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55-844: East European Platform or Russian Platform is a large and flat area of the East European Craton covered by sediments in Eastern Europe spanning from the Ural Mountains to the Tornquist Zone and from the Peri-Caspian Basin to the Barents Sea . Over geological time the platform area has experienced extension , inversion and compression. It has an area of about 6 million km . The East European Platform sediments can be classified into

110-489: A continuous supply of magma to a hotspot. As the overlying tectonic plate moves over this hotspot, the eruption of magma from the fixed plume 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 archetypal example. It has recently been discovered that the volcanic locus of this chain has not been fixed over time, and it thus joined

165-414: A core mantle heat flux of 20 mW/m , while the cycle time (the time between plume formation events) is about 2000 million years. 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

220-543: A high Sr/ Sr ratio. Helium in OIB shows a wider variation in the He/ He ratio than MORB, with some values approaching the primordial value. The composition of ocean island basalts is attributed to the presence of distinct mantle chemical reservoirs formed by subduction of oceanic crust. These include reservoirs corresponding to HUIMU, EM1, and EM2. These reservoirs are thought to have different major element compositions, based on

275-405: 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 resembles 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

330-615: 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 hotspots, 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

385-534: 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 mid-ocean ridge basalt (MORB). Ocean island basalt (OIB)

440-647: 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

495-562: 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

550-399: A plume developed into a weakly defined hypothesis, which as a general term is currently neither provable nor refutable. The dissatisfaction with the state of the evidence for mantle plumes and the proliferation of ad hoc hypotheses drove a number of geologists, led by Don L. Anderson , Gillian Foulger , and Warren B. Hamilton , to propose a broad alternative based on shallow processes in

605-511: 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. Mantle plumes were first proposed by J. Tuzo Wilson in 1963 and further developed by W. Jason Morgan in 1971 and 1972. A mantle plume

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660-507: 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

715-736: 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 conduit, postulated to connect the plume head to the core-mantle boundary, is viewed as providing

770-462: 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. This melt rises to

825-454: 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. Since the beginning of the 21st century, a paradigm debate "The great plume debate" has developed around plumes, in which

880-536: Is enriched in trace incompatible elements , with the light rare earth elements showing particular enrichment compared with heavier rare earth elements. Stable isotope ratios of the elements strontium , neodymium , hafnium , lead , and osmium show wide variations relative to MORB, which is attributed to the mixing of at least three mantle components: HIMU with a high proportion of radiogenic lead, produced by decay of uranium and other heavy radioactive elements; EM1 with less enrichment of radiogenic lead; and EM2 with

935-481: Is more diverse compositionally than MORB, and the great majority of ocean islands are composed of alkali basalt enriched in sodium and potassium relative to MORB. Larger islands, such as Hawaii or Iceland, are mostly tholeiitic basalt, with alkali basalt limited to late stages of their development, but this tholeiitic basalt is chemically distinct from the tholeiitic basalt of mid-ocean ridges. OIB tends to be more enriched in magnesium, and both alkali and tholeiitic OIB

990-438: Is posited to exist where super-heated material forms ( nucleates ) at the core-mantle boundary and rises through the Earth's mantle. Rather than a continuous stream, plumes should be viewed as a series of hot bubbles of material. Reaching the brittle upper Earth's crust they form diapirs . These diapirs are "hotspots" in the crust. In particular, the concept that mantle plumes are fixed relative to one another and anchored at

1045-482: Is that material and energy from Earth's interior are exchanged with the surface crust in two distinct and largely independent convective flows: The plume hypothesis was simulated by laboratory experiments 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. Based on these experiments, mantle plumes are now postulated to comprise two parts:

1100-738: The Chagos-Laccadive Ridge , the Louisville Ridge , the Ninety East Ridge and Kerguelen , Tristan , and Yellowstone . While there is evidence that the chains listed above are time-progressive, it has 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 the hotspot in addition to

1155-858: The Dnieper-Donets Rift , transects Sarmatia, dividing it into the Ukrainian Shield and the Voronezh Massif. The southwestern boundary is known as the Trans European Suture Zone and separates the East European craton from the Phanerozoic orogens of Western Europe (e.g. Carpathians ). The northwestern margin of the craton is overlaid by the fold-and-thrust Early Paleozoic Caledonian orogen . The most distinguishable physiographic aspect of

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1210-622: 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

1265-543: 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

1320-404: 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. Some common and basic lines of evidence cited in support of

1375-476: 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

1430-819: The East European Craton is the extensive 3-km and more-thick Riphean (middle to late Proterozoic) sedimentary cover over its 3000-km-wide platform area (East European Platform, EEP, also known as the Russian Platform). This is in sharp contrast to the exposed northwest portion of the Baltic Shield , and the Ukrainian Shield in the southwest. The lithospheric thickness also varies widely from 150–200 km in Ukraine to 120 km in southern Russia to over 250 km thick in

1485-542: The NE Baltic Shield, with extremely wide thickness fluctuations of the crustal layers. A shield in any craton is the area of exposed crystalline crust while the other part of the craton is the “ platform ” where the crystalline crust or basement is overlaid by younger sedimentary cover. Thus the crustal segments of the East European Craton comprise both the Baltic Shield and the Ukrainian Shield, and

1540-507: 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

1595-428: The bulbous head expands it may entrain some of the adjacent mantle into itself. The size and occurrence of mushroom mantle plumes can be predicted by the transient instability theory of Tan and Thorpe. The theory predicts mushroom-shaped mantle plumes with heads of about 2000 km diameter that have a critical time (time from onset of heating of the lower mantle to formation of a plume) of about 830 million years for

1650-589: 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. 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

1705-484: 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

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1760-466: The core-mantle boundary would provide a natural explanation for the time-progressive chains of older volcanoes seen extending out from some such hotspots, for example, the Hawaiian–Emperor seamount chain . However, paleomagnetic data show that mantle plumes can also be associated with Large Low Shear Velocity Provinces (LLSVPs) and do move relative to each other. The current mantle plume theory

1815-467: The core-mantle boundary. 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

1870-438: The correlation between major element compositions of OIB and their stable isotope ratios. Tholeiitic OIB is interpreted as a product of a higher degree of partial melting in particularly hot plumes, while alkali OIB is interpreted as a product of a lower degree of partial melting in smaller, cooler plumes. In 2015, based on data from 273 large earthquakes, researchers compiled a model based on full waveform tomography , requiring

1925-813: The development of nearby orogenies like the Timanide orogeny , the Uralian orogeny , the Hercynian orogeny and the Caledonian orogeny . The platform hosts numerous ancient rifts or aulacogens some of which date to the Riphean of the Proterozoic . In the Late Devonian rifting and magmatic activity occurred within the platform leading to the formation of the Dnieper-Donets Rift . This event

1980-523: 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

2035-568: The following groups: a "protoplatform" of metamorphosed sediments at the bottom, a "quasiplatform" of slightly deformed sediments, a "cataplatform", and a "orthoplatform" at the top. The Mesoproterozoic Jotnian sediments of the Baltic area are examples of a "quasiplatform". The oldest preserved continuous sedimentary cover in the platform date to the Vendian about 650 million years ago. The cycles of deposition of platform sediments are related to

2090-535: 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

2145-436: 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. Mantle plumes have been suggested as

2200-409: 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

2255-620: The plate motion. Another example is the Canary Islands in the northeast of Africa in the Atlantic Ocean. 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 elements such as uranium and thorium . Over time, helium in

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2310-412: The plume hypothesis has been challenged and contrasted with the more recent plate hypothesis ("Plates vs. Plumes"). The reason for this is that the mantle-plume hypothesis has not been suitable for making reliable predictions since its introduction in 1971 and has therefore been repeatedly adapted to observed hotspots depending on the situation. Over time, with the growing number of models, the concept of

2365-491: The sedimentary platform basement. The East European Craton has a very complex tectonic history with extensive Proterozoic and Paleozoic rifting, a large portion of which is of early deep mantle plume origin. Mantle plume A mantle plume is a proposed mechanism of convection within the Earth's mantle , hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths,

2420-463: The sense of columnar vertical features that span most of the Earth's mantle, transport large amounts of heat, and contribute to surface volcanism. 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

2475-550: 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

2530-734: 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). Many continental flood basalt events coincide with continental rifting. This

2585-425: 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

2640-411: The surface and erupts to form hotspots. 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 hotspots 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

2695-750: 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

2750-533: The theory are linear volcanic chains, noble gases , geophysical anomalies, and geochemistry . 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 hotspots with time-progressive volcanic chains behind them include Réunion ,

2805-556: The upper atmosphere is lost into space. Thus, the Earth has become progressively depleted in helium, and He is not replaced as He is. As a result, the ratio He/ He in the Earth has decreased over time. Unusually high He/ He have been observed in some, but not all, hotspots. This is explained by plumes tapping a deep, primordial reservoir in the lower mantle, where the original, high He/ He ratios have been preserved throughout geologic time. Other elements, e.g. osmium , have been suggested to be tracers of material arising from near to

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2860-480: The upper mantle and above, with an emphasis on plate tectonics as the driving force of magmatism. 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 because the plate hypothesis attributes volcanism to shallow, near-surface processes associated with plate tectonics, rather than active processes arising at

2915-457: 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

2970-590: 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. While not denying the presence of deep mantle convection and upwelling in general, the plate hypothesis holds that these processes do not result in mantle plumes, in

3025-582: Was possibly caused by a cluster of mantle plumes . East European Craton The Ural Mountains are the eastern margin of the East European Craton and mark the Late Paleozoic orogenic collision of the East European Craton with the Siberian cratons . The southern margin of the craton is where Sarmatia is buried beneath thick Phanerozoic sediments and the Alpine orogens . The intervening Late Palaeozoic Donbas Fold Belt, also known as part of

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