The Sveconorwegian orogeny was an orogenic system active 1140 to 960 million years ago and currently exposed as the Sveconorwegian orogenic belt in southwestern Sweden and southern Norway. In Norway the orogenic belt is exposed southeast of the front of the Caledonian nappe system and in nappe windows. The Sveconorwegian orogen is commonly grouped within the Grenvillian

Mesoproterozoic The Mesoproterozoic Era is a geologic era that occurred from . The Mesoproterozoic was the first era of Earth's history for which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic), ...

orogens. Contrary to many other known orogenic belts the Sveconorwegian orogens eastern border does not have any known suture zone with

ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is found ...

Tectonic segments

The Sveconorwegian orogen orogenic belt is composed of five segments largely made up of

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...

that were disrupted by both extension and compression in the timespan between 1140 and 980 million years ago. From west to east the segments are the

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its ow ...

s of Telemarkia, Bamble, Kongsberg and Idefjorden plus the Eastern Segment. The segments are separated from each other by large-scale

shear zone In geology, a shear zone is a thin zone within the Earth's crust or upper mantle that has been strongly deformed, due to the walls of rock on either side of the zone slipping past each other. In the upper crust, where rock is brittle, the she ...

s. *Bamble Terrane: The Bamble Terrane lies together with Kongsberg Terrane as a small sliver between the larger Idefjorden and Telemarkia terranes. The terrane displays

amphibolite Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flak ...

to granulite facies metamorphism. *Idefjorden Terrane: The Idefjorden Terrane originated from magmatic activity 1660 to 1520 million years ago and is composed of

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plat ...

, plutonic and metasedimentary rocks. This metamorphism, magmatism and accretion prior to the terranes' participation in the Sveconorwegian orogeny is known as the Gothian event. Between 1050 and 980 million years ago the involvement of the Idefjorden Terrane in the Sveconorwegian orogeny made its rocks reach

greenschist Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically and 2–10 kilobars (). Greenschists commonly have an abundance of green minerals such as chlorite ...

to amphibolites facies metamorphism, and even granulite facies in a few localities. To the east the terrane, along with the Eastern Segment, terminates along a

containing

mylonite Mylonite is a fine-grained, compact metamorphic rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. Mylonites can have many different mineralogical compositions; it is a ...

. The Mylonite Zone, as this shear zone is known, runs as an arc from the

Oslo graben The Oslo Graben or Oslo Rift is a graben formed during a geologic rifting event in Permian time, the last phase of the Variscan orogeny. The main graben forming period began in the late Carboniferous, which culminated with rift formation and volcan ...

to northern

Halland Halland () is one of the traditional provinces of Sweden (''landskap''), on the western coast of Götaland, southern Sweden. It borders Västergötland, Småland, Scania and the sea of Kattegat. Until 1645 and the Second Treaty of Brömseb ...

passing by

Lake Vänern A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

. The status of Idefjorden Terrane as a true terrane is disputed. *Kongsberg Terrane: The Kongsberg Terrane displays amphibolite to granulite facies metamorphism. It is positioned as a small wedge between the larger Idefjorden and Telemarkia terranes. *Telemarkia Terrane: The Telemarkia Terrane formed about 1520 to 1480 million years ago by a brief period of magmatism and is highly heterogeneous in its rock composition. The western part of the terrane hosts the Sirdal Magmatic Belt which is made up of granitoids including orthogneiss. The igneous rocks of the Sirdal Magmatic Belt are of calc-alkaline character which implies they are related to an ancient subduction system. It is not known if the Telemarkia Terrane originated from a transposed block of Fennoscandian crust or if it derives from another "exotic" craton, possibly

Amazonia The Amazon rainforest, Amazon jungle or ; es, Selva amazónica, , or usually ; french: Forêt amazonienne; nl, Amazoneregenwoud. In English, the names are sometimes capitalized further, as Amazon Rainforest, Amazon Forest, or Amazon Jungle. ...

. *Eastern Segment: In difference to the other segments that are allochthonous terranes the Eastern Segment is made up of local reworked

continental crust Continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called '' sial'' be ...

of the

Transscandinavian Igneous Belt The Transscandinavian Igneous Belt ( sv, Transskandinaviska magmatiska bältet), abbreviated TIB, is one of the major lithological units of the Baltic Shield. It consists of a series of batholiths in Sweden and Norway forming a ca. 1400 km l ...

. In other words, it has not been transported across from afar by

plate tectonic Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...

s. There is likely also reworked crust of the much older Svecofennian orogeny in the Eastern Segment. Rocks in the Eastern Segment reached extremely high pressures and temperatures during the Sveconorwegian orogeny resulting in eclogite and granulite facies metamorphism. Eclogites found in the Eastern Segment were at 35–40 kilometers depth during the orogeny-caused metamorphism that turned their protoliths into eclogite. The boundary of the Eastern Segment and the Sveconorwegian orogen with Svecofennian and Transcandinavian rocks of

Fennoscandia __NOTOC__ Fennoscandia ( Finnish, Swedish and no, Fennoskandia, nocat=1; russian: Фенноскандия, Fennoskandiya) or the Fennoscandian Peninsula is the geographical peninsula in Europe, which includes the Scandinavian and Kola penin ...

consist of the Sveconorwegian Frontal Deformation Zone and the Protogine Zone.

Development

The period between 1050 and 980 million years ago was the Sveconorwegian orogeny's most active phase with the Telemarkia and Idefjord Terranes being subject to

metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of ch ...

, thickening of their crust and deformation. This episode, known as the Agder phase, was followed by the Falkenberg phase that lasted until 970 million years ago during which the orogeny propagated eastward. There are differing views on the nature of the orogeny. One view, known as the "classical", postulates that a continent–continent collision, possibly with

, was responsible for giving the orogenic belts its current characteristics. An alternative view postulated in 2013 claims such collision did likely not occur as the characteristics of the orogen would be explained solely as the result of

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, ...

and accretion of smaller terranes. These different views have implications for the configuration of the ancient

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leav ...

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 and broke up 750–633 million years ago. were prob ...

. The southern part of what would eventually become the Western Gneiss Region of Norway formed

migmatite Migmatite is a composite rock found in medium and high-grade metamorphic environments, commonly within Precambrian cratonic blocks. It consists of two or more constituents often layered repetitively: one layer is an older metamorphic rock th ...

s and was

intruded Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March 2 ...

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...

s during the orogeny. About 920 million years ago, in the aftermath of the orogeny, Bohus granite intruded the Idefjorden terrane.

References

{{Geology of Europe Orogenies of Europe Geology of Norway Geology of Sweden Mesoproterozoic orogenies Mesoproterozoic Europe Neoproterozoic orogenies Neoproterozoic Europe