The geology of Finland is made up of a mix of geologically very young and very old materials. Common rock types are orthogneiss, granite, metavolcanics and metasedimentary rocks. On top of these lies a widespread thin layer of unconsolidated deposits formed in connection to the Quaternary ice ages, for example eskers, till and marine clay. The topographic relief is rather subdued because mountain massifs were worn down to a peneplain long ago.
The bedrock of Finland belongs to the Fennoscandian Shield [1] and was formed by a succession of orogenies during the Precambrian. [2] The oldest rocks of Finland, those of Archean age, are found in the east and north. These rocks are chiefly granitoids and migmatitic gneiss. [1] Rocks in central and western Finland originated or were emplaced during the Svecokarelian orogeny. [1] Following this last orogeny rapakivi granites intruded various locations of Finland during the Mesoproterozoic and Neoproterozoic, especially in Åland and in the southeast. [1] Jotnian sediments occur usually together with rapakivi granites. [3]
Mountains that existed in Precambrian time were eroded into a level terrain already during the Late Mesoproterozoic. [2] [4] With Proterozoic erosion amounting to tens of kilometers, [5] many of the Precambrian rocks seen today in Finland are the "roots" of ancient massifs. [2]
As Finland is in the older part of the Fennoscandian Shield, its basement rocks are within three of the shield's older subdivisions known as domains: the Kola, Karelian and Svecofennian domains. This subdivision, established by Gaál and Gorbachev in 1987, is based on the different geological histories of the domains prior to their final amalgamation 1,800 million years ago. [6]
The extreme northeast of Finland is part of the Kola Domain because it shows considerable affinity with the geology of the Kola Peninsula in Russia. Around Lake Inari there are paragneiss, orthogneiss and greenstone belts. Rocks in this part of Finland are of Archean and Proterozoic age. [7]
To the south and west of Lake Inari lies an elongate and arcuate zone of granulite rock known as the Lapland Granulite Belt. The belt is up to 80 km wide. The main rocks of the belt are migmatized greywacke and argillites. Studies of detrital zircon show that the sedimentary protolith of the metamorphic rocks of the belt could not be more than 2900–1940 million years old. [8] The belt has norite and enderbite intrusions of calc-alkaline chemistry. [9]
The Karelian Domain, or Karelian Block, makes up most of the bedrock of the northeastern part of Finland [10] extending into nearby areas of Russia. [6] The Karelian domain is made up of a collage of rock formed during Archean and Paleoproterozoic times. [10] [7] The boundary to the Kola Domain is made up of a gently dipping décollement where the Lapland Granulite Belt has been thrust southward over rocks of the Karelian Domain. [11]
Archean rocks in the Karelian Domain are north-south medium grade greenstone and metasedimentary belts. The belts are intruded by granitoids, usually monzogranite and granodiorite. Besides these belts and intrusions there is also metasedimentary gneiss formed at intermediate pressures. [6] Along the central part of the Finland–Russia border lies the Belomorian terrane, a subunit of the Karelian Domain thought to have formed by a collision between the Kola Domain with the Karelian Domain in the Paleoproterozoic. [6] [11] This collision marked the final merger of both crustal blocks. [12] Rocks of the Belomorian terrane, like the granitoid gneisses common there, are of high grade. [11]
The Central Lapland granitoid complex covers up much of the interior of northern Finland. These rocks were formed in the final stages of the Svecofennian orogeny and are mostly made up of coarse-grained granites. [13] An alignment of granitoid intrusions southeast of Oulu likely shares the same origin. [14]
Finland's three ophiolites crop out within the Karelian Domain. These are the Jormua, Outokumpu and Nuttio ophiolite complexes. [15] All of them were emplaced in Paleoproterozoic times. [16] The Jormua and Outokumpu ophiolites lie parallel to and near the boundary with the Svecofennian Domain. [15] Also towards the border with the Svecovefennian Domain there is a series of metamorphosed Archean rocks that are stacked into an imbrication pattern. [11]
The southwestern part of Finland is mainly made up of rocks of the Svecofennian Domain or Svecofennian orogen. [10] These rocks are invariably of Proterozoic age. Its boundary with the Karelian Domain (of mixed Archean and Paleoproterozoic rocks) is a northwest-southeast diagonal. [10] Plutonic rocks that formed during accretion of volcanic arcs or continental collisions of the Svecofennian orogeny are common in Svecofennian Domain. [17] [18] Among these rocks the largest grouping is the Central Finland granitoid complex covering up much of Central Finland, Southern Ostrobothnia and Pirkanmaa. [18] Granitoids that intruded in the aftermath of the Svercofennian orogeny are common in southern Finland occurring mostly within ca. 100 km of the Gulf of Finland or Lake Ladoga. [18] [19] These so-called Lateorogenic granites are distinguished by usually containing garnet and cordierite and being accompanied by rather few rocks of mafic and intermediate composition. [19] Scattered small granitoids crop out within the same zone. Formed 1810–1770 million years ago, these are the youngest granitoids in southern Finland associated with the Svecofennian orogeny. [14]
Jotnian sediments are the oldest known sediments in the Baltic area that have not been subject to significant metamorphism. [20] [21] These sediments are typically quartz-rich sandstones, siltstones, arkose, shale and conglomerates. [22] [20] The characteristic red colour of Jotnian sediments is due to their deposition in subaerial (e.g. non-marine) conditions. [21] In Finland, Jotnian sediments occur in the Muhos Graben near Oulu at the northeastern end of the Gulf of Bothnia [23] [21] and further south near the coast at Satakunta. [23] [24] Jotnian rocks are also found offshore between Finland and Sweden in the Gulf of Bothnia and the Åland Sea including South Kvarken. [23] [25] [26] Known Jotnian rocks at the Åland Sea are sandstones belonging to the informally defined Söderarm Formation. Above these there are Upper Riphean and Vendian sandstones and shales. [27] There is evidence suggesting that Jotnian rocks, or even a Jotnian platform, once covered much of Fennoscandia and were not restricted to a few localities like today. [26] [28] The limited geographical extent of Jotnian sediments at present is indebted to their erosion over geological time. [26] Sedimentary rocks as old as the Jotnian sediments have a low preservation potential. [29]
The distribution of some Jotnian sediments is spatially associated with the occurrence of rapakivi granite. [22] Korja and co-workers (1993) claim the Jotnian sediment–rapakivi granite coincidence at the Gulf of Finland and the Gulf of Bothnia is related to the existence of thin crust at these locations. [3]
Small outcrops of alkaline rocks, carbonatites and kimberlites exist in Finland [30] including the western and southernmost outcrops of the Permian-aged Kola Alkaline Province. [31] [30] The Kola Alkaline Province is commonly presumed to represent an igneous hotspot created by a mantle plume. [32] Carbonatites in Finland have wide range in ages but they all derive from a "well-mixed" portion of the upper mantle. The Siilinjärvi carbonatite complex of Archean age is one of the Earth's oldest carbonatites. [30] All known kimberlites are concentrated near the towns of Kuopio and Kaavi. These are grouped in two clusters and include diatremes and dykes. [33]
The youngest rocks in Finland are those found near Kilpisjärvi in Enontekiö (the northwesternmost part of the country's northwestern arm). [35] These rocks belong to the Scandinavian Caledonides that assembled in Paleozoic times. [2] During the Caledonian orogeny Finland was likely a sunken foreland basin covered by sediments; subsequent uplift and erosion would have eroded all of these sediments. [36] In Finland, Caledonian nappes overlie shield rocks of Archean age. [7] Despite occurring in about the same area the Scandinavian Caledonides and the modern Scandinavian Mountains are unrelated. [37] [38]
The ice sheet that covered Finland intermittently during the Quaternary grew out from the Scandinavian Mountains. [39] [upper-alpha 1] By some estimates the Quaternary glaciers eroded away on average 25 m of rock in Finland, [2] with the degree of erosion being highly variable. [5] Some of the material eroded in Finland has ended up in Germany, Poland, Russia and the Baltic states. [2] Ground till left by the Quaternary ice sheets is ubiquitous in Finland. [2] Relative to the rest of Finland, the southern coastal areas have a thin and patchy cover of till evidencing a more prominent role of glacial erosion in the area, whereas Ostrobothnia and parts of Lapland stand out for their thick till cover. [40] [upper-alpha 2] The central parts of the Weichsel ice sheet had cold-based conditions during the times of maximum extent. Therefore, pre-existing landforms and deposits in northern Finland escaped glacial erosion and are now particularly well preserved. [42] Northwest to southeast movement of the ice has left a field of aligned drumlins in central Lapland. Ribbed moraines found in the same area reflect a later west to east change in movement of the ice. [42]
During the last deglaciation, the first part of Finland to become ice-free was the southeastern coast; this occurred shortly before the Younger Dryas cold-spell 12,700 years before present (BP). While the ice cover continued to retreat in the southeast after Younger Dryas, retreat also occurred in the east and northeast. The retreat was fastest from the southeast resulting in the lower course of the Tornio river in northwest Finland becoming the last part of the country to be ice-free. Finally, by 10,100 years BP, the ice cover had all but left Finland, retreating to Sweden and Norway before fading away. [43] Ice retreat was accompanied by the formation of eskers and the dispersal of fine-grained sediment deposited as varves. [2]
As the ice sheet became thinner and retreated, the land began to rise due to post-glacial rebound. Much of Finland was under water when the ice retreated and was gradually uplifted in a process that continues today. [44] [upper-alpha 3] Not all areas were drowned at the same time and it is estimated that, at one time or another, about 62% has been under water. [45] The maximum height of the ancient shoreline varied from region to region: in southern Finland 150 to 160 m, in central Finland about 200 m and in eastern Finland up to 220 m. [44] Once free of ice and water, soils have developed in Finland. Podzols with till as parent material now cover about 60% of Finland's land area. [46]
| Material | Land surface % | Cultivated soil % | |
|---|---|---|---|
| Till | 53 | 16 | |
| Peat thicker than 30 cm | 15 | 18 | |
| Bare rock | 13 | - | |
| Marine and lacustrine silt and clay | 8 | 66 | |
| Eskers and glacifluvial material | 5 | ||
Mining for metals in Finland began in 1530 at the Ojamo iron mine [47] [upper-alpha 4] but mining in the country was minimal until the 1930s. [48] The Outokumpu ore deposit, discovered in 1910, was key to the development of mining in Finland during the 20th century. When Outokumpu opened in 1910 it was Finland's first sulphide ore to be mined. This mine closed in 1989. [47] Another important Finnish mining resource was the nickel of Petsamo, which was mined by Canadian INCO from the 1920s onwards. Petsamo and its mines were, however, lost to the Soviet Union in 1944 as result of the Moscow Armistice. [48]
From 2001 to 2004 the number of metallic ores being mined dropped from eleven to the following four: [48]
There are some uranium resources in Finland, but to date no commercially viable deposits have been identified for exclusive mining of uranium. [49] In the Karelian Domain, there are various layered mafic intrusions of early Paleoproterozoic age that have been exploited for vanadium. [50]
Most of Finland's metallic ores formed in the Paleoproterozoic during the Svecofennian orogeny or during the period of complex extensional tectonics that preceded it. [51]
Non-metallic resources Finland include phosphorus that has been mined at the Siilinjärvi carbonatite since 1979, the outcrop being originally discovered in 1950. [30] The bedrock of Finland contain various types of gemstones. [48] The Lahtojoki kimberlite has gem quality garnet and diamond xenocrysts. [52]
Finland has a thriving quarrying industry. Finnish dimension stone has been used historically for buildings in Helsinki and imperial Russia's Saint Petersburg and Reval. Today, the main importers of Finnish stone are China, Germany, Italy and Sweden. The dimension stone quarried in Finland includes granites, such as the wiborgite variety of rapakivi granite, and marble. Soapstone from Finland's schist zone is also quarried for use in ovens. [53]
The geography of Finland is characterized by its northern position, its ubiquitous landscapes of intermingled boreal forests and lakes, and its low population density. Finland can be divided into three areas: archipelagoes and coastal lowlands, a slightly higher central lake plateau and uplands to north and northeast. Bordering the Baltic Sea, Gulf of Bothnia, and Gulf of Finland, as well as Sweden, Norway, and Russia, Finland is the northernmost country in the European Union. Most of the population and agricultural resources are concentrated in the south. Northern and eastern Finland are sparsely populated containing vast wilderness areas. Taiga forest is the dominant vegetation type.
Lapland is the largest and northernmost region of Finland. The 21 municipalities in the region cooperate in a Regional Council. Lapland borders the region of North Ostrobothnia in the south. It also borders the Gulf of Bothnia, Norrbotten County in Sweden, Finnmark County and Troms County in Norway, and Murmansk Oblast and the Republic of Karelia in Russia. Topography varies from vast mires and forests of the South to fells in the North. The Arctic Circle crosses Lapland, so polar phenomena such as the midnight sun and polar night can be viewed in Lapland.
The Baltic Shield is a segment of the Earth's crust belonging to the East European Craton, representing a large part of Fennoscandia, northwestern Russia and the northern Baltic Sea. It is composed mostly of Archean and Proterozoic gneisses and greenstone which have undergone numerous deformations through tectonic activity. It contains the oldest rocks of the European continent with a thickness of 250–300 km.
Kenorland is a hypothetical Neoarchean supercontinent. If it existed, it would have been one of the earliest known supercontinents on Earth. It is thought to have formed during the Neoarchaean Era c. 2.72 billion years ago by the accretion of Neoarchaean cratons and the formation of new continental crust. It comprised what later became Laurentia, Baltica, Western Australia and Kalaharia.
The Central Lapland Greenstone Belt (CLGB) is a greenstone belt located in the northern part of the Fennoscandian Shield. The region belongs to Lapland, northern Finland. The CLGB is part of a much larger belt of Paleoproterozoic greenstones, a cover of metamorphosed volcanic and sedimentary rocks that cover the Archean basement, the latter which is representative of the Archaean Karelian craton. Deposition of the cover sequence occurred between about 2.5 Ga and 1.8 Ga, thus it preserves information about Earth's history from a period that encompass about 700 Ma.
Rapakivi granite is a hornblende-biotite granite containing large round crystals of orthoclase each with a rim of oligoclase. The name has come to be used most frequently as a textural term where it implies plagioclase rims around orthoclase in plutonic rocks. Rapakivi is a Finnish compound of "rapa" and "kivi", because the different heat expansion coefficients of the component minerals make exposed rapakivi crumble easily into sand.
The Churchill Craton is the northwest section of the Canadian Shield and stretches from southern Saskatchewan and Alberta to northern Nunavut. It has a very complex geological history punctuated by at least seven distinct regional tectonometamorphic intervals, including many discrete accretionary magmatic events. The Western Churchill province is the part of the Churchill Craton that is exposed north and west of the Hudson Bay. The Archean Western Churchill province contributes to the complicated and protracted tectonic history of the craton and marks a major change in the behaviour of the Churchill Craton with many remnants of Archean supracrustal and granitoid rocks.
The geology of the Rocky Mountains is that of a discontinuous series of mountain ranges with distinct geological origins. Collectively these make up the Rocky Mountains, a mountain system that stretches from Northern British Columbia through central New Mexico and which is part of the great mountain system known as the North American Cordillera.
The Wyoming Craton is a craton in the west-central United States and western Canada – more specifically, in Montana, Wyoming, southern Alberta, southern Saskatchewan, and parts of northern Utah. Also called the Wyoming Province, it is the initial core of the continental crust of North America.
The West African Craton (WAC) is one of the five cratons of the Precambrian basement rock of Africa that make up the African Plate, the others being the Kalahari craton, Congo craton, Saharan Metacraton and Tanzania Craton. Cratons themselves are tectonically inactive, but can occur near active margins, with the WAC extending across 14 countries in Western Africa, coming together in the late Precambrian and early Palaeozoic eras to form the African continent. It consists of two Archean centers juxtaposed against multiple Paleoproterozoic domains made of greenstone belts, sedimentary basins, regional granitoid-tonalite-trondhjemite-granodiorite (TTG) plutons, and large shear zones. The craton is overlain by Neoproterozoic and younger sedimentary basins. The boundaries of the WAC are predominantly defined by a combination of geophysics and surface geology, with additional constraints by the geochemistry of the region. At one time, volcanic action around the rim of the craton may have contributed to a major global warming event.
The Svecofennian orogeny is a series of related orogenies that resulted in the formation of much of the continental crust in what is today Sweden and Finland plus some minor parts of Russia. 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 arcs 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 of rocks.
The Lapland Granulite Belt is an elongate and arcuate zone of granulite rock in the Cap of the North spanning areas within Norway, Finland and Murmansk Oblast in Russia. At most the belt is 80 km broad. The main rocks of the belt are migmatized greywacke and argillites. Studies of detrital zircon show that the sedimentary protolith of the metamorphic rocks of the belt could not be older than 2900–1940 million years. The belt has norite and enderbite intrusions of calc-alkaline chemistry.
The Belomorian Province is an area of the Fennoscandian Shield spanning the parts of the Republic of Karelia and Murmansk Oblast in Northwest Russia. The province is named after the Russian name for the White Sea. The main rock types are orthogneiss, greenstone and paragneiss. Although these rocks formed in the Mesoarchean and Neoarchean, they were disturbed by tectonic movements and heat 1900–1800 million years ago in the Paleoproterozoic. Located between the Kola and Karelian domains the collision of these two blocks would have caused the disturbance. According to one view the Belomorian Province could just be a more metamorphosed part of the Karelian Province to the west.
The geology of Liberia is largely extremely ancient rock formed between 3.5 billion and 539 million years ago in the Archean and the Neoproterozoic, with some rocks from the past 145 million years near the coast. The country has rich iron resources as well as some diamonds, gold and other minerals in ancient sediment formations weathered to higher concentrations by tropical rainfall.
The geology of Ghana is primarily very ancient crystalline basement rock, volcanic belts and sedimentary basins, affected by periods of igneous activity and two major orogeny mountain building events. Aside from modern sediments and some rocks formed within the past 541 million years of the Phanerozoic Eon, along the coast, many of the rocks in Ghana formed close to one billion years ago or older leading to five different types of gold deposit formation, which gave the region its former name Gold Coast.
The geology of Ivory Coast is almost entirely extremely ancient metamorphic and igneous crystalline basement rock between 2.1 and more than 3.5 billion years old, comprising part of the stable continental crust of the West African Craton. Near the surface, these ancient rocks have weathered into sediments and soils 20 to 45 meters thick on average, which holds much of Ivory Coast's groundwater. More recent sedimentary rocks are found along the coast. The country has extensive mineral resources such as gold, diamonds, nickel and bauxite as well as offshore oil and gas.
The geology of Nigeria formed beginning in the Archean and Proterozoic eons of the Precambrian. The country forms the Nigerian Province and more than half of its surface is igneous and metamorphic crystalline basement rock from the Precambrian. Between 2.9 billion and 500 million years ago, Nigeria was affected by three major orogeny mountain-building events and related igneous intrusions. Following the Pan-African orogeny, in the Cambrian at the time that multi-cellular life proliferated, Nigeria began to experience regional sedimentation and witnessed new igneous intrusions. By the Cretaceous period of the late Mesozoic, massive sedimentation was underway in different basins, due to a large marine transgression. By the Eocene, in the Cenozoic, the region returned to terrestrial conditions.
The geology of Sweden is the regional study of rocks, minerals, tectonics, natural resources and groundwater in the country. The oldest rocks in Sweden date to more than 2.5 billion years ago in the Precambrian. Complex orogeny mountain building events and other tectonic occurrences built up extensive metamorphic crystalline basement rock that often contains valuable metal deposits throughout much of the country. Metamorphism continued into the Paleozoic after the Snowball Earth glaciation as the continent Baltica collided with an island arc and then the continent Laurentia. Sedimentary rocks are most common in southern Sweden with thick sequences from the last 250 million years underlying Malmö and older marine sedimentary rocks forming the surface of Gotland.
The geology of Nunavut began to form nearly three billion years ago in the Archean and the territory preserves some of the world's oldest rock units.
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