Kerguelen Plateau

The Kerguelen Plateau ( /ˈkɜːrɡələn/, /kərˈɡeɪlən/)[1] is an oceanic plateau and a large igneous province (LIP) located on the Antarctic Plate, in the southern Indian Ocean.[2] It is also a microcontinent and submerged continent. It is about 3,000 km (1,900 mi) to the southwest of Australia and is nearly three times the size of Japan. The plateau extends for more than 2,200 km (1,400 mi) in a northwest–southeast direction and lies in deep water.

The plateau was produced by the Kerguelen hotspot, starting with or following the breakup of Gondwana about 130 million years ago. A small portion of the plateau breaks sea level, forming the Kerguelen Islands (a French territory) plus the Heard and McDonald Islands (an Australian territory). Intermittent volcanism continues on the Heard and McDonald Islands.

KerguelenPlateau v1
Bathymetry of the Kerguelen Plateau
Orthographic projection centred over Kerguelen Island
Location of the plateau – the white spot is Kerguelen Island

Geographical extent

Symmetrically across the Indian Ocean ridge and due west of Australia is the Broken Ridge underwater volcanic plateau, which at one time was contiguous with the Kerguelen Plateau before rifting by the mid-ocean ridge.

To the north of Broken Ridge is the linear Ninety East Ridge which continues almost due north into the Bay of Bengal and is considered to be a hotspot track.

One of the largest igneous provinces (LIPs) in the world, the Kerguelen Plateau covers an area of 1,250,000 km2 (480,000 sq mi) and rises 2,000 m (6,600 ft) above the surrounding oceanic basins.[3]

Located on the Antarctic Plate, the Kerguelen Plateau is separated from Australia by the Southeast Indian Ridge (SEIR) and from Africa by the Southwest Indian Ridge (SWIR). These two ridges meet at the Rodriguez Triple Junction. It is separated from Antarctica by Princess Elizabeth Trough and the Cooperation Sea. The eastern margin north of the William Ridge is steep and formed during the breakup between the Kerguelen Plateau and the Broken Ridge. The southern part of the margin is separated from the Australian–Antarctic Basin by the deep Labuan Basin.[4]

Geological history

From the initial opening of the Indian Ocean until present, the Kerguelen hotspot has produced several now widely dispersed large-scale structures. The Southern Kerguelen Plateau (SKP) formed 119–110 Ma; the Elan Bank 108–107 Ma, named by Dennis E. Hayes of Lamont Doherty Easth Observatory}; the Central Kerguelen Plateau (CKP) 101–100 Ma; the Broken Ridge (connected to CKP before the Eocene breakup) formed 95–94 Ma; the Skiff Bank (east of Kerguelen archipelago) 69–68 Ma; Northern Kerguelen Plateau (NKP) 35–34 Ma; Ninety East Ridge formed 82–38 Ma north to south; the Bunbury Basalt (western Australia) formed at 137-130.5 Ma [5]; the Naturaliste Plateau (offshore western Australia) formed 132-128 Ma [6]; the Rajmahal Traps in northeast India 118–117 Ma; and finally lamprophyres in India and Antarctica 115–114 Ma.[7]

India–Australia breakup

The oldest volcanism that can be attributed to the Kerguelen plume are the Bunbury Basalt (137-130.5 Ma [5]) and Naturaliste Plateau (132-128 Ma [6]) in southwestern Australia, and the Rajmahal Traps in eastern India (118 Ma). The formation of the oldest portion of the Kerguelen LIP and these continental basalts are linked to the opening of the eastern Indian Ocean.[8] The Bunbury Basalt is not of flood basalt dimension which suggest that the mantle underlying the newly formed Kerguelen hotspot was neither significantly hot, wet, or voluminous. In contrast, the magmatism that produced the Australia–India breakup 136–158 Ma created the Wallaby Plateau, but no known hotspot has been linked to this event.[9]

India–Antarctica breakup

The output from the Kerguelen hotspot peaked 120–95 Ma, 12–70 Ma after the India–Antarctica breakup. No ridges or hotspot tracks such as WalvisRio Grande, Chagos–Laccadive, Greenland–Scotland have been found in the Princess Elizabeth Trough between SKP and Antarctica or along India's conjugate eastern continental margin. The relation between the Kerguelen hotspot and these continental breakup and volcanic margins is instead similar to that between the Réunion hotspot and the Deccan Traps and the breakup between western India and the Seychelles.[9]

The peak output of the Kerguelen hotspot coincides with one or several microcontinent formations, such as the Elan Bank.[9] Since the Indian Ocean began to open about 130 Ma, the Kerguelen hotspot has moved 3–10° southward and, consequently, the spreading ridge between India and Antarctica has jumped northward one or several times. Parts of the Kerguelen Plateau, the Elan Bank and the SKP, were originally attached to India and are composed of continental lithosphere. One or several ridge jumps transformed the Elan Bank into a microcontinent and dispersed continental fragments in the SKP, and these structures were eventually left behind as India moved northward.[9] The ridge jump that made the Elan Bank a microcontinent occurred after 124 Ma.[3] The development of the Southern Kerguelen Plateau (SKP) 118–119 Ma contributed to the oceanic anoxic event 1.[10]

Around 83.5 Ma sea floor spreading between India and Antarctica was asymmetric in the Kerguelen Plateau region with two-thirds of the sea floor created being added to the Antarctic Plate. A ridge jump eventually transferred parts of the Kerguelen Plateau from the Indian Plate to the Antarctic Plate.[11]

Cenozoic volcanism

The Kerguelen hotspot produced the 5,000 km (3,100 mi) long Ninety East Ridge 82–38 Ma, and geochemical evidence suggests that this occurred at or near a spreading ridge. The lack of a conjugate structure on the Antarctic Plate, however, makes it unlikely that the hotspot was located at a spreading ridge during this long period. As the Antarctic Plate then moved over the Kerguelen hotspot the NKP formed over relatively old oceanic crust. Flood basalts in the Kerguelen archipelago formed 30–24 Ma and less voluminous and more recent volcanism occurred until 1 Ma. During the last 21 Ma volcanic structures have formed on the CKP, including Heard Island, and both Heard and McDonald Islands have had recent eruptions.[9]

65 Ma, the CKP–Broken Ridge LIP was located near the Kerguelen plume and the plate boundaries of the Indian Ocean. The LIP was the product of 25 Ma of relatively high magmatic activity followed by a 40 Ma period of lower activity.[12]

Microcontinent

Schlich et al. 1971 described tilted basement blocks near the Kerguelen archipelago and was the first to identify the Kerguelen Plateau as of continental origin, in contrast to other LIPs.[3][13]

The presence of soil layers in the basalt which included charcoal and conglomerate fragments of gneiss indicate that much of the plateau was above sea level as what is termed a microcontinent for three periods between 100 million years ago and 20 million years ago.[14] (The charcoal was made by wildfires started by lightning or lava flows.) Large parts of the now submarine Southern (SKP) and Central Kerguelen Plateaus (CKP) were subaerial during the formation of the LIP. The SKP probably formed an island of 500,000 km2 (190,000 sq mi) with major peaks reaching 1,000–2,000 m (3,300–6,600 ft) above sea level.[15]

The Kerguelen microcontinent may have been covered by dense conifer forest in the mid-Cretaceous.[16]

It finally sank 20 million years ago and is now 1,000–2,000 m (3,300–6,600 ft) below sea level.[17]

Biodiversity

During the austral summer there is a high density of migratory whales including sperm, minke, and humpback whales along the southern end of the Kerguelen Plateau and the northern part of the adjacent Princess Elizabeth Trough. These whales choose this location for foraging because the Southern Front of the Antarctic Circumpolar Current is steered off by the plateau — resulting in a poleward extent for the Southern Front only found near the Kerguelen Plateau. This brings shoaled, nutrient-rich Upper Circumpolar Deep Water to the surface which brings macronutrients to the surface. Ice is additionally advected north along the eastern side of the plateau.[18]

See also

References

Notes

  1. ^ Oxford English Dictionary
  2. ^ UT Austin 1999
  3. ^ a b c Bénard et al. 2010, Introduction, pp. 1–2
  4. ^ Bénard et al. 2010, Geological and plate boundary setting, p. 2
  5. ^ a b Olierook, Hugo K.H.; Jourdan, Fred; Merle, Renaud E.; Timms, Nicholas E.; Kusznir, Nick; Muhling, Janet R. (2016-04-15). "Bunbury Basalt: Gondwana breakup products or earliest vestiges of the Kerguelen mantle plume?". Earth and Planetary Science Letters. 440: 20–32. doi:10.1016/j.epsl.2016.02.008. ISSN 0012-821X.
  6. ^ a b Direen, N. (2017). "Naturaliste Plateau: constraints on the timing and evolution of the Kerguelen Large Igneous Province and its role in Gondwana breakup" (PDF). Australian Journal of Earth Sciences. 64 (7): 851–869. doi:10.1080/08120099.2017.1367326. hdl:1912/9459.
  7. ^ Frey et al. 2003, Geochronology, p. 4
  8. ^ Ingle et al. 2004, Introduction, p. 84
  9. ^ a b c d e Frey et al. 2003, The Kerguelen Hotspot and Indian Ocean Plate Reconstructions, pp. 5–7
  10. ^ Wallace et al. 2002, 1105–1106
  11. ^ Müller, Gaina & Clark 2000, C34 Late Cretaceous (Santonian) 83.5 Ma, p. 9
  12. ^ Whittaker, Williams & Müller 2013, Abstract
  13. ^ Schlich et al. 1971, p. 2062: Toutes ces caractéristiques, épaisse série sédimentaire plus ou moins structurée avec l'ensemble inférieur lié à une tectonique de socle, importance des accidents tectonique limitant le bassin sédimentaire, sont en faveur d'une origine contintentale du plateau de Kerguelen-Heard.
  14. ^ "Leg 183 Summary: Kerguelen Plateau-Broken Ridge—A Large Igneous Province". Proceedings of the Ocean Drilling Program. 183.
  15. ^ Frey et al. 2003, Subsidence of the Kerguelen Plateau, pp. 16–17
  16. ^ Mohr, Wähnert & Lazarus 2002, Abstract
  17. ^ https://news.utexas.edu/1999/05/28/ut-austin-scientist-plays-major-role-in-study-of-underwater-micro-continent/
  18. ^ Tynan 1997, Introduction, p. 2793

Sources

External links

Coordinates: 55°12′S 76°06′E / 55.2°S 76.1°E

2007 in Antarctica

Events from the year 2007 in Antarctica

Antarctic

The Antarctic (US English , UK English or and or ) is a polar region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other island territories located on the Antarctic Plate or south of the Antarctic Convergence. The Antarctic region includes the ice shelves, waters, and all the island territories in the Southern Ocean situated south of the Antarctic Convergence, a zone approximately 32 to 48 km (20 to 30 mi) wide varying in latitude seasonally. The region covers some 20 percent of the Southern Hemisphere, of which 5.5 percent (14 million km2) is the surface area of the Antarctic continent itself. All of the land and ice shelves south of 60°S latitude are administered under the Antarctic Treaty System. Biogeographically, the Antarctic ecozone is one of eight ecozones of the Earth's land surface.

Antarctic Plate

The Antarctic Plate is a tectonic plate containing the continent of Antarctica, the Kerguelen Plateau and extending outward under the surrounding oceans. After breakup from Gondwana (the southern part of the supercontinent Pangea), the Antarctic plate began moving the continent of Antarctica south to its present isolated location causing the continent to develop a much colder climate. The Antarctic Plate is bounded almost entirely by extensional mid-ocean ridge systems. The adjoining plates are the Nazca Plate, the South American Plate, the African Plate, the Somali Plate, the Indo-Australian Plate, the Pacific Plate, and, across a transform boundary, the Scotia Plate.

The Antarctic Plate has an area of about 60,900,000 km2 (23,500,000 sq mi). It is the Earth's fifth-largest plate.

The Antarctic Plate's movement is estimated to be at least 1 cm (0.4 in) per year towards the Atlantic Ocean

Broken Ridge

Broken Ridge or Broken Plateau is an oceanic plateau in the south-eastern Indian Ocean. Broken Ridge once formed a large igneous province (LIP) together with the Kerguelen Plateau. When Australia and Antarctica started to separate, Broken Ridge and the Kerguelen Plateau got separated by the Southeast Indian Ridge. Alkalic basalt from Broken Ridge has been dated to 95 Ma.Broken Ridge stretches 1,200 km (750 mi) from the southern end of Ninety East Ridge towards the south-western corner of Australia. It is up to 400 km (250 mi) wide and reaches 1,000 m (3,300 ft) below sea level. It is separated from the Diamantina Fracture Zone on its southern side by a 3,000 m (9,800 ft) escarpment, while on the northern side the ridge slopes gently towards the abyssal Wharton Basin. The sediment cover on the ridge reaches 800 m (2,600 ft) and the Moho is found at about 20 km (12 mi). It is separated from the Naturaliste Plateau by the Dirck Hartog Ridge.

The Kerguelen LIP covered 2.3×10^6 km2 (0.89×10^6 sq mi) making it the second largest LIP on Earth (after the Ontong Java Plateau in the Pacific). Both these enormous LIPs reaches 2–4 km (1.2–2.5 mi) above the surrounding ocean floor and have a crustal thickness of 20–40 km (12–25 mi) (compared to oceanic crust typically around 7 km (4.3 mi) thick.)

The Broken Ridge and Kerguelen Plateau are now separated by 1,800 km (1,100 mi). When they broke-up, the southern flank of Broken Ridge was uplifted some 2,000 m (6,600 ft) and reached above sea level.The Kerguelen LIP has a long and complicated history, however, and is probably the least "typical" of all LIPs.

Rocks from both the Broken Ridge and the Kerguelen Plateau contain a continental component or "fingerprint". In the Early Cretaceous, the Kerguelen hotspot was split into several diapirs of various sizes, composition, and ascent rates. These separate diapirs created the Bunbury Basalt, the Southern Kerguelen Plateau, the Rajmahal Traps/Indian lamprophyres, Antarctic lamprophyres, and the Central Kerguelen Plateau/Broken Ridge. In the late Cretaceous, activity in the mantle slowed and the Kerguelen hotspot was reduced to a single plume which created the Ninety East Ridge.

120-95 Ma when the Southern and Central Kerguelen Plateau formed together with the Broken Ridge, the Kerguelen hotspot produced 1 km3 (0.24 cu mi)/year, but 95-25 Ma the output decreased to 0.1 km3 (0.024 cu mi).

Continental fragment

Continental crustal fragments, partially synonymous with microcontinents, are fragments of continents that have been broken off from main continental masses forming distinct islands, often several hundred kilometers from their place of origin. All continents are fragments; the terms "continental fragment" and "microcontinent" are usually restricted to those smaller than Australia, due to Australia being the smallest continent. They are not known to contain a craton or fragment of a craton. Continental fragments include some seamounts and underwater plateaus.

Some microcontinents are fragments of Gondwana or other ancient cratonic continents: these include Madagascar; the northern Mascarene Plateau, which includes the Seychelles; the island of Timor, etc. Other islands, such as several in the Caribbean Sea, are composed largely of granitic rock as well, but all continents contain both granitic and basaltic crust, and there is no clear dividing line between islands and microcontinents under such a definition. The Kerguelen Plateau is a large igneous province formed by a volcanic hot spot; however, it was associated with the breakup of Gondwana and was for a time above water, so it is considered a microcontinent, though not a continental fragment. Other hotspot islands such as Iceland and Hawaii are considered neither microcontinents nor continental fragments. Not all islands can be considered microcontinents: the British Isles, Sri Lanka, Borneo, and Newfoundland, for example, are each within the continental shelf of an adjacent continent, separated from the mainland by inland seas flooding its margins.

Several islands in the eastern Indonesian archipelago are considered continental fragments, although this designation is controversial. These include Sumba, Timor (Nusa Tenggara), Banggai-Sulu Islands (Sulawesi), Obi, southern Bacan, and the Buru-Seram-Ambon complex (Maluku).

Continental fragments (pieces of Pangaea smaller than Sahul)Azores Plateau

Bollons Seamount – A continental fragment seamount southeast of New Zealand

East Tasman Plateau – A submerged microcontinent south east of Tasmania

Gilbert Seamount

Jan Mayen Microcontinent – A fragment of continental crust within the oceanic part of the western Eurasian Plate northeast of Iceland

Madagascar – Island nation off the coast of Southeast Africa, in the Indian Ocean

Mascarene Plateau – A submarine plateau in the Indian Ocean, north and east of Madagascar.

Mauritia – A Precambrian microcontinent that broke away as India and Madagascar separated

Parts of Wallaby Plateau

Possibly Sumba, Timor, and other islands of eastern Indonesia; Sulawesi was formed via the subduction of a microcontinent

Rockall Plateau

Socotra – The largest of four islands of the Socotra archipelago, Yemen

South Orkney Microcontinent

Zealandia – Mostly submerged mass of continental crust containing New Zealand and New CaledoniaOther microcontinents (formed post-Pangaea)Barbados – Country in the Caribbean

Cuba, Hispaniola, Jamaica, and other granitic Caribbean islands

Kerguelen Plateau – Submerged micro-continent in the southern Indian Ocean

Early Cretaceous

The Early Cretaceous (geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 146 Ma to 100 Ma.

Elephant Spit

Elephant Spit is a 9 km long sand spit at the eastern end of subantarctic Heard Island, in the Australian territory of Heard Island and McDonald Islands, lying in the Southern Ocean on the Kerguelen Plateau about 450 km south-east of the Kerguelen Islands. The name refers to southern elephant seals, also known as sea elephants, which breed in large numbers on Heard Island and formed the basis for commercial sealing for oil there during the 19th century.

Etmopterus

Etmopterus is a genus of lantern sharks in the squaliform family Etmopteridae. They are found in deep sea ecosystems of the Atlantic, Indian and Pacific Oceans.

Flood basalt

A flood basalt is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Flood basalt provinces such as the Deccan Traps of India are often called traps, after the Swedish word trappa (meaning "stairs"), due to the characteristic stairstep geomorphology of many associated landscapes. Michael R. Rampino and Richard Stothers (1988) cited eleven distinct flood basalt episodes occurring in the past 250 million years, creating large volcanic provinces, lava plateaus, and mountain ranges. However, more have been recognized such as the large Ontong Java Plateau, and the Chilcotin Group, though the latter may be linked to the Columbia River Basalt Group. Large igneous provinces have been connected to five mass extinction events, and may be associated with bolide impacts.

Kerguelen Islands

The Kerguelen Islands ( or ; in French commonly Îles Kerguelen but officially Archipel des Kerguelen, pronounced [kɛʁɡelɛn]), also known as the Desolation Islands (Îles de la Désolation in French), are a group of islands in the Antarctic constituting one of the two exposed parts of the Kerguelen Plateau, a large igneous province mostly submerged by the southern Indian Ocean. They are among the most isolated places on Earth, located 450 km (280 mi) northwest of the uninhabited Heard Island and McDonald Islands (Australia) and more than 3,300 km (2,100 mi) from Madagascar, the nearest populated location (excluding the Alfred Faure scientific station in Île de la Possession, about 1,340 km, 830 mi from there, and the non-permanent station located in Île Amsterdam, 1,440 km, 890 mi away). The islands, along with Adélie Land, the Crozet Islands, Amsterdam and Saint Paul Islands, and France's Scattered Islands in the Indian Ocean, are part of the French Southern and Antarctic Lands and are administered as a separate district.

The main island, Grande Terre, is 6,675 km2 (2,577 sq mi) in area and is surrounded by a further 300 smaller islands and islets, forming an archipelago of 7,215 km2 (2,786 sq mi). The climate is raw and chilly with frequent high winds throughout the year. The surrounding seas are generally rough and they remain ice-free year-round. There are no indigenous inhabitants, but France maintains a permanent presence of 45 to 100 soldiers, scientists, engineers and researchers. There are no airports on the islands, so all travel and transport from the outside world is conducted by ship.

Kerguelen hotspot

The Kerguelen hotspot is a volcanic hotspot at the Kerguelen Plateau in the Southern Indian Ocean. The Kerguelen hotspot has produced basaltic lava for about 130 million years and has also produced the Kerguelen Islands, Heard Island, the McDonald Islands, and the Ninety East Ridge.

List of largest volcanic eruptions

In a volcanic eruption, lava, volcanic bombs and ash, and various gases are expelled from a volcanic vent and fissure. While many eruptions only pose dangers to the immediately surrounding area, Earth's largest eruptions can have a major regional or even global impact, with some affecting the climate and contributing to mass extinctions. Volcanic eruptions can generally be characterized as either explosive eruptions, sudden ejections of rock and ash, or effusive eruptions, relatively gentle outpourings of lava. A separate list is given below for each type.

There have probably been many such eruptions during Earth's history beyond those shown in these lists. However erosion and plate tectonics have taken their toll, and many eruptions have not left enough evidence for geologists to establish their size. Even for the eruptions listed here, estimates of the volume erupted can be subject to considerable uncertainty.

Mascarene Plateau

The Mascarene Plateau is a submarine plateau in the Indian Ocean, north and east of Madagascar. The plateau extends approximately 2,000 km (1,200 mi), from the Seychelles in the north to Réunion in the south. The plateau covers an area of over 115,000 km2 (44,000 sq mi) of shallow water, with depths ranging from 8–150 m (30–490 ft), plunging to 4,000 m (13,000 ft) to the abyssal plain at its edges. It is the second largest undersea plateau in the Indian Ocean after the Kerguelen Plateau.

Ninety East Ridge

The Ninety East Ridge (also rendered as Ninetyeast Ridge, 90E Ridge or 90°E Ridge) is a linear structure on the Indian Ocean floor named for its near-parallel strike along the 90th meridian at the center of the Eastern Hemisphere. It is approximately 5,000 kilometres (3,100 mi) in length and can be traced topographically from the Bay of Bengal southward towards the Southeast Indian Ridge (SEIR), though the feature continues to the north where it is hidden beneath the sediments of the Bengal Fan. The ridge extends between latitudes 33°S and 17°N and has an average width of 200 km.The ridge divides the Indian Ocean into the West and East Indian Ocean. The northeastern side is named the Wharton Basin and ceases at the western end of the Diamantina Fracture Zone which passes to the east and almost to the Australian continent.The ridge is primarily composed of Ocean Island Tholeiites (OIT), a subset of basalt which increase in age from approximately 43.2 ± 0.5 Ma in the south to 81.8 ± 2.6 Ma in the north though a more recent analysis using modern Ar–Ar techniques is currently pending publication. This age progression has led geologists to theorize that a hotspot in the mantle beneath the Indo-Australian Plate created the ridge as the plate has moved northward in the late Mesozoic and Cenozoic. This theory is supported by a detailed analysis of the chemistry of the Kerguelen Plateau and Rajmahal Traps, which together, geologists believe, represent the flood basalts erupted at the initiation of volcanism at the Kerguelen hotspot which was then sheared in two as the Indian subcontinent moved northward. However, the existence of so-called deep mantle hotspots is currently a topic of debate in the geologic community, with a few geochemists favoring an alternative hypothesis which postulates a much shallower origin for hotspot volcanism.The ridge has been surveyed several times in the past, including several times by the Deep Sea Drilling Program (DSDP). In 2007, the RV Roger Revelle collected bathymetric, magnetic and seismic data together with dredge samples from nine sites along the ridge as part of an Integrated Ocean Drilling Program (IODP) site survey intended to examine the hotspot hypothesis for the ridge.It had been assumed that the India and Australia are on a single tectonic plate for at least the last 32 million years. However, considering the high level of large earthquakes in the Ninety East Ridge area and the evidence of deformation in the central Indian Ocean, it is more appropriate to consider the deformed region in the central Indian Ocean as a broad plate boundary zone separating the Indian Plate and the Australian Plate.

Old World

The term 'Old World' is used commonly in the West to refer to Africa, Asia and Europe (Afro-Eurasia or the World Island), regarded collectively as the part of the world known to its population before contact with the 'New World' (the Americas and Oceania).

Southeast Indian Ridge

The Southeast Indian Ridge (SEIR) is a mid-ocean ridge in the southern Indian Ocean. A divergent tectonic plate boundary stretching almost 6,000 km (3,700 mi) between the Rodrigues Triple Junction (25°S 70°E) in the Indian Ocean and the Macquarie Triple Junction (63°S 165°E) in the Pacific Ocean, the SEIR forms the plate boundary between the Australian and Antarctic plates since the Oligocene (anomaly 13).The SEIR is the spreading centre closest to the Kerguelen and Amsterdam–Saint-Paul hotspot.

The SEIR has an intermediate full spreading rate of 65 mm/yr, and, because Antarctica is virtually stationary, this results in a northward ridge migration of half that rate.

Spreading rates along the SEIR varies from 69 mm/yr near 88°E to 75 mm/yr near 120°E.

Submerged continent

A submerged continent or sunken continent is a continental mass, extensive in size, but mainly undersea. The terminology is used by some paleogeologists and geographers in reference to some land masses.

The main examples in this class are the Kerguelen Plateau, Seychelles microcontinent, Mauritia, and Zealandia. There's also the hypothesis that the Rio Grande Rise is another sunken continent.

Submerged continents have been sought and speculated about in regard to a possible "lost continent" underwater in the Atlantic Ocean. There was also a search in the 1930s for Lemuria, believed to have possibly been a submerged continent between the Indian and African coasts.

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