The
AlpsThe Alps are 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 a part of a
TertiaryThe Tertiary is a term for a geologic period 65 million to 2.588 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
orogenicOrogeny refers to natural mountain building, and may be studied as a tectonic structural event, as a geographical event, and a chronological event...
belt of mountain chains, called the
Alpide beltThe 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 and Asia from the
AtlanticThe Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about 106.4 million square kilometres , it covers approximately one-fifth of the Earth's surface and about one-quarter of its water surface area. The first part of its name refers to the Atlas of Greek...
all the way to the
HimalayasThe Himalaya Range or Himalayas for short , meaning "abode of snow", is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...
. This belt of mountain chains was formed during the
Alpine orogenyThe 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 separates the Alps from the
CarpathiansThe Carpathian Mountains or Carpathians are a range of mountains forming an arc roughly long across Central and Eastern Europe, making them the largest mountain range in Europe...
off to the east. Orogeny took place continuously and
tectonicTectonics 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...
subsidenceSubsidence 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
AfricanThe 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....
and
EuropeanThe 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 western part of the
Tethys OceanThe 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:...
, which was formerly in between these continents, disappeared. Enormous
stressCompressive stress is the stress that, when applied, acts towards the center of that material. When a material is subjected to compressive stress, then this material is under compression. Usually, compressive stress applied to bars, columns, etc. leads to shortening.Loading a structural element or...
was exerted on
sedimentSediment is any particulate matter that can be transported by fluid flow, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers...
s of the
Tethys OceanThe 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:...
basin and its
MesozoicThe Mesozoic Era is one of three geologic eras of the Phanerozoic eon. The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the "Mesozoic" was "Secondary" The Mesozoic Era is one of three geologic eras of the...
and early
CenozoicThe Cenozoic Era The Cenozoic (also Cænozoic or Cainozoic) Era The Cenozoic (also Cænozoic or Cainozoic) Era (meaning "new life" (Greek (kainos), "new", and (zoe), "life"), is the most recent of the three classic geological eras and covers the period from 65.5 million years ago to the...
strataIn geology and related fields, a stratum is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers. Each layer is generally one of a number of parallel layers that lie one upon another, laid down by natural forces. They may extend over...
were pushed against the stable
EurasiaEurasia is a large landmass covering about 52,990,000 km
2 or about 10.6% of the Earth's surface...
n landmass by the northward-moving
AfricaAfrica 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. With a billion people in 61 territories, it accounts for about 14.8% of the...
n landmass. Most of this occurred during the
OligoceneThe Oligocene is a geologic epoch of the Paleogene period and extends from about 33.9 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
MioceneThe Miocene is a geological epoch of the Neogene period and extends from about 23.03 to 5.33 million years before the present . 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...
epochs. The pressure formed great recumbent folds, or
nappeIn geology, a nappe is a large sheetlike body of rock that has been moved more than 2 km 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...
s, that rose out of what had become the Tethys Sea and pushed northward, often breaking and sliding one over the other to form gigantic
thrust faultA 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. Thrust faults are the result...
s.
Crystalline basementIn 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, which are exposed in the higher central regions, are the rocks forming
Mont BlancMont Blanc or Monte Bianco is the highest mountain in the Alps and in Western Europe. It rises above sea level and is ranked 11th in the world in topographic prominence...
, the
MatterhornThe Matterhorn , Cervino or Cervin , is a mountain in the Pennine Alps. With its high summit, lying on the border between Switzerland and Italy, it is one of the highest peaks in the Alps and its north face is one of the Great north faces of the Alps...
, and high peaks in the
Pennine AlpsThe Pennine Alps are a mountain range in the western part of the Alps. They are located in Switzerland and Italy...
and
Hohe TauernThe Hohe Tauern, the highest range of the Alps east of the Brenner Pass, includes the highest mountains in Austria. The range is part of the Central Eastern Alps...
.
The formation of the
Mediterranean SeaThe 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 Africa, and on the east by the Levant. The sea is technically a part of the Atlantic Ocean, although it...
is a more recent development and does not mark the northern shore of the African landmass.
Geologic boundaries of the Alps
The Alps form a northward convex arc around their southeastern
foreland basinA 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 RiverThe Po 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...
basin (to be precise the south is in fact their
hinterlandThe hinterland is the land or district behind the borders of a coast or 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...
). Quarternary and
NeogeneThe Neogene is a geologic period and system starting 23.03 ± 0.05 million years ago and lasting either until today or ending 2.588 million years ago with the beginning of the Quaternary. The Neogene Period follows the Paleogene Period of the Cenozoic Era...
sedimentSediment is any particulate matter that can be transported by fluid flow, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers...
s in this basin lie
discordant over the southernmost
thrustA 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. Thrust faults are the result...
units. In the northeast southward
dippingStrike and dip refer to the orientation or attitude of a geologic feature. The strike 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 parallel...
and internally thrusted
TertiaryThe Tertiary is a term for a geologic period 65 million to 2.588 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
foreland deposits (
flyschFlysch 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
molasseThe 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
BavariaBavaria , with an area of and almost 12.5 million inhabitants, is located in the southeast of Germany and is the largest state of Germany by area, forming almost 20% of the total land area of Germany...
n and
SwissSwitzerland , officially the Swiss Confederation , is a federal republic consisting of 26 states named cantons, with Bern as the seat of the federal authorities...
foreland basinA 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 BasinThe 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 mountainsThe 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. The mountain range sensu Johann Gottfried Ebel is located in France, Switzerland, and Germany...
, an external fold-and-thrust belt, which can geologically be seen as part of the Alps. The western part of the
Molasse basinThe 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
MittellandThe 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
ApenninesThe Apennines or Apennine Mountains is a mountain range stretching c. 1,200 km from the north to the south of Italy along its east coast, traversing the entire peninsula, and forming the backbone of the country...
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 BasinThe Pannonian Basin or Carpathian Basin is a large basin in Central Europe.The basin forms a topographically discrete unit set in the European landscape, surrounded by imposing geographic boundaries that have created a fairly unified cultural area that looks more towards the south and east than to...
, 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 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 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.The Eastern Alps...
, 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. MargrethenSt. Margrethen is a municipality in the Wahlkreis of Rheintal in the canton of St. Gallen in Switzerland.It has 5300 inhabitants....
,
ChurChur ; ; , and ) is the capital of the Swiss canton of Graubünden and lies in the northern part of the canton.-History:...
and
SondrioSondrio is an Italian town and comune located in the heart of the Valtellina. Sondrio counts approximately 22,600 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
sutureA suture is in structural geology a major fault zone through an orogen or mountain range. Sutures separate terranes: tectonic units that have different plate tectonic, metamorphic and paleogeographic histories.- Overview :...
(big shear zone) in the Alps is called the
Periadriatic SeamThe 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...
and runs through the Alps from east to west. This is the boundary between materials from the (former) European and
ApulianThe 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 folded and thrusted units of the
Southern AlpsThe 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
palaeogeographicPalaeogeography 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
vergenceIn structural geology, the vergence of a deformed rock is the direction in which the next antiform can be found. Geometrically the vergence is the up-dip direction of the bedding perpendicular to the planes of the regional foliation in the rock....
(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 AlpsEastern 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.The Eastern Alps...
, while in the west these nappes are, with the exception of a few places (the
Dent BlancheThe 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 unitThe 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,
erodedErosion is a gravity driven process that moves solids in the natural environment or their source and deposits them elsewhere...
away. In the Western Alps the Helvetic nappes can be found to the north and west, sometimes still under
klippethumb|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 [[autochthon]]ous material....
s of the Penninic nappes, as in the Préalpes du Sud south of
Lake GenevaLake Geneva or Lake Léman is the largest natural freshwater lake in western Europe . In addition it is the largest body of freshwater in continental Europe in term of volume . 60% of it comes under the jurisdiction of Switzerland , and 40% 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
outcropAn outcrop is an exposure of bedrock or superficial deposits at the surface of the Earth.Outcrops do not cover the majority of the Earth's land surface. In most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be seen or examined closely...
s as
windowsthumb|right|350px|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]]. A [[klippe]] is a solitary outcrop of the nappe in the middle of [[autochthon]]ous material.A tectonic...
. At the level of one of these windows (the
Hohe Tauern windowThe 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
rigidIn 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 lineThe 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 domeThe 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
crustIn geology, a crust is the outermost solid shell of a rocky planet or moon, which is chemically distinct from the underlying mantle. The crusts of Earth, our Moon, Mercury, Venus, Mars, Io, and other planetary bodies have been generated largely by igneous processes, and these crusts are richer in...
intrusions are found that formed during or just after the
Hercynian orogenyThe 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 determinationRadiometric dating is a technique used to date materials, 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
MaAnnum is a form of the Latin noun annus meaning year, from which are derived words such as annual and annuity. Annum is the accusative singular of the 2nd declension masculine noun annus , anni...
. Slightly younger
felsicFelsic 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. The term combines the words "feldspar" and "silica." Felsic minerals are usually light in color and have specific...
intrusions formed by
PermianThe Permian
[The 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...]
and
TriassicThe Triassic is a geologic period and system that extends from about 251 to 199 Ma . 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.
IntrusionAn intrusion is any formation of intrusive igneous rock; rock formed from magma that cools and solidifies within the crust of a planet. In contrast, an extrusion consists of extrusive rock; rock formed above the surface of the crust....
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
migmatiteMigmatite 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 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. Both mineralogical, chemical and crystallographic changes can occur during this process.Three types...
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 uplift
Uplift may refer to:* Biological uplift, the theoretical prospect of upgrading the capacities of a species or a civilization.** Uplift Universe, the setting for a series of novels by David Brin in which Biological Uplift is a central aspect...
, which gives them amphibolite facies at most.
- in the Austroalpine nappes eclogite
Eclogite is a coarse-grained 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 CretaceousThe Cretaceous , Latin language for "chalky", 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 on 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
pressurePressure 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 :...
–
temperatureIn physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the higher temperature. Temperature is one of the principal parameters of thermodynamics...
conditions that normally occur in the Earth’s
mantleThe mantle is a part of an astronomical object. 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. Earth's mantle is about 2,970 km thick rocky shell that...
. This means the Penninic nappes consist of material that was
subductedIn 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. A subduction zone is an area on Earth where two tectonic plates move towards one another and...
into the mantle and was later
obductedObduction 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 (
TertiaryThe Tertiary is a term for a geologic period 65 million to 2.588 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
convergentIn plate tectonics, a convergent boundary or convergent plate 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
CarboniferousThe Carboniferous is a geologic period and system that extends from the end of the Devonian period, about 359.2 ± 2.5 Ma , to the beginning of the Permian period, about 299.0 ± 0.8 Ma ....
period (300 Ma ago), the Hercynian or Variscan orogeny, in which the supercontinent
PangaeaPangaea, Pangæa, or Pangea was the supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration.The name was first used by the German originator of the continental...
formed from
GondwanaGondwana , originally Gondwanaland, is the name given to a southern precursor-supercontinent. Its final joining occurred between ca. 570 and 510 Ma ago, joining East Gondwana to West Gondwana. It later separated from Laurasia 180- during the breakup of the Pangaea supercontinent that existed about...
and
LaurasiaLaurasia was a supercontinent that most recently existed as a part of the split of the Pangaea supercontinent in the late Mesozoic era. It included most of the landmasses which make up today's continents of the northern hemisphere, chiefly Laurentia , Baltica, Siberia, Kazakhstania, and the North...
, was ended. East of the terranes that now form the Alps was the
Paleo-Tethys OceanThe 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
windWind is the flow of air or other gases that compose an atmosphere . On Earth, wind consists of the bulk movement of air...
and
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
were able to chemically and mechanically
erodeErosion is a gravity driven process that moves solids in the natural environment or their source and deposits them elsewhere...
and destroy the Hercynic mountain ranges. In the
PermianThe Permian
[The 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...]
, the main deposits in Europe were
sandstoneSandstone 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 color, but the most common colors are tan, brown, yellow,...
and
conglomerateA 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
isostaticallyIsostasy 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
felsicFelsic 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. The term combines the words "feldspar" and "silica." Felsic minerals are usually light in color and have specific...
volcanism occurred. This was the first phase of rifting between Europe and Africa. Due to the rising sealevel in the
TriassicThe Triassic is a geologic period and system that extends from about 251 to 199 Ma . 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
evaporiteEvaporites are water-soluble mineral sediments that result from the evaporation of bodies of surficial water. Evaporites are considered sedimentary rocks.- Formation of evaporite rocks :...
s and
limestoneLimestone is a sedimentary rock composed largely of the mineral calcite . The deposition of limestone strata is often a by-product and indicator of biological activity in the geologic record...
s were deposited.
Jurassic
In the early Jurassic period (180
MaAnnum is a form of the Latin noun annus meaning year, from which are derived words such as annual and annuity. Annum is the accusative singular of the 2nd declension masculine noun annus , anni...
ago), 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 is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima...
that was formed in the process is known as the
Piemont-Liguria OceanThe 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 OceanThe 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
peninsulaA peninsula is a piece of land that is nearly surrounded by water but connected to mainland via an isthmus. Word origin: Latin paenīnsula : paene, almost + īnsula, island.A peninsula can also be a headland, cape, island promontory, bill, point, or spit....
r piece of continental crust of the African plate called the
Apulian plateThe 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 OceanThe Valais Ocean is a disappeared piece of oceanic crust which was situated between the continent Europe and the microcontinent Iberia or so called Briançonnais microcontinent...
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 SeaThe 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
Rift ValleyIn order of specificity, Rift Valley can refer to:*a rift valley in general*the Great Rift Valley*the valley of the East African Rift*Rift Valley Province, Kenya and border with Uganda...
. 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 trenchThe oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. They are also the deepest parts of the ocean floor....
es formed in the eastern Alps. In these, deep marine sediments were deposited, such as
radiolariteRadiolarite or radiolarian chert is a high silica sedimentary rock which may be considered a variety of chert. It is formed as primary deposits and contains radiolarian microfossils...
s and
lutiteLutite is any sedimentary clastic rock with clay or silt grain size less than 1/16 mm .The term is used in the classification of clastic carbonatic limestones, as the granulometrically equivalent term siltstone or claystone is not appropriate for limestone.Lutites mainly form by erosion of...
s.
Eo-Alpine phase in the Cretaceous
The
divergentIn 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. These areas can form in the middle of continents but eventually form ocean basins...
movement of the European and African plates was relatively short-lived. When the Atlantic Ocean formed between Africa and South America (about 100
MaAnnum is a form of the Latin noun annus meaning year, from which are derived words such as annual and annuity. Annum is the accusative singular of the 2nd declension masculine noun annus , anni...
ago) 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 kilometers (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 arcAn island arc is a type of archipelago formed by plate tectonics as one oceanic tectonic plate subducts under another and produces magma. Island arcs that develop along the edges of a continent may be known as a volcanic arc, though most people find the distinction of little benefit.In the...
s.
Volcanic rockVolcanic rock is an igneous rock of volcanic origin.- Texture :Volcanic rocks are usually fine-grained or aphanitic to glassy in texture. They often contain clasts of other rocks and phenocrysts. Phenocrysts are crystals that are larger than the matrix and are identifiable with the unaided eye...
s produced in these island arcs are found among the ophiolites of the Penninic nappes.
In the
late CretaceousThe Late Cretaceous is the youngest of two epochs in which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
the first
continental collisionContinental 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
anoxicAnoxic 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....
clayClay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired...
took place in the deep-marine realms of the Piemont-Liguria and Valais Oceans. This clay would later become the
Bündner slateThe 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 plate in the
PaleoceneThe Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from 65.5 ± 0.3 Ma to 55.8 ± 0.2 Ma . It is the first epoch of the Palaeogene Period in the modern Cenozoic era...
, the
Briançonnais microcontinentThe 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, arrived at the subduction zone. The Briançonnais microcontinent and Valais Ocean (with island arcs) subducted beneath the Apulian plate. They stayed at around 70 kilometers (45 mi) below the surface during the
EoceneThe Eocene epoch, lasting from 55.8 ± 0.2 to 33.9 ± 0.1 Ma , is a major division of the geologic timescale and the second epoch of the Palaeogene period in the Cenozoic era. The Eocene spans the time from the end of the Paleocene epoch to the beginning of the Oligocene epoch. The start of the...
, reaching the eclogite facies and becoming intruded by
migmatiteMigmatite 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 can refer to:-Physical objects and substances:* A broad flat square or rectangular piece of wood, stone or other solid material used to construct buildings, pavements, patios, paths, etc: see Paver and flagstone....
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
MioceneThe Miocene is a geological epoch of the Neogene period and extends from about 23.03 to 5.33 million years before the present . 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...
, 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 SeamThe 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...
. The zone also accommodated dextral shear that resulted from the west–east extension. With the exception of the
allochthonthumb|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 windowThe 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
decollementA décollement horizon in tectonics is a surface that acts as a gliding plane between two masses in a thrust fault relationship. A décollement horizon can either form due to a low bulk modulus between bodies , or can form along planes of high pore pressures....
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 is the decomposition of Earth's rocks, soils and minerals through direct contact with the planet's atmosphere. Weathering occurs in situ, or "with no movement", and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice,...
effects. Also, there are many active
seismicSeismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth...
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 thrustfrontThe 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 basinA 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 ageThe general term "ice age" or, more precisely, "glacial age" denotes a geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in an expansion of continental ice sheets, polar ice sheets and alpine glaciers. Within a long-term ice age, individual...
s have done much to remodel the region. The tremendous
glacierA glacier is a perennial mass of ice which moves over land. A glacier forms in locations where the mass accumulation of snow and ice exceeds ablation over many years...
s that flowed out of the mountain valleys repeatedly covered all of the Swiss plain and shoved the
topsoilTopsoil 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. Plants generally concentrate their roots in and obtain most of their nutrients from this layer...
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 NeuchatelLake Neuchâtel is a lake in Western 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 meters (0.6 mi) in depth and flowed out of the region behind
Lake GenevaLake Geneva or Lake Léman is the largest natural freshwater lake in western Europe . In addition it is the largest body of freshwater in continental Europe in term of volume . 60% of it comes under the jurisdiction of Switzerland , and 40% under France...
some 100 kilometers (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
climateClimate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and numerous other meteorological elements in a given region over long periods of time...
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
moraineA 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 ice age. This debris may have been plucked off the 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 RiverThe Aar , a tributary of the Rhine, is the longest river that both rises and ends entirely within Switzerland.Its total length from its source to its junction with the Rhine comprises about 295 km , during which distance it descends , draining an area of .-Course:The Aar rises in the great Aar...
, which now drains western Switzerland into the Rhine River, eventually opened the natural
damA 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...
, the water levels in the plain fell to near the present levels.
In the last 150 years
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
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 is the scientific study of earthquakes and the propagation of elastic waves through the Earth...
. 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 researchGeodesy , also called 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
tomographyTomography is imaging by sections or sectioning, through the use of wave of energy. A device used in tomography is called a tomograph, while the image produced is a tomogram. The method is used in medicine, archaeology, biology, geophysics, oceanography, materials science, astrophysics and other...
the subducting slab of the European plate can be mapped. Tomography also shows some older detached slabs deeper in the mantle.
External links
Literature
; 2003:
HP metamorphic belt of the western Alps, Episodes
26(3), pp 200-204.; 2000:
Post-collisional large-scale extension in the Eastern Alps, Tectonophysics
327, p 239; 2009:
Geologie der Alpen, Haupt Verlag, Bern/Stuttgart/Wien, ISBN 978-3-8252-8416-9. ; 2004:
Tectonic map and overall architecture of the Alpine orogen, Eclogae Geologicae Helvetiae
97, p 93.; 2000:
The arc of the western Alps in the light of geophysical data on deep crustal structure, Tectonics
19, p 62.; 1996:
Geophysical-geological transect and tectonic evolution of the Swiss-Italian Alps, Tectonics
15, p 1036.; 2002:
Western Alps geological constraints on western Tethyan reconstructions, in: ; 2002:
Reconstruction of the evolution of the Alpine-Himalayan orogeny, Journal of the Virtual Explorer; 1993:
Le Briançonnais, terrain exotique dans les Alps?, Eclogae Geologicae Helvetiae
86, p 1 ; 1988:
Evolution of the Arctic-North Atlantic and the Western Tethys, American Association of Petroleum Geologists Memoir
43