what type of magma formed at mid-ocean ridges
basalt gabbro
5030583
as lava, creating new crust upon cooling. A mid-ocean ridge demarcates the boundary between two tectonic plates, and consequently is termed a divergent plate boundary. Mid-ocean ridges are geologically active, with continuing volcanism and seismicity. New magma steadily emerges onto the ocean floor and intrudes into the ocean crust at and near rifts along the ridge axes. The crystallized magma forms new crust of basalt (known as MORB for mid-ocean ridge basalt) and below it (in the lower oceanic crust), gabbro. MORs are formed by two oceanic plates moving away from each other. Hydrothermal vents are a common feature at
Mid-ocean ridge
5030583
as lava, creating new crust upon cooling. A mid-ocean ridge demarcates the boundary between two tectonic plates, and consequently is termed a divergent plate boundary. Mid-ocean ridges are geologically active, with continuing volcanism and seismicity. New magma steadily emerges onto the ocean floor and intrudes into the ocean crust at and near rifts along the ridge axes. The crystallized magma forms new crust of basalt (known as MORB for mid-ocean ridge basalt) and below it (in the lower oceanic crust), gabbro. MORs are formed by two oceanic plates moving away from each other. Hydrothermal vents are a common feature at
Mid-ocean ridge
3747722
frozen in the basalt. A symmetrical pattern of positive and negative magnetic lines emanates from the mid-ocean ridge. New rock is formed by magma at the mid-ocean ridges, and the ocean floor spreads out from this point. When the magma cools to form rock, its magnetic polarity is aligned with the then-current positions of the magnetic poles of the Earth. New magma then forces the older cooled magma away from the ridge. This process results in parallel sections of oceanic crust of alternating magnetic polarity. Oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of a tectonic
Oceanic crust
7494672
rocks may have a fine, glassy groundmass, as may other types of basalt. Tholeiitic rocks are the most common igneous rocks on Earth, produced by submarine volcanism at mid-ocean ridges and make up much of the ocean crust. Tholeiitic basaltic magmas are initially generated as partial melts of peridotite (olivine and pyroxene) produced by decompression melting of the Earth's mantle. Tholeiitic basalts constituting the oceanic crust are termed MORBs: mid-ocean-ridge basalts. Throughout the process of igneous differentiation, the oceanic crust acts to reduce the magma, producing the tholeiitic trend. In contrast, alkali basalts are not typical of ocean ridges, but
Tholeiitic magma series
1802227
magma chambers beneath mid-ocean ridges. Seismic sounding of mid-ocean ridges has revealed only a few magma chambers beneath ridges, and these are quite thin. A few deep drill holes into oceanic crust have intercepted gabbro, but it is not layered like ophiolite gabbro. The circulation of hydrothermal fluids through young oceanic crust causes serpentinization, alteration of the peridotites and alteration of minerals in the gabbros and basalts to lower temperature assemblages. For example, plagioclase, pyroxenes, and olivine in the sheeted dikes and lavas will alter to albite, chlorite, and serpentine, respectively. Often, ore bodies such as iron-rich sulfide deposits are
Ophiolite
170629
Gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is chemically equivalent to rapid-cooling, fine-grained basalt. Much of the Earth's oceanic crust is made of gabbro, formed at mid-ocean ridges. Gabbro is also found as plutons associated with continental volcanism. Due to its variant nature, the term "gabbro" may be applied loosely to a wide range of intrusive rocks, many of which are merely "gabbroic". The term "gabbro" was used in the 1760s to name a
Gabbro
3747715
at mid-ocean ridges, but also at scattered hotspots, and also in rare but powerful occurrences known as flood basalt eruptions. But most magma crystallises at depth, within the lower oceanic crust. There, newly intruded magma can mix and react with pre-existing crystal mush and rocks. Although a complete section of oceanic crust has not yet been drilled, geologists have several pieces of evidence that help them understand the ocean floor. Estimations of composition are based on analyses of ophiolites (sections of oceanic crust that are thrust onto and preserved on the continents), comparisons of the seismic structure of the oceanic
Oceanic crust
14063530
high alkali content. The theory of plate tectonics provides excellent explanations for both the existence of volcanic eruptions at plate boundaries—such as ocean ridges and subduction zones—and why geological processes produce basalts of different geochemical properties at these plate boundaries. The existence of basaltic eruptions in the interior of tectonic plates, however, is not directly related to plate tectonism and models involving magma upwelling from deep mantle sources (such as mantle plumes and hotspots) have been developed to explain this intra-plate volcanism. These models explain why OIBs contain more geochemically enriched basalt than mid-ocean ridge basalts (MORBs) that originate from
Ocean island basalt
12323894
is composed of the Earth's rocky crust and the deeper mostly solid outer layer of the mantle. On land the crust is known as the continental crust while under the sea it is known as the oceanic crust. The latter is composed of relatively dense basalt and is some five to ten kilometres (three to six miles) thick. The relatively thin lithosphere floats on the weaker and hotter mantle below and is fractured into a number of tectonic plates. In mid-ocean, magma is constantly being thrust through the seabed between adjoining plates to form mid-oceanic ridges and here convection currents
Sea
1303989
the magnetic field as they are deposited on an ocean floor or lake bottom. This is called "detrital remanent magnetization". Thermoremanent magnetization is the main source of the magnetic anomalies around mid-ocean ridges. As the seafloor spreads, magma wells up from the mantle, cools to form new basaltic crust on both sides of the ridge, and is carried away from it by seafloor spreading. As it cools, it records the direction of the Earth's field. When the Earth's field reverses, new basalt records the reversed direction. The result is a series of stripes that are symmetric about the ridge. A
Earth's magnetic field
18326742
ocean water. Under the pillow basalts is a basaltic sheeted dike complex, that represent cooled magma conduits. The bottom units represent the crystallized magma chamber, feeding the mid-ocean ridge at which the crust was formed. It is composed of 1–5 km thick layered gabbro atop <7 km thick layer of ultramafic rocks (e.g. wehrlite, harzburgite, dunite, and chromite). Oceanic crust is referred to as a metabasite. Every year, 1–2 x 10 trillion kilograms of water descend into subduction zones. Approximately 90–95% of that water is contained in hydrous minerals, including mica, phengite, amphibole, lawsonite, chlorite, talc, zoisite, and serpentine. The
Subduction zone metamorphism
5030595
will form at a faster rate than it can be destroyed at subduction zones. The mid-ocean ridge will then expand and form a broader ridge, taking up more space in the ocean basin and causing sea levels to rise. Sea-level change can be attributed to other factors (thermal expansion, ice melting). Over very long timescales, however, it is the result of changes in the volume of the ocean basins which are, in turn, affected by rates of sea-floor spreading along the mid-ocean ridges. Mid-ocean ridges are global scale ion-exchange systems. Rapid spreading rates will expand the mid-ocean ridge causing basalt
Mid-ocean ridge
3136732
uppermost mantle below ocean basins, or masses of subcontinental mantle emplaced along thrust faults in mountain belts. Layered peridotites are igneous sediments and form by mechanical accumulation of dense olivine crystals. Some peridotite forms by precipitation and collection of cumulate olivine and pyroxene from mantle-derived magmas, such as those of basalt composition. Peridotites associated with Alaskan-type ultramafic complexes are cumulates that probably formed in the root zones of volcanoes. Cumulate peridotites are also formed in komatiite lava flows. Basaltic magma is formed from lherzolites in the mantle. Once the magma moves out it leaves harzburgites behind in the mantle. However
Peridotite
2331946
geochemically distinct from those found at mid-ocean ridges and volcanoes associated with subduction zones (island arc basalts). "Ocean island basalt" is also similar to basalts found throughout the oceans on both small and large seamounts (thought to be formed by eruptions on the sea floor that did not rise above the surface of the ocean). They are also compositionally similar to some basalts found in the interiors of the continents (e.g., the Snake River Plain). In major elements, ocean island basalts are typically higher in iron (Fe) and titanium (Ti) than mid-ocean ridge basalts at similar magnesium (Mg) contents. In
Mantle plume
5887264
aware of sea floor spreading, where the ocean bed acts as a 'conveyor belt' moving away from the central ridge. Vine's work, with that of Drummond Matthews and Lawrence Morley of the Geological Survey of Canada, helped put the variations in the magnetic properties of the ocean crust into context in what is now known as the Vine–Matthews–Morley hypothesis. Specifically they supported Dietz's ("Nature" 1961) idea that sea floor spreading was occurring at mid-ocean ridges. Vine and Matthews showed that basalt created at a mid-ocean ridge records earth's current magnetic field polarity (and strength), thus turning Hess's theoretical 'conveyor belt'
Frederick Vine
540440
of the other lanthanides, which tend to only form 3+ cations. Mid-ocean ridge basalts (MORB) and their intrusive equivalents, gabbros, are the characteristic igneous rocks formed at mid-ocean ridges. They are tholeiitic basalts particularly low in total alkalis and in incompatible trace elements, and they have relatively flat rare earth element (REE) patterns normalized to mantle or chondrite values. In contrast, alkali basalts have normalized patterns highly enriched in the light REE, and with greater abundances of the REE and of other incompatible elements. Because MORB basalt is considered a key to understanding plate tectonics, its compositions have been much
Basalt
16178405
melting is different from those of MORB (mid-ocean ridge basalt), making a recycled mantle slab a more likely source. A decrease in magma volume with time is more consistent with the involvement of a mantle plume. It formed during the Late Jurassic and Early Cretaceous at the Pacific–Farallon–Izanagi triple junction, probably making it the oldest unaltered ocean plateau. Because this occurred before the so-called Cretaceous silent period, a long period without magnetic reversals, its formation can be precisely dated. Magnetic lineations on and surrounding Shatsky Rise range from M21 (147 Ma) at the south-western edge to M1 (124 Ma) at
Shatsky Rise
5030592
mm/yr. Ridges that spread at rates <20 mm/yr are referred to as ultraslow spreading ridges (e.g., the Gakkel Ridge in the Arctic Ocean and the Southwest Indian Ridge) and they provide a much different perspective on crustal formation than their faster spreading brethren. The mid-ocean ridge systems form new oceanic crust. As crystallized basalt extruded at a ridge axis cools below Curie points of appropriate iron-titanium oxides, magnetic field directions parallel to the Earth's magnetic field are recorded in those oxides. The orientations of the field in the oceanic crust preserve a record of directions of the Earth's magnetic field
Mid-ocean ridge
9701927
deformed by motion along faults ("moonquakes") in the Moon's crust more than 3 billion years ago. The weight of several kilometers of mare basalt in these areas caused the Moon's surface to sag somewhat, and this motion caused the surface to buckle in some places, forming the wrinkle ridges. However, other scientists suggested that these ridges are volcanic features, formed by the flow of magma either on the Moon's surface or within the crust. The Lunar Sounder Experiment studied several wrinkle ridges in southern Mare Serenitatis in detail, providing information about both the topography of these ridges and about structures
ALSE
3957051
general, which shows that the basalt flood magma was contaminated as it passed through the continental crust. It is this contamination that explains the difference between the two kinds of basalt mentioned above. The low phosphorus and titanium type has an excess of elements from the crust such as potassium and strontium. The content in incompatible elements of flood basalts is lower than that of ocean island basalts, but higher than that of mid-ocean ridge basalts. Basalt floods on the planet Venus are larger than those on Earth. Representative continental flood basalts (also known as "traps") and oceanic plateaus, arranged
Flood basalt
3729257
mantle is partially melted into magma as it moves upwards under mid-ocean ridges. This upwelling magma then cools and solidifies by conduction and convection of heat to form new oceanic crust. Accretion occurs as mantle is added to the growing edges of a tectonic plate, usually associated with seafloor spreading. The age of oceanic crust is therefore a function of distance from the mid-ocean ridge. The youngest oceanic crust is at the mid-ocean ridges, and it becomes progressively older, cooler and denser as it migrates outwards from the mid-ocean ridges as part of the process called mantle convection. The lithosphere,
Abyssal plain
5849081
The Downs in Malvern, and then Bryanston School in Dorset. He became head boy at both. Alfred Wegener's theory of continental drift had never gained much scientific support due to its lack of any satisfactory mechanism to drive the process. During the 1950s, however, extensive surveys of the ocean floor revealed a global, linked system of mid-ocean ridges, all of which exhibited high thermal flow and considerable seismic activity. Hess hypothesized that new ocean crust was being formed at the ocean ridges by extrusions of magma from the Earth's mantle, and that convection currents within the mantle were continuously carrying
Drummond Matthews
3741583
Ridge push Ridge push or sliding plate force is a proposed driving force for plate motion in plate tectonics that occurs at mid-ocean ridges as the result of the rigid lithosphere sliding down the hot, raised asthenosphere below mid-ocean ridges. Although it is called ridge push, the term is somewhat misleading; it is actually a body force that acts throughout an ocean plate, not just at the ridge, as a result of gravitational pull. The name comes from earlier models of plate tectonics in which ridge push was primarily ascribed to upwelling magma at mid-ocean ridges pushing or wedging the
Ridge push
5030601
ridges and that every year of new seafloor is formed by this process. With a crustal thickness of , this amounts to about of new ocean crust formed every year. Mid-ocean ridge A mid-ocean ridge (MOR) is an underwater mountain system formed by plate tectonics. It consists of various mountains linked in chains, typically having a valley known as a rift running along its spine. This type of oceanic mountain ridge is characteristic of what is known as an 'oceanic spreading center', which is responsible for seafloor spreading. The production of new seafloor results from mantle upwelling in response to
Mid-ocean ridge
5030582
Mid-ocean ridge A mid-ocean ridge (MOR) is an underwater mountain system formed by plate tectonics. It consists of various mountains linked in chains, typically having a valley known as a rift running along its spine. This type of oceanic mountain ridge is characteristic of what is known as an 'oceanic spreading center', which is responsible for seafloor spreading. The production of new seafloor results from mantle upwelling in response to plate spreading; this isentropic upwelling solid mantle material eventually exceeds the solidus and melts. The buoyant melt rises as magma at a linear weakness in the oceanic crust, and emerges
Mid-ocean ridge
18326744
to liquid phases that contain of fluid-mobile trace elements due to the breakdown of hydrous minerals such as phengite, lawsonite and zoisite. This creats a unique type of trace element distribution pattern for arc magma. Arc magmas and the continental crust formed from arc magmas are enriched in boron, lead, arsenic, and antimony derived from the dehydration within the subducting slab. Hydrothermal fluids released from the slab mobilize these elements and allow them to be incorporated into arc magmas, distinguishing arc magmas from those produced at mid-ocean ridges and hotspots. Basalts may first metamorphose under zeolite facies conditions (50–150 °C
Subduction zone metamorphism
6001718
Submarine volcano Submarine volcanoes are underwater vents or fissures in the Earth's surface from which magma can erupt. A large number of submarine volcanoes are located near areas of tectonic plate movement, known as mid-ocean ridges. The volcanoes at mid-ocean ridges alone are estimated to account for 75% of the magma output on Earth. Although most submarine volcanoes are located in the depths of seas and oceans, some also exist in shallow water, and these can discharge material into the atmosphere during an eruption. The total number of submarine volcanoes is estimated to be over 1 million, of which some
Submarine volcano
6001725
video and audio together let researchers learn the sounds made by slow lava bursting and the different noises made by hundreds of gas bubbles. Submarine volcano Submarine volcanoes are underwater vents or fissures in the Earth's surface from which magma can erupt. A large number of submarine volcanoes are located near areas of tectonic plate movement, known as mid-ocean ridges. The volcanoes at mid-ocean ridges alone are estimated to account for 75% of the magma output on Earth. Although most submarine volcanoes are located in the depths of seas and oceans, some also exist in shallow water, and these can
Submarine volcano
5030590
new oceanic crust at mid-ocean ridges is the "mantle conveyor" (see image). However, there have been some studies which have shown that the upper mantle (asthenosphere) is too plastic (flexible) to generate enough friction to pull the tectonic plate along. Moreover, unlike in the image above, mantle upwelling that causes magma to form beneath the ocean ridges appears to involve only its upper , as deduced from seismic tomography and from studies of the seismic discontinuity at about . The relatively shallow depths from which the upwelling mantle rises below ridges are more consistent with the "slab-pull" process. On the
Mid-ocean ridge
336038
Hess and Dietz had begun to theorise that mid-ocean ridges mark structurally weak zones where the ocean floor was being ripped in two lengthwise along the ridge crest (see the previous paragraph). New magma from deep within the Earth rises easily through these weak zones and eventually erupts along the crest of the ridges to create new oceanic crust. This process, at first denominated the "conveyer belt hypothesis" and later called seafloor spreading, operating over many millions of years continues to form new ocean floor all across the 50,000 km-long system of mid-ocean ridges. Only four years after the maps
Plate tectonics
15537270
for them, but the general mechanisms are uncertain. A question that is most commonly asked is what happened to the rock occupying the space now occupied by the pluton? A viable method proposed to make room from ascending magma is a zone of lateral extension which can be found at mid ocean ridges, strike slip faults and "dilational jogs" (areas of tension along a fault offset). A problem with this method is that the extension rates are too slow and the slip magnitudes are too small to allow a magma chamber to form by intrusion of magma by the extension
Methods of pluton emplacement
15586435
the geographic poles. There is considerable paleomagnetic evidence supporting this hypothesis. Over the life of the Earth, the orientation of Earth's magnetic field has reversed many times, with geomagnetic north becoming geomagnetic south and vice versa – an event known as a geomagnetic reversal. Evidence of geomagnetic reversals can be seen at mid-ocean ridges where tectonic plates move apart. As magma seeps out of the mantle and solidifies to become new ocean floor, the magnetic minerals in it are magnetized in the direction of the magnetic field. Thus, starting at the most recently formed ocean floor, one can read out
Geomagnetic pole
12037854
hypothesis came from Cox et al. (1967) when he measured the remnant magnetization of lavas from land sites. Walter C. Pitman offered further evidence with a remarkably symmetric profile from the Pacific-Antarctic Ridge. The Vine-Matthews hypothesis correlates the symmetric magnetic patterns seen on the seafloor with geomagnetic field reversals. At mid-ocean ridges, new crust is created by the injection, extrusion, and solidification of magma. After the magma has cooled through the Curie point, ferromagnetism becomes possible and the magnetic minerals in the newly formed crust orient themselves with the current background geomagnetic field. Lithospheric creation at the ridge is considered
Vine–Matthews–Morley hypothesis
11319133
Submarine eruption Submarine eruptions are those volcano eruptions which take place beneath the surface of water. These occur at constructive margins, subduction zones and within tectonic plates due to hotspots. This eruption style is far more prevalent than subaerial activity. For example, it is believed that 70 to 80% of the Earth’s magma output takes place at mid-ocean ridges. Submarine eruptions are less studied than subaerial volcanoes due to their inaccessibility. Developments in technology mean that submarine volcanoes can now be studied in greater detail. Despite this progress, understanding is still limited. Mid ocean ridges for example are the most
Submarine eruption
480015
Magma Magma (from Ancient Greek μάγμα ("mágma") meaning "thick unguent") is the molten or semi-molten natural material from which all igneous rocks are derived. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural satellites. Besides molten rock, magma may also contain suspended crystals and gas bubbles. Magma is produced by melting of the mantle and/or the crust at various tectonic settings, including subduction zones, continental rift zones, mid-ocean ridges and hotspots. Mantle and crustal melts migrate upwards through the crust where they are thought to
Magma
18326741
Subduction zone metamorphism Arc magmas are produced by partial melting of metasomatic domains in the mantle wedge, which was reacted with liquid phases derived from dehydration melting of minerals contained in the subducting oceanic crust formed at mid-ocean ridges. The subducting oceanic crust consists of a four major units. The topmost unit is a thin cap of pelagic sediments up to 0.3 km thick composed of siliceous and calcareous shells, meteoric dusts, and variable amounts of volcanic ash. The next unit is composed of 0.3–0.7 km thick pillow basalts, formed by the quenching of basaltic magma as it erupts into
Subduction zone metamorphism
3747718
continuously being created at mid-ocean ridges. As plates diverge at these ridges, magma rises into the upper mantle and crust. As it moves away from the ridge, the lithosphere becomes cooler and denser, and sediment gradually builds on top of it. The youngest oceanic lithosphere is at the oceanic ridges, and it gets progressively older away from the ridges. As the mantle rises it cools and melts, as the pressure decreases and it crosses the solidus. The amount of melt produced depends only on the temperature of the mantle as it rises. Hence most oceanic crust is the same thickness
Oceanic crust
5897334
and 101 mW/m over oceanic crust. This is 0.087 watt/square meter on average (0.03 percent of solar power absorbed by the Earth ), but is much more concentrated in areas where the lithosphere is thin, such as along mid-ocean ridges (where new oceanic lithosphere is created) and near mantle plumes. The Earth's crust effectively acts as a thick insulating blanket which must be pierced by fluid conduits (of magma, water or other) in order to release the heat underneath. More of the heat in the Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges. The final
Geothermal gradient
788305
in viscosity of the erupting lava. They occur wherever lava is extruded under water, such as along marine hotspot volcano chains and the constructive plate boundaries of mid-ocean ridges. As new oceanic crust is formed, thick sequences of pillow lavas are erupted at the spreading center fed by dykes from the underlying magma chamber. Pillow lavas and the related sheeted dyke complexes form part of a classic ophiolite sequence (when a segment of oceanic crust is thrust over the continental crust, thus exposing the oceanic segment above sea level). The presence of pillow lavas in the oldest preserved volcanic sequences
Pillow lava
8425315
Magmatism Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of magma or lava. Volcanism is the surface expression of magmatism. Magmatism is one of the main processes responsible for mountain formation. The nature of magmatism depends on the tectonic setting. For example, andesitic magmatism associated with the formation of island arcs at convergent plate boundaries or basaltic magmatism at mid-ocean ridges during sea-floor spreading at divergent plate boundaries. On Earth,
Magmatism
6189
volcanic zone a volcano belongs to, there are significant differences inside volcanic zones and even between neighbouring volcanoes. Despite being a type location for calc-alkalic and subduction volcanism, the Andean Volcanic Belt has a large range of volcano-tectonic settings, such as rift systems and extensional zones, transpressional faults, subduction of mid-ocean ridges and seamount chains apart from a large range of crustal thicknesses and magma ascent paths, and different amount of crustal assimilations. The Andes Mountains host large ore and salt deposits and some of their eastern fold and thrust belt acts as traps for commercially exploitable amounts of hydrocarbons.
Andes
10111038
neighboring volcanoes. Despite being a type location for calc-alkalic and subduction volcanism, the Andean Volcanic Belt has a large range of volcano-tectonic settings, such as rift systems and extensional zones, transpressional faults, subduction of mid-ocean ridges and seamount chains apart from a large range on crustal thicknesses and magma ascent paths, and different amount of crustal assimilations. Romeral in Colombia is the northernmost active member of the Andean Volcanic Belt. South of latitude 49° S within the Austral Volcanic Zone volcanic activity decreases with the southernmost volcano Fueguino in Tierra del Fuego archipelago. The Andean Volcanic Belt is segmented into
Andean Volcanic Belt
1293807
asthenosphere, which is ductile, or plastic, and the brittle lithosphere (crust and upper mantle). Seafloor spreading helps explain continental drift in the theory of plate tectonics. When oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere. The motivating force for seafloor spreading ridges is tectonic plate pull rather than magma pressure, although there is typically significant magma activity at spreading ridges. At a spreading center, basaltic magma rises up the fractures and cools on the ocean floor to form new seabed. Hydrothermal vents are common at spreading centers. Older rocks will be found farther away from the
Seafloor spreading
3729256
typically in the abyssal zone, at depths from 3000 to 6000 metres. The table below illustrates the classification of oceanic zones: Oceanic crust, which forms the bedrock of abyssal plains, is continuously being created at mid-ocean ridges (a type of divergent boundary) by a process known as decompression melting. Plume-related decompression melting of solid mantle is responsible for creating ocean islands like the Hawaiian islands, as well as the ocean crust at mid-ocean ridges. This phenomenon is also the most common explanation for flood basalts and oceanic plateaus (two types of large igneous provinces). Decompression melting occurs when the upper
Abyssal plain
3741584
plates apart. Ridge push is the result of gravitational forces acting on the young, raised oceanic lithosphere around mid-ocean ridges, causing it to slide down the similarly raised but weaker asthenosphere and push on lithospheric material farther from the ridges. Mid-ocean ridges are long underwater mountain chains that occur at divergent plate boundaries in the ocean, where new oceanic crust is formed by upwelling mantle material as a result of tectonic plate spreading and relatively shallow (above ~60 km) decompression melting. The upwelling mantle and fresh crust are hotter and less dense than the surrounding crust and mantle, but cool
Ridge push
17955112
along these mid-ocean ridges, are fissures from which geothermally heated water flows. The water flowing out of vents is dominantly seawater drawn into the system through the faults, porous sediments, and volcanic rocks. As the cool seawater moves through the sediment and rock towards the hot magma, the water becomes super heated (300-400 °C) and rich in dissolved mineral elements (such as sulphur, iron, zinc and copper) from the young ocean crust. When the hot effluent is expelled, it encounters the cold, ambient seawater (about 2 °C) minerals precipitate from the element-rich vent water. At the Endeavour segment, a notably
Ocean Networks Canada
1870952
volcanic arc and are associated with extensional tectonics and high heat flow, often being home to seafloor spreading centers. These spreading centers are like mid ocean ridges, though the magma composition of back arc basins is generally more varied and contains a higher water content than mid ocean ridge magmas. Back arc basins are often characterized by thin, hot lithosphere. Opening of back arc basins are still being studied but it’s possible that movement of hot asthenosphere into lithosphere causes extension. Oceanic trenches are narrow topographic lows that mark convergent boundaries or subduction zones. Oceanic trenches can be average 50
Convergent boundary
9935459
the Miocene until the present time, the earth was an "icehouse", with icesheets covering the poles. In the intervening years, the earth was a "greenhouse", with high global temperatures and elevated atmospheric CO. Volcanic activity was also high in the greenhouse years. These long periods of continental emergence helped produce changes in ocean currents and the distribution of atmospheric heat. There are two competing arguments for second-order sea-level changes. The first states the sea level can be affected by the number of and the volume of the magma being produced at mid-ocean ridges. During times of increased sea floor spreading,
Stratigraphic cycles
3729258
which rides atop the asthenosphere, is divided into a number of tectonic plates that are continuously being created and consumed at their opposite plate boundaries. Oceanic crust and tectonic plates are formed and move apart at mid-ocean ridges. Abyssal hills are formed by stretching of the oceanic lithosphere. Consumption or destruction of the oceanic lithosphere occurs at oceanic trenches (a type of convergent boundary, also known as a destructive plate boundary) by a process known as subduction. Oceanic trenches are found at places where the oceanic lithospheric slabs of two different plates meet, and the denser (older) slab begins to
Abyssal plain
11778100
Mid Atlantic Ridge have been shown to relate to interactions with the hotspot beneath the Azores. Gravity field modelling studies have shown that the crustal thickness in this area is 60% greater than normal, there is an elevated spreading ridge. The influence of the hotspot on the spreading ridge is mainly asymmetrical to the hotspot (north and south). It is thought that crust at ridges is formed by a combination of processes (magmatic and tectonic) with magma addition coming from short lived magma chambers. The hotspot is suggested to be responsible of increased melt production within the mantle supporting a
Azores hotspot
336034
of the ocean crust was performed using Heezen's mechanism of spreading along the ridges. Hess therefore concluded that the Atlantic Ocean was expanding while the Pacific Ocean was shrinking. As old oceanic crust is "consumed" in the trenches (like Holmes and others, he thought this was done by thickening of the continental lithosphere, not, as now understood, by underthrusting at a larger scale of the oceanic crust itself into the mantle), new magma rises and erupts along the spreading ridges to form new crust. In effect, the ocean basins are perpetually being "recycled," with the creation of new crust and
Plate tectonics
10994527
Oceanic core complex An oceanic core complex, or megamullion, is a seabed geologic feature that forms a long ridge perpendicular to a mid-ocean ridge. It contains smooth domes that are lined with transverse ridges like a corrugated roof. They can vary in size from 10 to 150 km in length, 5 to 15 km in width, and 500 to 1500 m in height. The first oceanic core complexes described were identified in the Atlantic Ocean. Since then numerous such structures have been identified primarily in oceanic lithosphere formed at intermediate, slow- and ultra-slow spreading mid-ocean ridges, as well as back-arc
Oceanic core complex
19999079
3481-3504. doi:10.1016/S0016-7037(02)00909-2. Sims, K.W.W., M.T. Murrell, D.J. DePaolo, W.S. Baldridge, S.J. Goldstein, D. Clague and M. Jull (1999). "“Porosity of the melting zone and variations in the solid mantle upwelling rate beneath Hawaii: Inferences from U–Th–Ra and U-Pa disequilibria.”" Geochimimica et Cosmochimica Acta, 63, 23, 4119-4138, doi: 10.1016/S0016-7037(99)00313-0. Sims, K.W.W. and D.J. DePaolo (1997). “"Inferences about mantle magma sources from incompatible element concentration ratios in oceanic basalts.”" Geochimica et Cosmochimica Acta, 61, 4, 765-784. doi: 10.1016/S0016-7037(96)00372-9. Sims, K.W.W., D.J. DePaolo, M.T. Murrrell, W.S. Baldridge, S.J. Goldstein, and D. Clague (1995"). “Mechanisms of magma generation beneath Hawaii and Mid–Ocean ridges: U–Th
Kenneth Sims (geologist)
485454
steeper, a mountain. Major mountains tend to occur in long linear arcs, indicating tectonic plate boundaries and activity. Volcanoes are formed when a plate is pushed below another plate, or at a mid-ocean ridge or hotspot. At a depth of around 100 km, melting occurs in rock above the slab (due to the addition of water), and forms magma that reaches the surface. When the magma reaches the surface, it often builds a volcanic mountain, such as a shield volcano or a stratovolcano. Examples of volcanoes include Mount Fuji in Japan and Mount Pinatubo in the Philippines. The magma does
Mountain
3729260
a rugged topography. The roughness of this topography is a function of the rate at which the mid-ocean ridge is spreading (the spreading rate). Magnitudes of spreading rates vary quite significantly. Typical values for fast-spreading ridges are greater than 100 mm/yr, while slow-spreading ridges are typically less than 20 mm/yr. Studies have shown that the slower the spreading rate, the rougher the new oceanic crust will be, and vice versa. It is thought this phenomenon is due to faulting at the mid-ocean ridge when the new oceanic crust was formed. These faults pervading the oceanic crust, along with their bounding
Abyssal plain
5489758
lower ultramafic part of ophiolite complexes (although harzburgite is more common in this setting), from alpine-type peridotite massifs, from fracture zones adjacent to mid-oceanic ridges, and as xenoliths in kimberlite pipes and alkali basalts. Partial melting of spinel lherzolite is one of the primary sources of basaltic magma. The name is derived from the Lherz Massif, an alpine peridotite complex (also known as orogenic lherzolite complex), (the type locality) at Étang de Lers, near Massat in the French Pyrenees; Lherz is the archaic spelling of this location. The Lherz massif also contains harzburgite and dunite, as well as layers of
Lherzolite
1294386
25% of the total volume of magma produced each year on Earth (approximately thirty to thirty-five cubic kilometers), much less than the volume produced at mid-ocean ridges, and they contribute to the formation of new continental crust. Arc volcanism has the greatest impact on humans, because many arc volcanoes lie above sea level and erupt violently. Aerosols injected into the stratosphere during violent eruptions can cause rapid cooling of Earth's climate and affect air travel. The strains caused by plate convergence in subduction zones cause at least three different types of earthquakes. Earthquakes mainly propagate in the cold subducting slab
Subduction
3741590
zones were primarily the result of convection currents in the mantle dragging on the crust and supplying fresh, hot magma at mid-ocean ridges. Further developments of the theory suggested that some form of ridge push helped supplement convection in order to keep the plates moving, but in the 1990s, calculations indicated that slab pull, the force that a subducted section of plate exerts on the attached crust on the surface, was an order of magnitude stronger than ridge push. As of 1996, slab pull was generally considered the dominant mechanism driving plate tectonics. Modern research, however, indicates that the effects
Ridge push
3741588
upwelling magma wedging the lithosphere apart. In 1964 and 1965, Egon Orowan proposed the first gravitational mechanism for spreading at mid-ocean ridges, postulating that spreading can be derived from the principles of isostasy. In Orowan's proposal, pressure within and immediately under the elevated ridge is greater than the pressure in the oceanic crust to either side due to the greater weight of overlying rock, forcing material away from the ridge, while the lower density of the ridge material relative to the surrounding crust would gradually compensate for the greater volume of rock down to the depth of isostatic compensation. Similar
Ridge push
2886329
the planet and is chemically and mechanically different from underlying mantle. It has been generated greatly by igneous processes in which magma cools and solidifies to form solid rock. Beneath the lithosphere lies the mantle which is heated by the decay of radioactive elements. The mantle though solid is in a state of rheic convection. This convection process causes the lithospheric plates to move, albeit slowly. The resulting process is known as plate tectonics. Volcanoes result primarily from the melting of subducted crust material or of rising mantle at mid-ocean ridges and mantle plumes. Most water is found in one
Natural environment
3741587
as one of the driving forces of plate tectonics, ridge push was not included in any of Alfred Wegener's 1912-1930 proposals of continental drift, which were produced before the discovery of mid-ocean ridges and lacked any concrete mechanisms by which the process might have occurred. Even after the development of acoustic depth sounding and the discovery of global mid-ocean ridges in the 1930s, the idea of a spreading force acting at the ridges was not mentioned in scientific literature until Harry Hess's proposal of seafloor spreading in 1960, which included a pushing force at mid-ocean ridges as a result of
Ridge push
3729248
oceanic crust. Magma rises from above the asthenosphere (a layer of the upper mantle), and as this basaltic material reaches the surface at mid-ocean ridges, it forms new oceanic crust, which is constantly pulled sideways by spreading of the seafloor. Abyssal plains result from the blanketing of an originally uneven surface of oceanic crust by fine-grained sediments, mainly clay and silt. Much of this sediment is deposited by turbidity currents that have been channelled from the continental margins along submarine canyons into deeper water. The rest is composed chiefly of pelagic sediments. Metallic nodules are common in some areas of
Abyssal plain
12719197
that are necessary for life to exist, sparking the synthesis of organic compounds. These changes in temperature are caused by the cooling of the magma once it penetrates the surface of the Earth, making contact with the seawater. These hydrothermal fluids can reach temperatures for up to 402 °C. Hydrothermal vents are located at mid-ocean ridges, where an abundance of life is present, providing high biodiversity of productivity. They provide habitats for many unique species of animals. The Juan De Fuca Ridge is home to 60 unique species in the world. Specifically in the Endeavour Segment, there are 12 species
Endeavour Hydrothermal Vents
480019
geothermal gradient and the radioactive decay within the rock. The geothermal gradient averages about 25 °C/km with a wide range from a low of 5–10 °C/km within oceanic trenches and subduction zones to 30–80 °C/km under mid-ocean ridges and volcanic arc environments. It is usually very difficult to change the bulk composition of a large mass of rock, so composition is the basic control on whether a rock will melt at any given temperature and pressure. The composition of a rock may also be considered to include "volatile" phases such as water and carbon dioxide. The presence of volatile phases
Magma
9094666
of hafnium, tungsten, samarium, and neodymium. The magma ocean formed about 70 million years after the history of the Solar System began, and most of the ocean had crystallized by about 215 million years after that beginning (Brandon, 2007). Lunar magma ocean According to the giant impact hypothesis a large amount of energy was liberated in the formation of the Moon and it is inferred that as a result a large portion of the Moon was once completely molten, forming a lunar magma ocean. Evidence for the magma ocean hypothesis comes from the highly anorthositic compositions of the crust in
Lunar magma ocean
20488419
Detrick (1992) modelled a schematic cross section of an axial magma chamber beneath a slow-spreading ridge such as the Mid-Atlantic Ridge. Due to the reduced heat and magma supply, a steady-state eruptible magma lens is relinquished in favor of a sill-like mush zone and a smaller transition zone beneath the well-developed rift valley. Convection and mixing in the magma chamber is far less likely than at fast ridges. Thermal constrains led to the development of different models to reconstruct the accretion history. The “infinite leek” model suggests small magma batches, forming small “nested” intrusions. Another model proposed that crystallization could
Lower oceanic crust
11097753
constructed run parallel to an ancient spreading center which has since been replaced in its role by the San Andreas Fault system. They are unique in this origin, as they are formed from the remnants of an old ocean-ridge spreading center. A series of "knobs" are aligned with the ridges; however the distinctive summit crater, evident in many oceanic volcanoes, is absent. This lack of a collapse crater suggests that magma was never stored in a chamber within the structure, as with most other volcanoes. Analysis of argon–argon dating studies indicate that Davidson formed between 9 and 15 million years
Davidson Seamount
20488415
m thick and < 2 km wide). The lens is maintained by reinjection of primitive magma. The lack of any detectable large magma chamber and the common detection of small lens/mush zone at fast-spreading ridges emphasize the small magma chamber model. Modally and compositionally layered gabbroic rock is often found (or abundant) in the lower crustal sections of ophiolite. The layered lower crust is thus one of the key features of all models of fast-spreading lower crust. Nevertheless, distinct modal layering as observed in major ophiolites has rarely been observed or sampled on the ocean floor. The IODP expedition 345
Lower oceanic crust
8425318
collisions are accompanied by major crustal thickening, leading to heating and anatexis within the crust, generally in the form of peraluminous granitic intrusions. Post-collisional magmatism is a result of decompression melting associated with isostatic rebound and possible extensional collapse of the thickened crust formed during the collision. Slab detachment has also been proposed as a cause of late to post-collisional magmatism. The new crust that is formed at divergent boundaries within oceanic crust is almost entirely magmatic in origin. Mid-ocean ridge spreading centres are the sites of almost continuous magmatism. The basalts erupted at mid-ocean ridges are tholeiitic in character
Magmatism
11787489
the Scotia Plate) and the Maud Rise (off Antarctica) were located next to the Agulhas Plateau (south of South Africa) where the Bouvet hotspot formed the Southern Ocean Large Igneous Province (112–93 Ma). The Bouvet Triple Junction, today considered an R-F-F (ridge-fault-fault) type triple junction, was an R-R-R type before anomaly 28 (c. 64 Ma), which means that before the Scotia Plate started to develop in the Mid-Tertiary, only ridges and transform faults separated Africa, Antarctica, and South America. The north–south motion of Antarctica relative to Africa and South America before anomaly 28 changed to a slow east–west clockwise motion
South American–Antarctic Ridge
1488199
constantly created through the upwelling of new basaltic magma. With new seafloor being pushed and pulled out, the older seafloor slowly slides away from the mid-oceanic ridges toward the continents. Although separated only by tens of kilometers, this separation between segments of the ridges causes portions of the seafloor to push past each other in opposing directions. This lateral movement of seafloors past each other is where transform faults are currently active. Transform faults move differently from a strike-slip fault at the mid-oceanic ridge. Instead of the ridges moving away from each other, as they do in other strike-slip faults,
Transform fault
1443249
Seamount, Eratosthenes Seamount, Axial Seamount and Gorringe Ridge. If all known seamounts were collected into one area, they would make a landform the size of Europe. Their overall abundance makes them one of the most common, and least understood, marine structures and biomes on Earth, a sort of exploratory frontier. Most seamounts are built by one of two volcanic processes, although some, such as the Christmas Island Seamount Province near Australia, are more enigmatic. Volcanoes near plate boundaries and mid-ocean ridges are built by decompression melting of rock in the upper mantle. The lower density magma rises through the crust
Seamount
616356
giant-impact hypothesis implies that a surface magma ocean would have formed following the impact. Yet there is no evidence that the Earth ever had such a magma ocean and it is likely there exists material that has never been processed in a magma ocean. A number of compositional inconsistencies need to be addressed. If the Moon was formed by such an impact, it is possible that other inner planets also may have been subjected to comparable impacts. A moon that formed around Venus by this process would have been unlikely to escape. If such a moon-forming event had occurred there,
Giant-impact hypothesis
19089052
Laboratory (IOSDL), Wormley (1992), Leeds University (1993), Oxford University (1994), the Geological Society of London (1994, 1995 and 1997), Cambridge University (1996), Southampton Oceanography Centre (1997) and Bristol University (1998). In addition BRIDGE science was reported at other meetings nationally and internationally, for example: at the Royal Society meeting "Mid-Ocean Ridges: Dynamics of Processes Associated with Creation of New Ocean Crust" (1996), the 1996 British Association for the Advancement of Science annual science festival at Birmingham in a BRIDGE session entitled "Abyssal Inferno: Seafloor volcanoes, hot vents and exotic life at the mid-ocean ridges", at "Geoscience 98", Keele University (1998),
British Mid-Ocean Ridge Initiative
5030585
the ocean ridges. Moving away from the mid-ocean ridge, ocean depth progressively increases; the greatest depths are in ocean trenches. As the oceanic crust moves away from the ridge axis, the peridotite in the underlying mantle cools and becomes more rigid. The crust and the relatively rigid peridotite below it make up the oceanic lithosphere. The bathymetry, or profile of a MOR is largely determined by the seafloor spreading rate at the ridge. Slow spreading ridges (< 5 cm/yr) like the Mid-Atlantic Ridge (MAR) generally have large, wide rift valleys, sometimes as wide as , and very rugged terrain at
Mid-ocean ridge
1854656
Landform A landform is a natural feature of the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Typical landforms include hills, mountains, plateaus, canyons, and valleys, as well as shoreline features such as bays, peninsulas, and seas, including submerged features such as mid-ocean ridges, volcanoes, and the great ocean basins. Landforms are categorized by characteristic physical attributes such as elevation, slope, orientation, stratification, rock exposure, and soil type. Gross physical features or landforms include intuitive elements such as berms, mounds, hills, ridges,
Landform
2549651
carbonate and formations left by the evaporation of water called evaporites. What covers the peninsula is the result of simultaneous processes of deposits of sands, shells, and coral, and erosion from water and weather. As ocean water has retreated and progressed, the peninsula has been covered with sea water at least seven times. Waves compressed sands, calcium carbonate, and shells into limestone; at the ocean's edge, beach ridges were created by this depositional forming. North-south axis rivers, such as the St. Johns, were created by past beach ridges which were often divided by swales. As ocean water retreated, lagoons formed
St. Johns River
17616015
the 2008-2013 time window relevant for inclusion in the Research Excellence Framework. Whaler was interviewed for the Royal Society of Edinburgh's 14th edition of Science Scotland and this was reported in an article entitled "Magnetic Field Personality". The article spans across the full range of her research, even going back several decades. In September 2013 she was interviewed by Becky Oskin from LiveScience.com in "Giant Underground Blob of Magma Puzzles Scientists"., for her contribution to an article in Nature Geoscience: "A mantle magma reservoir beneath an incipient mid-ocean ridge in Afar, Ethiopia". This type of science - magnetotellurics - researched
Kathryn Whaler
1447469
their other examples. Another factor contributing to the guyots being underwater has to do with the oceanic ridges, such as the Mid-Atlantic Ridge in the Atlantic Ocean. Mid-ocean ridges gradually spread apart over time, due to molten lava being pushed up under the surface of the earth and creating new rock. As the mid-ocean ridges spread apart, the guyots move with them, thus continually sinking deeper into the depths of the ocean. Thus, the greater amount of time that passes, the deeper the guyots become. Although guyots can be hundreds of millions of years old, there have been some recently
Guyot
5030600
a new task: explaining how such an enormous geological structure could have formed. In the 1960s, geologists discovered and began to propose mechanisms for seafloor spreading. The discovery of mid-ocean ridges and the process of seafloor spreading allowed for Wegner's theory to be expanded so that it included the movement of oceanic crust as well as the continents. Plate tectonics was a suitable explanation for seafloor spreading, and the acceptance of plate tectonics by the majority of geologists resulted in a major paradigm shift in geological thinking. It is estimated that 20 volcanic eruptions occur each year along earth's mid-ocean
Mid-ocean ridge
5030591
other hand, some of the world's largest tectonic plates such as the North American Plate are in motion, yet are nowhere being subducted. The rate at which the mid-ocean ridge creates new material is known as the spreading rate, and is typically measured in mm/yr. As a general rule, fast ridges have spreading (opening) rates of more than 90 mm/year. Intermediate ridges have a spreading rate of 50–90 mm/year while slow spreading ridges have a rate less than 50 mm/year. The spreading rate of the North Atlantic Ocean is ~ 25 mm/yr, while in the Pacific region, it is 80–120
Mid-ocean ridge
9515321
volcanism is driven by various processes. Volcanoes near plate boundaries and mid-ocean ridges are built by the decompression melting of mantle rock that rises on an upwelling portion of a convection cell to the crustal surface. Eruptions associated with subducting zones, meanwhile, are driven by subducting plates that add volatiles to the rising plate, lowering its melting point. Each process generates different rock; mid-ocean ridge volcanics are primarily basaltic, whereas subduction flows are mostly calc-alkaline, and more explosive and viscous. Spreading rates along mid-ocean ridges vary widely, from per year at the Mid-Atlantic Ridge, to up to along the East
Types of volcanic eruptions
5030586
the ridge crest that can have relief of up to a . By contrast, fast spreading ridges (>8 cm/yr) like the East Pacific Rise (EPR) are narrow, sharp incisions surrounded by generally flat topography that slopes away from the ridge over many hundreds of miles. Ultra-slow spreading ridges (< 2 cm/yr), like the Southwest India and the Arctic Ridges form both magmatic and amagmatic ridge segments without transform faults. The spreading center or axis, commonly connects to a transform fault oriented at right angles to the axis. The flanks of mid-ocean ridges are in many places marked by the inactive
Mid-ocean ridge
335985
mid-ocean ridge where it was formed. For a typical distance that oceanic lithosphere must travel before being subducted, the thickness varies from about thick at mid-ocean ridges to greater than at subduction zones; for shorter or longer distances, the subduction zone (and therefore also the mean) thickness becomes smaller or larger, respectively. Continental lithosphere is typically about 200 km thick, though this varies considerably between basins, mountain ranges, and stable cratonic interiors of continents. The location where two plates meet is called a "plate boundary". Plate boundaries are commonly associated with geological events such as earthquakes and the creation of
Plate tectonics
1293816
at fast rates an axial high is found within the crustal accretion zone. The differences in spreading rates affect not only the geometries of the ridges but also the geochemistry of the basalts that are produced. Since the new oceanic basins are shallower than the old oceanic basins, the total capacity of the world's ocean basins decreases during times of active sea floor spreading. During the opening of the Atlantic Ocean, sea level was so high that a Western Interior Seaway formed across North America from the Gulf of Mexico to the Arctic Ocean. At the Mid-Atlantic Ridge (and in
Seafloor spreading
5397166
°C for the eastern Pacific) and "d" is the depth of the ridge below the ocean surface. After plugging in rough numbers for the sea floor, the equation becomes: where "d" is in meters and "t" is in millions of years, so that just-formed crust at the mid-ocean ridges lies at about 2,500 m depth, whereas 50-million-year-old seafloor lies at a depth of about 5,000 m. As the mean level of the sea floor decreases, the volume of the ocean basins increases, and if other factors that can control sea level remain constant, sea level falls. The converse is also
Supercontinent cycle
8780020
floor. The thickness of sediment that collected in basin decreased toward the center of the basin. The idea that thickness and age of sediment on the sea floor is related to the age of the oceanic crust was proposed by Harry Hess . Magnetic anomalies (see Vine-Matthews-Morley hypothesis) of the crust formed in back-arc basins deviated in form from the crust formed at mid-ocean ridges . In many areas the anomalies do not appear parallel. The profiles of the magnetic anomalies in the basin do not show symmetry or a central anomaly as a traditional ocean basin does. This has
Back-arc basin
17961873
compression near the summit. The most widely accepted belief is that Irnini Mons formed as a shield volcano, and experienced a crater collapse later in its geologic life. Shield Volcanoes on Venus develop as a result of mantle upwelling occurring under thick lithosphere in a constant location over a relatively long period of time. Effusive flows from the magma chamber emitted low viscosity, basaltic lava which resurfaced the regional tessera plains of Venus. The placid flows eventually formed a shallow sloping volcano with its summit above the magma pressurized center. Radiating fractures and ridges due to compression formed simultaneously with
Irnini Mons
9683972
rising magma. Scientific studies have indicated nearly 80% of the magma was erupted in one million years or less. The source for this volcanic activity was the Iceland plume along with its surface expression, the Iceland hotspot. This volcanic activity formed part of a large igneous province that is sunken beneath the northern Labrador Sea. Another period of volcanic activity began in the same region about 55 million years ago during the Eocene period when the north-south trending Mid-Atlantic Ridge began to form under the northern Atlantic Ocean east of Greenland. The cause of this volcanism might be related to
Volcanology of Canada
13266764
was being created from rising magma. Scientific studies have indicated nearly 80% of the magma was erupted in one million years or less. The source for this volcanic activity was the Iceland plume along with its surface expression, the Iceland hotspot. This volcanic activity formed part of a large igneous province that is now sunken beneath the northern Labrador Sea. Another period of volcanic activity began in the same region about 55 million years ago during the Eocene period when the north-south trending Mid-Atlantic Ridge began to form under the northern Atlantic Ocean east of Greenland. The cause of this
Volcanology of Northern Canada
10735237
above a center of upwelling magma called a mantle plume. The seamounts comprising the Kodiak-Bowie Seamount chain would be formed above the mantle plume and carried away from the mantle plume's magmatic source as the Pacific Plate moves in a northwesterly direction towards the Aleutian Trench, along the southern coastline of Alaska. The volcanic rocks which make up some of the seamounts in the Kodiak-Bowie Seamount chain are unusual in that they have an acid-neutralizing chemical substance like typical ocean-island basalts but a low percentage of strontium as found at mid-ocean ridge basalts. However, the strontium-bearing volcanic rocks comprising Bowie
Bowie Seamount
4343435
the Atlantic Ocean for rock type, geological structures and fossils. He noticed that there was a significant similarity between matching sides of the continents, especially in fossil plants. From 1912, Wegener publicly advocated the existence of "continental drift", arguing that all the continents were once joined together in a single landmass and had since drifted apart. He supposed that the mechanisms causing the drift might be the centrifugal force of the Earth's rotation ("") or the astronomical precession. Wegener also speculated about sea-floor spreading and the role of the mid-ocean ridges, stating that "the Mid-Atlantic Ridge ... zone in which
Alfred Wegener
1293825
~ Tx/L, where L is the distance between the ridge to the continental shelf (roughly half the ocean width), and T is the ocean age. Seafloor spreading Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Earlier theories (e.g. by Alfred Wegener and Alexander du Toit) of continental drift postulated that continents "ploughed" through the sea. The idea that the seafloor itself moves (and also carries the continents with it) as it expands from a central axis was proposed by Harry Hess
Seafloor spreading
5649971
repeated opening and closing of ocean basins, in particular focusing on the current Atlantic Ocean area. This concept, a part of the plate tectonics revolution, became known as the "Wilson cycle". The Wilson cycle has had profound effects on the modern interpretation of the rock cycle as plate tectonics became recognized as the driving force for the rock cycle. At the mid-ocean divergent boundaries "new" magma is produced by mantle upwelling and a shallow "melting zone". This "juvenile" basaltic magma is an early phase of the igneous portion of the cycle. As the tectonic plates on either side of the
Rock cycle
5397164
are together and high when they are apart. For example, sea level was low at the time of formation of Pangaea (Permian) and Pannotia (latest Neoproterozoic), and rose rapidly to maxima during Ordovician and Cretaceous times, when the continents were dispersed. This is because the age of the oceanic lithosphere provides a major control on the depth of the ocean basins, and therefore on global sea level. Oceanic lithosphere forms at mid-ocean ridges and moves outwards, conductively cooling and shrinking, which decreases the thickness and increases the density of the oceanic lithosphere, and lowers the seafloor away from mid-ocean ridges.
Supercontinent cycle
190966
a belt between southern Africa and south-western Australia. Pack ice and icebergs are found throughout the year south of about 65° south latitude. The average northern limit of icebergs is 45° south latitude. As the youngest of the major oceans, the Indian Ocean has active spreading ridges that are part of the worldwide system of mid-ocean ridges. In the Indian Ocean these spreading ridges meet at the Rodrigues Triple Point with the Central Indian Ridge, including the Carlsberg Ridge, separating the African Plate from the Indian Plate; the Southwest Indian Ridge separating the African Plate from the Antarctic Plate; and
Indian Ocean
3741594
flat slab subduction, one of the few places in the world where this currently occurs. Ridge push Ridge push or sliding plate force is a proposed driving force for plate motion in plate tectonics that occurs at mid-ocean ridges as the result of the rigid lithosphere sliding down the hot, raised asthenosphere below mid-ocean ridges. Although it is called ridge push, the term is somewhat misleading; it is actually a body force that acts throughout an ocean plate, not just at the ridge, as a result of gravitational pull. The name comes from earlier models of plate tectonics in which
Ridge push
11787465
Bouvet Triple Junction The Bouvet Triple Junction is a geologic triple junction of three tectonic plates located on the seafloor of the South Atlantic Ocean. It is named after Bouvet Island, which lies 275 kilometers to the east. The three plates which meet here are the South American Plate, the African Plate, and the Antarctic Plate. The Bouvet Triple Junction is an R-R-R type, that is, the three plate boundaries which meet here are mid-ocean ridges: the Mid-Atlantic Ridge (MAR), the Southwest Indian Ridge (SWIR), and the South American-Antarctic Ridge (SAAR). There are two prominent transform valleys in the area:
Bouvet Triple Junction
1802244
theorized, was either due to the Andes being preceded by a shallow geosyncline or representing just the margin of a geosyncline. Thus, Cordilleran-type and Alpine-type mountains were to be different in this regard. In Hans Stille's models a type of geosyncline called eugesynclines were characterized by producing an "initial magmatism" that in some cases corresponded to ophiolitic magmatism. As plate tectonic theory prevailed in geology and geosyncline theory became outdated ophiolites were interpreted in the new framework. They were recognized as fragments of oceanic lithosphere, and dykes were viewed as the result of extensional tectonics at mid-ocean ridges. The plutonic
Ophiolite
1983007
and thickening of 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 the
Tectonics
4260055
Eustatic sea level The eustatic sea level is the distance from the center of the earth to the sea surface. An increase of the eustatic sea level can be generated by decreasing glaciation, slower spreading rates of the mid-ocean ridges or fewer mid-oceanic ridges. Conversely increasing glaciation, faster spreading rates or more mid-ocean ridges lead to a fall of the eustatic sea level. Changes in the eustatic sea level lead to changes in accommodation and therefore affect the deposition of sediments in marine environments. Eustatic (global) sea level refers to the sea level change of the volume of Earth’s oceans.
Eustatic sea level