Geology of the Alps
Encyclopedia
The Alps
form part of a Tertiary
orogenic
belt of mountain chains, called the Alpide belt
, that stretches through southern Europe
and Asia
from the Atlantic
all the way to the Himalayas
. This belt of mountain chains was formed during the Alpine orogeny
. A gap in these mountain chains in central Europe
separates the Alps from the Carpathians
to the east. Orogeny took place continuously and tectonic
subsidence
has produced the gaps in between.
The Alps arose as a result of the collision of the African
and Eurasian
tectonic plates, in which the Alpine Tethys, which was formerly in between these continent
s, disappeared. Enormous stress was exerted on sediment
s of the Alpine Tethys basin and its Mesozoic
and early Cenozoic
strata
were pushed against the stable Eurasia
n landmass by the northward-moving Africa
n landmass. Most of this occurred during the Oligocene
and Miocene
epochs. The pressure formed great recumbent folds, or nappe
s, that rose out of what had become the Alpine Tethys and pushed northward, often breaking and sliding one over the other to form gigantic thrust fault
s. Crystalline basement
rocks
, which are exposed in the higher central regions, are the rocks forming Mont Blanc
, the Matterhorn
, and high peaks in the Pennine Alps
and Hohe Tauern
.
The formation of the Mediterranean Sea
is a more recent development and does not mark the northern shore of the African landmass.
The Alps form a northward convex arc around their southeastern foreland basin
, the Po River
basin (to be precise the south is in fact their hinterland
). Quaternary
and Neogene
sediment
s in this basin lie discordant over the southernmost thrust
units. In the northeast southward dipping
and internally thrusted Tertiary
foreland deposits (flysch
and molasse
) are found. This Bavaria
n and Swiss
foreland basin
is called the Molasse Basin
. The foreland basin deposits are overthrusted from the south by the thrustfront of the Alpine nappes. In Switzerland the Molasse Basin is rimmed to the northwest by the Jura mountains
, an external fold-and-thrust belt, which can geologically be seen as part of the Alps. The western part of the Molasse basin
forms the plateau of the Mittelland
between the Alps and Jura Mountains. The Jura Mountains' location is still a topic for debate. A possible tectonic factor is the north-south extensional Rhine graben to the north.
The Alps continue more or less smoothly into the following related Alpine mountain ranges: the Apennines
to the southwest, the Dinarides to the southeast and the Carpathians to the northeast. In the east the Alps are bounded by the Viennese Basin and the Pannonian Basin
, where east–west stretching of the crust takes place.
.
, Central Alps and Western Alps, even though the boundaries between these subdivision are rather arbitrary. The division between the Eastern and Central Alps is approximately the line between St. Margrethen
, Chur
and Sondrio
, the division between the Central and Western Alps is unclear . The main suture
(big shear zone
) in the Alps is called the Periadriatic Seam
and runs through the Alps from east to west. This is the boundary between materials from the (former) European and Apulian
plates. South of this line are ffold
ed and thrusted units of the Southern Alps
.
North of the Periadriatic seam, rocks from three main palaeogeographic
"domains" are found: the Helvetic or Dauphinois, the Penninic and the Austroalpine domains. This subdivision is made according to the paleogeographical origins of the rocks: the Helvetic Zone contains material from the European plate, the Austroalpine Zone material from the Apulian plate, the Penninic Zone material from the domains that existed in between the two plates.
(direction of fold asymmetry) in these units is to the north. In the Southern Alps the thrusts are to the south so the vergence is dominantly southward.
The rocks of the Austroalpine nappes form most of the outcrops in the Eastern Alps
, while in the west these nappes are, with the exception of a few places (the Dent Blanche
and Sesia unit
s), eroded
away. In the Western Alps the Helvetic nappes can be found to the north and west, sometimes still under klippe
s of the Penninic nappes, as in the Préalpes du Sud south of Lake Geneva
.
In many spots in the central zone north of the Periadriatic seam large antiforms called anticlinoria can be found, sometimes they are displayed in the outcrop
s as windows
. At the level of one of these windows (the Hohe Tauern window
) the Periadriatic seam curves to the north, which suggests that the Apulian plate is more rigid
in this particular spot, working as a so-called indentor.
In the central part of Switzerland uplift took place along a ductile north–south normal faultzone called the Rhône-Simplon line
. The structure thus formed is called the Lepontin dome
.
intrusions are found that formed during or just after the Hercynian orogeny
. These intrusions are older than the Alps and have nothing to do with their formation. Radiometric age determination
yields ages around 320 Ma. Slightly younger felsic
intrusions formed by Permian
and Triassic
extension can also be found.
Intrusion
s from the formation of the Alps themselves are relatively rare. The largest ones can be found along the Periadriatic seam, the largest one is the Adamello granite. In the Penninic nappes migmatite
s and small melts can be found.
in the major Alpine phases in the Tertiary. Any high grade metamorphic rocks in these units will not have become metamorphic due to the formation of the Alps. Other possibilities are:
Tertiary eclogites do occur in the Penninic nappes, which contain material that has been through blueschist or eclogite facies. These nappes show a Barrovian field gradient. This type of metamorphism can only occur when a rock is in pressure
–temperature
conditions that normally occur in the Earth’s mantle
. This means the Penninic nappes consist of material that was subducted
into the mantle and was later obducted
onto the crust.
Alpine (Tertiary
) contact- or Buchan metamorphism is rare in the Alps, because intrusions are rare.
movements of the European and Apulian plates.
period (300 Ma), the Hercynian or Variscan orogeny, in which the supercontinent Pangaea
formed from Gondwana
and Laurasia
, was ended. East of the terranes that now form the Alps was the Paleo-Tethys Ocean
.
The effects of wind
and water
were able to chemically and mechanically erode
and destroy the Hercynic mountain ranges. In the Permian
, the main deposits in Europe were sandstone
and conglomerate
, products of erosion in the Hercynic mountain range. At the same time, crustal extension took place because the mountain range was isostatically
unstable (this is called orogenic collapse). Due to extension, basins formed along the axis of the mountain range and felsic
volcanism
occurred. This was the first phase of rifting between Europe and Africa. Due to the rising sealevel in the Triassic
period, the eastern margin of Pangaea was flooded. Shallow shelf seas and epicontinental seas existed in which evaporite
s and limestone
s were deposited.
that was formed in the process is known as the Piemont-Liguria Ocean
. This ocean is generally regarded as an eastern extension of the Tethys Ocean
. Although it was not really connected to it, a peninsula
r piece of continental crust of the African plate called the Apulian plate
lay in between the African and European plates and was involved in subdividing the Tethys and early Alps formation. Sometimes the names Alpine Tethys or Western Tethys Ocean are used to describe a number of small oceanic basins that formed southwest of the European plate, to distinguish them from the Neo-Tethys Ocean in the east. Because the Jurassic was a time with high sealevels, all these oceans were connected by shallow seas. On the continents, shallow sea deposits (limestones) were formed during the entire Mesozoic.
In the late Jurassic the [microcontinent Iberia] broke away from the European plate and the [Valais Ocean] was formed between the two plates. Both Piemont-Liguria and Valais Oceans were never large oceans such as today’s Atlantic Ocean. What they might have been like is the opening below the Red Sea
, continuing down through Africa, forming the Great Rift Valley
. Eventually, a new ocean will cut through east Africa as the rift develops, dividing a large section of land from the main continent.
When at the end of the Jurassic the Apulian plate began to move toward the European plate, [oceanic trench]es formed in the eastern Alps. In these, deep marine sediments were deposited, such as [radiolarite]s and [lutite]s.
movement of the European and African plates was relatively short-lived. When the Atlantic Ocean formed between Africa and South America (about 100 Ma) Africa began moving northeast.
As a result of this process, the soft layers of ocean sediment in the Alpine Tethys Oceans were compressed and folded as they were slowly thrust upwards. Caught in the middle of the merging continents, the area of the Tethys Sea between Africa and Eurasia began to shrink as oceanic crust subducted beneath the Apulian plate. The tremendous forces at work in the lower continental foundation caused the European base to bend downward into the hot mantle and soften. The southern (African) landmass then continued its northward movement over some 1,000 km (600 mi). The slow folding and pleating of the sediments as they rose up from the depths is believed to have initially formed a series of long east–west volcanic island arc
s. Volcanic rock
s produced in these island arcs are found among the ophiolites of the Penninic nappes.
In the late Cretaceous
the first continental collision
took place as the northern part of the Apulian subplate collided with Europe. This is called the Eo-Alpine phase, and is sometimes regarded as the first phase of the formation of the Alps. The part of the Apulian plate that was deformed in this phase is the material that would later form the Austroalpine nappes and the Southern Alps. In some fragments of the Piemont-Liguria Ocean now in the Penninic nappes an Eo-Alpine deformation phase can also be recognized.
Apart from the Eo-Alpine fold and thrust belt other regions were still in the marine domain during the Cretaceous. On the southern margins of the European continent shallow seas formed limestone deposits, that would later be (in the Alps) incorporated into the Helvetic nappes. At the same time sedimentation of anoxic
clay
took place in the deep-marine realms of the Piemont-Liguria and Valais Oceans. This clay would later become the Bündner slate
s from the Penninic nappes.
in the Paleocene
, the Briançonnais microcontinent
, according to some a piece of the Iberian plate
, arrived at the subduction zone. The Briançonnais microcontinent and Valais Ocean (with island arcs) subducted beneath the Apulian plate. They stayed at around 70 km (45 mi) below the surface during the Eocene
, reaching the eclogite facies and becoming intruded by migmatite
s. This material would later become the Penninic nappes, but a large part of the Briançonnais terrane subducted further into the mantle and was lost. Meanwhile, at the surface the upper crust of the Apulian plate (the later Austroalpien nappes) was thrusted over the European crust. This was the main collisional phase in the formation of the Alps.
broke off (slab breakoff, slab pull
) and fell away, the subducted crust began moving up. This led to the uplift of the thickened continental crust which led, in the Miocene
, to extension. In the case of the Alps, the extension could only take place in a west–east direction because the Apulian plate was still converging from the south. An enormous thrustzone evolved that would later become the Periadriatic Seam
. The zone also accommodated dextral shear that resulted from the west–east extension. With the exception of the allochthon
Austroalpine material, this thrust evolved at the boundary of the Apulian and European plates. The central zones of the Alps rose and were subsequently eroded. Tectonic windows and domes as the Hohe Tauern window
were formed in this way.
Meanwhile, the thrust front of the Penninic and Austroalpine nappes moved on, pushing all material in its way northward. Due to this pressure a decollement
developed over which thrusting took place. The thrusted material would become the Helvetic nappes.
effects. Also, there are many active seismic
areas under the mountains that show that stresses continue to be released along deep fault lines. In the process, the core of the Alps, with the terranes that were subducted in the Paleocene and Eocene, still moves upward. Northward thrusting takes place along a line called the Penninic thrustfront
. The formation of the foreland basin
s (Po basin and Bavarian basin) goes on with the crust subsiding in these areas.
s have done much to remodel the region. The tremendous glacier
s that flowed out of the mountain valleys repeatedly covered all of the Swiss plain and shoved the topsoil
into the low rolling hills seen today. They scooped out the lakes and rounded off the limestone hills along the northern border.
The last glacier advance in the Alps ended some 10,000 years ago, leaving the large lake now known as Lake Neuchatel
. The ice in this region reached some 1,000 m (0.6 mi) in depth and flowed out of the region behind Lake Geneva
some 100 km (60 mi) to the South. Today large granite boulders are found scattered in the forests in the region. These were carried and pushed by the glaciers that filled this part of the western plain for some 80,000 years during the last ice age. From their composition it has been possible to determine the precise area from which they began their journey. As the last ice age ended, it is believed that the climate
changed so rapidly that the glaciers retreated back into the mountains in only some 200 to 300 years time.
Besides leaving an Arctic-like wasteland of barren rock and gravel, the huge moraine
of material that was dropped at the front of the glaciers blocked huge masses of melt water that poured onto the central plain during this period. A huge lake resulted, flooding the region to a depth of several hundred meters for many years. The old shoreline can be seen in some places along the low hills at the foot of the mountains – the hills actually being glacial side-moraines. As the Aare River, which now drains western Switzerland into the Rhine River, eventually opened the natural dam
, the water levels in the plain fell to near the present levels .
In the last 150 years human
s have changed the flow and levels of all the rivers and most of the extensive wetlands and small lakes have disappeared under the effects of farming and other development.
. The result was a number of detailed geological cross-sections, enhancing our knowledge of the deep structures below the Alps. When seismic research is combined with insights from gravitational research
and mantle tomography
the subducting slab of the European plate can be mapped. Tomography also shows some older detached slabs deeper in the mantle.
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....
form part of a Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
orogenic
Orogeny
Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...
belt of mountain chains, called the Alpide belt
Alpide belt
The Alpide belt is a mountain range which extends along the southern margin of Eurasia. Stretching from Java to Sumatra through the Himalayas, the Mediterranean, and out into the Atlantic, it includes the Alps, the Carpathians, the mountains of Asia Minor and Iran, the Hindu Kush, the Himalayas,...
, that stretches through southern Europe
Southern Europe
The term Southern Europe, at its most general definition, is used to mean "all countries in the south of Europe". However, the concept, at different times, has had different meanings, providing additional political, linguistic and cultural context to the definition in addition to the typical...
and Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
from the Atlantic
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
all the way to the Himalayas
Himalayas
The Himalaya Range or Himalaya Mountains Sanskrit: Devanagari: हिमालय, literally "abode of snow"), usually called the Himalayas or Himalaya for short, is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...
. This belt of mountain chains was formed during 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...
. A gap in these mountain chains in central Europe
Central Europe
Central Europe or alternatively Middle Europe is a region of the European continent lying between the variously defined areas of Eastern and Western Europe...
separates the Alps from the Carpathians
Carpathian Mountains
The Carpathian Mountains or Carpathians are a range of mountains forming an arc roughly long across Central and Eastern Europe, making them the second-longest mountain range in Europe...
to the east. Orogeny took place continuously and tectonic
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
subsidence
Subsidence
Subsidence is the motion of a surface as it shifts downward relative to a datum such as sea-level. The opposite of subsidence is uplift, which results in an increase in elevation...
has produced the gaps in between.
The Alps arose as a result of the collision of the African
African Plate
The African Plate is a tectonic plate which includes the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges.-Boundaries:...
and Eurasian
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...
tectonic plates, in which the Alpine Tethys, which was formerly in between these continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
s, disappeared. Enormous stress was exerted on sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s of the Alpine Tethys basin and its Mesozoic
Mesozoic
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...
and early 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...
strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
were pushed against the stable Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
n landmass by the northward-moving Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
n landmass. Most of this occurred 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...
and 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...
epochs. The pressure formed great recumbent folds, or 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, that rose out of what had become the Alpine Tethys and pushed northward, often breaking and sliding one over the other to form gigantic thrust fault
Thrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
s. Crystalline basement
Basement (geology)
In geology, the terms basement and crystalline basement are used to define the rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin...
rocks
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
, which are exposed in the higher central regions, are the rocks forming Mont Blanc
Mont Blanc
Mont Blanc or Monte Bianco , meaning "White Mountain", is the highest mountain in the Alps, Western Europe and the European Union. It rises above sea level and is ranked 11th in the world in topographic prominence...
, the Matterhorn
Matterhorn
The Matterhorn , Monte Cervino or Mont Cervin , is a mountain in the Pennine Alps on the border between Switzerland and Italy. Its summit is 4,478 metres high, making it one of the highest peaks in the Alps. The four steep faces, rising above the surrounding glaciers, face the four compass points...
, and high peaks in the Pennine Alps
Pennine Alps
The Pennine Alps are a mountain range in the western part of the Alps. They are located in Switzerland and Italy...
and Hohe Tauern
Hohe Tauern
The Hohe Tauern or High Tauern are a mountain range on the main chain of the Central Eastern Alps, comprising the highest peaks east of the Brenner Pass. The crest forms the southern border of the Austrian state of Salzburg with Carinthia and East Tyrol, while a small part in the southwest belongs...
.
The formation of the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
is a more recent development and does not mark the northern shore of the African landmass.
Geologic boundaries of the Alps
Foreland basin
A foreland basin is a depression that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithosphere to bend, by a process known as lithospheric flexure...
, the Po River
Po River
The Po |Ligurian]]: Bodincus or Bodencus) is a river that flows either or – considering the length of the Maira, a right bank tributary – eastward across northern Italy, from a spring seeping from a stony hillside at Pian del Re, a flat place at the head of the Val Po under the northwest face...
basin (to be precise the south is in fact their hinterland
Hinterland
The hinterland is the land or district behind a coast or the shoreline of a river. Specifically, by the doctrine of the hinterland, the word is applied to the inland region lying behind a port, claimed by the state that owns the coast. The area from which products are delivered to a port for...
). Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
and Neogene
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s in this basin lie discordant over the southernmost thrust
Thrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
units. In the northeast southward dipping
Strike and dip
Strike and dip refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented...
and internally thrusted Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
foreland deposits (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...
and molasse
Molasse
The term "molasse" refers to the sandstones, shales and conglomerates formed as terrestrial or shallow marine deposits in front of rising mountain chains. The molasse is deposited in a foreland basin, especially on top of flysch, for example that left from the rising Alps, or erosion in the Himalaya...
) are found. This Bavaria
Bavaria
Bavaria, formally the Free State of Bavaria is a state of Germany, located in the southeast of Germany. With an area of , it is the largest state by area, forming almost 20% of the total land area of Germany...
n and Swiss
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
foreland basin
Foreland basin
A foreland basin is a depression that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithosphere to bend, by a process known as lithospheric flexure...
is called the Molasse Basin
Molasse basin
The Molasse basin is a foreland basin north of the Alps, that formed during the Oligocene and Miocene epochs. The basin formed due to the flexure of the European plate under the weight of the orogenic wedge of the Alps that was forming to the south....
. The foreland basin deposits are overthrusted from the south by the thrustfront of the Alpine nappes. In Switzerland the Molasse Basin is rimmed to the northwest by the Jura mountains
Jura mountains
The Jura Mountains are a small mountain range located north of the Alps, separating the Rhine and Rhone rivers and forming part of the watershed of each...
, an external fold-and-thrust belt, which can geologically be seen as part of the Alps. The western part of the Molasse basin
Molasse basin
The Molasse basin is a foreland basin north of the Alps, that formed during the Oligocene and Miocene epochs. The basin formed due to the flexure of the European plate under the weight of the orogenic wedge of the Alps that was forming to the south....
forms the plateau of the Mittelland
Swiss plateau
The Swiss Plateau or Central Plateau constitutes one of the three major landscapes in Switzerland alongside the Jura mountains and the Swiss Alps. It covers about 30% of the Swiss surface...
between the Alps and Jura Mountains. The Jura Mountains' location is still a topic for debate. A possible tectonic factor is the north-south extensional Rhine graben to the north.
The Alps continue more or less smoothly into the following related Alpine mountain ranges: the Apennines
Apennine mountains
The Apennines or Apennine Mountains or Greek oros but just as often used alone as a noun. The ancient Greeks and Romans typically but not always used "mountain" in the singular to mean one or a range; thus, "the Apennine mountain" refers to the entire chain and is translated "the Apennine...
to the southwest, the Dinarides to the southeast and the Carpathians to the northeast. In the east the Alps are bounded by the Viennese Basin and the Pannonian Basin
Pannonian Basin
The Pannonian Basin or Carpathian Basin is a large basin in East-Central Europe.The geomorphological term Pannonian Plain is more widely used for roughly the same region though with a somewhat different sense - meaning only the lowlands, the plain that remained when the Pliocene Pannonian Sea dried...
, where east–west stretching of the crust takes place.
Geologic structure of the Alps
The Alps have a complex geology, but the general structure is the same as for other mountain ranges formed by continental collisionContinental 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...
.
Subdivisions
The Alps are often divided into EasternEastern Alps
Eastern Alps is the name given to the eastern half of the Alps, usually defined as the area east of the Splügen Pass in eastern Switzerland. North of the Splügen Pass, the Posterior Rhine forms the border, and south of the pass, the Liro river and Lake Como form the boundary line.-Geography:The...
, Central Alps and Western Alps, even though the boundaries between these subdivision are rather arbitrary. The division between the Eastern and Central Alps is approximately the line between St. Margrethen
St. Margrethen
St. Margrethen is a municipality in the Wahlkreis of Rheintal in the canton of St. Gallen in Switzerland.-Geography:...
, Chur
Chur
Chur or Coire is the capital of the Swiss canton of Graubünden and lies in the northern part of the canton.-History:The name "chur" derives perhaps from the Celtic kora or koria, meaning "tribe", or from the Latin curia....
and Sondrio
Sondrio
Sondrio is an Italian town and comune located in the heart of the Valtellina. Sondrio counts approximately 22,000 inhabitants and it is the administrative centre for the Lombard Province of Sondrio.- History :...
, the division between the Central and Western Alps is unclear . The main suture
Suture (geology)
In structural geology, a suture is a major fault zone through an orogen or mountain range. Sutures separate terranes, tectonic units that have different plate tectonic, metamorphic and paleogeographic histories...
(big shear zone
Shear zone
A shear zone is a very important structural discontinuity surface in the Earth's crust and upper mantle. It forms as a response to inhomogeneous deformation partitioning strain into planar or curviplanar high-strain zones. Intervening blocks stay relatively unaffected by the deformation...
) in the Alps is called the Periadriatic Seam
Periadriatic Seam
The Periadriatic Seam is a distinct geologic fault in Southern Europe, running S-shaped about 1000 km from the Tyrrhenian Sea through the whole Southern Alps as far as Hungary. It forms the division between the Adriatic plate and the European plate...
and runs through the Alps from east to west. This is the boundary between materials from the (former) European and Apulian
Apulian Plate
The Adriatic or Apulian Plate is a small tectonic plate carrying primarily continental crust that broke away from the African plate along a large transform fault in the Cretaceous period. The name Adriatic Plate is usually used when referring to the northern part of the plate...
plates. South of this line are ffold
Fold (geology)
The term fold is used in geology when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in...
ed and thrusted units of the Southern Alps
Southern Alps (geology)
The Southern Alps are a geological subdivision of the European Alps. The Southern Alps are the part of the Alps that are found south of the Periadriatic Seam, a major geological faultzone across the Alps...
.
North of the Periadriatic seam, rocks from three main palaeogeographic
Palaeogeography
Palaeogeography is the study of what the geography was in times past. It is most often used about the physical landscape, although nothing excludes its use in reference to the human or cultural environment...
"domains" are found: the Helvetic or Dauphinois, the Penninic and the Austroalpine domains. This subdivision is made according to the paleogeographical origins of the rocks: the Helvetic Zone contains material from the European plate, the Austroalpine Zone material from the Apulian plate, the Penninic Zone material from the domains that existed in between the two plates.
Structural geology
Folds and thrusts north of the Periadriatic seam are generally directed to the north, the dominant vergenceVergence (geology)
In structural geology, the vergence of a fold is the direction in which an antiform is inclined or overturned. The term vergence comes from the German vergenz, which means "overturn"....
(direction of fold asymmetry) in these units is to the north. In the Southern Alps the thrusts are to the south so the vergence is dominantly southward.
The rocks of the Austroalpine nappes form most of the outcrops in the Eastern Alps
Eastern Alps
Eastern Alps is the name given to the eastern half of the Alps, usually defined as the area east of the Splügen Pass in eastern Switzerland. North of the Splügen Pass, the Posterior Rhine forms the border, and south of the pass, the Liro river and Lake Como form the boundary line.-Geography:The...
, while in the west these nappes are, with the exception of a few places (the Dent Blanche
Dent Blanche klippe
The Dent Blanche nappe or Dent Blanche klippe is a geologic nappe and klippe that crops out in the Pennine Alps. The nappe is tectonostratigraphically on top of the Penninic nappes and by most researchers seen as Austroalpine....
and Sesia unit
Sesia unit
The Sesia unit or Sesia nappe, also called the Sesia-Dent Blanche unit is a tectonic unit or terrane in the Swiss and Italian Alps. The zone crops out in the Pennine Alps and in the southeastern part of the Aosta Valley...
s), eroded
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
away. In the Western Alps the Helvetic nappes can be found to the north and west, sometimes still under klippe
Klippe
thumb|right|350px|Schematic overview of a thrust system. The shaded material is called a [[nappe]]. The erosional hole is called a [[window |window or fenster]]. The klippe is the isolated block of the nappe overlying autochthonous material....
s of the Penninic nappes, as in the Préalpes du Sud south of Lake Geneva
Lake Geneva
Lake Geneva or Lake Léman is a lake in Switzerland and France. It is one of the largest lakes in Western Europe. 59.53 % of it comes under the jurisdiction of Switzerland , and 40.47 % under France...
.
In many spots in the central zone north of the Periadriatic seam large antiforms called anticlinoria can be found, sometimes they are displayed in the outcrop
Outcrop
An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. -Features:Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be...
s as windows
Window (geology)
thumb|right|350px|Schematic overview of a thrust system. The [[fault |hanging wall block]] is called a [[nappe]]. If an [[erosion]]al hole is created in the nappe that is called a window. A [[klippe]] is a solitary outcrop of the nappe in the middle of autochthonous material.A tectonic window...
. At the level of one of these windows (the Hohe Tauern window
Hohe Tauern window
The Hohe Tauern window is a geological structure in the Austrian Central Eastern Alps. It is a window in the Austroalpine nappes where high-grade metamorphic rocks of the underlying Penninic nappes crop out...
) the Periadriatic seam curves to the north, which suggests that the Apulian plate is more rigid
Rigid
In mathematics, a rigid collection C of mathematical objects is one in which every c ∈ C is uniquely determined by less information about c than one would expect....
in this particular spot, working as a so-called indentor.
In the central part of Switzerland uplift took place along a ductile north–south normal faultzone called the Rhône-Simplon line
Rhône-Simplon line
The Rhone-Simplon line is a large geologic faultzone in the Swiss Alps.The line runs from the Ossola valley over the Simplon Pass and then follows the Rhône valley in an east-west direction. Somewhere south of Sion it goes over smoothly into the Penninic thrustfront.Geologically speaking, the line...
. The structure thus formed is called the Lepontin dome
Lepontin dome
The Lepontine dome or Lepontin dome is a region of tectonic uplift in the Swiss part of the Alps. It is located in the Lepontine Alps and Glarus Alps....
.
Intrusions
In older rocks from the lower crustCrust (geology)
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...
intrusions are found that formed during or just after the Hercynian 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:...
. These intrusions are older than the Alps and have nothing to do with their formation. Radiometric age determination
Radiometric dating
Radiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates...
yields ages around 320 Ma. Slightly younger felsic
Felsic
The word "felsic" is a term used in geology to refer to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium....
intrusions formed by 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...
and 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...
extension can also be found.
Intrusion
Intrusion
An intrusion is liquid rock that forms under Earth's surface. Magma from under the surface is slowly pushed up from deep within the earth into any cracks or spaces it can find, sometimes pushing existing country rock out of the way, a process that can take millions of years. As the rock slowly...
s from the formation of the Alps themselves are relatively rare. The largest ones can be found along the Periadriatic seam, the largest one is the Adamello granite. In the Penninic nappes 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 and small melts can be found.
Metamorphism
The rocks of the Helvetic and Austroalpine nappes and the southern Alps did not experience high grade metamorphismMetamorphism
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...
in the major Alpine phases in the Tertiary. Any high grade metamorphic rocks in these units will not have become metamorphic due to the formation of the Alps. Other possibilities are:
- they were originally from lower regions of the crust and got to the surface by upliftTectonic upliftTectonic uplift is a geological process most often caused by plate tectonics which increases elevation. The opposite of uplift is subsidence, which results in a decrease in elevation. Uplift may be orogenic or isostatic.-Orogenic uplift:...
, which gives them amphibolite facies at most. - in the Austroalpine nappes 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...
s occur that were formed during the CretaceousCretaceousThe Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
period, in an early phase of mountain building called the Eo-Alpine orogeny. These are high-grade metamorphic rocks, but their metamorphism is unrelated to the (later) formation of the Alps.
Tertiary eclogites do occur in the Penninic nappes, which contain material that has been through blueschist or eclogite facies. These nappes show a Barrovian field gradient. This type of metamorphism can only occur when a rock is in pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
–temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
conditions that normally occur in the Earth’s mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
. This means the Penninic nappes consist of material that was subducted
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"...
into the mantle and was later obducted
Obduction
Obduction is the overthrusting of continental crust by oceanic crust or mantle rocks at a convergent plate boundary. It can occur during an orogeny, or mountain-building episode....
onto the crust.
Alpine (Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
) contact- or Buchan metamorphism is rare in the Alps, because intrusions are rare.
Tectonic history
The Alps are a fold and thrust belt. Folding and thrusting is the expression of crustal shortening which is caused by the convergentConvergent boundary
In plate tectonics, a convergent boundary, also known as a destructive plate boundary , is an actively deforming region where two tectonic plates or fragments of lithosphere move toward one another and collide...
movements of the European and Apulian plates.
Breakup of Pangea
At the end of the CarboniferousCarboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
period (300 Ma), the Hercynian or Variscan orogeny, in which the supercontinent Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....
formed from 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,...
and Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
, was ended. East of the terranes that now form the Alps was the Paleo-Tethys Ocean
Paleo-Tethys Ocean
The Paleo-Tethys Ocean was an ancient Paleozoic ocean. It was located between the paleocontinent Gondwana and the so called Hunic terranes. These are divided into the European Hunic and Asiatic Hunic...
.
The effects of wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
were able to chemically and mechanically erode
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
and destroy the Hercynic mountain ranges. In the 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...
, the main deposits in Europe were sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
and 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...
, products of erosion in the Hercynic mountain range. At the same time, crustal extension took place because the mountain range was isostatically
Isostasy
Isostasy is a term used in geology to refer to the state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density. This concept is invoked to explain how different topographic...
unstable (this is called orogenic collapse). Due to extension, basins formed along the axis of the mountain range and felsic
Felsic
The word "felsic" is a term used in geology to refer to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium....
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....
occurred. This was the first phase of rifting between Europe and Africa. Due to the rising sealevel in 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...
period, the eastern margin of Pangaea was flooded. Shallow shelf seas and epicontinental seas existed in which evaporite
Evaporite
Evaporite is a name for a water-soluble mineral sediment that result from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporate deposits, marine which can also be described as ocean deposits, and non-marine which are found in standing bodies of...
s and 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 were deposited.
Jurassic
In the early Jurassic period (180 Ma), a narrow ocean began to form between the northern (North America and Eurasia) and southern (Africa and South America) parts of Pangaea. The oceanic crustOceanic crust
Oceanic 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 was formed in the process is known as the Piemont-Liguria Ocean
Piemont-Liguria Ocean
The Piemont-Liguria basin or the Piemont-Liguria Ocean was a former piece of oceanic crust that is seen as part of the Tethys Ocean...
. This ocean is generally regarded as an eastern extension of the Tethys Ocean
Tethys Ocean
The Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.-Modern theory:...
. Although it was not really connected to it, a peninsula
Peninsula
A peninsula is a piece of land that is bordered by water on three sides but connected to mainland. In many Germanic and Celtic languages and also in Baltic, Slavic and Hungarian, peninsulas are called "half-islands"....
r piece of continental crust of the African plate called the Apulian plate
Apulian Plate
The Adriatic or Apulian Plate is a small tectonic plate carrying primarily continental crust that broke away from the African plate along a large transform fault in the Cretaceous period. The name Adriatic Plate is usually used when referring to the northern part of the plate...
lay in between the African and European plates and was involved in subdividing the Tethys and early Alps formation. Sometimes the names Alpine Tethys or Western Tethys Ocean are used to describe a number of small oceanic basins that formed southwest of the European plate, to distinguish them from the Neo-Tethys Ocean in the east. Because the Jurassic was a time with high sealevels, all these oceans were connected by shallow seas. On the continents, shallow sea deposits (limestones) were formed during the entire Mesozoic.
In the late Jurassic the [microcontinent Iberia] broke away from the European plate and the [Valais Ocean] was formed between the two plates. Both Piemont-Liguria and Valais Oceans were never large oceans such as today’s Atlantic Ocean. What they might have been like is the opening below the Red Sea
Red Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
, continuing down through Africa, forming the Great Rift Valley
Great Rift Valley
The Great Rift Valley is a name given in the late 19th century by British explorer John Walter Gregory to the continuous geographic trench, approximately in length, that runs from northern Syria in Southwest Asia to central Mozambique in South East Africa...
. Eventually, a new ocean will cut through east Africa as the rift develops, dividing a large section of land from the main continent.
When at the end of the Jurassic the Apulian plate began to move toward the European plate, [oceanic trench]es formed in the eastern Alps. In these, deep marine sediments were deposited, such as [radiolarite]s and [lutite]s.
Eo-Alpine phase in the Cretaceous
The divergentDivergent boundary
In plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts which produce rift valleys...
movement of the European and African plates was relatively short-lived. When the Atlantic Ocean formed between Africa and South America (about 100 Ma) Africa began moving northeast.
As a result of this process, the soft layers of ocean sediment in the Alpine Tethys Oceans were compressed and folded as they were slowly thrust upwards. Caught in the middle of the merging continents, the area of the Tethys Sea between Africa and Eurasia began to shrink as oceanic crust subducted beneath the Apulian plate. The tremendous forces at work in the lower continental foundation caused the European base to bend downward into the hot mantle and soften. The southern (African) landmass then continued its northward movement over some 1,000 km (600 mi). The slow folding and pleating of the sediments as they rose up from the depths is believed to have initially formed a series of long east–west volcanic 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....
s. Volcanic rock
Volcanic rock
Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it is an igneous rock of volcanic origin...
s produced in these island arcs are found among the ophiolites of the Penninic nappes.
In the late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
the first 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...
took place as the northern part of the Apulian subplate collided with Europe. This is called the Eo-Alpine phase, and is sometimes regarded as the first phase of the formation of the Alps. The part of the Apulian plate that was deformed in this phase is the material that would later form the Austroalpine nappes and the Southern Alps. In some fragments of the Piemont-Liguria Ocean now in the Penninic nappes an Eo-Alpine deformation phase can also be recognized.
Apart from the Eo-Alpine fold and thrust belt other regions were still in the marine domain during the Cretaceous. On the southern margins of the European continent shallow seas formed limestone deposits, that would later be (in the Alps) incorporated into the Helvetic nappes. At the same time sedimentation of anoxic
Anoxic sea water
Anoxic waters are areas of sea water or fresh water that are depleted of dissolved oxygen. This condition is generally found in areas that have restricted water exchange....
clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
took place in the deep-marine realms of the Piemont-Liguria and Valais Oceans. This clay would later become the Bündner slate
Bündner slate
The Bündner schist or Bündner slate is a collective name for schistose rocks that form a number of geologic formations in the Penninic nappes of the Alps...
s from the Penninic nappes.
Paleocene and Eocene
When the Piemont-Liguria oceanic crust had completely subducted beneath the Apulian plateApulian Plate
The Adriatic or Apulian Plate is a small tectonic plate carrying primarily continental crust that broke away from the African plate along a large transform fault in the Cretaceous period. The name Adriatic Plate is usually used when referring to the northern part of the plate...
in 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 Briançonnais microcontinent
Briançonnais microcontinent
The Briançonnais zone or Briançonnais terrane is a piece of continental crust found in the Penninic nappes of the Alps.According to some paleogeographic reconstructions the rocks of the Briançonnais zone were in fact a part of the microcontinent Iberia, that encompassed not only the Iberian...
, according to some a piece of the Iberian plate
Iberian plate
The microcontinent Iberia encompassed not only the Iberian Peninsula but also Corsica, Sardinia, the Balearic Islands, and the Briançonnais zone of the Penninic nappes of the Alps...
, arrived at the subduction zone. The Briançonnais microcontinent and Valais Ocean (with island arcs) subducted beneath the Apulian plate. They stayed at around 70 km (45 mi) below the surface during the 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...
, reaching the eclogite facies and becoming intruded by 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. This material would later become the Penninic nappes, but a large part of the Briançonnais terrane subducted further into the mantle and was lost. Meanwhile, at the surface the upper crust of the Apulian plate (the later Austroalpien nappes) was thrusted over the European crust. This was the main collisional phase in the formation of the Alps.
Oligocene and Miocene
When the subducting slabSlab
-Physical materials:* Slab , a length of metal* Concrete slab, a flat plate used in construction* A piece of stone or concrete used to pave sidewalks or road surfaces* Slab : That portion of a tectonic plate that is subducting...
broke off (slab breakoff, slab pull
Slab pull
The Slab pull force is a tectonic plate force due to subduction. Plate motion is partly driven by the weight of cold, dense plates sinking into the mantle at trenches. This force and the slab suction force account for most of the overall force acting on plate tectonics, and the ridge push force...
) and fell away, the subducted crust began moving up. This led to the uplift of the thickened continental crust which led, in 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...
, to extension. In the case of the Alps, the extension could only take place in a west–east direction because the Apulian plate was still converging from the south. An enormous thrustzone evolved that would later become the Periadriatic Seam
Periadriatic Seam
The Periadriatic Seam is a distinct geologic fault in Southern Europe, running S-shaped about 1000 km from the Tyrrhenian Sea through the whole Southern Alps as far as Hungary. It forms the division between the Adriatic plate and the European plate...
. The zone also accommodated dextral shear that resulted from the west–east extension. With the exception of the allochthon
Allochthon
thumb|right|250px|Schematic overview of a thrust system. The hanging wall block is called a [[nappe]]. If an [[erosion]]al hole is created in the nappe that is called a [[window |window]]...
Austroalpine material, this thrust evolved at the boundary of the Apulian and European plates. The central zones of the Alps rose and were subsequently eroded. Tectonic windows and domes as the Hohe Tauern window
Hohe Tauern window
The Hohe Tauern window is a geological structure in the Austrian Central Eastern Alps. It is a window in the Austroalpine nappes where high-grade metamorphic rocks of the underlying Penninic nappes crop out...
were formed in this way.
Meanwhile, the thrust front of the Penninic and Austroalpine nappes moved on, pushing all material in its way northward. Due to this pressure a decollement
Decollement
Décollement is a gliding plane between two rock masses. In French, "décoller" means "to detach from" or "to rip off" and was first used by geologists studying the structure of the Swiss Jura Mountains, but is also known as a detachment zone. This is a structure of strata owing to deformation,...
developed over which thrusting took place. The thrusted material would become the Helvetic nappes.
Neogene
At present, the Apulian and European plates are still converging. The process of mountain building continues to this day. Measurements in the road and railway tunnels show that the Alps continue to rise somewhere between a millimeter and a centimeter each year. This is held in an overall balance by weatheringWeathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
effects. Also, there are many active seismic
Seismology
Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic,...
areas under the mountains that show that stresses continue to be released along deep fault lines. In the process, the core of the Alps, with the terranes that were subducted in the Paleocene and Eocene, still moves upward. Northward thrusting takes place along a line called the Penninic thrustfront
Penninic thrustfront
The Penninic thrustfront is a major tectonic thrustfront in the French Alps. The thrustfront moves over a developing decollement horizon, and separates the high grade metamorphic rocks of the Penninic nappes from the sedimentary rocks and crystalline basement of the Helvetic nappes...
. The formation of the foreland basin
Foreland basin
A foreland basin is a depression that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithosphere to bend, by a process known as lithospheric flexure...
s (Po basin and Bavarian basin) goes on with the crust subsiding in these areas.
Geomorphology
The formation of the Alpine landscape seen today is a recent development – only some two million years old. Since then, five known ice ageIce 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...
s have done much to remodel the region. The tremendous glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s that flowed out of the mountain valleys repeatedly covered all of the Swiss plain and shoved the topsoil
Topsoil
Topsoil is the upper, outermost layer of soil, usually the top to . It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs.-Importance:...
into the low rolling hills seen today. They scooped out the lakes and rounded off the limestone hills along the northern border.
The last glacier advance in the Alps ended some 10,000 years ago, leaving the large lake now known as Lake Neuchatel
Lake Neuchâtel
Lake Neuchâtel is a lake in Romandy, Switzerland . The lake lies mainly in the canton of Neuchâtel, but is also shared by the cantons of Vaud, of Fribourg, and of Bern....
. The ice in this region reached some 1,000 m (0.6 mi) in depth and flowed out of the region behind Lake Geneva
Lake Geneva
Lake Geneva or Lake Léman is a lake in Switzerland and France. It is one of the largest lakes in Western Europe. 59.53 % of it comes under the jurisdiction of Switzerland , and 40.47 % under France...
some 100 km (60 mi) to the South. Today large granite boulders are found scattered in the forests in the region. These were carried and pushed by the glaciers that filled this part of the western plain for some 80,000 years during the last ice age. From their composition it has been possible to determine the precise area from which they began their journey. As the last ice age ended, it is believed that the climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
changed so rapidly that the glaciers retreated back into the mountains in only some 200 to 300 years time.
Besides leaving an Arctic-like wasteland of barren rock and gravel, the huge 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...
of material that was dropped at the front of the glaciers blocked huge masses of melt water that poured onto the central plain during this period. A huge lake resulted, flooding the region to a depth of several hundred meters for many years. The old shoreline can be seen in some places along the low hills at the foot of the mountains – the hills actually being glacial side-moraines. As the Aare River, which now drains western Switzerland into the Rhine River, eventually opened the natural dam
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
, the water levels in the plain fell to near the present levels .
In the last 150 years human
Human
Humans are the only living species in the Homo genus...
s have changed the flow and levels of all the rivers and most of the extensive wetlands and small lakes have disappeared under the effects of farming and other development.
Geologic research
The Alps were the first mountain system to be extensively studied by geologists, and many of the geologic terms associated with mountains and glaciers originated there. The term Alps has been applied to mountain systems around the world that exhibit similar traits.Geophysics
In the 1980s and 1990s a number of teams have been mapping the structures in the lower crust by seismologySeismology
Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic,...
. The result was a number of detailed geological cross-sections, enhancing our knowledge of the deep structures below the Alps. When seismic research is combined with insights from gravitational research
Geodesy
Geodesy , also named geodetics, a branch of earth sciences, is the scientific discipline that deals with the measurement and representation of the Earth, including its gravitational field, in a three-dimensional time-varying space. Geodesists also study geodynamical phenomena such as crustal...
and mantle tomography
Tomography
Tomography refers to imaging by sections or sectioning, through the use of any kind of penetrating wave. A device used in tomography is called a tomograph, while the image produced is a tomogram. The method is used in radiology, archaeology, biology, geophysics, oceanography, materials science,...
the subducting slab of the European plate can be mapped. Tomography also shows some older detached slabs deeper in the mantle.
External links
- Geophysical research and the geology of the Alps
- The tectonic evolution of the western and central Alps and their forelands, website of prof. S.M. Schmid
- Alpine geology
- Paleoreconstructions of the Alpine Tethys region, IGCP369 project website
- Platetectonic maps of the North Atlantic (including the Mediterranean) by Peter Ziegler
- Plate tectonic reconstruction of the opening and closing of the Valais and Ligurian Oceans, website of Christian Nicollet (in French)