The Baltic Shield (or Fennoscandian 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.
31-785: The Baltic Shield is divided into five provinces : the Svecofennian and Sveconorwegian (or Southwestern gneiss) provinces in Fennoscandia, and the Karelian , Belomorian and Kola provinces in Russia. The latter three are divided further into several blocks and complexes and contain the oldest of the rocks, at 3100–2500 Ma (million years) old. The youngest rocks belong to the Sveconorwegian province, at 1700–900 Ma old. Thought to be formerly part of an ancient continent,
62-569: 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 . Geologist Baltybaev (2013) have identified
93-562: A thin layer of humus on top. Vast forests, featuring almost exclusively the three species pine, spruce and birch, dominate the landscape, clearly demarcating its boundaries. The soil is acidic and has next to no carbonates such as limestone . The scouring by the ancient glaciers and the acidity of the soil have destroyed all palaeontologically interesting materials, such as fossils. The Baltic Shield yields important industrial minerals and ores , such as those of iron , nickel , copper and platinum group metals. Because of its similarity to
124-810: 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 Lithuania . The boundary of the Svecofennian orogen with
155-484: 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
186-464: Is therefore of importance to geophysicists studying the geologic history and dynamics of eastern Europe. The scouring and compression of the Baltic Shield by glacial movements created the area's many lakes and streams, the land retaining only a thin layer of sandy sediment collected in depressions and eskers . Most soil consists of moraine , a grayish yellow mixture of sand and rocks, with
217-599: 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 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
248-536: The Altai region of Russia. A summit accordance (sometimes also known by the German loan word gipfelflur ) exists when hills and mountaintops, and eventually also plateaux , have such a disposition that they form a geometric plane that may be either horizontal or tilted. Summit accordances can be the vestiges of former continuous erosion surfaces that were uplifted and eroded . Other proposed explanations include:
279-539: The Caledonian orogeny , Finland was likely a sunken foreland basin covered by sediments; subsequent uplift and erosion would have eroded all of these sediments. While Finland has remained buried or very close to sea-level since the formation of the Sub-Cambrian peneplain, some further relief was formed by a slight uplift, resulting in the carving of valleys by rivers. The slight uplift also means that in places
310-558: The Canadian Shield and cratons of southern Africa and Western Australia , the Baltic Shield had long been a suspected source of diamonds and gold . Currently, the Central Lapland Greenstone Belt in the north is considered to be an unexplored area that has the potential to hold exploitable gold deposits. Recent exploration has revealed a significant number of diamond-bearing kimberlites in
341-583: The Kola Peninsula , and (possibly extensive) deposits of gold in Finland . Mountains that existed in Precambrian time were eroded into a subdued terrain already during the late Mesoproterozoic , when the rapakivi granites intruded. Further erosion made the terrain rather flat at the time of the deposition of Jotnian sediments. With Proterozoic erosion amounting to tens of kilometers, many of
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#1732757509399372-626: The Sarmatian Craton . Prior to the onset of orogeny the Archean -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 ophiolites about 1950 million years ago. In
403-735: The Stockholm archipelago were subject to considerable glacial erosion in the form of scraping during the Quaternary. The Quaternary ice ages resulted in the glacier's erosion of irregularly distributed weak rock, weathered rock mantles, and loose materials. When the ice masses retreated , eroded depressions turned into the many lakes seen now in Finland and Sweden. Fractures in the bedrock were particularly affected by weathering and erosion, leaving as result straight sea and lake inlets. Svecofennian orogeny The Svecofennian orogeny
434-540: 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. Cited book Summit accordance [REDACTED] The highest of hills in this picture show fairly similar heights making up a summit accordance. Aerial photograph from
465-480: The Baltic Shield grew in size through collisions with neighbouring crustal fragments. The mountains created by these tectonic processes have since been eroded to their bases, the region being largely flat today. Through five successive Pleistocene glaciations and subsequent retreats, the Baltic Shield has been scoured clean of its overlying sediments, leaving expansive areas (most within Scandinavia) exposed. It
496-504: The Fennian orogeny. The until then linear Fennian orogen was "buckled" from 1870 million years ago onwards due to an orthogonal change in tectonic compressive stress . This resulted in various oroclines around the Gulf of Bothnia . 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
527-537: 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 postulates subduction included alternating extension and compression cycles, with the orogenic activity ceasing after the collision between the Fennoscandian Craton and
558-614: The Precambrian rocks seen today in Finland are the "roots" of ancient massifs. The last major leveling event resulted in the formation of the Sub-Cambrian peneplain in late Neoproterozoic time. Laurentia and Baltica collided in the Silurian and Devonian , producing a Himalayas -sized mountain range named the Caledonian Mountains roughly over the same area as the present-day Scandinavian Mountains . During
589-563: The Scandinavian Mountains and the South Swedish Dome can be likened to a giant anticlinal lithospheric folds . Folding could have been caused by horizontal compression acting on a thin to thick crustal transition zone (as are all passive margins). The uplift of the Scandinavian Mountains resulted in the progressive tilt of northern Sweden, contributing to create the parallel drainage pattern of that region. As
620-600: The South Swedish Dome uplifted, this resulted in the formation of a piedmonttreppen and the obstruction of the Eridanos River , diverting it to the south. While being repeatedly covered by glaciers during the Quaternary (last 2.58 million years), Fennoscandia has seen little effect on any changes in its topography from glacial erosion. Denudation during this time is geographically highly variable but averages tens of meters. The southern coast of Finland, Åland and
651-554: 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
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#1732757509399682-471: 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
713-540: 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
744-453: 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
775-678: The later stages of the Lapland-Savo orogeny an island arc , the Knaften arc, accreted to the Keitele-Karelia-Norrbotten collage . 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
806-456: 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
837-921: The possibility that erosion becomes more effective at height, tearing down mountains that stand out that isostasy regulates the height of individual mountain masses meaning that small mountains might be uplifted and large mountains dragged down that landscape dissection by uniformly spaced streams eventually reach a state in which summits attain similar heights that summit accordance is derivative of structural planes exposed by erosion See also [ edit ] Dissected plateau Glacial buzzsaw Syrt References [ edit ] ^ Lidmar-Bergström, Karna . "Toppkonstans" . Nationalencyklopedin (in Swedish). Cydonia Development . Retrieved June 22, 2015 . ^ Beckinsale, Robert P.; Chorley, Richard J. (2003) [1991]. "Chapter Seven: American Polycyclic Geomorphology". The History of
868-680: The uplift of the northern Scandinavian Mountains in the Paleogene. The northern Scandinavian Mountains had their main uplift in the Paleogene, while the southern Scandinavian Mountains and the South Swedish Dome were largely uplifted in the Neogene . The uplift events were concurrent with the uplift of Eastern Greenland . All of these uplifts are thought to be related to far-field stresses in Earth's lithosphere . According to this view,
899-728: The uplifted peneplain can be traced as summit accordances . Denudation in the Mesozoic is counted at most in hundreds of meters. The inselberg plain of Finnish Lapland is estimated to have formed in Late Cretaceous or Paleogene times, either by pediplanation or etchplanation . Any older Mesozoic surface in Finnish Lapland is unlikely to have survived erosion. Further west, the Muddus plains and its inselbergs formed—also by etching and pediplanation—in connection to
930-452: 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 continental crust collapsed under
961-493: Was associated with a period of metamorphism in southern Finland that peaked about 1820 million years ago. 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