Geology of Sweden
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| Geology of Sweden | |
|---|---|
| Country | Sweden |
| Geological timespan | Archean to Quaternary |
| Major features | Fennoscandian Shield, Caledonian orogeny, Baltic Sea |
| Mineral resources | Iron ore, copper, lead, zinc, gold |
| Governing body | Geological Survey of Sweden |
Geology of Sweden. The geology of Sweden is dominated by the ancient, stable Fennoscandian Shield, which forms part of the Baltic Shield. This crystalline basement, composed primarily of Precambrian rocks, was assembled over billions of years and later affected by the Caledonian orogeny. The country's geological evolution has endowed it with significant mineral resources and a landscape profoundly shaped by Quaternary glaciation.
Geological history
The geological history of Sweden spans from the Archean Eon to the present Quaternary period. The oldest rocks, found in the northern part of the country, are Archean gneisses and greenstone belts, such as those in the Norrbotten County region. During the Paleoproterozoic, major orogenic events, including the Svecofennian orogeny, led to the formation of vast granite and metavolcanic terrains across central Sweden. The Mesoproterozoic was marked by the emplacement of anorogenic rapakivi granite suites, like the Åland massif, and the development of the Sveconorwegian orogeny in the southwest. The Phanerozoic record is dominated by the early Paleozoic Caledonian orogeny, which created the Scandinavian Mountains, and subsequent periods of erosion, sedimentation, and repeated glaciation.
Bedrock and lithology
Sweden's bedrock is predominantly Precambrian, classified into several major lithological units. The Archean Pajala Province contains granulite and amphibolite-facies gneiss complexes. The extensive Svecofennian Domain is characterized by metagraywacke, volcanic arc sequences, and voluminous granitoid plutons, such as those near Stockholm. The Transscandinavian Igneous Belt is a prominent feature composed of Mesoproterozoic granite and porphyry. In southern Sweden, the Sveconorwegian Province consists of reworked gneisses and mafic intrusions. Younger Cambrian to Silurian sedimentary rocks, including limestone and shale, are preserved in a thin cover on the shield, particularly on the island of Öland.
Tectonic structure and evolution
The tectonic framework of Sweden is defined by the stable Fennoscandian Shield and its margins. The shield itself is a collage of Archean cratons and Paleoproterozoic accretionary orogens sutured together during the Svecofennian orogeny. Major crustal-scale shear zones, like the Protogine Zone and the Mylonite Zone, separate different geological provinces. The western margin of the shield was intensely deformed during the Caledonian orogeny, a collision between Laurentia and Baltica that thrust ancient Baltoscandian sediments onto the platform, forming the Caledonian nappes. Post-orogenic extension led to the formation of the Oslo Rift and the subsidence of the Baltic Sea basin.
Quaternary geology and glaciation
The Quaternary geology of Sweden is overwhelmingly influenced by the Weichselian glaciation. The Fennoscandian Ice Sheet repeatedly covered the land, depositing thick sequences of till and sculpting the classic glacial landforms seen today. These include numerous roche moutonnées, esker ridges like the Uppsalaåsen, and vast fields of drumlins. Post-glacial isostatic rebound has been significant, raising former littoral zones, such as the High Coast (Höga kusten), a UNESCO World Heritage Site. Extensive deposits of glaciofluvial sediment, varve clay, and peat fill valleys and lowlands.
Mineral resources and economic geology
Sweden is exceptionally rich in metallic mineral resources, a direct result of its Precambrian geology. The Kiruna district in Norrbotten County hosts the world's largest underground iron ore mine, within Kirunavaara, associated with apatite-magnetite deposits. The Skellefteå District is a major volcanic-hosted massive sulfide province yielding copper, lead, zinc, gold, and silver, with mines like Boliden and Garpenberg. Other significant resources include tungsten from the Yxsjöberg mine, uranium at Ranstad, and industrial minerals like feldspar and quartz. Exploration continues for rare-earth elements and lithium.
Geological research and surveys
Systematic geological research in Sweden began in the 17th century with pioneers like Urban Hjärne and was advanced by Johan Gottschalk Wallerius. The Geological Survey of Sweden (SGU), founded in 1858, is the primary institution for mapping and resource assessment. Key figures in Swedish geology include Arvid Gustaf Högbom, who studied glacial geology, and Pentti Eskola, a founder of metamorphic facies theory. Modern research is conducted at universities like Uppsala University and Luleå University of Technology, and involves deep drilling projects such as the Gravberg-1 well and studies of the Siljan Ring impact structure.