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 volcanism , with associated rhomb porphyry lava flows. This activity was followed by uplifting , and ended with intrusions about 65 million years after the onset of the formation. It is located in the area around the Norwegian capital Oslo .
33-531: The lava production was high when the rhomb porphyry lavas were deposited. The lavas reflect a period of abundant earthquake-related movements, when tectonic forces tore the crust apart. In the Vestfold district, one lava flow was deposited on average every 250,000 years, resulting in a 3000-metre thick sequence of mainly volcanic material. In the Oslo area, lavas were deposited on average every 800,000 years. Only
66-508: A rift valley . Several of the old magma plumes are now quarried, the rich black larvikite (named from Larvik , a town south of Oslo) being one. The Särna alkaline complex in western Sweden, also of Late Carboniferous age, is thought to be related to the Oslo Graben as it is aligned to it. 59°48′04″N 10°33′23″E / 59.8011°N 10.5564°E / 59.8011; 10.5564 This Norway location article
99-419: A combination of regional tectonics, recent instrumentally recorded events, accounts of historical earthquakes, and geomorphological evidence. This information can then be used to quantify the seismic hazard of an area. Impact tectonics is the study of modification of the lithosphere through high velocity impact cratering events. Techniques used in the analysis of tectonics on Earth have also been applied to
132-460: A few plant remains have been found between these lavas. The bedrock in this area, roughly from Skien to Oslo and Mjøsa , results in soil rich in nutrients important for plant growth. Since the Permian, erosion has removed the volcanic peaks and indeed most of the lava layer and laid bare the magma chambers and volcanic pipes deep below, allowing scientist a rare view of what goes on beneath
165-524: A process ultimately driven by the continuous loss of heat from the Earth's interior. There are three main types of plate boundaries: divergent , where plates move apart from each other and new lithosphere is formed in the process of sea-floor spreading ; transform , where plates slide past each other, and convergent , where plates converge and lithosphere is "consumed" by the process of subduction . Convergent and transform boundaries are responsible for most of
198-442: A relatively brief interval, about 50 million years long. The process begins as two continents (different bits of continental crust ), separated across a tract of ocean (and oceanic crust ), approach each other, while the oceanic crust is slowly consumed at a subduction zone. The subduction zone runs along the edge of one of the continents and dips under it, raising volcanic mountain chains at some distance behind it, such as
231-402: A time period that is less than 10% of the life of a typical collision zone). River systems form, and glaciers may grow on the highest peaks. Erosion accelerates as the mountains rise, and great volumes of sediment are shed into the rivers, which carry sediment away from the mountains to be deposited in sedimentary basins in the surrounding lowlands. Crustal rocks are thrust faulted over
264-532: Is a stub . You can help Misplaced Pages by expanding it . This plate tectonics article is a stub . You can help Misplaced Pages by expanding it . Tectonic Tectonics (from Latin tectonicus ; from Ancient Greek τεκτονικός ( tektonikós ) 'pertaining to building ') are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of planetary tectonics extends
297-415: Is found at divergent plate boundaries, in continental rifts , during and after a period of continental collision caused by the lateral spreading of the thickened crust formed, at releasing bends in strike-slip faults , in back-arc basins , and on the continental end of passive margin sequences where a detachment layer is present. Thrust tectonics is associated with the shortening and thickening of
330-445: Is only half correct – viscous flow of weak lower mantle also reduces relief with time, especially once the collision is complete and the two continents are completely sutured. Convergence between the continents continues because the crust is still being pulled down by oceanic lithosphere sinking in the subduction zone to either side of the collision as well as beneath the impinging continent. The pace of mountain building associated with
363-638: Is only known to occur on Earth. Continental collision is not an instantaneous event, but may take several tens of millions of years before the faulting and folding caused by collisions stops. The collision between India and Asia has been going on for about 50 million years already and shows no signs of abating. Collision between East and West Gondwana to form the East African Orogen took about 100 million years from beginning (610 Ma) to end (510 Ma). The collision between Gondwana and Laurasia to form Pangea occurred in
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#1732783213462396-537: Is the collision of Arabia with Asia , which is squeezing the Anatolian sub-plate (present day Turkey ). As a result, Turkey is moving west and south into the Mediterranean Sea and away from the collision zone. These far-field effects may result in the formation of rifts, and rift valleys such as that occupied by Lake Baikal , the deepest lake on Earth. Continental collisions are a critical part of
429-412: Is thick (~45 km thick) and buoyant, composed mostly of granitic rocks (average density about 2.5 g/cm ). Continental crust is subducted with difficulty, but it is subducted to depths of 90–150 km or more, as evidenced by ultra- high pressure (UHP) metamorphic suites . Normal subduction continues as long as the ocean exists, but the subduction system is disrupted as the continent carried by
462-400: Is underway when mountains begin to grow in the collision zone. There are other modes of mountain formation and orogeny but certainly continental collision is one of the most important. Rainfall and snowfall increase on the mountains as these rise, perhaps at a rate of a few millimeters per year (at a growth rate of 1 mm/year, a 5,000 m tall mountain can form in 5 million years,
495-451: The Andes of South America today. Subduction involves the whole lithosphere , the density of which is largely controlled by the nature of the crust it carries. Oceanic crust is thin (~6 km thick) and dense (about 3.3 g/cm ), consisting of basalt , gabbro , and peridotite . Consequently, most oceanic crust is subducted easily at an oceanic trench . In contrast, continental crust
528-408: The supercontinent cycle and have happened many times in the past. Ancient collision zones are deeply eroded but may still be recognized because these mark sites of intense deformation, metamorphism, and plutonic activity that separate tracts of continental crust having different geologic histories prior to the collision. Old collision zones are commonly called "suture zones" by geologists, because this
561-834: The Western Alps , the Himalaya of India , the Kokchetav Massif of Kazakhstan , the Bohemian Massif of Europe, the North Qaidam of Northwestern China , the Western Gneiss Region of Norway , and Mali . Most UHP terranes consist of an imbricated sheets or nappes . The fact that most UHP terranes consist of thin sheets suggests that much thicker, volumetrically dominant tracts of continental crust are more deeply subducted. An orogeny
594-431: The collision is measured by radiometric dating of igneous rocks or units that have been metamorphosed during the collision and by examining the record of sediments shed from the rising mountains into the surrounding basins. The pace of ancient convergence can be determined with paleomagnetic measurements, while the present rate of convergence can be measured with GPS . The effects of the collision are felt far beyond
627-432: The concept to other planets and moons. These processes include those of mountain-building , the growth and behavior of the strong, old cores of continents known as cratons , and the ways in which the relatively rigid plates that constitute the Earth's outer shell interact with each other. Principles of tectonics also provide a framework for understanding the earthquake and volcanic belts that directly affect much of
660-405: The crust of the Earth is dissected by thousands of different types of tectonic elements which define the subdivision into numerous smaller microplates which have amalgamated into the larger Plates. Salt tectonics is concerned with the structural geometries and deformation processes associated with the presence of significant thicknesses of rock salt within a sequence of rocks. This is due both to
693-656: The crust, or the lithosphere. This type of tectonics is found at zones of continental collision , at restraining bends in strike-slip faults, and at the oceanward part of passive margin sequences where a detachment layer is present. Strike-slip tectonics is associated with the relative lateral movement of parts of the crust or the lithosphere. This type of tectonics is found along oceanic and continental transform faults which connect offset segments of mid-ocean ridges . Strike-slip tectonics also occurs at lateral offsets in extensional and thrust fault systems. In areas involved with plate collisions strike-slip deformation occurs in
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#1732783213462726-408: The downgoing plate enters the trench. Because it contains thick continental crust, this lithosphere is less dense than the underlying asthenospheric mantle and normal subduction is disrupted. The volcanic arc on the upper plate is slowly extinguished. Resisting subduction, the crust buckles up and under, raising mountains where a trench used to be. The position of the trench becomes a zone that marks
759-440: The global population. Tectonic studies are important as guides for economic geologists searching for fossil fuels and ore deposits of metallic and nonmetallic resources. An understanding of tectonic principles can help geomorphologists to explain erosion patterns and other Earth-surface features. Extensional tectonics is associated with the stretching and thinning of the crust or the lithosphere . This type of tectonics
792-413: The growing mountain mass, forming rifts near the crest of the mountain range. The lower crust may partially melt , forming anatectic granites which then rise into the overlying units, forming granite intrusions . Crustal thickening provides one of two negative feedbacks on mountain growth in collision zones, the other being erosion. The popular notion that erosion is responsible for destroying mountains
825-407: The immediate site of collision and mountain-building. As convergence between the two continents continues, the region of crustal thickening and elevation will become broader. If there is an oceanic free face, the adjacent crustal blocks may move towards it. As an example of this, the collision of India with Asia forced large regions of crust to move south to form modern Southeast Asia . Another example
858-418: The low density of salt, which does not increase with burial, and its low strength. Neotectonics is the study of the motions and deformations of the Earth's crust ( geological and geomorphological processes) that are current or recent in geological time . The term may also refer to the motions and deformations themselves. The corresponding time frame is referred to as the neotectonic period . Accordingly,
891-411: The over-riding plate in zones of oblique collision and accommodates deformation in the foreland to a collisional belt. In plate tectonics, the outermost part of the Earth known as the lithosphere (the crust and uppermost mantle ) act as a single mechanical layer. The lithosphere is divided into separate "plates" that move relative to each other on the underlying, relatively weak asthenosphere in
924-470: The preceding time is referred to as palaeotectonic period . Tectonophysics is the study of the physical processes associated with deformation of the crust and mantle from the scale of individual mineral grains up to that of tectonic plates. Seismotectonics is the study of the relationship between earthquakes, active tectonics, and individual faults in a region. It seeks to understand which faults are responsible for seismic activity in an area by analysing
957-414: The sediments and the mountain belt broadens as it rises in height. A crustal root also develops, as required by isostasy ; mountains can be high if underlain by thicker crust. Crustal thickening may happen as a result of crustal shortening or when one crust overthrusts the other. Thickening is accompanied by heating, so the crust becomes weaker as it thickens. The lower crust begins to flow and collapse under
990-424: The study of the planets and their moons, especially icy moons . Continental collision In geology , continental collision is a phenomenon of plate tectonics that occurs at convergent boundaries . Continental collision is a variation on the fundamental process of subduction , whereby the subduction zone is destroyed, mountains produced, and two continents sutured together. Continental collision
1023-452: The surface as ultra- high pressure (UHP) metamorphic terranes, which contain metamorphic coesite and/or diamond plus or minus unusual silicon -rich garnets and/or potassium -bearing pyroxenes . The presence of these minerals demonstrate subduction of continental crust to at least 90–140 km deep. Examples of UHP terranes are known from the Dabie–Sulu belt of east-central China ,
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1056-404: The suture between the two continental terranes . Suture zones are often marked by fragments of the pre-existing oceanic crust and mantle rocks, known as ophiolites . The continental crust on the downgoing plate is deeply subducted as part of the downgoing plate during collision, defined as buoyant crust entering a subduction zone. An unknown proportion of subducted continental crust returns to
1089-520: The world's major ( M w > 7) earthquakes . Convergent and divergent boundaries are also the site of most of the world's volcanoes , such as around the Pacific Ring of Fire . Most of the deformation in the lithosphere is related to the interaction between plates at or near plate boundaries. The latest studies, based on the integration of available geological data, and satellite imagery and Gravimetric and magnetic anomaly datasets have shown that
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