The Svecofennian orogeny is a series of related orogenies that resulted in the formation of much of the

continental crust Continental crust is the layer of igneous, metamorphic, and sedimentary 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 '' si ...

in what is today

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and

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along with minor parts of

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, mainly within what is today the Republic of Karelia. The orogenies lasted from about 2000 to 1800 million years ago during the Paleoproterozoic Era. The resulting orogen is known as the Svecofennian orogen or Svecofennides. To the west and southwest the Svecofennian orogen limits with the generally younger Transscandinavian Igneous Belt. It is assumed that the westernmost fringes of the Svecofennian orogen have been reworked by the Sveconorwegian orogeny just as the western parts of the Transscandinavian Igneous Belt has. The Svecofennian orogeny involved the accretion of numerous

island arc Island arcs are long archipelago, chains of active volcanoes with intense earthquake, seismic activity found along convergent boundary, convergent plate tectonics, tectonic plate boundaries. Most island arcs originate on oceanic crust and have re ...

s in such manner that the pre-existing craton grew with this new material from what is today northeast to the southwest. The accretion of the island arcs was also related to two other processes that occurred in the same period; the formation of magma that then cooled to form igneous rocks and the

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

of rocks.

Development of the orogeny

The Svecofennian orogeny developed as a succession of four orogenies which by chronological order are: the Lapland-Savo orogeny, the Fennian orogeny, the Svecobaltic orogeny and the Nordic orogeny. In broad terms, regardless of details, it has been proposed that the Svecofennian orogeny involved more-less continuous subduction with subduction zones progressively migrating to the southwest. An alternative

model A model is an informative representation of an object, person, or system. The term originally denoted the plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin , . Models can be divided in ...

postulates subduction included alternating extension and compression cycles, with the orogenic activity ceasing after the collision between the Fennoscandian Craton and the Sarmatian Craton.

Lapland-Savo orogeny

Prior to the onset of orogeny the

Archean The Archean ( , also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of the four geologic eons of Earth's history of Earth, history, preceded by the Hadean Eon and followed by the Proterozoic and t ...

-aged craton of what is today northeastern Fennoscandia rifted creating an ocean basin, the "pre-Svecofennian Ocean", that then closed during the Svecofennian orogeny. The closure of this basin was indebted to subduction and resulted thus both in the formation of igneous rocks and the emplacement of the Jormua and Outokumpu

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

s about 1950 million years ago. In the later stages of the Lapland-Savo orogeny an

, the Knaften arc, accreted to the Keitele-Karelia-Norrbotten collage.

Fennian orogeny

The stage to the Fennian orogeny was set by a collision between Keitele and Karelia about 1920–1910 million years ago which resulted in a reorganization of the local plate tectonics. As a consequence the Bergslagen microcontinents collided with the Keitele–Karelia collage starting the Fennian orogeny. The until then linear Fennian orogen was "buckled" from 1870 million years ago onwards due to an

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change in tectonic compressive stress. This resulted in various oroclines around the Gulf of Bothnia.

Svecobaltic orogeny

Prior to the Svecobaltic orogeny proper there was period of northward-directed subduction at what is now south-central Sweden and southern Finland. The subduction lasted from 1860 to 1840 million years ago and was accompanied by magmatic activity. Two trends in the southern Svecofennian orogen variously overlapped in time and space: extension (1870 to 1840 million years ago) and continent-continent collision (1870 to 1790 million years ago). Magmatic activity and metamorphism in southern Finland ended gradually after 1870 million years ago. The orogen at southern Finland with its presumed mountains and thick

collapsed under the influence of gravity and spread out. By 1850 million years ago this collapse had evolved to a dynamic of extensional tectonics. In this extensional milieu short-lived sedimentary basins formed. The Svecobaltic orogeny developed when subduction bought the Fennoscandian Craton into an oblique collision with the Sarmatian Craton. The mentioned sedimentary basins were destroyed by basin inversion 1830 million years ago. This last event of basin inversion was associated with a period of metamorphism in southern Finland that peaked about 1820 million years ago.

Nordic orogeny and later development

Two models exist regarding the origin of the Nordic orogeny: one proposes it as an Andean-type orogeny with subduction but no accretion or continental collision and the other poses it might have resulted from the collision of the Fennoscandian Craton with the Amazonia continent. The Svecofennian orogen underwent a gravitational collapse from 1790 to 1770 million years ago. The late magmatism following the orogeny overlaps in time with the early magmatism of the Transscandinavian Igneous Belt. This magmatism was largely the result of anatexis forming migmatites and large plutons. Another characteristic of the late magmatism is the apparent lack of mafic and intermediate compositions among the magmas, which are nearly all felsic.

Features of the orogen

Tectonostratigraphic units

Geologist Baltybaev (2013) have identified the following terranes as composing the Svecofennian orogen (parenthesis indicate location): ''Skellefteå Terrane'' ( Skellefte River Basin), ''Bothnian Terrane'' ( Västernorrland and Ostrobothnia), ''Pyhäsalmi Terrane'' ( Northern Savonia), ''Central Terrane'' (Central Finland), ''Western Terrane'' ( Gävleborg), ''Ladoga Terrane'' (southern Finland–Russia border) and the ''Southern Terrane'' ( Bergslagen and Southern Finland). Baltybaev further distinguishes between an ''outer zone'' in the northeast and an ''inner zone'' in the southwest. The ''inner zone'' is characterized by I-type calc-alkaline granitoids. In contrast the ''outer zone'' contains more S-type granitoids. There are differences between the metamorphosed sediments found in the two zones while the outer zone contains metagreywackes the inner zone hosts metapelites. Rocks of the outer zone are estimated to have formed 1890–1860 million years ago and granitoids of the inner zone 1840–1790 million years ago. In addition to those two zones Baltybaev identifies a narrow ''zone of conjugation with Archean complexes'' between the ''outer zone'' and the Archean craton to the north and east. Nironen and Mänttäri (2012) uses the terms ''Central Svecofennian terrane'' and ''Southern Svecofennian terrane'' for approximately the same areas Baltybaev calls ''outer'' and ''inner zone'' respectively. The ''Oskarshamn-Jönköping belt'' is a granitoid region of the Svecofennian orogen completely surrounded by rocks of Transscandinavian Igneous Belt. As the name implies the ''Oskarshamn-Jönköping belt'' runs as sliver from the vicinity of Oskarshamn northwest to the Jönköping area. It has been proposed that the Oskarshamn-Jönköping belt continues beneath the East European Platform in

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Major faults and sutures

The boundary of the Svecofennian orogen with the Archean "Kola-Karelian orogen" to the northwest is made up by the ''Luleå-Kuopio suture zone''. The dextral ''South Finland Shear Zone'' runs across much of southern Finland in a west–east direction.

Notes

References

Cited book * {{Geology of Fennoscandia Orogenies of Europe Geology of Finland Geology of European Russia Geology of Sweden Paleoproterozoic orogenies