Madagascar Plate

The Madagascar Plate or Madagascar block was once attached to the Gondwana supercontinent and later the Indo-Australian Plate.

Rifting in the Somali Basin began at the end of the Carboniferous 300 million years ago, as a part of the Karoo rift system. The initiation of Gondwana breakup, and transform faulting along the Davie Fracture Zone, occurred in the Toarcian (about 182 million years ago) following the eruption of the Bouvet (Karoo) mantle plume. At this time East Gondwana, comprising the Antarctic, Madagascar, Indian, and Australian plates, began to separate from the African Plate. East Gondwana then began to break apart about 115–120 million years ago when India began to move northward.[1] Between 84–95 million years ago rifting separated Seychelles and India from Madagascar.

Since its formation the Madagascar block has moved roughly in conjunction with Africa, and thus there are questions as to whether the Madagascar Plate should be still considered a separate plate.[2][3]

Assembly of Gondwana

Madagascar was formerly located in the central part of the supercontinent Gondwana. It contains part of the East African Orogen, which formed in the Neoproterozoic to Cambrian assembly of the Gondwana. This heavily influenced the geology of central and northern Madagascar.[4]

The entire island can be divided into four tectonic and geologic units:[5] the Antongil block, the Antananarivo block, the Bekily Belt in the south, and the Bemarivo Belt in the far north.

  • The Antongil Block is characterized by a 3.2 Ga gneiss intruded by granite that has undergone greenschist facies metamorphism.
  • The Antananarivo Block contains 2.5 Ga gneiss layered with younger granitoids and gabbros. It has metamorphosed to granulite facies conditions.
  • The Bemarivo Belt contains two regions, metasedimentary gneisses in the southern part and granitic domes in the north.
  • The Bekily Belt is made up of mostly sedimentary protoliths and granulite and upper amphibolite grade gneisses.

The blocks in the northern part of the island are made up of Archean cratonic material.[5] The Antongil block has been linked with the Dharwar Formation of India, however the Antananarivo block to the west has been too heavily altered to link easily to another continent.[5]

The central part of the island contains metasediments from African and Indian continental shelves. This is the Itremo Group, which also contains intrusions of material from the Antongil block. The Itremo sheet was folded in the amalgamation of Madagascar ~700 Mya, and now contains upright folds, divergent reverse faults, and strike-slip faults.[4]

Rifting

The Madagascar plate experienced two major rifting events during the break-up of Gondwana. First, it separated from Africa about 160 Mya, then from the Seychelles and India 66–90 Mya.[6]

The first rifting event, separation from Somalia and the rest of Africa, caused displacement along the Davie Ridge, in the Mozambique Channel to the west of the islands, a now extinct transform. The rifting is also associated with extensive deformation as well as volcanism in the late Cretaceous and Cenozoic (Eocene to Miocene).

The second separation caused volcanism in the southern part of the island as well as further south, such as on Marion Island.[6] The volcanism was so extensive that in the late Cretaceous Madagascar may have been entirely covered in flood basalts from volcanism associated with this second rifting event.[6] It was at this point in the end of the Cretaceous that Madagascar became entirely isolated from any other continent.

Modern tectonics

Madagascar remains seismically and volcanically active. The most seismically active area is beneath the Ankaratra Plateau in the centre of the island, which experienced magnitude 5.2 and 5.5 earthquakes in 1985 and 1991. The Aloatra-Ankay rift to the north of the plateau is also seismically active, as well as the Davie Ridge off the coast, which is an extension of the East African Rift Zone.[7]

The Ankaratra Plateau contains a major volcanic field with volcanic cones and extensive flows. It was active from the Neogene to the Quaternary. To the northwest, there are the recently active Comoro Islands, which are hypothesized to be related to a hot spot.[6]

The Madagascar plate now moves mostly in conjunction with the African plate, so some believe it should not be still considered an independent plate.[6]

References

  1. ^ Plummer, P. S., and E. R. Belle (1995), Mesozoic tectono–stratigraphic evolution of the Seychelles microcontinent, Sedimentary Geology, 96, 73–91.
  2. ^ Timothy M. Kusky; Erkan Toraman & Tsilavo Raharimahefa (2006). "The Great Rift Valley of Madagascar: An extension of the Africa–Somali diffusive plate boundary?".
  3. ^ Timothy M. Kusky; Erkan Toraman; Tsilavo Raharimahefa; Christine Rasoazanamparany (2010). "Active tectonics of the Alaotra–Ankay Graben System, Madagascar: Possible extension of Somalian–African diffusive plate boundary?". doi:10.1016/j.gr.2010.02.003.
  4. ^ a b Collins, Alan S., and Brian F. Windley. "The tectonic evolution of central and northern Madagascar and its place in the final assembly of Gondwana." The Journal of Geology 110.3 (2002): 325–339.
  5. ^ a b c Wit, Maarten J. de. "Madagascar: heads it's a continent, tails it's an island." Annual Review of Earth and Planetary Sciences 31.1 (2003): 213–248.
  6. ^ a b c d e Kusky, Timothy M., Erkan Toraman, and Tsilavo Raharimahefa. "The Great Rift Valley of Madagascar: An extension of the Africa–Somali diffusive plate boundary?." Gondwana Research 11.4 (2007): 577–579.
  7. ^ Grimison, Nina L., and Wang‐Ping Chen. "Earthquakes in the Davie Ridge‐Madagascar region and the southern Nubian‐Somalian plate boundary." Journal of Geophysical Research: Solid Earth (1978–2012) 93.B9 (1988): 10439-10450.
Blue Nile Basin

The Blue Nile Basin is a major geological formation in the northwestern Ethiopian Plateau formed in the Mesozoic Era during a period of crustal extension associated with the break-up of Gondwana, and filled with sedimentary deposits. The modern Blue Nile river cuts across part of the sedimentary basin.

Congo Basin

The Congo Basin is the sedimentary basin of the Congo River. The Congo Basin is located in Central Africa, in a region known as west equatorial Africa. The Congo Basin region is sometimes known simply as the Congo.

The basin begins in the highlands of the East African Rift system with input from the Chambeshi River, the Uele and Ubangi Rivers in the upper reaches and the Lualaba River draining wetlands in the middle reaches. Due to the young age and active uplift of the East African Rift at the headlands, the river's yearly sediment load is very large but the drainage basin occupies large areas of low relief throughout much of its area. The basin is a total of 3.7 million square kilometers and is home to some of the largest undisturbed stands of tropical rainforest on the planet, in addition to large wetlands. The basin ends where the river empties its load in the Gulf of Guinea on the Atlantic Ocean. The climate is equatorial tropical, with two rainy seasons including very high rainfalls, and high temperature year round. The basin is home to the endangered western lowland gorilla.

The basin was the watershed of the Congo River populated by pygmy peoples, and eventually Bantu peoples migrated there and founded the Kingdom of Kongo. Belgium, France, and Portugal later established colonial control over the entire region by the late 19th century. The General Act of the Berlin Conference of 1885 gave a precise definition to the "conventional basin" of the Congo, which included the entire actual basin plus some other areas. The General Act bound its signatories to neutrality within the conventional basin, but this was not respected during the First World War.

El Djouf

El Djouf (Arabic: الجوف‎) is a desert, an arid natural region of sand dunes and rock salt which covers northeastern Mauritania and part of northwestern Mali. El Djouf is a part of the Sahara Desert in the north.

A meteorite of a rare type of carbonaceous chondrite was found in el Djouf in October 1989.

Geology of Madagascar

The geology of Madagascar comprises a variety of rocks of Precambrian age which make up the larger part of the east and centre of the island. They are intruded by basalts and rhyolites of Mesozoic to Cenozoic age. In contrast, the western part of the island is formed from sedimentary rocks of Carboniferous to Quaternary age. Archean rocks occur from the northeast portion of the island down to the south in the Ranotsara shear zone. Rocks in the northern portion of Madagascar are greenstone belts, from the Archean or Paleoproterozoic age.

Iullemmeden Basin

The Iullemmeden Basin is a major sub-Saharan inland basin in West Africa, extending about 1,000 kilometres (620 mi) north to south and 800 kilometres (500 mi) east to west. It covers western Niger and portions of Algeria, Mali, Benin and Nigeria. It is named after the Iullemmeden, a federation of Tuareg people who live in the central region of Niger. Its geographic range is largely coincident with the Azawagh region.

List of tectonic plates

This is a list of tectonic plates on the Earth's surface. Tectonic plates are pieces of Earth's crust and uppermost mantle, together referred to as the lithosphere. The plates are around 100 km (62 mi) thick and consist of two principal types of material: oceanic crust (also called sima from silicon and magnesium) and continental crust (sial from silicon and aluminium). The composition of the two types of crust differs markedly, with mafic basaltic rocks dominating oceanic crust, while continental crust consists principally of lower-density felsic granitic rocks.

Niger Delta Basin (geology)

The Niger Delta Basin, also referred to as the Niger Delta province, is an extensional rift basin located in the Niger Delta and the Gulf of Guinea on the passive continental margin near the western coast of Nigeria with suspected or proven access to Cameroon, Equatorial Guinea and São Tomé and Príncipe. This basin is very complex, and it carries high economic value as it contains a very productive petroleum system. The Niger delta basin is one of the largest subaerial basins in Africa. It has a subaerial area of about 75,000 km2, a total area of 300,000 km2, and a sediment fill of 500,000 km3. The sediment fill has a depth between 9–12 km. It is composed of several different geologic formations that indicate how this basin could have formed, as well as the regional and large scale tectonics of the area. The Niger Delta Basin is an extensional basin surrounded by many other basins in the area that all formed from similar processes. The Niger Delta Basin lies in the south westernmost part of a larger tectonic structure, the Benue Trough. The other side of the basin is bounded by the Cameroon Volcanic Line and the transform passive continental margin.

Ogaden Basin

The Ogaden Basin is an area of Ogadenia that may hold significant reserves of crude oil and natural gas. The basin covers an area of some 350,000 square

kilometres (135,000 square miles) and is formed from sedimentary rocks up to 10,000 meters (6 miles) thick. It has geological similarities to other hydrocarbon-rich basins in the Middle East.

Tindouf Basin

The Tindouf Basin is a major sedimentary basin in West Africa, to the south of the little Atlas region, Morocco. It stretches from west to east about 700 kilometres (430 mi) and covers about 100,000 square kilometres (39,000 sq mi), mostly in Algeria but with a western extension into Morocco and Western Sahara.

Turkana Basin

The greater Turkana Basin in East Africa (mainly northwestern Kenya and southern Ethiopia, smaller parts of eastern Uganda and southeastern South Sudan) determines a large endorheic basin, a drainage basin with no outflow centered around the north-southwards directed Gregory Rift system in Kenya and southern Ethiopia. The deepest point of the basin is the endorheic Lake Turkana, a brackish Soda lake with a very high ecological productivity in the Gregory Rift.

A narrower definition for the term Turkana Basin is also in widespread use and means Lake Turkana and its environment within the confines of the Gregory Rift in Kenya and Ethiopia. This includes the lower Omo River valley in Ethiopia. The Basin in the narrower definition is a site of geological subsidence containing one of the most continuous and temporally well controlled fossil records of the Plio-Pleistocene with some fossils as old as the Cretaceous. Among the Basin's critical fossiliferous sites are Lothagam, Allia Bay, and Koobi Fora.

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