Utsira High ( Norwegian : Utsirahøgda ) is a basement high and horst in the southwest of the Norwegian continental shelf . It lies east of the Viking Graben and west of the Stord and Egersund basins 190 km west of Stavanger . It was on the Balder oil field at the flank of the Utsira High that oil was first discovered in Norway in 1967.
32-578: The basement is of Utsira High is composed of granite that formed in Ordovician times. Parts of these granites contain saprolite and saprock that formed from weathering above sea level during the Early Mesozoic . before they became buried in Late Jurassic and Early Cretaceous -aged sandstone . These weathered rocks may be unconventional petroleum reservoirs . The strandflat at Bømlo island
64-422: A sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin. In the same way, the sediments or sedimentary rocks on top of the basement can be called a "cover" or "sedimentary cover". Crustal rocks are modified several times before they become basement, and these transitions alter their composition. Basement rock
96-407: A terrane was accreted to the edge of the continent. Any of this material may be folded, refolded and metamorphosed. New igneous rock may freshly intrude into the crust from underneath, or may form underplating , where the new igneous rock forms a layer on the underside of the crust. The majority of continental crust on the planet is around 1 to 3 billion years old, and it is theorised that there
128-453: A weak zone on which the harder (stronger) limestone cover was able to move over the hard basement, making the distinction between basement and cover even more pronounced. In Andean geology the basement refers to the Proterozoic , Paleozoic and early Mesozoic ( Triassic to Jurassic ) rock units as the basement to the late Mesozoic and Cenozoic Andean sequences developed following
160-473: A plate of oceanic crust is subducted beneath an overriding plate of oceanic crust, as the underthrusting crust melts, it causes an upwelling of magma that can cause volcanism along the subduction front on the overriding plate. This produces an oceanic volcanic arc , like Japan . This volcanism causes metamorphism , introduces igneous intrusions , and thickens the crust by depositing additional layers of extrusive igneous rock from volcanoes. This tends to make
192-516: A relatively thin veneer, but can be more than 5 kilometres (3 mi) thick. The basement rock of the crust can be 32–48 kilometres (20–30 mi) thick or more. The basement rock can be located under layers of sedimentary rock, or be visible at the surface. Basement rock is visible, for example, at the bottom of the Grand Canyon , consisting of 1.7- to 2-billion-year-old granite ( Zoroaster Granite ) and schist ( Vishnu Schist ). The Vishnu Schist
224-587: Is believed to be highly metamorphosed igneous rocks and shale , from basalt , mud and clay laid from volcanic eruptions, and the granite is the result of magma intrusions into the Vishnu Schist. An extensive cross section of sedimentary rocks laid down on top of it through the ages is visible as well. The basement rocks of the continental crust tend to be much older than the oceanic crust. The oceanic crust can be from 0–340 million years in age, with an average age of 64 million years. Continental crust
256-531: Is considered a sedimentary rock -free equivalent to the Utsira High. This article about structural geology is a stub . You can help Misplaced Pages by expanding it . Basement (geology) In geology , basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The basement rocks lie below
288-495: Is older because continental crust is light and thick enough so it is not subducted, while oceanic crust is periodically subducted and replaced at subduction and oceanic rifting areas. The basement rocks are often highly metamorphosed and complex, and are usually crystalline . They may consist of many different types of rock – volcanic, intrusive igneous and metamorphic. They may also contain ophiolites , which are fragments of oceanic crust that became wedged between plates when
320-413: Is the thick foundation of ancient, and oldest, metamorphic and igneous rock that forms the crust of continents , often in the form of granite . Basement rock is contrasted to overlying sedimentary rocks which are laid down on top of the basement rocks after the continent was formed, such as sandstone and limestone . The sedimentary rocks which may be deposited on top of the basement usually form
352-569: The British Isles , ( Paleogene ) denudation is linked with magmatic underplating. It has been shown that the wavelength and amplitude of denudation can be determined by the density and distribution of the underplating in a given area. Modeling of data brought on by studies of the British Isles shows that a large amount of high velocity material occurs around the Mohorovičić discontinuity under
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#1733084701806384-470: The Irish Sea . Epeirogenic uplift is a long-wavelength form of uplift and be split up into two separate categories, which is transient and permanent. Permanent epeirogenic uplift is possibly mainly produced by magmatic underplating, while transient uplift is more involved with mantle convection . Magmatic underplating is important for causing quick epeirogenic uplift in certain areas. It has been argued that
416-607: The Rajmahal Traps , there is a 10–15 km thick igneous layer at the base of the crust beneath this area. The thickness of the layer is different in various parts of the area; it is in the center, where the thickness is the greatest, where it is possible that the magma is being fed to the Rajmahal Traps up above. Presence of underplating is also found in the Cambay rift at the depth range of 25 and 31 km through gravity modeling. In
448-529: The crust . Entrapment (or 'stalling out') of magmas within the crust occurs due to the difference in relative densities between the rising magma and the surrounding rock. Magmatic underplating can be responsible for thickening of the crust when the magma cools. Geophysical seismic studies (as well as igneous petrology and geochemistry ) utilize the differences in densities to identify underplating that occurs at depth. Magmatic underplating has been identified using multiple techniques that are non-specific to
480-427: The (typically Precambrian ) crystalline basement is not of interest as it rarely contains petroleum or natural gas . The term economic basement is also used to describe the deeper parts of a cover sequence that are of no economic interest. Magmatic underplating Magmatic underplating occurs when basaltic magmas are trapped during their rise to the surface at the Mohorovičić discontinuity or within
512-538: The Earth's continents being accreted into one giant supercontinent . Most continents, such as Asia, Africa and Europe, include several continental cratons, as they were formed by the accretion of many smaller continents. In European geology , the basement generally refers to rocks older than the Variscan orogeny . On top of this older basement Permian evaporites and Mesozoic limestones were deposited. The evaporites formed
544-678: The Kachchh rift However, tomographic studies in Norway undertaken to identify the source of locally thickened crust found uneven thicknesses restricted by several lineaments . The morphology of the lower crust was not conclusively identified as magmatic underplating, and may in fact be the remnants of the Caledonian root. Proximity to large igneous provinces may also be helpful in identifying magmatic underplating. Unsolidified areas of magmatic underplating (a magma chamber ) may feed magma to volcanoes. In
576-475: The area in which they are used. Geochemistry allows geologists to determine levels of association between igneous units: in the Karoo Province of southern Africa, large volumes of rhyolite along the continental margin were produced from melts with initially basaltic compositions. Xenoliths of mantle material can carry information about the ultimate source of a magma, as well as reveal heterogeneities within
608-416: The crust thicker and less dense, making it immune to subduction. Oceanic crust can be subducted, while continental crust cannot. Eventually, the subduction of the underthrusting oceanic crust can bring the volcanic arc close to a continent, with which it may collide. When this happens, instead of being subducted, it is accreted to the edge of the continent and becomes part of it. Thin strips or fragments of
640-489: The crust. This uplift occurred because of two separate processes. One of these processes is due to magmatic underplating, while the other involves only isostasy . Research has shown that during the Oxfordian Stage a peak transgressive event occurred which was followed by the deposition of shale and sandstone . It is possible that the lower units may represent a decrease in sea level; the sea began to withdraw because of
672-511: The edge of the continent. There are exceptions, however, such as exotic terranes . Exotic terranes are pieces of other continents that have broken off from their original parent continent and have become accreted to a different continent. Continents can consist of several continental cratons – blocks of crust built around an initial original core of continents – that gradually grew and expanded as additional newly created terranes were added to their edges. For instance, Pangea consisted of most of
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#1733084701806704-589: The greatest denudation happened in the Paleogene due to records of clastic deposition in sedimentary basins . Some of these sedimentary basins include the North Sea Basin and the Porcupine Basin off the southwest coast of Ireland. It has also been argued that Paleogene denudation was mainly caused by magmatic underplating. Studies have been done on the phenomenon of magmatic underplating in various areas around
736-432: The heating up of the lower crust causing metamorphism and anatexis , and even managed to moderately heat up the top of the lower crust. The results also showed that final heating began at the same time as extension in shallower crustal levels, while in deeper parts, extension occurred later than the thermal peak of metamorphism. It was also shown that magmatic underplating during a time period of about thirty million years
768-566: The magma mixing and assimilation of host magmas at depth. Gabbro fractionation allows geologists to determine the smallest possible mass of concealed material. Studies of geomorphology in the Karoo Province have identified regional uplift, associated with the underplating and consequent thickening of the crust. Seismic studies of the crust at depth have done a great deal to identify magmatic underplating, but without direct samples to look at, it can be problematic for geologists to agree on
800-703: The onset of subduction along the western margin of the South American Plate . When discussing the Trans-Mexican Volcanic Belt of Mexico the basement include Proterozoic, Paleozoic and Mesozoic age rocks for the Oaxaquia, the Mixteco and the Guerrero terranes respectively. The term basement is used mostly in disciplines of geology like basin geology , sedimentology and petroleum geology in which
832-519: The source of an anomaly. Seismic studies of the Laccadive Islands in the Indian Ocean revealed a high-velocity layer of thickened crust between 16 and 24 km below the surface; these were corroborated with tomographic work in the nearby Kutch District , which identified a large mafic body at depth, close to the mantle. Gravity modelling also found mafic intrusive body in the lower crust in
864-463: The subducting slab . When the buoyant partial melt rises upwards through the mantle , it will usually stall at the base of the crust and pond there. This is because the crust is usually less dense than the underplating magma , and this is the point at which the ascending magma reaches a level of neutral buoyancy. The evolving melt will remain there until it fractionates enough (through melting-assimilation-storage-homogenization (MASH) processes) that
896-414: The underthrusting oceanic plate may also remain attached to the edge of the continent so that they are wedged and tilted between the converging plates, creating ophiolites . In this manner, continents can grow over time as new terranes are accreted to their edges, and so continents can be composed of a complex quilt of terranes of varying ages. As such, the basement rock can become younger going closer to
928-472: The uplift related to the magmatic underplating. Underplating is the accumulation of partial melts at the base of the crust where an ocean plate is subducting under continental crust . Underplating is the result of partial melts being produced in the mantle wedge above a subducting plate . The partial melting is induced by a lowering of the melting temperature, the solidus , by the input of water and other volatiles supplied by phase transitions in
960-536: The world. In northern Italy, the effects of magmatic underplating were studied along a traverse through the Strona-Ceneri Zone and the Ivrea Verbano Zone . The studies included a thermal modeling method which split the cross section up into three different sections: the upper crust, the lower crust, and the upper mantle . The model displayed multiple magmatic intrusions spreading over time, which resulted in
992-562: Was at least one period of rapid expansion and accretion to the continents during the Precambrian. Much of the basement rock may have originally been oceanic crust, but it was highly metamorphosed and converted into continental crust . It is possible for oceanic crust to be subducted down into the Earth's mantle , at subduction fronts, where oceanic crust is being pushed down into the mantle by an overriding plate of oceanic or continental crust. When
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1024-581: Was strong enough to erase all tectono – metamorphic history in the Ivera Verbano Zone. This information was preserved in the Strona-Ceneri Zone because areas in the upper crust were not affected nearly as much. Other research has been conducted in the Kutch District of Northwest India. It was concluded that the uplift that occurred in the area was due to intrusions of magma in the lower part of
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