volcanic
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates are ...
hotspot which is responsible for the volcanic activity which forms the volcanoes in the southern
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe ...
. It is thought to have formed the island of
Tristan da Cunha
Tristan da Cunha (), colloquially Tristan, is a remote group of volcanic islands in the South Atlantic Ocean. It is the most remote inhabited archipelago in the world, lying approximately from Cape Town in South Africa, from Saint Helena ...
and the
Walvis Ridge
The Walvis Ridge (''walvis'' means whale in Dutch and Afrikaans) is an aseismic ocean ridge in the southern Atlantic Ocean. More than in length, it extends from the Mid-Atlantic Ridge, near Tristan da Cunha and the Gough Islands, to the Africa ...
on the
African Plate
The African Plate is a major tectonic plate that includes much of the continent of Africa (except for its easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plat ...
.
Geology
It is also believed to be closely connected with the Paraná and Etendeka flood basalt provinces, which formed over the hotspot during the opening of the South Atlantic Ocean.
The Tristan and Gough hotspots are widely spaced end-members of the volcanic system that generated the Walvis Ridge on the African plate and the
Rio Grande Rise
The Rio Grande Rise, also called the Rio Grande Elevation or Bromley Plateau, is an aseismic ocean ridge in the southern Atlantic Ocean off the coast of Brazil. Together with the Walvis Ridge off Africa, the Rio Grande Rise forms a V-shaped stru ...
on the South American plate beginning at when the Paraná and Etendeka traps formed. Whether or not Tristan and Gough represent two distinct volcanic centers is still debated.
argued that the Walvis Ridge is not the product of a deep mantle plume or the Tristan hotspot, but that changes in the internal stress in the spreading African and South American plates trigger changes in the magmatic processes in the Mid-Atlantic Ridge. The Walvis Ridge should then have developed as a result of these periodic stress releases along the Mid-Atlantic Ridge..
found that the hotspot trails in the eastern South Atlantic (Tristan, Gough, Discovery,
Shona
Shona often refers to:
* Shona people, a Southern African people
* Shona language, a Bantu language spoken by Shona people today
Shona may also refer to:
* ''Shona'' (album), 1994 album by New Zealand singer Shona Laing
* Shona (given name)
* ...
, and possibly Bouvet) started forming synchronously . Older
seamount
A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abr ...
s east of these hotspot trails formed at the edge of the African swell where the oceanic crust was spreading apart and are not the product of hotspot volcanism. The Tristan-Gough trail switched from forming a series of aseismic ridges to a broader line of
guyot
In marine geology, a guyot (pronounced ), also known as a tablemount, is an isolated underwater volcanic mountain (seamount) with a flat top more than below the surface of the sea. The diameters of these flat summits can exceed .
The hotspots of the eastern South Atlantic formed along the plume generation zones (PGZs) of the African large low seismic velocity province (LLSVP). LLSVPs are dense and stable structures, and most of the plumes,
kimberlite
Kimberlite is an igneous rock and a rare variant of peridotite. It is most commonly known to be the main host matrix for diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an diamond called the Star of S ...
s, and
large igneous province
A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation ...
s (LIPs) on Earth can be rotated back to the PGZs. All major African LIPs (
Karoo
The Karoo ( ; from the Afrikaans borrowing of the South Khoekhoe !Orakobab or Khoemana word ''ǃ’Aukarob'' "Hardveld") is a semi-desert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its e ...
Agulhas Agulhas (''needles'' in the Portuguese language — or ) may refer to:
* Cape Agulhas, the southernmost point of Africa
* L'Agulhas, a town near the Cape
* Cape Agulhas Lighthouse, located at the Cape
* Cape Agulhas Local Municipality, the municip ...
) formed at the PGZs of the African LLSVP but the Tristan-Gough hotspot was the only hotspot located at a spreading boundary and therefore the only African hotspot that started to form a volcanic trail.
Palaeoclimatic and evolutionary role
Based on molecular estimates, found that the ''Homo''-''Pan'' divergence occurred (in contrast to earlier estimates that suggested around 5 Ma). Arnason et al. also estimated the '' Platyrrhini''-''
Catarrhini
The parvorder Catarrhini , catarrhine monkeys, Old World anthropoids, or Old World monkeys, consisting of the Cercopithecoidea and apes (Hominoidea). In 1812, Geoffroy grouped those two groups together and established the name Catarrhini, "Old W ...
'' divergence to have occurred around and found that the latter evolved in South America before their dispersal into Africa. Arnason et al. hypothesised that the Rio Grande-Walvis Ridge system was exposed above sea level and formed a chain of islands across the South Atlantic during the
Maastrichtian
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the inter ...
and
Palaeocene
The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''palai ...
allowing the primates to disperse across the ocean. Other researchers dismiss the hypothesis of Arnason et al. instead favouring a less spectacular rafting event.
Other hints of transoceanic
island hopping
Leapfrogging, also known as island hopping, was a military strategy employed by the Allies in the Pacific War against the Empire of Japan during World War II.
The key idea is to bypass heavily fortified enemy islands instead of trying to capt ...
in the fossil record is ''
Lavocatavis
''Lavocatavis'' is an extinct genus of phorusrhacoid or "terror bird" from the Eocene of Algeria. A fossilized femur was described from the Glib Zegdou Formation in 2011 and is the only known specimen of ''Lavocatavis''. The species was desig ...
Eocene
The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', "da ...
layers in Algeria, the only one found outside South America.