HOME

TheInfoList



OR:

The Scandinavian Caledonides are the vestiges of an ancient, today deeply eroded
orogenic belt An orogenic belt, orogen, or mobile belt, is a zone of Earth's crust affected by orogeny. An orogenic belt develops when a continental plate crumples and is uplifted to form one or more mountain ranges; this involves a series of geological proc ...
formed during the
Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...
Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
continental collision In geology, continental collision is a phenomenon of plate tectonics that occurs at Convergent boundary, convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroy ...
of
Baltica Baltica is a paleocontinent that formed in the Paleoproterozoic and now constitutes northwestern Eurasia, or Europe north of the Trans-European Suture Zone and west of the Ural Mountains. The thick core of Baltica, the East European Craton, i ...
and
Laurentia Laurentia or the North American craton is a large continental craton that forms the Geology of North America, ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of ...
, which is referred to as the Scandian phase of the
Caledonian orogeny The Caledonian orogeny was a mountain-building cycle recorded in the northern parts of the British Isles, the Scandinavian Caledonides, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events tha ...
. The size of the Scandinavian Caledonides at the time of their formation can be compared with the size of the Himalayas. The area east of the Scandinavian Caledonides, including parts of Finland, developed into a
foreland basin A foreland basin is a structural basin 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 lithospher ...
where old rocks and surfaces were covered by sediments. Today, the Scandinavian Caledonides underlie most of the western and northern Scandinavian Peninsula, whereas other parts of the Caledonides can be traced into West and Central Europe as well as parts of Greenland and eastern North America.


Plate-tectonic history

The Caledonian Wilson cycle commenced with the continental break-up of
Rodinia Rodinia (from the Russian родина, ''rodina'', meaning "motherland, birthplace") was a Mesoproterozoic and Neoproterozoic supercontinent that assembled 1.26–0.90 billion years ago (Ga) and broke up 750–633 million years ago (Ma). wer ...
and the opening of the Iapetus ocean about 616–583 Ma (
mega-annum A year is a unit of time based on how long it takes the Earth to orbit the Sun. In scientific use, the tropical year (approximately 365 solar days, 5 hours, 48 minutes, 45 seconds) and the sidereal year (about 20 minutes longer) are more exa ...
) ago. The Iapetus was at its widest in the
Late Cambrian The Furongian is the fourth and final Epoch (geology), epoch and Series (stratigraphy), series of the Cambrian. It lasted from to million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocia ...
Early Ordovician before it began to close by
subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...
of Iapetus
oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramaf ...
along the Gondawanan and Laurentian margins starting between 500 and 488 Ma ago. Subduction of Iapetus crust continued until about 430 Ma ago until the final
continental collision In geology, continental collision is a phenomenon of plate tectonics that occurs at Convergent boundary, convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroy ...
of Laurentia with Baltica, i.e. the Scandian phase of the Caledonian orogeny. The time of the continental collision is estimated by the cessation of subduction-related magmatism and a common apparent polar wander path ( APWP) for Laurentia and Baltica. During the collision, the Baltican
continental margin A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental marg ...
was deeply subducted beneath Laurentia and eclogitized. The time of the maximal burial of the Baltican margin is estimated at 410 Ma ago by radiometric age dating of the ultra-high pressure (UHP) metamorphism in the Western Gneiss Region (WGR). Also during the collision, the Caledonian
allochthon upright=1.6, Schematic overview of a thrust system. The hanging wall block is (when it has reasonable proportions) called a window. A klippe is a solitary outcrop of the nappe in the middle of autochthonous material. An allochthon, or an alloc ...
s were thrust over the Baltican margin. Peak metamorphism in the allochthons is estimated to have occurred somewhat earlier than in the autochthon at about 420 Ma ago. Following the subduction of the Baltican continental margin and thrusting of the nappes over the Baltican basement, the orogen began to collapse in the
Early Devonian The Early Devonian is the first of three Epoch (geology), epochs comprising the Devonian period, corresponding to the Lower Devonian Series (stratigraphy), series. It lasted from and began with the Lochkovian Stage , which was followed by the Pr ...
, which was associated with extensional tectonics and sinistral motion between the Laurentian and Baltican tectonic plates.


Disposition of rocks

The Caledonian orogeny put in place most of the
bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bed ...
now seen in the
Scandinavian Mountains The Scandinavian Mountains or the Scandes is a mountain range that runs through the Scandinavian Peninsula. The western sides of the mountains drop precipitously into the North Sea and Norwegian Sea, forming the fjords of Norway, whereas to th ...
. Caledonian rocks overlie rocks of the much older Svecokarelian and Sveconorwegian
provinces A province is an administrative division within a country or state. The term derives from the ancient Roman , which was the major territorial and administrative unit of the Roman Empire's territorial possessions outside Italy. The term ''provi ...
. The Caledonian rocks form large nappes () that have been thrust over the older rocks. Much of the Caledonian rocks have been eroded since they were put in place meaning that they were once thicker and more contiguous. It is also implied from the erosion that the nappes of Caledonian rock originally reached further east than they do today. The erosion has left remaining massifs of Caledonian rocks and
windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...
of
Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...
-aged rock. While there are some disagreements, geologists generally recognize four
units Unit may refer to: General measurement * Unit of measurement, a definite magnitude of a physical quantity, defined and adopted by convention or by law **International System of Units (SI), modern form of the metric system **English units, histo ...
among the nappes: an Uppermost, an Upper, a Middle and a Lower one. The last one is made up
Ediacaran The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...
(
Vendian The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...
),
Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
,
Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...
and
Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...
-aged
sedimentary rocks Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedim ...
. Pieces of Precambrian
shield A shield is a piece of personal armour held in the hand, which may or may not be strapped to the wrist or forearm. Shields are used to intercept specific attacks, whether from close-ranged weaponry like spears or long ranged projectiles suc ...
rocks are in some places also incorporated into the Lower nappes.


Present-day topography of Scandinavia

Despite occurring in roughly the same area, the ancient Scandinavian Caledonian Mountains and the modern Scandinavian Mountains are not synonymous. The overlap between the Scandinavian Caledonides and the Scandinavian Mountains has led to various suggestions that the modern Scandinavian Mountains are a remnant of the Caledonide mountains. A version of this argument was put forward in 2009 with the claim that the uplift of the mountains was attained by
buoyancy Buoyancy (), or upthrust, is the force exerted by a fluid opposing the weight of a partially or fully immersed object (which may be also be a parcel of fluid). In a column of fluid, pressure increases with depth as a result of the weight of t ...
of the surviving "mountain roots" of the Caledonian orogen. This concept has been criticized because there is only a tiny "mountain root" beneath the southern Scandinavian Mountains and no "root" at all in the north. Further, the Caledonian Mountains in Scandinavia are known to have undergone orogenic collapse for a long period starting in the
Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
. Another problem with this model is that it does not explain why other former mountains dating back to the Caledonian orogeny are eroded and buried in sediments and not uplifted by their "roots". Others claim that molten magma exists below the Caledonides of Norway, causing the uplift.


See also

* Caledonian rocks of northern Finland * Origin of the Scandinavian Mountains * Timanide Orogen * Weichselian glaciation


Notes


References

{{Geology of Fennoscandia Orogenies of Europe Ordovician orogenies Silurian orogenies Devonian orogenies Paleozoic Europe Geology of Norway Geology of Finland Geology of Sweden Ordovician Norway Silurian Norway Devonian Norway