Misplaced Pages

Aegir Ridge

Article snapshot taken from Wikipedia with creative commons attribution-sharealike license. Give it a read and then ask your questions in the chat. We can research this topic together.

The Aegir Ridge is an extinct segment of the Mid-Atlantic Ridge in the far-northern Atlantic Ocean . It marks the initial break-up boundary between Greenland and Norway , along which seafloor spreading was initiated at the beginning of the Eocene epoch to form the northern Atlantic Ocean. Towards the end of the Eocene, the newly forming Kolbeinsey Ridge propagated northwards from Iceland , splitting the Jan Mayen Microcontinent away from the Greenland plate . As the Kolbeinsey Ridge formed, so activity on the Aegir Ridge reduced, ceasing completely at the end of the Oligocene epoch when the Kolbeinsey Ridge reached the Jan Mayen Fracture Zone .

#474525

61-501: The relatively thin crust and short lifespan of the Aegir Ridge is anomalous given its proximity to the Iceland hotspot . Mantle hotspots deliver warm, actively-upwelling material to mid-ocean ridges, increasing mantle melting and crustal production. Likely, the stresses associated with plate tectonics and the mechanical structure of the lithosphere created a situation in which spreading at

122-506: A hot conduit 100 km (62 mi) across that extends to the lower mantle. Foulger et al. believe the Icelandic plume reaches only to the mantle transition layer and can therefore not come from the same source as Hawaii. Bijwaard and Spakman, however, believe the Icelandic plume does reach to the mantle, and therefore comes from the same source as Hawaii. While the Hawaiian island chain and

183-418: A mantle plume at all, but that the volcanism there results from processes related to plate tectonics and is restricted to the upper mantle . According to one of those models, a large chunk of the subducted plate of a former ocean has survived in the uppermost mantle for several hundred million years, and its oceanic crust now causes excessive melt generation and the observed volcanism. This model, however,

244-529: A part of the submarine volcanic system of mid-oceanic ridges . The initial plume head may have been several thousand kilometers in diameter, and it erupted volcanic rocks on both sides of the present ocean basin to produce the North Atlantic Igneous Province . Upon further opening of the ocean and plate drift, the plume and the mid-Atlantic Ridge are postulated to have approached one another, and finally met. The excess magmatism that accompanied

305-504: A region of higher temperature than the surrounding mantle , the hotspot is believed to have a higher concentration of water . The presence of water in magma reduces the melting temperature, which may also play a role in enhancing Icelandic volcanism. There is an ongoing discussion about whether the hotspot is caused by a deep mantle plume or originates at a much shallower depth. Recently, seismic tomography studies have found seismic wave speed anomalies under Iceland, consistent with

366-456: A sample of iron–nickel alloy was subjected to the core-like pressure by gripping it in a vise between 2 diamond tips ( diamond anvil cell ), and then heating to approximately 4000 K. The sample was observed with x-rays, and strongly supported the theory that Earth's inner core was made of giant crystals running north to south. The composition of Earth bears strong similarities to that of certain chondrite meteorites, and even to some elements in

427-407: A third of the basaltic lavas erupted in recorded history have been produced by Icelandic eruptions. Notable eruptions have included that of Eldgjá , a fissure of Katla , in 934 (the world's largest basaltic eruption ever witnessed), Laki in 1783 (the world's second largest), and several eruptions beneath ice caps , which have generated devastating glacial bursts , most recently in 2010 after

488-508: Is a hotspot which is partly responsible for the high volcanic activity which has formed the Iceland Plateau and the island of Iceland . It contributes to understanding the geological deformation of Iceland . Iceland is one of the most active volcanic regions in the world, with eruptions occurring on average roughly every three years (in the 20th and 21st century until 2010 there were 45 volcanic eruptions on and around Iceland). About

549-546: Is a distinct change of seismic wave velocity. This is caused by a change in the rock's density – immediately above the Moho, the velocities of primary seismic waves ( P wave ) are consistent with those through basalt (6.7–7.2 km/s), and below they are similar to those through peridotite or dunite (7.6–8.6 km/s). Second, in oceanic crust, there is a chemical discontinuity between ultramafic cumulates and tectonized harzburgites , which has been observed from deep parts of

610-576: Is a marker that indicates the origin of the mantle involved in eruptions. Helium-3 is captured during planetary accretion, thus is associated with relatively deeper or lower mantle. Helium-4 is created from the decay of uranium and thorium parent isotopes. A low ratio of He to He is strongly correlated with mid ocean ridge eruptions due to its shallow source of mantle, while high ratios of He to He are correlated with ocean island basalts due to its deeper source of mantle. Both high and low ratios of He to He are found on Iceland. High ratios are associated with

671-456: Is a postulated upwelling of anomalously hot rock in the Earth's mantle beneath Iceland . Its origin is thought to lie deep in the mantle, perhaps at the boundary between the core and the mantle at about 2,880 km (1,790 mi) depth. Opinions differ as to whether seismic studies have imaged such a structure. In this framework, the volcanism of Iceland is attributed to this plume, according to

SECTION 10

#1732852218475

732-499: Is about 6 × 10  kg . The average density of Earth is 5.515  g/cm . The structure of Earth can be defined in two ways: by mechanical properties such as rheology , or chemically. Mechanically, it can be divided into lithosphere , asthenosphere , mesospheric mantle , outer core , and the inner core . Chemically, Earth can be divided into the crust, upper mantle, lower mantle, outer core, and inner core. The geologic component layers of Earth are at increasing depths below

793-454: Is based on observations of topography and bathymetry , observations of rock in outcrop , samples brought to the surface from greater depths by volcanoes or volcanic activity, analysis of the seismic waves that pass through Earth, measurements of the gravitational and magnetic fields of Earth, and experiments with crystalline solids at pressures and temperatures characteristic of Earth's deep interior. Note: In chondrite model (1),

854-420: Is composed of silicate rocks richer in iron and magnesium than the overlying crust. Although solid, the mantle's extremely hot silicate material can flow over very long timescales. Convection of the mantle propels the motion of the tectonic plates in the crust. The source of heat that drives this motion is the decay of radioactive isotopes in Earth's crust and mantle combined with the initial heat from

915-453: Is estimated to measure 2.5 milliteslas (25 gauss), 50 times stronger than the magnetic field at the surface. The magnetic field generated by core flow is essential to protect life from interplanetary radiation and prevent the atmosphere from dissipating in the solar wind . The rate of cooling by conduction and convection is uncertain, but one estimate is that the core would not be expected to freeze up for approximately 91 billion years, which

976-512: Is generally composed primarily of iron and some nickel. Since this layer is able to transmit shear waves (transverse seismic waves), it must be solid. Experimental evidence has at times been inconsistent with current crystal models of the core. Other experimental studies show a discrepancy under high pressure: diamond anvil (static) studies at core pressures yield melting temperatures that are approximately 2000 K below those from shock laser (dynamic) studies. The laser studies create plasma, and

1037-453: Is more than 20 million years old and was formed at an old oceanic spreading center in the Westfjords (Vestfirðir) region. The westward movement of the plates and the ridge above the plume and the strong thermal anomaly of the latter caused this old spreading center to cease 15 million years ago and lead to the formation of a new one in the area of today's peninsulas Skagi and Snæfellsnes ; in

1098-449: Is not backed by dynamical calculations, nor is it exclusively required by the data, and it also leaves unanswered questions concerning the dynamical and chemical stability of such a body over that long period or the thermal effect of such massive melting. Another model proposes that the upwelling in the Iceland region is driven by lateral temperature gradients between the suboceanic mantle and

1159-412: Is regarded to lie at about 150 parts per million. The presence of such a large amount of water in the source of the lavas would tend to lower its melting point and make it more productive for a given temperature. It would also produce the higher melt temperatures found, than typical of mid-ocean ridge basalts. The north Atlantic is characterized by strong, large-scale anomalies of the gravity field and

1220-563: Is well after the Sun is expected to expand, sterilize the surface of the planet, and then burn out. The layering of Earth has been inferred indirectly using the time of travel of refracted and reflected seismic waves created by earthquakes. The core does not allow shear waves to pass through it, while the speed of travel ( seismic velocity ) is different in other layers. The changes in seismic velocity between different layers causes refraction owing to Snell's law , like light bending as it passes through

1281-585: Is whether the plume is thought to have ascended from the deep mantle only at that time or whether it is much older and also responsible for the old volcanism in northern Greenland, on Ellesmere Island , and at Alpha Ridge in the Arctic. As the northern Atlantic opened to the east of Greenland during the Eocene, North America and Eurasia drifted apart; the Mid-Atlantic Ridge formed as an oceanic spreading center and

SECTION 20

#1732852218475

1342-715: The Emperor Seamounts show a clear time-progressive volcanic track caused by the movement of the Pacific Plate over the Hawaiian hotspot, no such track can be seen at Iceland. It is proposed that the line from Grímsvötn volcano to Surtsey shows the movement of the Eurasian Plate , and the line from Grímsvötn volcano to the Reykjanes volcanic belt shows the movement of the North American Plate. The Iceland plume

1403-463: The Kolbeinsey Ridge. Depending on which elements are considered and how large the area covered is, one can identify up to six different mantle components, which are not all present in any single location. Furthermore, some studies show that the amount of water dissolved in mantle minerals is two to six times higher in the Iceland region than in undisturbed parts of the mid-oceanic ridges, where it

1464-735: The Scandinavian Mountains by producing changes in the density of the lithosphere and asthenosphere during the opening of the North Atlantic. To the south the Paleogene uplift of the English chalklands that resulted in the formation of the Sub-Paleogene surface has also been attributed to the Iceland plume. An extinct ridge exists in western Iceland, leading to the theory that the plume has shifted east with time. The oldest crust of Iceland

1525-433: The crust . The core is thus believed to largely be composed of iron (80%), along with nickel and one or more light elements, whereas other dense elements, such as lead and uranium , either are too rare to be significant or tend to bind to lighter elements and thus remain in the crust (see felsic materials ). Some have argued that the inner core may be in the form of a single iron crystal . Under laboratory conditions

1586-469: The geoid . The geoid rises up to 70 m (230 ft) above the geodetic reference ellipsoid in an approximately circular area with a diameter of several hundred kilometers. In the context of the plume hypothesis, this has been explained by the dynamic effect of the upwelling plume which bulges up the surface of the Earth. Furthermore, the plume and the thickened crust cause a positive gravity anomaly of about 60 mGal (=0.0006 m/s²) (free-air). Since

1647-463: The plume model, the source of Icelandic volcanism lies deep beneath the center of the island. The earliest volcanic rocks attributed to the plume are found on both sides of the Atlantic. Their ages have been determined to lie between 64 and 58 million years. This coincides with the opening of the north Atlantic in the late Paleocene and early Eocene , which has led to suggestions that the arrival of

1708-512: The Earth#Core The internal structure of Earth are the layers of the Earth , excluding its atmosphere and hydrosphere . The structure consists of an outer silicate solid crust , a highly viscous asthenosphere , and solid mantle , a liquid outer core whose flow generates the Earth's magnetic field , and a solid inner core . Scientific understanding of the internal structure of Earth

1769-492: The Kolbeinsey Ridge was energetically favorable to spreading at the Aegir Ridge. As the Kolbeinsey Ridge began rifting, hotspot material would then draw out of the Aegir Ridge and flow preferentially towards the Kolbeinsey Ridge, leading to the ultimate extinction of the spreading center. This tectonics article is a stub . You can help Misplaced Pages by expanding it . Iceland hotspot The Iceland hotspot

1830-474: The alloy portion that corresponds to the core of Earth. Dynamo theory suggests that convection in the outer core, combined with the Coriolis effect , gives rise to Earth's magnetic field . The solid inner core is too hot to hold a permanent magnetic field (see Curie temperature ) but probably acts to stabilize the magnetic field generated by the liquid outer core. The average magnetic field in Earth's outer core

1891-465: The area under consideration is "illuminated" from all sides with seismic waves from earthquakes from as many different directions as possible; these waves are recorded with a network of seismometers . The size of the network is crucial for the extent of the region which can be imaged reliably. For the investigation of the Iceland Plume, both global and regional tomography have been used; in the former,

Aegir Ridge - Misplaced Pages Continue

1952-432: The basalt in subducted slabs and is more easily fusible than peridotite. The origin of the latter is assumed to be metamorphosed, very old oceanic crust which sank into the mantle several hundreds of millions of years ago during the subduction of an ocean, then upwelled from deep within the mantle. Studies using the major and trace-element compositions of Icelandic volcanics showed that the source of present-day volcanism

2013-502: The crust fall into two major categories – sial (aluminium silicate) and sima (magnesium silicate). It is estimated that sima starts about 11 km below the Conrad discontinuity , though the discontinuity is not distinct and can be absent in some continental regions. Earth's lithosphere consists of the crust and the uppermost mantle . The crust-mantle boundary occurs as two physically different phenomena. The Mohorovičić discontinuity

2074-410: The enhanced igneous crustal thickness found along the southern Aegir and Kolbeinsey ridges may be results of interaction between the plume and the Mid-Atlantic Ridge . The plume stem is believed to be quite narrow, perhaps 100 km (62 mi) across and extending down to at least 400–650 km (250–400 mi) beneath the Earth's surface, and possibly down to the core-mantle boundary , while

2135-458: The eruption of Eyjafjallajökull . Iceland's location astride the Mid-Atlantic Ridge , where the Eurasian and North American Plates are moving apart, is partly responsible for this intense volcanic activity, but an additional cause is necessary to explain why Iceland is a substantial island while the rest of the ridge mostly consists of seamounts , with peaks below sea level . As well as being

2196-401: The geochemical signature of the lavas present on Iceland and in the north Atlantic. The resulting picture is consistent in several important respects. For instance, it is not contested that the source of the volcanism in the mantle is chemically and petrologically heterogeneous: it contains not only peridotite , the principal mantle rock type, but also eclogite, a rock type that originates from

2257-463: The inner core and outer core is located approximately 5,150 km (3,200 mi) beneath Earth's surface. Earth's inner core is the innermost geologic layer of the planet Earth . It is primarily a solid ball with a radius of about 1,220 km (760 mi), which is about 19% of Earth's radius [0.7% of volume] or 70% of the Moon 's radius. The inner core was discovered in 1936 by Inge Lehmann and

2318-413: The investigation of postulated plumes, gravimetric , geoid and in particular seismological methods along with geochemical analyses of erupted lavas have proven especially useful. Numerical models of the geodynamical processes attempt to merge these observations into a consistent general picture. An important method for imaging large-scale structures in Earth's interior is seismic tomography , by which

2379-499: The latter there is still some activity in the form of the Snæfellsjökull volcano. The spreading center, and hence the main activity, shifted eastward again 9 to 7 million years ago and formed the current volcanic zones in the south–west ( Reykjanes , Hofsjökull ) and north–east ( Tjörnes ). Presently, a slow decrease of the activity in the north–east takes place, while the volcanic zone in the south–east ( Katla , Vatnajökull ), which

2440-515: The light element in the core is assumed to be Si. Chondrite model (2) is a model of chemical composition of the mantle corresponding to the model of core shown in chondrite model (1). Measurements of the force exerted by Earth's gravity can be used to calculate its mass . Astronomers can also calculate Earth's mass by observing the motion of orbiting satellites . Earth's average density can be determined through gravimetric experiments, which have historically involved pendulums . The mass of Earth

2501-416: The magma was originally at a depth of 24 km (15 mi). The resulting velocity of the magma ascension was calculated to be 0.02-0.1 m/s so that magma takes a mean of 10 days to reach the surface of Iceland from the Moho discontinuity which is faster than previously thought. 64°24′00″N 17°18′00″W  /  64.4000°N 17.3000°W  / 64.4000; -17.3000 Structure of

Aegir Ridge - Misplaced Pages Continue

2562-455: The mantle transition zone at roughly 600 km (370 mi) depth. The velocities of seismic waves are reduced by up to 3% ( P waves ) and more than 4% ( S waves ), respectively. These values are consistent with a small percentage of partial melt, a high magnesium content of the mantle, or elevated temperature. It is not possible to unambiguously separate out which effect causes the observed velocity reduction. Numerous studies have addressed

2623-455: The mechanics of magma movement under Iceland. A study on the Borgarhraun basalt flow helped to constrain the velocity of magma transport from great depths to the surface. Geothermal barometry and statistical analysis of aluminium within olivine crystals allowed the researchers to determine the depth that these crystals were formed in and how long it took them to reach the surface. In this case,

2684-417: The mid-1990s several attempts have been made to explain the observations with numerical geodynamical models of mantle convection . The purpose of these calculations was, among other things, to resolve the paradox that a broad plume with a relatively low temperature anomaly is in better agreement with the observed crustal thickness, topography, and gravity than a thin, hot plume, which has been invoked to explain

2745-494: The neighbouring Greenland craton and therefore also restricted to the upper 200–300 km (120–190 mi) of the mantle. However, this convection mechanism is probably not strong enough under the conditions prevailing in the north Atlantic, with respect to the spreading rate, and it does not offer a simple explanation for the observed geoid anomaly. Information about the structure of Earth's deep interior can be acquired only indirectly by geophysical and geochemical methods. For

2806-423: The oceanic crust that have been obducted onto the continental crust and preserved as ophiolite sequences . Many rocks making up Earth's crust formed less than 100 million years ago; however, the oldest known mineral grains are about 4.4 billion years old, indicating that Earth has had a solid crust for at least 4.4 billion years. Earth's mantle extends to a depth of 2,890 km (1,800 mi), making it

2867-427: The outer portion of the Sun. Beginning as early as 1940, scientists, including Francis Birch , built geophysics upon the premise that Earth is like ordinary chondrites, the most common type of meteorite observed impacting Earth. This ignores the less abundant enstatite chondrites, which formed under extremely limited available oxygen, leading to certain normally oxyphile elements existing either partially or wholly in

2928-430: The planet's formation (from the potential energy released by collapsing a large amount of matter into a gravity well , and the kinetic energy of accreted matter). Due to increasing pressure deeper in the mantle, the lower part flows less easily, though chemical changes within the mantle may also be important. The viscosity of the mantle ranges between 10 and 10 pascal-second , increasing with depth. In comparison,

2989-475: The planet's thickest layer. [This is 45% of the 6,371 km (3,959 mi) radius, and 83.7% of the volume - 0.6% of the volume is the crust]. The mantle is divided into upper and lower mantle separated by a transition zone . The lowest part of the mantle next to the core-mantle boundary is known as the D″ (D-double-prime) layer. The pressure at the bottom of the mantle is ≈140 G Pa (1.4 M atm ). The mantle

3050-407: The plume head may be greater than 1,000 km (620 mi) in diameter. It is suggested that the lack of a time-progressive track of seamounts is due to the location of the plume beneath the thick Greenland craton (Laurentia) for ~ 15 Myr after continental breakup, and the later entrenchment of the plume material into the northern Mid-Atlantic Ridge following its formation. According to

3111-412: The plume was linked to, and has perhaps contributed to, the breakup of Laurasia . In the framework of the plume hypothesis, the volcanism was caused by the flow of hot plume material initially beneath thick continental lithosphere and then beneath the lithosphere of the growing ocean basin as rifting proceeded. The exact position of the plume at that time is a matter of disagreement between scientists, as

SECTION 50

#1732852218475

3172-466: The results are suggestive that constraining inner core conditions will depend on whether the inner core is a solid or is a plasma with the density of a solid. This is an area of active research. In early stages of Earth's formation about 4.6 billion years ago, melting would have caused denser substances to sink toward the center in a process called planetary differentiation (see also the iron catastrophe ), while less-dense materials would have migrated to

3233-438: The seismological and geochemical observations. The most recent models prefer a plume that is 180–200 °C (356–392 °F) hotter than the surrounding mantle and has a stem with a radius of about 100 km (62 mi). Such temperatures have not yet been confirmed by petrology , however. Understanding how magma is transported from great depths near the Moho discontinuity to the surface has implications for understanding

3294-465: The surface. Earth's crust ranges from 5 to 70 kilometres (3.1–43.5 mi) in depth and is the outermost layer. The thin parts are the oceanic crust , which underlies the ocean basins (5–10 km) and is mafic -rich (dense iron-magnesium silicate mineral or igneous rock ). The thicker crust is the continental crust , which is less dense and is felsic -rich (igneous rocks rich in elements that form feldspar and quartz ). The rocks of

3355-482: The theory of W. Jason Morgan . It is believed that a mantle plume underlies Iceland, of which the hotspot is thought to be the surface expression, and that the presence of the plume enhances the volcanism already caused by plate separation. Additionally, flood basalts on the continental margins of Greenland and Norway , the oblique orientation of the Reykjanes Ridge segments to their spreading direction, and

3416-463: The transition from flood volcanism on Greenland, Ireland and Norway to present-day Icelandic activity was the result of ascent of the hot mantle source beneath progressively thinning lithosphere, according to the plume model, or a postulated unusually productive part of the mid-ocean ridge system. Some geologists have suggested that the Iceland plume could have been responsible for the Paleogene uplift of

3477-574: The viscosity of water at 300 K (27 °C; 80 °F) is 0.89 millipascal-second and pitch is (2.3 ± 0.5) × 10 pascal-second. Earth's outer core is a fluid layer about 2,260 km (1,400 mi) in height (i.e. distance from the highest point to the lowest point at the edge of the inner core) [36% of the Earth's radius, 15.6% of the volume] and composed of mostly iron and nickel that lies above Earth's solid inner core and below its mantle . Its outer boundary lies 2,890 km (1,800 mi) beneath Earth's surface. The transition between

3538-449: The western portion of the island, while lower ratios are associated with the eastern part of the island. These ratio trends correlate well with geophysical anomalies, and the decrease of this and other geochemical signatures with increasing distance from Iceland. Combined, they indicate that the extent of the compositional anomaly reaches about 1,500 km (930 mi) along the Reykjanes Ridge and at least 300 km (190 mi) along

3599-421: The whole mantle is imaged at relatively low resolution using data from stations all over the world, whereas in the latter, a denser network only on Iceland images the mantle down to 400–450 km (250–280 mi) depth with higher resolution. Regional studies from the 1990s and 2000s show that there is a low seismic-wave-speed anomaly beneath Iceland, but opinion is divided as to whether it continues deeper than

3660-434: Was about 100 °C (212 °F) greater than that of the source of mid-ocean ridge basalts. The variations in the concentrations of trace elements such as helium , lead , strontium , neodymium , and others show clearly that Iceland is compositionally distinct from the rest of the north Atlantic. An example of this is seen in the ratio of helium-3 ( He) to helium-4 ( He) isotopes . The ratio of helium-3 and helium-4

3721-407: Was initiated 3 million years ago, develops. The reorganisation of the plate boundaries in Iceland has also been attributed to microplate tectonics, and an independent Hreppar microplate exists. The weak visibility of the postulated plume in tomographic images of the lower mantle and the geochemical evidence for eclogite in the mantle source have led to the theory that Iceland is not underlain by

SECTION 60

#1732852218475
#474525