A mantle plume is a proposed mechanism of convection of abnormally hot rock within the Earth's mantle. Because the plume head partly melts on reaching shallow depths, a plume is often invoked as the cause of volcanic hotspots, such as Hawaii or Iceland, and large igneous provinces such as the Deccan and Siberian traps. Some such volcanic regions lie far from tectonic plate boundaries, while others represent unusually large-volume volcanism near plate boundaries or in large igneous provinces.
The hypothesis of mantle plumes from depth is not universally accepted as explaining all such volcanism. It has required progressive hypothesis-elaboration leading to variant propositions such as mini-plumes and pulsing plumes. Another hypothesis for unusual volcanic regions is the "Plate model". This proposes shallower, passive leakage of magma from the mantle onto the Earth's surface where extension of the lithosphere permits it, attributing most volcanism to plate tectonic processes, with volcanoes far from plate boundaries resulting from intraplate extension.
The theory was first proposed by J. Tuzo Wilson in 1963 and further developed by W. Jason Morgan in 1971. A mantle plume is posited to exist where hot rock nucleates at the core-mantle boundary and rises through the Earth's mantle becoming a diapir in the Earth's crust. In particular, the concept that mantle plumes are fixed relative to one another, and anchored at the core-mantle boundary, would provide a natural explanation for the time-progressive chains of older volcanoes seen extending out from some such hot spots, such as the Hawaiian–Emperor seamount chain. However, new paleomagnetic data now shows, that mantle plumes can be associated with Large Low Shear Velocity Provinces (LLSVPs) and do move.
Two largely independent convective processes are proposed:
The plume hypothesis was studied using laboratory experiments conducted in small fluid-filled tanks in the early 1970s. Thermal or compositional fluid-dynamical plumes produced in that way were presented as models for the much larger postulated mantle plumes. On the basis of these experiments, mantle plumes are now postulated to comprise two parts: a long thin conduit connecting the top of the plume to its base, and a bulbous head that expands in size as the plume rises. The entire structure is considered to resemble a mushroom. The bulbous head of thermal plumes forms because hot material moves upward through the conduit faster than the plume itself rises through its surroundings. In the late 1980s and early 1990s, experiments with thermal models showed that as the bulbous head expands it may entrain some of the adjacent mantle into the head.
The sizes and occurrence of mushroom mantle plumes can be predicted easily by transient instability theory developed by Tan and Thorpe. The theory predicts mushroom shaped mantle plumes with heads of about 2000 km diameter that have a critical time of about 830 Myr for a core mantle heat flux of 20 mW/m2, while the cycle time is about 2 Gyr. The number of mantle plumes is predicted to be about 17.
When a plume head encounters the base of the lithosphere, it is expected to flatten out against this barrier and to undergo widespread decompression melting to form large volumes of basalt magma. It may then erupt onto the surface. Numerical modelling predicts that melting and eruption will take place over several million years. These eruptions have been linked to flood basalts, although many of those erupt over much shorter time scales (less than 1 million years). Examples include the Deccan traps in India, the Siberian traps of Asia, the Karoo-Ferrar basalts/dolerites in South Africa and Antarctica, the Paraná and Etendeka traps in South America and Africa (formerly a single province separated by opening of the South Atlantic Ocean), and the Columbia River basalts of North America. Flood basalts in the oceans are known as oceanic plateaus, and include the Ontong Java plateau of the western Pacific Ocean and the Kerguelen Plateau of the Indian Ocean.
The narrow vertical pipe, or conduit, postulated to connect the plume head to the core-mantle boundary, is viewed as providing a continuous supply of magma to a fixed location, often referred to as a "hotspot". As the overlying tectonic plate (lithosphere) moves over this hotspot, the eruption of magma from the fixed conduit onto the surface is expected to form a chain of volcanoes that parallels plate motion. The Hawaiian Islands chain in the Pacific Ocean is the type example. It has recently been discovered that the volcanic locus of this chain has not been fixed over time, and it thus joined the club of the many type examples that do not exhibit the key characteristic originally proposed.
The eruption of continental flood basalts is often associated with continental rifting and breakup. This has led to the hypothesis that mantle plumes contribute to continental rifting and the formation of ocean basins. In the context of the alternative "Plate model", continental breakup is a process integral to plate tectonics, and massive volcanism occurs as a natural consequence when it onsets.
The current mantle plume theory is that material and energy from Earth's interior are exchanged with the surface crust in two distinct modes: the predominant, steady state plate tectonic regime driven by upper mantle convection, and a punctuated, intermittently dominant, mantle overturn regime driven by plume convection. This second regime, while often discontinuous, is periodically significant in mountain building and continental breakup.
The chemical and isotopic composition of basalts found at hotspots differs subtly from mid-ocean-ridge basalts. These basalts, also called ocean island basalts (OIBs), are analysed in their radiogenic and stable isotope compositions. In radiogenic isotope systems the originally subducted material creates diverging trends, termed mantle components. Identified mantle components are DMM (depleted mid-ocean ridge basalt (MORB) mantle), HIMU (high U/Pb-ratio mantle), EM1 (enriched mantle 1), EM2 (enriched mantle 2) and FOZO (focus zone). This geochemical signature arises from the mixing of near-surface materials such as subducted slabs and continental sediments, in the mantle source. There are two competing interpretations for this. In the context of mantle plumes, the near-surface material is postulated to have been transported down to the core-mantle boundary by subducting slabs, and to have been transported back up to the surface by plumes. In the context of the Plate hypothesis, subducted material is mostly re-circulated in the shallow mantle and tapped from there by volcanoes.
Stable isotopes like Fe are used to track processes that the uprising material experiences during melting.
The processing of oceanic crust, lithosphere, and sediment through a subduction zone decouples the water-soluble trace elements (e.g., K, Rb, Th) from the immobile trace elements (e.g., Ti, Nb, Ta), concentrating the immobile elements in the oceanic slab (the water-soluble elements are added to the crust in island arc volcanoes). Seismic tomography shows that subducted oceanic slabs sink as far as the bottom of the mantle transition zone at 650 km depth. Subduction to greater depths is less certain, but there is evidence that they may sink to mid-lower-mantle depths at about 1,500 km depth.
The source of mantle plumes is postulated to be the core-mantle boundary at 3,000 km depth. Because there is little material transport across the core-mantle boundary, heat transfer must occur by conduction, with adiabatic gradients above and below this boundary. The core-mantle boundary is a strong thermal (temperature) discontinuity. The temperature of the core is approximately 1,000 degrees Celsius higher than that of the overlying mantle. Plumes are postulated to rise as the base of the mantle becomes hotter and more buoyant.
Plumes are postulated to rise through the mantle and begin to partially melt on reaching shallow depths in the asthenosphere by decompression melting. This would create large volumes of magma. The plume hypothesis postulates that this melt rises to the surface and erupts to form "hot spots".
The most prominent thermal contrast known to exist in the deep (1000 km) mantle is at the core-mantle boundary at 2900 km. Mantle plumes were originally postulated to rise from this layer because the "hot spots" that are assumed to be their surface expression were thought to be fixed relative to one another. This required that plumes were sourced from beneath the shallow asthenosphere that is thought to be flowing rapidly in response to motion of the overlying tectonic plates. There is no other known major thermal boundary layer in the deep Earth, and so the core-mantle boundary was the only candidate.
The base of the mantle is known as the D″ layer, a seismological subdivision of the Earth. It appears to be compositionally distinct from the overlying mantle, and may contain partial melt.
Two very broad, large low-shear-velocity provinces, exist in the lower mantle under Africa and under the central Pacific. It is postulated that plumes rise from their surface or their edges. Their low seismic velocities were thought to suggest that they are relatively hot, although it has recently been shown that their low wave velocities are due to high density caused by chemical heterogeneity.
Various lines of evidence have been cited in support of mantle plumes. There is some confusion regarding what constitutes support, as there has been a tendency to re-define the postulated characteristics of mantle plumes after observations have been made.
The age-progressive distribution of the Hawaiian-Emperor seamount chain has been explained as a result of a fixed, deep-mantle plume rising into the upper mantle, partly melting, and causing a volcanic chain to form as the plate moves overhead relative to the fixed plume source. Other "hot spots" with time-progressive volcanic chains behind them include Réunion, the Chagos-Laccadive Ridge, the Louisville Ridge, the Ninety East Ridge and Kerguelen, Tristan, and Yellowstone.
An intrinsic aspect of the plume hypothesis is that the "hot spots" and their volcanic trails have been fixed relative to one another throughout geological time. Whereas there is evidence that the chains listed above are time-progressive, it has, however, been shown that they are not fixed relative to one another. The most remarkable example of this is the Emperor chain, the older part of the Hawaii system, which was formed by migration of volcanic activity across a geo-stationary plate.
Many postulated "hot spots" are also lacking time-progressive volcanic trails, e.g., Iceland, the Galapagos, and the Azores. Mismatches between the predictions of the hypothesis and observations are commonly explained by auxiliary processes such as "mantle wind", "ridge capture", "ridge escape" and lateral flow of plume material.
Helium-3 is a primordial isotope that formed in the Big Bang. Very little is produced, and little has been added to the Earth by other processes since then. Helium-4 includes a primordial component, but it is also produced by the natural radioactive decay of U and Th. Over time, He in the upper atmosphere is lost into space. Thus, the Earth has become progressively depleted in He, and 3He is not replaced as 4He is. As a result, the ratio 3He/4He in the Earth has decreased over time.
Unusually high 3He/4He have been observed in some, but not all, "hot spots". In mantle plume theory, this is explained by plumes tapping a deep, primordial reservoir in the lower mantle, where the original, high 3He/4He ratios have been preserved throughout geologic time. In the context of the Plate hypothesis, the high ratios are explained by preservation of old material in the shallow mantle. Ancient, high 3He/4He ratios would be particularly easily preserved in materials lacking U or Th, so 4He was not added over time. Olivine and dunite, both found in subducted crust, are materials of this sort.
Other elements, e.g. osmium, have been suggested to be tracers of material arising from near to the Earth's core, in basalts at oceanic islands. However, so far conclusive proof for this is lacking.
The plume hypothesis has been tested by looking for the geophysical anomalies predicted to be associated with them. These include thermal, seismic, and elevation anomalies. Thermal anomalies are inherent in the term "hotspot". They can be measured in numerous different ways, including surface heat flow, petrology, and seismology. Thermal anomalies produce anomalies in the speeds of seismic waves, but unfortunately so do composition and partial melt. As a result, wave speeds cannot be used simply and directly to measure temperature, but more sophisticated approaches must be taken.
Seismic anomalies are identified by mapping variations in wave speed as seismic waves travel through Earth. A hot mantle plume is predicted to have lower seismic wave speeds compared with similar material at a lower temperature. Mantle material containing a trace of partial melt (e.g., as a result of it having a lower melting point), or being richer in Fe, also has a lower seismic wave speed and those effects are stronger than temperature. Thus, although unusually low wave speeds have been taken to indicate anomalously hot mantle beneath "hot spots", this interpretation is ambiguous. The most commonly cited seismic wave-speed images that are used to look for variations in regions where plumes have been proposed come from seismic tomography. This method involves using a network of seismometers to construct three-dimensional images of the variation in seismic wave speed throughout the mantle.
Seismic waves generated by large earthquakes enable structure below the Earth's surface to be determined along the ray path. Seismic waves that have traveled a thousand or more kilometers (also called teleseismic waves) can be used to image large regions of Earth's mantle. They also have limited resolution, however, and only structures at least several hundred kilometers in diameter can be detected.
Seismic tomography images have been cited as evidence for a number of mantle plumes in Earth's mantle. There is, however, vigorous on-going discussion regarding whether the structures imaged are reliably resolved, and whether they correspond to columns of hot, rising rock.
The mantle plume hypothesis predicts that domal topographic uplifts will develop when plume heads impinge on the base of the lithosphere. An uplift of this kind occurred when the north Atlantic Ocean opened about 54 million years ago. Some scientists have linked this to a mantle plume postulated to have caused the breakup of Eurasia and the opening of the north Atlantic, now suggested to underlie Iceland. Current research has shown that the time-history of the uplift is probably much shorter than predicted, however. It is thus not clear how strongly this observation supports the mantle plume hypothesis.
Basalts found at oceanic islands are 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 trace elements, they are typically more enriched in the light rare-earth elements than mid-ocean ridge basalts. Compared to island arc basalts, ocean island basalts are lower in alumina (Al2O3) and higher in immobile trace elements (e.g., Ti, Nb, Ta).
These differences result from processes that occur during the subduction of oceanic crust and mantle lithosphere. Oceanic crust (and to a lesser extent, the underlying mantle) typically becomes hydrated to varying degrees on the seafloor, partly as the result of seafloor weathering, and partly in response to hydrothermal circulation near the mid-ocean-ridge crest where it was originally formed. As oceanic crust and underlying lithosphere subduct, water is released by dehydration reactions, along with water-soluble elements and trace elements. This enriched fluid rises to metasomatize the overlying mantle wedge and leads to the formation of island arc basalts. The subducting slab is depleted in these water-mobile elements (e.g., K, Rb, Th, Pb) and thus relatively enriched in elements that are not water-mobile (e.g., Ti, Nb, Ta) compared to both mid-ocean ridge and island arc basalts.
Ocean island basalts are also relatively enriched in immobile elements relative to the water-mobile elements. This, and other observations, have been interpreted as indicating that the distinct geochemical signature of ocean island basalts results from inclusion of a component of subducted slab material. This must have been recycled in the mantle, then re-melted and incorporated in the lavas erupted. In the context of the plume hypothesis, subducted slabs are postulated to have been subducted down as far as the core-mantle boundary, and transported back up to the surface in rising plumes. In the plate hypothesis, the slabs are postulated to have been recycled at shallower depths – in the upper few hundred kilometers that make up the upper mantle. However, the plate hypothesis is inconsistent with both the geochemistry of shallow asthenosphere melts (i.e., Mid-ocean ridge basalts) and with the isotopic compositions of ocean island basalts.
In 2015, based on data from 273 large earthquakes, researchers compiled a model based on full waveform tomography, requiring the equivalent of 3 million hours of supercomputer time. Due to computational limitations, high-frequency data still could not be used, and seismic data remained unavailable from much of the seafloor. Nonetheless, vertical plumes, 400 C hotter than the surrounding rock, were visualized under many hotspots, including the Pitcairn, Macdonald, Samoa, Tahiti, Marquesas, Galapagos, Cape Verde, and Canary hotspots. They extended nearly vertically from the core-mantle boundary (2900 km depth) to a possible layer of shearing and bending at 1000 km. They were detectable because they were 600–800 km wide, more than three times the width expected from contemporary models. Many of these plumes are in the large low-shear-velocity provinces under Africa and the Pacific, while some other hotspots such as Yellowstone were less clearly related to mantle features in the model.
The unexpected size of the plumes leaves open the possibility that they may conduct the bulk of the Earth's 44 terawatts of internal heat flow from the core to the surface, and means that the lower mantle convects less than expected, if at all. It is possible that there is a compositional difference between plumes and the surrounding mantle that slows them down and broadens them.
Many different localities have been suggested to be underlain by mantle plumes, and scientists cannot agree on a definitive list. Some scientists suggest that several tens of plumes exist, whereas others suggest that there are none. The theory was really inspired by the Hawaiian volcano system. Hawaii is a large volcanic edifice in the center of the Pacific Ocean, far from any plate boundaries. Its regular, time-progressive chain of islands and seamounts superficially fits the plume theory well. However, it is almost unique on Earth, as nothing as extreme exists anywhere else. The second strongest candidate for a plume location is often quoted to be Iceland, but according to opponents of the plume hypothesis its massive nature can be explained by plate tectonic forces along the mid-Atlantic spreading center.
Mantle plumes have been suggested as the source for flood basalts. These extremely rapid, large scale eruptions of basaltic magmas have periodically formed continental flood basalt provinces on land and oceanic plateaus in the ocean basins, such as the Deccan Traps, the Siberian Traps the Karoo-Ferrar flood basalts of Gondwana, and the largest known continental flood basalt, the Central Atlantic magmatic province (CAMP).
Others have pointed out the coincidence of many continental flood basalt events with continental rifting. This is consistent with a system that tends toward equilibrium: as matter rises in a mantle plume, other material is drawn down into the mantle, causing rifting.
In parallel with the mantle plume model, two alternative explanations for the observed phenomena have been considered: the plate hypothesis and the impact hypothesis.
The plate hypothesis suggests that "anomalous" volcanism results from lithospheric extension that permits melt to rise passively from the asthenosphere beneath. It is thus the conceptual inverse of the plume hypothesis, attributing volcanism to shallow, near-surface processes associated with plate tectonics, rather than active processes arising at the core-mantle boundary. The plate hypothesis argues that deep mantle plumes causing surface, time-progressive volcanism .
Lithospheric extension is attributed to processes related to plate tectonics. These processes are well understood at mid-ocean ridges, where most of Earth's volcanism occurs. It is less commonly recognised that the plates themselves deform internally, and can permit volcanism in those regions where the deformation is extensional. Well-known examples are the Basin and Range Province in the western USA, the East African Rift valley, and the Rhine Graben. Under this hypothesis, variable volumes of magma are attributed to variations in chemical composition (large volumes of volcanism corresponding to more easily molten mantle material) rather than to temperature differences.
The plate hypothesis thus attributes all of Earth's volcanism to a single process – plate tectonics – rather than to two independent processes (plumes and plate tectonics), but does not address issues of core–mantle heat and/or material transfer.
Under the umbrella of the plate hypothesis, the following sub-processes, all of which can contribute to permitting surface volcanism, are recognised:
In addition to these processes, impact events such as ones that created the Addams crater on Venus and the Sudbury Igneous Complex in Canada are known to have caused melting and volcanism. In the impact hypothesis, it is proposed that some regions of hotspot volcanism can be triggered by certain large-body oceanic impacts which are able to penetrate the thinner oceanic lithosphere, and flood basalt volcanism can be triggered by converging seismic energy focused at the antipodal point opposite major impact sites. Impact-induced volcanism has not been adequately studied and comprises a separate causal category of terrestrial volcanism with implications for the study of hotspots and plate tectonics.
In 1997 it became possible using seismic tomography to image submerging tectonic slabs penetrating from the surface all the way to the core-mantle boundary.
For the Hawaii hotspot, long-period seismic body wave diffraction tomography provided evidence that a mantle plume is responsible, as had been proposed as early as 1971. For the Yellowstone hotspot, seismological evidence began to converge from 2011 in support of the plume model, as concluded by James et al., "we favor a lower mantle plume as the origin for the Yellowstone hotspot." Data acquired through Earthscope, a program collecting high-resolution seismic data throughout the contiguous United States has accelerated acceptance of a plume underlying Yellowstone.
Although there is strong evidence that at least two deep mantle plumes rise to the core-mantle boundary, confirmation that other hypotheses can be dismissed may require similar tomographic evidence for other hot spots.
The Anahim hotspot is a volcanic hotspot located in the West-Central Interior of British Columbia, Canada. One of the few hotspots in North America, the Anahim plume is responsible for the creation of the Anahim Volcanic Belt. This is a 300 km (190 mi) long chain of volcanoes and other magmatic features that have undergone erosion. The chain extends from the community of Bella Bella in the west to near the small city of Quesnel in the east. While most volcanoes are created by geological activity at tectonic plate boundaries, the Anahim hotspot is located hundreds of kilometres away from the nearest plate boundary.
This hotspot's existence was first proposed in the 1970s by three scientists who used John Tuzo Wilson's classic hotspot theory. This theory proposes that a single, fixed mantle plume builds volcanoes that then, cut off from their source by the movement of the North American Plate, become increasingly inactive and eventually erode over millions of years. A more recent theory, published in 2001 by the Geological Society of America, suggests that the Anahim hotspot might be supplied by a mantle plume from the upper mantle rather than a deep-seated plume proposed by Wilson. The plume has since been tomographically imaged, showing it to be roughly 400 km (250 mi) deep. This measurement, however, could be an underestimate as the plume might originate deeper within Earth.
Volcanism as early as 14.5 million years ago has been linked to the Anahim hotspot, with the latest eruption having taken place in the last 8,000 years. This volcanic activity has produced rocks that show a bimodal distribution in composition. While these rocks were being deposited, the hotspot coincided with periods of crustal extension and uplift. Activity in modern times has been limited to earthquakes and volcanic gas emissions.Balleny hotspot
The Balleny hotspot is a volcanic hotspot located in the Southern Ocean. The hotspot created the Balleny Islands, which forms a chain that extends for about 160 km (99 mi) in a northwest-southeast direction. Due to plate tectonics the hot spot was under different parts of the ocean bed in the past, and this has resulted in a chain of seamounts extending from the East Tasman Plateau. Isotopes and trace elements in the volcanic rocks indicated a high U/Pb mantle source. The same pattern is seen in basalt from Tasmania, but not from Victoria.Benue Trough
The Benue Trough is a major geological structure underlying a large part of Nigeria and extending about 1,000 km northeast from the Bight of Benin to Lake Chad.
It is part of the broader Central African Rift System.Devana Chasma
Devana Chasma is a weak extensional rift zone on Venus, with a length of 4000 km, a width of 150–250 km, and a depth reaching 5 km. Most of the faults are facing north-south. The rift is located in Beta Regio, a 3000 km rise created by volcanic activity. Mantle plumes rising from the bottom are the reason behind the formation of the rift zone. The slow extension rates in the rift may be driven by the same reason.Dnieper-Donets Rift
The Dnieper-Donets Rift or Pripyat-Dnieper-Donets Rift (also referred as a "paleorift" and "aulacogen") is an east-west running rift in the Sarmatian Craton that developed and was most active in the Paleozoic. The rift extends from the Caspian Depression in Russia to northern Ukraine passing by the Donbass region. The rift separates the Voronezh Massif in the north from the Ukrainian Shield in south.The Dnepr-Donets Paleorift was the site of Devonian magmatic activity that begun in Late Frasnian and peaked in the Famennian caused by a mantle plume. Extensional tectonics were also most active during the Famennian.There have been suggestions that the Dnepr-Donets Paleorift is related to the coeval Kola Alkaline Province.Emeishan Traps
The Emeishan Traps constitute a flood basalt volcanic province, or large igneous province, in south-western China, centred in Sichuan province. It is sometimes referred to as the Permian Emeishan Large Igneous Province or Emeishan Flood Basalts. Like other volcanic provinces or "traps", the Emeishan Traps are multiple layers of igneous rock laid down by large mantle plume volcanic eruptions. The Emeishan Traps eruptions were serious enough to have global ecological and paleontological impact.It is named for Emeishan, a mountain in Sichuan.
As of September 2019, there is emerging evidence that the Emishian Traps caused a mass extinction event.Epeirogenic movement
In geology, epeirogenic movement (from Greek epeiros, land, and genesis, birth) is upheavals or depressions of land exhibiting long wavelengths and little folding apart from broad undulations. The broad central parts of continents are called cratons, and are subject to epeirogeny. The movement may be one of subsidence toward, or of uplift from, the centre of the Earth. The movement is caused by a set of forces acting along an Earth radius, such as those contributing to isostasy and faulting in the lithosphere.
Epeirogenic movement can be permanent or transient. Transient uplift can occur over a thermal anomaly due to convecting anomalously hot mantle, and disappears when convection wanes. Permanent uplift can occur when igneous material is injected into the crust, and circular or elliptical structural uplift (that is, without folding) over a large radius (tens to thousands of km) is one characteristic of a mantle plume.In contrast to epeirogenic movement, orogenic movement is a more complicated deformation of the Earth's crust, associated with crustal thickening, notably associated with the convergence of tectonic plates. Such plate convergence forms orogenic belts that are characterized by "the folding and faulting of layers of rock, by the intrusion of magma, and by volcanism".Epeirogenic movements may divert rivers and create drainage divides by upwarping of the crust along axes. Example of this is the deflection of Eridanos River in the Pliocene Epoch by the uplift of the South Swedish Dome or the present-day drainage divides between Limpopo and Zambezi rivers in southern Africa.Geology of the Comoros
The Comoros island chain in the Mozambique Channel is the result of the rifting of Madagascar away from Africa as well as "hotspot" mantle plume activity. The region is also impact by seismicity and deformation associated with the East African Rift system and the Comoros region is one of the best places in the world to study rift-hotspot interactions. The islands remain volcanically active.Iceland hotspot
The Iceland hotspot is a hotspot which is partly responsible for the high volcanic activity which has formed the Iceland Plateau and the island 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 century there were 39 volcanic eruptions on and around Iceland). About 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 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 a region of higher temperature than the surrounding mantle, it 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.Lava field
A lava field, also called a lava plain or lava bed, is a large expanse of nearly flat-lying lava flows. Such features are generally composed of highly fluid basalt lava, and can extend for tens or even hundreds of miles across the underlying terrain. The extent of large lava fields is most readily grasped from the air or in satellite photos, where their typically dark, nearly black color contrasts sharply with the rest of the landscape.
According to the US Geological Survey, monogenetic volcanic fields are collections of cinder cones, and/or maar vents and associated lava flows and pyroclastic deposits. Sometimes a stratovolcano
is at the center of the field, as at the San Francisco Volcanic Field in Arizona.
Some of the most ancient geological remnants of basaltic plains lie in Canada's Precambrian Shield. Eruption of plateau lavas near the Coppermine River southwest of Coronation Gulf in the Arctic, built an extensive plateau about 1200 million years ago with an area of about 170,000 km2 (66,000 sq mi), representing a volume of lavas of at least 500,000 km3 (120,000 cu mi). The lavas are thought to have originated from a mantle plume center called the Mackenzie hotspot.Mackenzie dike swarm
The Mackenzie dike swarm, also called the Mackenzie dikes, form a large igneous province in the western Canadian Shield of Canada. It is part of the larger Mackenzie Large Igneous Province and is one of more than three dozen dike swarms in various parts of the Canadian Shield.
The Mackenzie dike swarm is the largest dike swarm known on Earth, more than 500 km (310 mi) wide and 3,000 km (1,900 mi) long, extending in a northwesterly direction across the whole of Canada from the Arctic to the Great Lakes. The mafic dikes cut Archean and Proterozoic rocks, including those in the Athabasca Basin in Saskatchewan, Thelon Basin in Nunavut and the Baker Lake Basin in the Northwest Territories.
The source for the Mackenzie dike swarm is considered to have been a mantle plume center called the Mackenzie hotspot. About 1,268 million years ago, the Slave craton was partly uplifted and intruded by the giant Mackenzie dike swarm. This was the last major event to affect the core of the Slave craton, although later on some younger mafic magmatism registered along its edges.Madagascar Plate
The Madagascar Plate or Madagascar block was once attached to the Gondwana supercontinent and later the Indo-Australian Plate.
Rifting in the Somali Basin began at the end of the Carboniferous 300 million years ago, as a part of the Karoo rift system. The initiation of Gondwana breakup, and transform faulting along the Davie Fracture Zone, occurred in the Toarcian (about 182 million years ago) following the eruption of the Bouvet (Karoo) mantle plume. At this time East Gondwana, comprising the Antarctic, Madagascar, Indian, and Australian plates, began to separate from the African Plate. East Gondwana then began to break apart about 115–120 million years ago when India began to move northward. Between 84–95 million years ago rifting separated Seychelles and India from Madagascar.
Since its formation the Madagascar block has moved roughly in conjunction with Africa, and thus there are questions as to whether the Madagascar Plate should be still considered a separate plate.Marathon Large Igneous Province
The Marathon Large Igneous Province is a Paleoproterozoic large igneous province along the southern Superior craton of Ontario, Canada, located around the northern margin of Lake Superior. It consists of three diabase dike swarms known as Marathon, Kapuskasing and Fort Frances. The Kapuskasing and Marathon dike swarms range in age from about 2,126 to 2,101 million years old while the Fort Frances dike swarm is between 2,076 and 2,067 million years old.A single, periodically active mantle plume was responsible for the creation of the Marathon Large Igneous Province due to the lack of apparent polar wander during the formation of the igneous province. The large magmatic event covers an area of at least 400,000 km2 (150,000 sq mi) and the entire large igneous province was constructed in 60 million years.Mount Gambier (volcano)
Mount Gambier (also known as Ereng Balam, meaning eagle hawk) is a maar complex in South Australia associated with the Newer Volcanics Province. It contains four lake-filled maars called Blue Lake, Valley Lake, Leg of Mutton Lake, and Browns Lake. Both Brown and Leg of Mutton lakes are dry in recent years, due to the lowering of the water table.
It is one of Australia's youngest volcanoes, but estimates of the age have ranged from over 28,000 to less than 4,300.
The most recent estimate, based on radiocarbon dating of plant fibers in the main crater (Blue Lake) suggests an eruption a little before 6000 years ago.
It is believed to be dormant rather than extinct.
Mount Gambier is thought to have formed by a mantle plume centre called the East Australia hotspot which may currently lie offshore.The mountain was sighted by Lieutenant James Grant on 3 December 1800 from the survey brig HMS Lady Nelson and named for Lord James Gambier, Admiral of the Fleet.This area is part of the UNESCO-endorsed Kanawinka Geopark.
Of the original four lakes found within the maars, only two remain. The Leg of Mutton Lake (named for the outline of its shoreline) became permanently dry in the 1990s. Browns Lake suffered a similar fate during the late 1980s. Both these lakes were quite shallow; their demise is attributed to the lowering of the water table as a result of many years of land drainage to secure farmland.
The city of Mount Gambier partially surrounds the maar complex.Natkusiak flood basalts
The Natkusiak flood basalts are a sequence of Neoproterozoic continental flood basalts of the Franklin Large Igneous Province on Victoria Island, Canada. The flood basalts were erupted about 720 million years ago after uplift began three to five million years prior to the flood basalt volcanism. This uplift and flood basalt volcanism was caused by a mantle plume. This flood basalt sequence is related to the Franklin magmatic event.Noronha hotspot
Noronha hotspot is a hypothesized hotspot in the Atlantic Ocean. It has been proposed as the candidate source for volcanism in the Fernando de Noronha archipelago of Brazil, as well as of other volcanoes also in Brazil and even the Bahamas and the Central Atlantic Magmatic Province.
The presence of a mantle plume is controversial owing to equivocal seismic tomography images of the mantle and the inconsistent age progression in the volcanoes, especially the Brazilian ones.Ocean island basalt
Ocean island basalt (OIB) is a volcanic rock, usually basaltic in composition, erupted in oceans away from tectonic plate boundaries. Although ocean island basaltic magma is mainly erupted as basalt lava, the basaltic magma is sometimes modified by igneous differentiation to produce a range of other volcanic rock types, for example, rhyolite in Iceland, and phonolite and trachyte at the intraplate volcano Fernando de Noronha. Unlike mid-ocean ridge basalts (MORBs), which erupt at spreading centers (divergent plate boundaries), and volcanic arc lavas, which erupt at subduction zones (convergent plate boundaries), ocean island basalts are the result of intraplate volcanism. However, some ocean island basalt locations coincide with plate boundaries like Iceland, which sits on top of a mid-ocean ridge, and Samoa, which is located near a subduction zone.In the ocean basins, ocean island basalts form seamounts, and in some cases, enough material is erupted that the rock protrudes from the ocean and forms an island, like at Hawaii, Samoa, and Iceland. Over time, however, thermal subsidence and mass loss via subaerial erosion causes islands to become completely submarine seamounts or guyots. Many ocean island basalts erupt at volcanic hotspots, which are thought to be the surface expressions of melting of thermally buoyant, rising conduits of hot rock in the mantle, called mantle plumes. Mantle plume conduits may drift slowly, but Earth’s tectonic plates drift more rapidly relative to mantle plumes. As a result, the relative motion of Earth’s tectonic plates over mantle plumes produces age-progressive chains of volcanic islands and seamounts with the youngest, active volcanoes located above the axis of the mantle plume while older, inactive volcanoes are located progressively farther away from the plume conduit (see Figure 1). Hotspot chains can record tens of millions of years of continuous volcanic history; for example, the oldest seamounts in the Hawaiian–Emperor seamount chain are over 80 million years old.
Not all ocean island basalts are the product of mantle plumes. There are thousands of seamounts that are not clearly associated with upwelling mantle plumes, and there are chains of seamounts that are not age progressive. Seamounts that are not clearly linked to a mantle plume indicate that regional mantle composition and tectonic activity may also play important roles in producing intraplate volcanism.Okavango Dyke Swarm
The Okavango Dyke Swarm is a giant dyke swarm of the Karoo Large Igneous Province in northeast Botswana, southern Africa. It consists of a group of Proterozoic and Jurassic dykes, trending east-southeast across Botswana, spanning a region nearly 2,000 kilometres (1,200 mi) long and 110 kilometres (68 mi) wide. The Jurassic dykes were formed approximately 179 million years ago, composed of mainly tholeiitic mafic rocks. The formation is related to the magmatism at the Karoo triple junction, induced by the plate tectonic break up of the Gondwana supercontinent in the early Jurassic.Sclavia Craton
The Sclavia Craton is a late Archean supercraton thought to be parental to the Slave and Wyoming Cratons in North America, the Dharwar Craton in southern India, and the Zimbabwe Craton in southern Africa. Sclavia was proposed by Bleeker 2003 who estimated the number of Archean cratons to ca. 35; cratonic fragments which he suggested were derived from a single or a few supercratons.The break-up of Sclavia, and possibly other continents or supercratons, can be linked to a global pulse of magmatic activity around 2.33–2.1 Gya probably caused by increased mantle plume activity. Related results of this mantle activity include the 2.3 Ga-old Precambrian dyke swarms in the Dharwar Craton in southern India which were emplaced in only five million years. Similar swarms have been found in what is today Antarctica, Australia, Finland, Greenland, and North America.There is growing evidences that support that the Slave and Dharwar cratons shared a common history through the Archean but the exact configuration of the Archean supercraton from which they were derived is unknown.Kenorland, a proposed supercontinent, is a "one-piece" alternative to three separate supercratons: Superia, Vaalbara, and Sclavia.