terrigenous sedimentation ultimately gains the upper hand. Various shallow marine, partly calcareous sandstone formations are formed. The origin of the detritus is the Aragon / Pyrenees region, which is experiencing an initial epirogenetic uplift . The fluvial delta sediments of the Formation de Mixe , which come from the south, and the very heterogeneous, up to 1000 meters thick, conglomerate poudingues de Mendibelza , which are interpreted as the top set of a delta front, are also related to this.

Upper Chalk

Before the beginning of the Upper Cretaceous, the Pyrenees in the Albium split into two very different facies areas. On the north side of Iberia (South Pyrenees Zone and Primary Axis Zone) large-scale shelf carbonates are deposited; they have only reduced thicknesses due to repeated drying. In the northern Pyrenees zone, however, due to shear movements ( transtension ) occurring under crustal expansion, a very strongly sinking flysch trough forms, which essentially follows the east-west arranged Variscan fracture zones and is split into two sub-branches by the massifs of the northern Pyrenees zone (the so called sillon aturien with up to 2500 meters at flysch ardoisier in the south branch and flysch noir in the north branch). The trough sinks towards the Atlantic and runs out again before it reaches the Aude. On its north side it is accompanied by the relatively stable Aquitaine shelf. There had probably been very significant crust thinning along its course from the Atlantic.

This transtensive crustal expansion is likely to be the cause of the Pyrenees metamorphosis, which is characterized by an increased heat flow but relatively low pressures . The minerals biotite , diopside and scapolite form new ones . The metamorphosis is diachronic, in the eastern northern Pyrenees it was dated radiometrically as Albium, whereas in the Basque Country in the west it took place much later, namely in the Campanian (for example in the Basque marble ceiling). For some authors, the metamorphosis persists in a weakened form even up to the K / T limit , even up to the beginning of the Eocene.

During the Upper Cretaceous two deformation phases occur with the formation of foliations (Upper Albian to Lower Cenomanian and Santonian to Maastrichtian ). At the same time, the sedimentary sequence is affected by several discordances . The flysch trough is narrowed and an orogenic bulge develops at the edge of Iberia, which slowly begins to migrate north towards the foreland. This shifts the flysch sedimentation originating from it and the trough axis to the north (transition from the northern Pyrenees basin to the sub- Pyrenees basin during the santonium, in which 1000 to 4000 meters of flysch à fucoides are sedimented).

Throughout the Upper Cretaceous, the Variscan fracture zones were of crucial importance for the sedimentary development. This is underlined by the penetration of alkaline magmatites in the period from middle Albium to the end of Coniacium. Submarine basalt lavas were delivered within the western northern Pyrenees zone, and various intrusive bodies in layers of the Upper Cretaceous gave way in the Béarn and Bigorre .

Cenozoic

The layer sequences of the Paleocene illustrate the differences between the eastern and western Pyrenees. In the west, the marine shelf sedimentation continues and the flysch trough continues to show subsidence. In the east, however, are since the late Cretaceous and during the Danian the continental red beds of garumnischen facies sold - alluvial Schwemmsedimente and marsh deposits. During the Paleoocene, crustal constrictions and uplifts due to tectonically induced crusts already occurred in the eastern Pyrenees.

Marine sedimentation also continued in the western Pyrenees during the Eocene . Limes, marls and sandstones with foraminifera and benthic fauna are sedimented in two sinking basins north and south of today's chain. However, the Eocene on the northern French edge of the chain (Northern Pyrenees zone) is only thin and full of facies changes. Short-term transgressions and regressions as far as Languedoc can be tracked in it. In the course of the Ypresium , strong conglomerate deposits then set in.

These conglomerate deposits are signs of a significant orogenic phase in the Pyrenees, which was accompanied by strong deformations and uplifting movements ( Pyrenees main phase ). The so-called Poudingues de Palassou were formed , which are then discordantly overlaid by layers of the end of the Eocene. The deformation phase can thus be assigned to the Ypresium and the Lutetium , the period from 50 to 40 million years.

On the Catalan south side of the Pyrenees, folded conglomerate beds could be dated as Upper Lutetian to Bartonian (about 44 to 37 million years ago). They are also covered discordantly by layers of the end of the Eocene with continental fauna.

The main phase of the Pyrenees manifested itself on both sides of the axial zone as thrust and thrust faults with relatively large offsets. The movements took place north on the French side and south on the Spanish side. However, they were not symmetrical - so the Spanish side shows much flatter angles of incidence. Not only the Mesozoic and Paleogenic shell sediments were affected, but also large parts of the Variscan basement. The variscical not only followed rigidly the fracture structures sketched out in the Paleozoic, but was also often intensively deformed in alpine fashion according to its heterogeneities and anisotropies.

Other phases of deformation of lesser importance followed the main phase of the Pyrenees and ultimately gave the chain its current character. For example, on the northern edge of the Ebro Basin at the level of the Sierras Marginales, the folded Oligocene is discordantly obscured by the flat, detritic, continental Miocene . This suggests a tectonic phase in the late Oligocene (around 25 million years BP).

Already during the entire Miocene the prominent orogen was intensely eroded. This is expressed as enormous molasse deposits in the foreland basins, such as B. the Aquitaine Basin. In the Pliocene , the Pyrenees chain was raised again, leading to the formation of alluvial alluvial fans at the foot of the mountain. One example is the huge Lannemezan rubble fan . Another consequence of the highlights is the leveling area that can be found at different altitudes (3000 to 2000 meters in the Axial Zone, around 1000 meters in the Pays de Sault , 400 meters in the Agly massif and only 100 meters in the Corbières). They are generally deeper and deeper towards the east and testify to elevations at the end of the Oligocene, towards the end of the Miocene ( Pontic planarization ) and towards the end of the Pliocene ( Villa-Franchian planarization ).

Neogene sediments have been preserved in the Pyrenees mainly in smaller collapse basins on the edge of the Mediterranean (such as at Cerdagne ). These collapse basins were often flooded by the Mediterranean (rift breaks near Ampurdan and in Roussillon with Pliocene fauna). In this case, too, movements on old fracture systems were decisive. The volcanic area around Olot could ultimately be traced back to the same cause.

The Ossoue glacier on Pic Montferrat in the Vignemale massif

In the Quaternary , the Pyrenees were covered by glaciation , but of much less intensity than, for example, the Alps. More important glacier advances took place on the north side of France in the valleys of the Gave d'Ossau , the Gave de Pau , the Garonne and the Ariège . However, the Pyrenees glaciers have seen a drastic decline since 1850 due to global warming . In 2016 there were still 19 smaller real glaciers, as well as glacier remnants and Kar glaciers (examples are the glaciers on Aneto, the Ossoue glacier on the Vignemale , and glaciers on the Maladeta and Monte Perdido). In 1850, the glacier surface was still around 20.6 square kilometers, in 2016 it was only 2.4 square kilometers.

archeology

The Pyrenees were undoubtedly visited by humans a long time ago. The best example of this is the Arago Cave , in which about 450,000 year old " Homo erectus " finds were made. But there are also caves with a much younger age of settlement ( Gravettien , Magdalenien ) such as Altamira near Santander , especially known for their excellent ceiling paintings, or Gargas, Isturitz and of course the Mas d'Azil cave . Of tools are Palaeolithic chopper and other stone tools of Roussillon to lead.

Geodynamic development

The Pyrenees orogen undoubtedly has a very long geological development and was also involved in several mountain formations . Neoproterozoic remains (Canigou, Agly) may already indicate Cadomian crustal areas. The signs of Caledonian movements are already clearer (conglomerates and volcanic rocks in the Ordovician). During the Variscan orogeny in Pennsylvania, the Primary Axial Zone and the Southern Pyrenees became an integral part of the later individualizing microcontinent of Iberia. The Sierras Marginales can already be assigned to the so-called Ebro Block , a north-eastern part of Iberia. The position of the northern Pyrenees zone cannot be clearly determined. The sub-Pyrenean zone, on the other hand, was part of the microcontinent of Aquitania . Iberia and Aquitania lay south of the southern Variscan thrust front and were thus the southern foreland of the Variscan orogen. Both micro-continents originally emerged from the northern continental margin of Gondwana .

After the conclusion of the Variscan orogeny, Iberia was connected to northwestern France via the Armorican massif to the north and probably formed the northwestern extension of Aquitania. His later movements were to become decisive for the alpine cycle of the Pyrenees. There is agreement among geologists on this fact, but opinions differ somewhat about the precise sequence of movements.

As early as the Upper Jura , an arm of the rift began to advance out of the spreading central Atlantic along the north-western French continental margin towards Aquitaine . Tithonium is usually set as the time for this . As a result, Iberia then moved south from the Armorican massif. From the middle Albium onwards, oceanic crust formed in the space released . The complete oceanization of the Bay of Biscay was completed 84 million years ago at the turn of the Santonium / Campanium, as evidenced by the magnetic anomaly C 34. Paleomagnetic measurements have shown a counterclockwise rotation of 35 ° for Iberia. The drift of Iberia took up the entire Lower Cretaceous. Due to the rotation component, the northeastern edge of Iberia moved closer to Aquitania. One consequence was the emergence of transient pull-apart trenches in the northern Pyrenees zone from the middle Albium , which were filled with flyschen. The strong crust thinning below the Northern Pyrenees caused an increased heat flow and ultimately led to a high temperature / low pressure metamorphosis, the beginning of which is dated 108 million years ago. At about the same time the Lherzolites were finally placed . Associated with the transtensive movements are also the alkaline plutonites , which penetrated from the middle albium to the end of the coniacium. The temporal migration of the metamorphosis to the west suggests a significant sinistral sense of movement between Aquitania and Iberia (estimated offset around 200 kilometers) - the metamorphosis did not reach the Basque Country until the Campanian around 80 million years ago.

With the beginning of the Turonian 90 million years ago, the transtensive phase came to an end and was subsequently replaced by narrowing . The rifting in the Basko-Cantabrian Basin, Northern Pyrenees and Sub-Pyrenees Basins came to a standstill and, in return, the basin inversion began . H. their emphasis on former faults, which have now been converted into suspension or thrust orbits. This first, still relatively weak compression phase with shortening rates of less than 0.5 millimeters / year lasted until the end of the Thanetium . On the Spanish side, the first ceilings were placed during this phase (Upper Pedraforca, Bóixols and Turbón ceilings).

From the Ilerdian and the Cuisian ( Paleocene / Eocene border, Thanetian / Ypresian , about 55 million years ago BP) the Pyrenees were finally severely narrowed in higher crustal areas. Today's zoning and structuring of orogen was created. Due to the subduction of Iberia under Aquitania, the mountains were forced out asymmetrically in a fan shape. This can be recognized by the Moho , which suddenly sinks along the North Pyrenees Fault from 30 kilometers to over 50 kilometers and then rises again only insignificantly to the south. This strongest deformation phase, also called the main phase of the Pyrenees , lasted up to 47 million years (beginning of the Lutetium ). It is characterized by very high shortening rates of 4.0 to 4.4 millimeters / year and is responsible for the thrusts of the Lower Pedraforca and Montsec Nappe.

The main phase of the Pyrenees was followed by further compressive tectonic phases in the Oligocene and Pliocene . From the Neogene , the mountains are subject to post-orogenic collapse (collapse basin in the eastern section, volcanism near Olot), which is related to the expansion movements in the Gulf of Lion and the opening of the Valenciatroge . Currently, the mountains continue to experience the strong erosion that began in the Eocene, isostatic compensatory movements and post-kinematic expansion (north-south in the western Pyrenees), which can lead to medium-strong earthquakes (examples of this are the earthquakes near Arudy in 1980 with a magnitude of 5.1, at Lourdes in 2006 with a magnitude of 5.0 and the historic Arette earthquake in 1967 with a magnitude ≥ 6.0, to which more than 40% of the buildings including the church tower fell victim).

Structural interpretations

The asymmetrical, fan-shaped structure of the Pyrenees (in profile section) has so far been interpreted as follows:

• as a more or less vertical, autochthonous collision structure, whereby the thrusts and thrusts are rooted in steep faults.
• as an allochthonous orogen in which Iberia pushed itself over Aquitania.
• as an allochthonous orogen in which Iberia pushed itself under Aquitania. It is also assumed that the steep faults are shallow at depth.

At the present time, subduction of Iberia below Aquitania is believed to be the most likely. This interpretation is also supported by the reflection seismic Pyrenees transverse profile ECORS and magnetotelluric investigations.

Estimates of the narrowing across strike are generally between 100 and 150 kilometers. With the help of the ECORS profile, Muñoz (1992) arrives at a shortening of 147 kilometers, 110 kilometers of which are due to the subduction of the middle and lower crust of Iberia. The ECORS profile also highlights the 50 kilometer thick crust of Iberia, which is pushed under the only 30 kilometer thick crust of Aquitania. A consequence of this subduction was the formation of a flat, intracrustal detachment horizon at a depth of 15 kilometers above the middle and lower crust of Iberia. Along this shear horizon, the rocks of the Axial Zone, the South Pyrenees Zone and the Sierras Marginales had slid southwards, only to rise again to the surface along the respective ceiling forehead. With the progressive narrowing of the orogen, the axial zone bulged into a southwardly inclined, anticlinoric pile of blankets . Towards the end of the subduction, a back thrust formed near the North Pyrenees fault; in its ascent through the crustal area of ​​Aquitania it used the faults created during the distensive phase. After the subduction was completely blocked, parts of the Axis and Northern Pyrenees, together with squeezed crustal segments and lherzolites, were finally pressed in a northerly direction over the Sub-Pyrenees.

Individual evidence

1. ↑ Boillot, G. & Capdevila, R .: The Pyrenees: subduction and collision . In: Earth Planet. Soc. Lett. tape 35 , 1977, pp. 151-160 .
2. ↑ Choukroune, P .: Tectonic evolution of the Pyrenees . In: Annu. Rev. Earth Planet. Sci. tape 20 , 1992, pp. 143-158 .
3. ^ Vergés, J. & Muñoz, JA: Thrust sequence in the southern central Pyrenees . In: Bull. Soc. Géol. France . tape 8 , 1990, pp. 265-271 .
4. ↑ Vergés, J .: Estudi geològic del vessant sud del Pirineu oriental i central. Evolució cinemàtica en 3D . In: Servei Geològic, Monografia Tècnica . No. 7 , 1999, p. 192 ff .
5. ↑ Cocherie, A. et al .: U-Pb zircon (ID-TIMS and SHRIMP) evidence for the early Ordovician intrusion of metagranites in the Late Proterozoic Canaveilles Group of the Pyrenees and the Montagne Noire (France) . In: Bulletin de la Société Géologique de France . tape 176 , 2005, pp. 269-282 .
6. ^ Vissers, RLM: Variscan extension in the Pyrenees . In: Tectonics . tape 11 , 1992, pp. 1369-1384 .
7. ↑ Ibai Rico et al. a .: Current Glacier Area in the Pyrenees: An Updated Assessment 2016 . In: Pirineos . tape 172 , e029, 2017, doi : 10.3989 / Pirineos.2017.172004 .
8. ↑ Vergés, J. et al .: The Pyrenean orogen: pre-, syn- and postcollisional evolution . In: Rosenbaum, G. and Lister, GS (Eds.): Reconstruction of the evolution of the Alpine-Himalayan Orogen. Journal of the Virtual Explorer . tape 8 , 2002, p. 55-74 .
9. ↑ P. Courjault-Rade, J. Darrozes, P. Gaillot: The M = 5.1 1980 Arudy earthquake sequence (western Pyrenees, France): a revisited multi-scale integrated seismologic, geomorphologic and tectonic investigation . In: International Journal of Earth Sciences . tape 98 , no. 7 , 2009, p. 1705-1719 .
10. ↑ M. Sylvander, et al .: The 2006 November, ML = 5.0 earthquake near Lourdes (France): new evidence for NS extension across the Pyrenees . In: Geophysical Journal International . tape 175 , no. 2 , 2008, p. 649-664 .
11. ^ E. Banda, SM Wickham: The geological evolution of the Pyrenees . In: Tectonophysics . tape 129 (1-4) , 1986, pp. 381 ff .
12. ↑ P. Choukroune, B. Pinet, F. Roure, M. Cazes: Major Hercynian thrusts along the ECORS Pyrenees and Biscay lines . In: Bulletin de la Societe Geologique de France . tape 6 , no. 2 , March 1990, ISSN  0037-9409 , p. 313-320 , doi : 10.2113 / gssgfbull.VI.2.313 . 6th
13. ↑ J. Pous, JJ Ledo, P. Queralt, JA Muñoz: Constraints on the Deep Structure of the Pyrenees from New Magnetotelluric Data . tape 8 , no. 4 , 1995, p. 395-400 .
14. ^ JA Muñoz: Evolution of a continental collision belt: ECORS-Pyrenees crustal balanced cross section . In: KR McClay (Ed.): Thrust Tectonics . Chapman & Hall, London 1992, pp. 235-246 .

Web links

Commons : Geology of the Pyrenees  - Collection of images, videos and audio files

• J. Vergés, et al .: The Pyrenean orogen: pre-, syn- and postcollisional evolution . 2002 ( researchgate.net [PDF; 4.8 MB ]).

swell

• G.-I. Ábalos, et al .: Pyrenees . In: W. Gibbons, et al. (Ed.): The geology of Spain . S. 179–182 ( section on the Varisci of the Pyrenees in the Google book search).
• J. Auboin, J. Debelmas, M. Latreille: Géologie des chaînes alpines issues de la Téthys . In: Mémoire de BRGM No. 115 , 1980, ISBN 2-7159-5019-5 .
• J. Canérot: Les Pyrénées. Histoire géologique (Volume 1). Itinéraires de découverte (Volume 2) . In: Atlantica - Brgméditions . 2008.
• J. Chantraine, A. Autran, C. Cavelier et al .: Carte géologique de la France au millionième . In: Éditions BRGM. Service Géologique National . 1996, ISBN 2-7159-2128-4 .
• A. Debourle, R. Deloffre: Pyrénées Occidentales - Béarn, Pays Basque . In: Guides géologiques régionaux . Masson, 1976, ISBN 2-225-44132-4 .
• M. Jaffrezo: Pyrénées Orientales - Corbières . In: Guides géologiques régionaux . Masson, 1997, ISBN 2-225-47290-4 .
• T. McCann: The Geology of Central Europe: Precambrian and Paleozoic . ( Sections on the Precambrian and the Paleozoic Pyrenees in the google book search).
• R. Mirouse: Introducción a la geología del pirineo . In: Boletin Geológico y Minero . T. XCI-I. Año 1980, 1980, p. 91-106 .
• R. Mirouse: Pyrénées - Géology . In: Encyclopædia Universalis . 1995, ISBN 2-85229-290-4 .
• EM Moores, RW Fairbridge: Encyclopedia of European and Asian geology . S. 251–255 ( section from CA Hall about the Pyrenees in Google Books).