Superswell

A superswell is a large area of anomalously high topography and shallow ocean regions. These areas of anomalous topography are byproducts of large upwelling of mantle material from the core–mantle boundary, referred to as superplumes.[1] Two present day superswells have been identified: the African superswell and the South Pacific superswell. In addition to these, the Darwin Rise in the south central Pacific Ocean is thought to be a paleosuperswell, showing evidence of being uplifted compared to surrounding ancient ocean topography.[2]

SuperSwellExample
The image above illustrates the interaction between superplumes and superswells.

Superplume

Data shows a dramatic increase in crustal production from 125-120 Ma. (million years) to 70 Ma, largely in East Pacific Rise areas, although the marked increase in production rates of crustal material was also seen in the Gondwana ridges, as well as in oceanic plateaus. This period of increased crustal production is interpreted as a superplume event. This "pulse" of increased crustal production peaked soon after the initial plume (between 120 Ma and 100 Ma), and then declined over the next thirty million years.[1] Along with the increase in crustal output from ridges, there is an extended period in the time frame from 125 Ma to 40 Ma where the earth's magnetic field reversal frequency declines sharply.[3] The last remnants of this superplume event are the South Pacific superswell located underneath Tahiti.[1]

Superplume mechanism of action

Superplume/superswell creation is a large upwelling of material. Normal upwellings in the mantle are a common occurrence, as it is generally accepted that these upwellings are the driving force behind mantle convection and subsequent plate motion. In the case of the upwelling in the mid-Cretaceous Period along the East Pacific Rise, its origin lies deep within the earth, near the core–mantle boundary. This conclusion is taken from the fact that the earth retained a constant field polarity at the same time that this upwelling occurred.[1]

South Africa Topography
South Africa Topography

A more current superplume/superswell is in the southern and eastern region of Africa. Seismic analysis shows a large low-shear-velocity province, which coincides with a region of upwelling of semi-liquid material which is a poor conductor of seismic waves.[4] While there are several processes at work in the formation of these high topography zones, lithospheric thinning and lithospheric heating have been unable to predict the topographic upwelling on the African plate. Dynamic topography models have, on the other hand, been able to predict this upwelling utilizing calculations of the instantaneous flow of Earth's mantle.[4]

Evidence for mid-Cretaceous superswell

Isotopic samples taken from the Pacific-Antarctic ridge basalts have disassembled the long-held belief that there was a coherent geochemical province stretching from the Australian-Antarctic discordance to the Juan de Fuca plate. Instead, samples have shown that there are instead two distinct geochemical domains above and below the Easter microplate. Measurements of the average depth of ridge axes also shows that this boundary line lies on the southeastern side of the Darwin Rise/Pacific Superswell. It was concluded that this upwelling was responsible for the disparity between the two geochemical regions.[5]

Volcanic island chain offsets by superswell activity

One of the many ways that plate motions are mapped is by using hotspot activity and volcanic island chains. It is assumed that hotspots are stable relative to the motion of the island chain, and is therefore used as a point of reference. In the case of the Marquesas Islands, an island chain in the region of the South Pacific Superswell, the age progression of the island chain is much shorter than models have predicted. Also, the path that these island chains take does not coincide with the motion of the plate.[6]

References

  1. ^ a b c d Larson, R.L. (June 1991). "Last Pulse of Earth: Evidence for a mid-Cretaceous Superplume". Geology. 19: 547. doi:10.1130/0091-7613(1991)019<0547:lpoeef>2.3.co;2.
  2. ^ McNutt, M. K. (1998). "Superswells". Reviews of Geophysics. 36 (2): 211. Bibcode:1998RvGeo..36..211M. doi:10.1029/98RG00255.
  3. ^ Kurazhkovskii, A.Yu. (2010). "The Earth's magnetic field history for the past 400 Myr". Russian Geology and Geophysics. 51: 380–386. doi:10.1016/j.rgg.2010.03.005.
  4. ^ a b Lithgow-Bertelloni, Carolina; et al. (17 September 1998). "Dynamic topography, plate driving forces and the African superswell". Nature. 395: 269–272. doi:10.1038/26212.
  5. ^ Vlaste´ lic,, I.; et al. (May 27, 1999). "Large-scale Chemical and Thermal Division of the Pacific Mantle". Nature: 345.CS1 maint: extra punctuation (link)
  6. ^ Adam, Claudia; et al. (January 11, 2014). "Geodynamic Modeling of the South Pacific Superswell". Physics of the Earth and Planetary Interiors. 229: 24–39. doi:10.1016/j.pepi.2013.12.014.
African Surface

The African Surface or African Erosion Surface is a land surface formed by erosion covering large swathes of Africa. The type area of the surface lies in South Africa where the surface was first identified as such by Lester Charles King in the mid-20th century.The term was coined by King for certain high surfaces in Southern Africa. Over the years he redefined it various times leaving some confusion not on its reality but on the matter of its precise meaning and extent. Burke and Gunnell redefined it as a composite surface. According to Guillocheau et al. (2008) the African Surface is made up by etchplains formed between 70 and 40 million years ago. In this sense the existence of parts of the African Surface at different elevations is the result of continental-scale warping due to endogenic forces.In Central Africa the African Surface can be found in uplifted position in several domes and elongated bulges between these domes and also in downwarped basins. The domes include the East African, Ethiopian, Cameroon and Angola. The Central African Atlantic Swell and the Central African Rise. Subdued regions include the Congo Basin where the African Surface lies about 300 m a.s.l. and the Turkana Gap. In the interior of Western Africa the so-called Bauxitic Surface has been identified as equivalent to the African Surface.

African superswell

The African superswell is a region including the Southern and Eastern African plateaus and the Southeastern Atlantic basin where exceptional tectonic uplift has occurred, resulting in terrain much higher than its surroundings. The average elevation of cratons is about 400–500 meters above sea level. Southern Africa exceeds these elevations by more than 500 m, and stands at over 1 km above sea level. The Southern and Eastern African plateaus show similar uplift histories, allowing them to be considered as one topographic unit. When considered this way, the swell is one of the largest topographic anomalies observed on any continent, and spans an area of over 10 million km2. Uplift extends beyond the continents into the Atlantic Ocean, where extremely shallow ocean depths are visible through bathymetric survey. The region can indeed be considered as one large swell because the bathymetric anomaly to the southwest of Africa is on the same order as the topographic anomaly of the plateaus (approximately 500 m).The superswell is a relatively recent phenomenon, probably beginning between 5 and 30 million years ago.

Agulhas Plateau

The Agulhas Plateau is an oceanic plateau located in the south-western Indian Ocean about 500 km (310 mi) south of South Africa. It is a remainder of a large igneous province (LIP), the Southeast African LIP, that formed 140 to 95 million years ago (Ma) at or near the triple junction where Gondwana broke-up into Antarctica, South America, and Africa. The plateau formed 100 to 94 Ma together with Northeast Georgia Rise and Maud Rise (now located near the Falkland Island and Antarctica respectively) when the region passed over the Bouvet hotspot.

Alaji Basalts

The Alaji (upper) Basalts are the youngest series of the Ethiopian flood basalts. The most recent flows are only 15 million years old.

Arago hotspot

Arago hotspot is a hotspot in the Pacific Ocean, presently located below the Arago seamount close to the island of Rurutu, French Polynesia.

Arago is part of a family of hotspots in the southern Pacific, which include the Society hotspot and the Macdonald hotspot among others. These are structures beneath Earth's crust which generate volcanoes and which are in part formed by mantle plumes, although Arago itself might have a shallower origin. As the Pacific plate moves over the hotspots, new volcanoes form and old volcanoes are carried away; sometimes an older volcano is carried over the hotspot and is then uplifted as happened with Rurutu.

The Arago hotspot is responsible for the formation of Arago seamount and uplift on Rurutu; however reconstructions of the past positions of tectonic plates and geochemistry suggest that other islands and seamounts were constructed by the Arago hotspot during the past 120 million years. These potentially include Tuvalu, Gilbert Islands, the Ratak Chain of the Marshall Islands as well as part of the Austral Islands and Cook Islands.

Darwin Rise

The Darwin Rise is broad triangular region in the north central Pacific Ocean where there is a concentration of atolls.

During his voyage across the globe Charles Darwin realised that vertical crustal motion must be responsible for the formation of continents and ocean basins, as well as isolated atolls in the Pacific. He deduced that the central basin of the Pacific had subsided while surrounding areas had risen. In 1964 U.S. geologist Henry Menard subsequently named the uplifted area in the Pacific after the English naturalist.

Dike swarm

A dike swarm or dyke swarm is a large geological structure consisting of a major group of parallel, linear, or radially oriented dikes intruded within continental crust. They consist of several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive event, and are magmatic and stratigraphic. Such dike swarms may form a large igneous province and are the roots of a volcanic province.

The occurrence of mafic dike swarms in Archean and Paleoproterozoic terrains is often cited as evidence for mantle plume activity associated with abnormally high mantle potential temperatures.

Dike swarms may extend over 400 km (250 mi) in width and length. The largest dike swarm known on Earth is the Mackenzie dike swarm in the western half of the Canadian Shield in Canada, which is more than 500 km (310 mi) wide and 3,000 km (1,900 mi) long.The number of known giant dike swarms on Earth is small, only about 25. However, the primary geometry of most giant dike swarms is poorly known due to their age and subsequent tectonic activity.

Dike swarms have also been found on Venus and Mars.

Dynamic topography

The term dynamic topography is used in geodynamics to refer to elevation differences caused by the flow within the Earth's mantle.

Large low-shear-velocity provinces

Large low-shear-velocity provinces, LLSVPs, also called LLVPs or superplumes, are characteristic structures of parts of the lowermost mantle (the region surrounding the outer core) of the Earth. These provinces are characterized by slow shear wave velocities and were discovered by seismic tomography of the deep Earth. There are two main provinces: the African LLSVP and the Pacific LLSVP. Both extend laterally for thousands of kilometers and possibly up to 1000 km vertically from the core-mantle boundary. The Pacific LLSVP has specific dimensions of 3000 km across and 300 m higher than the surrounding ocean-floor, and is situated over four hotspots that suggest multiple mantle plumes underneath. These zones represent around 8% of the volume of the mantle (6% of the Earth). Other names for LLSVPs include superwells, thermo-chemical piles, or hidden reservoirs. Some of these names, however, are more interpretive of their geodynamical or geochemical effects, while many questions remain about their nature.

Macdonald hotspot

The Macdonald hotspot is a volcanic hotspot in the southern Pacific Ocean. The hotspot was responsible for the formation of the Macdonald Seamount, and possibly the Austral-Cook Islands chain. It probably did not generate all of the volcanism in the Austral and Cook Islands as age data imply that several additional hotspots were needed to generate some volcanoes.

In addition to the volcanoes in the Austral Islands and Cook Islands, Tokelau, the Gilbert Islands, the Phoenix Islands and several of the Marshall Islands as well as several seamounts in the Marshall Islands may have been formed by the Macdonald hotspot.

Mantle convection

Mantle convection is the very slow creeping motion of Earth's solid silicate mantle caused by convection currents carrying heat from the interior to the planet's surface.The Earth's surface lithosphere rides atop the asthenosphere and the two form the components of the upper mantle. The lithosphere is divided into a number of plates that are continuously being created and consumed at their opposite plate boundaries. Accretion occurs as mantle is added to the growing edges of a plate, associated with seafloor spreading. This hot added material cools down by conduction and convection of heat. At the consumption edges of the plate, the material has thermally contracted to become dense, and it sinks under its own weight in the process of subduction usually at an ocean trench.This subducted material sinks through the Earth's interior. Some subducted material appears to reach the lower mantle, while in other regions, this material is impeded from sinking further, possibly due to a phase transition from spinel to silicate perovskite and magnesiowustite, an endothermic reaction.The subducted oceanic crust triggers volcanism, although the basic mechanisms are varied. Volcanism may occur due to processes that add buoyancy to partially melted mantle, which would cause upward flow of the partial melt due to decrease in its density. Secondary convection may cause surface volcanism as a consequence of intraplate extension and mantle plumes.Mantle convection causes tectonic plates to move around the Earth's surface. It seems to have been much more active during the Hadean period, resulting in gravitational sorting of heavier molten iron, nickel, and sulphides to the core and lighter silicate minerals to the mantle.

Marcia McNutt

Marcia Kemper McNutt (born February 19, 1952), ForMemRS, is an American geophysicist and the 22nd president of the National Academy of Sciences (NAS) of the United States. Previously, she served as editor-in-chief of the peer-reviewed journal Science from 2013 to 2016. McNutt holds a visiting appointment at the Scripps Institution of Oceanography. She is a member of the National Academies of Sciences, Engineering, and Medicine advisory committee for the Division on Earth and Life Studies and the Forum on Open Science. McNutt chaired the NASEM climate intervention committee who delivered two reports in 2015.McNutt was the 15th director of the United States Geological Survey (USGS) (and first woman to hold the post) as well as science adviser to the United States Secretary of the Interior. Before working for USGS, McNutt was president and chief executive officer of the Monterey Bay Aquarium Research Institute (MBARI), an oceanographic research center in the United States, professor of marine geophysics at the Stanford University School of Earth Sciences and professor of marine geophysics at University of California, Santa Cruz.

Mid-Pacific Mountains

The Mid-Pacific Mountains (MPM) is a large oceanic plateau located in the central North Pacific Ocean or south of the Hawaiian–Emperor seamount chain. Of volcanic origin and Mesozoic in age, it is located on the oldest part of the Pacific Plate and rises up to 2 km (1.2 mi) (Darwin Rise) above the surrounding ocean floor and is covered with several layers of thick sedimentary sequences that differ from those of other plateaux in the North Pacific. About 50 seamounts are distributed over the MPM. Some of the highest points in the range are above sea level which include Wake Island and Marcus Island.

The ocean floor of the MPM dates back to the Jurassic-Cretaceous, some of the oldest oceanic crust on Earth.The MPM is a range of guyots with a lava composition similar to those found in Iceland and the Galapagos Islands, and they probably formed similarly at or near a rift system.

In the Cretaceous, they formed large tropical islands located closer to the Equator that began to sink in the late Mesozoic.The MPM formed in the Early Cretaceous (at c. 110 Ma) over a hotspot that uplifted the ocean floor of the still young Pacific Plate. Reefs developed on the subsiding islands and renewed volcanism in the Late Cretaceous helped maintain some of eastern islands but inevitably the guyots sank to their present depth.

It has been proposed that the MPM has crossed over several hotspots, and the MPM guyots are indeed older on the western MPM than the eastern part, but the guyots do not form chains that can be traced to any known hotspots. The MPM, nevertheless, must have originated over the South Pacific Superswell. Among the guyots in the Mid-Pacific Mountains are Allison Guyot, Horizon Guyot, Resolution Guyot and Darwin Guyot.The western half of the Easter hotspot chain, a lineament that includes the Line Islands and Tuamotu archipelago, begins near the eastern part of the MPM. The formation of the MPM thus probably occurred at the Pacific-Farallon Ridge and the Easter hotspot, or where the Easter Microplate is now located.

Newfound Blob

Newfound Blob may refer to:

Lyman-alpha blob 1 (LAB-1), one of the first discovered Lyman-alpha blobs

Himiko (Lyman-alpha blob)

EQ J221734.0+001701, the SSA22 Protocluster

a gas cloud orbiting Sagittarius A*

the magma plume causing the African superswell

Phlegra Montes

The Phlegra Montes are a system of eroded Hesperian–Noachian-aged massifs and knobby terrain in the mid-latitudes of the northern lowlands of Mars, extending northwards from the Elysium Rise towards Vastitas Borealis for nearly 1,400 km (870 mi). The mountain ranges separate the large plains provinces of Utopia Planitia (west) and Amazonis Planitia (east), and were named in the 1970s after a classical albedo feature. The massif terrains are flanked by numerous parallel wrinkle ridges known as the Phlegra Dorsa.

The mountain ranges were first mapped against imagery taken during NASA's Viking program in the 1970s, and the area is thought to have been uplifted due to regional-scale compressive stresses caused by the contemporary formations of the Elysium and Tharsis volcanic provinces. Recent research has unveiled the presence of extensive thrust faulting bounding the massif terrains. Since the 2010s, researchers have proposed the presence of a significant late Amazonian glaciation event along the Martian northern mid-latitudes, citing the presence of lineated valley fills, lobate debris aprons, and concentric crater fills. The presence of ring mold craters imply that significant stores of water ice may continue to persist in these terrains. Features interpreted as eskers have been observed in the southern Phlegra Montes. However, whether this glaciation was localized or of regional scale remains subject to debate in the scientific community.

Phofo

Phofo is a music producer from New York (now living in Los Angeles). He is best known for composing the score for Disney's Club Penguin, Sushi Pack (a Saturday morning cartoon on CBS), the animated feature film, "Los Campeones de La Lucha Libre" (Porchlight), and Shep & Tiffany Watch TV (Bravo). Alongside MF DOOM and De La Soul's Prince Paul (producer), Phofo was responsible for producing MC Paul Barman's critically acclaimed Paullelujah! LP (Coup d'État). Phofo was a contributing writer to McSweeney's "Created in Darkness by Troubled Americans" (Knopf/Random House) and a music consultant to PRI's This American Life.

Rano Rahi seamounts

Rano Rahi (Rapa Nui: "Many volcanoes") is a field of seamounts in the Pacific Ocean. These seamounts in part form a series of ridges on the Pacific Plate pointing away from the neighbouring East Pacific Rise and which were volcanically active until about 230,000 years ago, and possibly even more recently.

The origin of these seamounts is unclear. Proposals include the effect of tectonic forces on the Pacific Plate and the presence of mantle flow towards the East Pacific Rise.

Rarotonga hotspot

The Rarotonga hotspot is a volcanic hotspot in the southern Pacific Ocean. The hotspot was responsible for the formation of Rarotonga and some volcanics of Aitutaki.

In addition to these volcanoes in the Cook Islands, the composition of volcanic rocks in Samoa and in the Lau Basin may have been influenced by the Rarotonga hotspot, and some atolls and seamounts in the Marshall Islands may have formed on the hotspot as well.

Tarava seamounts

The Tarava seamounts are a group of seamounts in the southern Pacific Ocean, southwest of the Society Islands. They are formed by five guyots and a number of cone-shaped seamounts. Of Eocene-Oligocene age, they may have formed under the influence of a hotspot.

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