Mascarene Plateau

Early Jurassic breakup of Gondwana (left) and A- Early Cretaceous, B- Late Cretaceous, C-Paleocene, D- Present Day (right)

Early Jurassic breakup of Gondwana
Gondwana breakup

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.[1] It is the second largest undersea plateau in the Indian Ocean after the Kerguelen Plateau.

Coordinates: 12°S 61°E / 12°S 61°E

Mascarene Plateau topography
Topography of the plateau

Geography

The northern part of the Mascarene plateau includes the Seychelles and Agaléga Islands. The southern part of the Mascarene plateau includes the Mascarene Islands, Saya de Malha Bank, Nazareth Bank, Soudan Banks, and Hawkins Bank. The Mascarene Islands are the mountainous islands of Mauritius, Réunion, Rodrigues, and the Cargados Carajos Shoals.

Geology

The Indian subcontinent was at one time next to the east coast of the Seychelles, but seafloor spreading has moved the landmass to its current position, where it has collided and fused with the continent of Asia.

The northern part of the Mascarene plateau is formed of granite, and is a fragment of the ancient supercontinent of Gondwana. The granite is topped with deposits of limestone and basalt. The basalt deposits in the Seychelles are from the Deccan Traps eruption, which occurred in the central part of the Indian subcontinent 66 million years ago, at the end of the Cretaceous period.

The southern part of the Mascarene plateau, also known as Southern Mascarene plateau (SMP), was formed by the Réunion volcanic hotspot along with the Chagos-Laccadive Ridge.[2] The banks and shoals of the southern part of the Mascarene plateau were once volcanic islands, much like Mauritius and Réunion, which have now sunk or eroded to below sea level or, in the case of the Cargados Carajos, to low coral islands. The Saya de Malha Bank formed 35 million years ago, and the Nazareth Bank and the Cargados Carajos shoals formed later. Limestone banks found on the plateau are the remnants of coral reefs, indicating that the plateau was once a succession of islands. Some of the banks may have been islands as recently as 18,000–6,000 years ago, when sea levels were up to 130 meters lower during the most recent ice age. Mauritius formed 8–10 million years ago, and Rodrigues and Réunion formed around two million years ago. Piton de la Fournaise volcano on Réunion is one of the most active volcanoes in the world.

See also

References

  1. ^ Encyclopædia Britannica (2010). "Seychelles-Mauritius Plateau". Encyclopædia Britannica Online. Retrieved 27 June 2010.
  2. ^ Ashalatha, B.; Subrahmanyam, C.; Singh, R. N. (1991). "Origin and compensation of Chagos-Laccadive ridge, Indian ocean, from admittance analysis of gravity and bathymetry data". Earth and Planetary Science Letters. 105 (1–3): 47–54. doi:10.1016/0012-821X(91)90119-3.

External links

Central Indian Ridge

The Central Indian Ridge (CIR) is a north-south-trending mid-ocean ridge in the western Indian Ocean.

Chryseofusus

Chryseofusus is a genus of sea snails, marine gastropod mollusks in the family Fasciolariidae, the spindle snails, the tulip snails and their allies.Originally a subgenus of Fusinus, Chryseofusus was raised to the rank of genus by Callomon & Snyder, 2009

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

Geography of Seychelles

The Seychelles is a small island nation located in the Somali sea northeast of Madagascar and about 835 mi (1,344 km) from Mogadishu, Somalia, its nearest foreign mainland city, while Antsiranana is the nearest foreign city overall. Seychelles lies between approximately 4ºS and 10ºS and 46ºE and 54ºE. The nation is an archipelago of 115 tropical islands, some granite and some coral. the majority of which are small and uninhabited. The landmass is only 452 km2 (175 sq mi), but the islands are spread wide over an Exclusive Economic Zone of 1,336,559 km2 (516,048 sq mi). About 90 percent of the population of 90,000 live on Mahé, 9 percent on Praslin and La Digue. Around a third of the land area is the island of Mahé and a further third the atoll of Aldabra.

There are two distinct regions, the granitic islands, the world's only oceanic islands of granitic rock and the coralline outer islands. The granite islands are the world’s oldest ocean islands, while the outer islands are mainly very young, though the Aldabra group and St Pierre (Farquhar Group) are unusual, raised coral islands that have emerged and submerged several times during their long history, the most recent submergence dating from about 125,000 years ago

Geology of Réunion

Réunion is a mafic island formed as a result of the Réunion hotspot in the Indian Ocean, the same hotspot that produced the massive basalt flows of the Deccan Traps, when it was beneath India more than 66 million years ago.

Granitic Seychelles

The Granitic Seychelles are the islands in the Seychelles which lie in central position on the Seychelles Bank and are composed of granite rock. They make up the majority of the Inner Islands, which in addition include the coral islands along of the rim of the Seychelles Bank, namely Bird Island and Denis Island.

There are mafic xenolith intrusions in the granite in some areas. The Granitic Seychelles are fragments of the ancient supercontinent of Gondwana, and have been separated from other continents for 75 million years. The Granitic Seychelles form the northernmost part of the Mascarene Plateau. Mahé is the largest and tallest island in the Seychelles, at 145 square km and up to 905 m elevation.

The Granitic Seychelles contrast with the Coralline Seychelles or Outer Islands, several island groups made up of low coral islands with dry, infertile soils.

The Granitic Seychelles are home to tropical moist forests, with several endemic species, including the coco de mer (Lodoicea maldivica), and the jellyfish tree (Medusagyne oppositifolia).

There are 42 granitic islands, in descending order of size: Mahé, Praslin, Silhouette, La Digue, Curieuse, Félicité, Frégate, Ste. Anne, North, Cerf, Marianne, Grand Sœur, Thérèse, Aride, Conception, Petite Sœur, Cousin, Cousine, Long, Récif, Round (Praslin), Anonyme, Mamelles, Moyenne, Ile aux Vaches Marines, L'Islette, Beacon (Ile Sèche), Cachée, Cocos, Round (Mahé), L'Ilot Frégate, Booby, Chauve Souris (Mahé), Chauve Souris (Praslin), Ile La Fouche, Hodoul, L'Ilot, Rat, Souris, St. Pierre (Praslin), Zavé, Harrison Rocks (Grand Rocher).

Hawkins Bank

Hawkins Bank is a large, submerged bank off the Mascarene Plateau. It is considered a dependency of Mauritius (in terms of fishing banks, much like Saya de Malha Bank, Nazareth Bank and the Soudan Banks). The bank is abundant with fish and Mauritian vessels often fish in the waters in and around the bank.

Janthina exigua

Janthina exigua, also known as the dwarf janthina, is a species of small holoplanktonic sea snail, a marine gastropod mollusk in the family Epitoniidae , the violet snails or purple storm snails.

Mascarene Islands

The Mascarene Islands (English: , French: Mascareignes) or Mascarenes or Mascarenhas Archipelago is a group of islands in the Indian Ocean east of Madagascar consisting of Mauritius, Réunion and Rodrigues. Their name derives from the Portuguese navigator Pedro Mascarenhas, who first visited them in April 1512. The islands share a common geologic origin in the volcanism of the Réunion hotspot beneath the Mascarene Plateau and form a distinct ecoregion with a unique flora and fauna.

Mascarenichthys

Mascarenichthys is a genus of viviparous brotulas. They have mostly been collected from the region of Mascarene Plateau in the Indian Ocean and this is referred to in their generic name.

Mascaromyia

Mascaromyia is a genus of fly in the family Dolichopodidae. It is named after the main distribution of the genus, the islands of the submarine Mascarene Plateau, combining it with "myia" (the Greek word for fly).

Nazareth Bank

Nazareth Bank is a large submerged bank in the Indian Ocean.

Réunion hotspot

The Réunion hotspot is a volcanic hotspot which currently lies under the island of Réunion in the Indian Ocean. The Chagos-Laccadive Ridge and the southern part of the Mascarene Plateau are volcanic traces of the Réunion hotspot.The hotspot is believed to have been active for over 65 million years. A huge eruption of this hotspot 65 million years ago is thought to have laid down the Deccan Traps, a vast bed of basalt lava that covers part of central India, and opened a rift which separated India from the Seychelles Plateau. The Deccan Traps eruption coincided roughly with the nearly antipodal Chicxulub impactor and the Cretaceous–Paleogene extinction of the dinosaurs, and there is considerable speculation that the three events were related. As the Indian plate drifted north, the hotspot continued to punch through the plate, creating a string of volcanic islands and undersea plateaux. The Laccadive Islands, the Maldives, and the Chagos Archipelago are atolls resting on former volcanoes created 60–45 million years ago that subsequently submerged below sea level. About 45 million years ago the mid-ocean rift crossed over the hotspot, and the hotspot passed under the African Plate.

The hotspot appears to have been relatively quiet 45–10 million years ago, when activity resumed, creating the Mascarene Islands, which include Mauritius, Réunion, and Rodrigues. Mauritius and Rodrigues Ridge were created 8–10 million years ago, and Rodrigues and Réunion Islands in the last two million years. Piton de la Fournaise, a shield volcano on the southeastern corner of Réunion, is one of the most active volcanoes in the world, erupting last in February 2019.

Saurida

Saurida is a genus of fish in the family Synodontidae.

Saya de Malha Bank

The Saya de Malha Bank (also Sahia de Malha Bank, Modern Portuguese: saia de malha, English mesh skirt) is the largest submerged ocean bank in the world, part of the vast undersea Mascarene Plateau.

Semicassis bondarevi

Semicassis bondarevi is a species of marine gastropod in the family Cassidae, endemic to the submarine Mascarene Plateau (primarily the Saya de Malha Bank) and southern Mozambique.

Somali Plate

The Somali Plate is a minor tectonic plate, which straddles the equator in the eastern hemisphere. It is approximately centered on the island of Madagascar and includes about half of the East coast of Africa, from the Gulf of Aden in the North through the East African Rift Valley. The southern boundary with the Nubian-African Plate is a diffuse plate boundary consisting of the Lwandle Plate.

Soudan Banks

The Soudan Banks are a group of underwater high points and reefs off the coast of Africa, known for their good fishing yields as fishing banks. They are administered by Mauritius. The five banks (actually a single feature) lie on the Mascarene plateau. North Soudan contains large salmon stocks. South Soudan is the largest of the banks, with many reefs and passes. West Soudan is small, rocky, and shallow, and is the least fished of the banks. Central Soudan is the most fished area, with huge reefs and open waters containing a huge abundance of fish. East Soudan, until the 1970s, was considered to be a completely different formation altogether, since it is located more than 100 miles away from the other banks. The other banks are closely linked, separated by small shallows or channels.

Two million years ago, Soudan was a large island, as were Nazareth, Cargados Carajos and Saya de Malha. These islands were more than ten times the size of Mauritius and Reunion. However, they have submerged under the ocean, apart from some small islands in the Cargados Carajos.

St. Brandon

Saint Brandon, also known as the Cargados Carajos Shoals, is an Indian Ocean archipelago about 430 kilometres (270 mi) northeast of Mauritius consisting of a number of sand banks, shoals and islets. Saint Brandon consists of five island groups, with about 28–40 islands and islets in total, depending on seasonal storms and related sand movements. There are 22 named islands and shoals. The archipelago is low-lying and is prone to substantial submersion in severe weather. It has an aggregate land area estimated variously at 1.3 km2 (0.50 sq mi) and 500 acres (2.0 km2). Economic activity in the region is limited to fishing on the very extensive shallow bank covering approximately 900 sq mi (2,300 km2) around the islands. By the early 19th century, most of the islands were in use as fishing stations. Geographically, the archipelago is part of the Mascarene Islands and is situated on the Mascarene Plateau formed by the separation of the Mauritia microcontinent during the separation of India and Madagascar about 60 million years ago.

Politically, Saint Brandon is part of the territory of Mauritius and is grouped within the Outer Islands of Mauritius along with Agaléga, Tromelin (sovereignty disputed with France) and the Chagos Archipelago (sovereignty disputed with Britain), including Diego Garcia. The Outer Islands are defined as "all the islands comprised in the State of Mauritius other than the Islands of Mauritius and Rodrigues". They are administered from Port Louis by the Outer Island Development Corporation (OIDC), which is responsible for their management and development and reports to the prime minister's office. Under a judgment by the Judicial Committee of the Privy Council on 30 July 2008, 13 of the outer islands were deemed to have been a permanent grant to the Raphael Fishing Company Ltd.The reef measures more than 50 kilometres (31 mi) from north to south, and is 5 kilometres (3.1 mi) wide, cut by three passes. The reef area is 190 km2 (73 sq mi). The islands have a small transient population, mostly fishermen, counted at 63 people on census night in 2001. The bulk of this transitory population, approximately 40 people, live on Île Raphael, with smaller settlements existing on Avocaré, Coco, and Île du Sud. A settlement on Albatross Island was abandoned in 1988. The islands are rich in marine flora and fauna, but on some islands the latter have been severely affected by the uncontrolled presence of rats.

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