Mid-Atlantic Ridge

The Mid-Atlantic Ridge (MAR) is a mid-ocean ridge, a divergent tectonic plate or constructive plate boundary located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. In the North Atlantic, it separates the Eurasian and North American plates, and in the South Atlantic, it separates the African and South American plates. The ridge extends from a junction with the Gakkel Ridge (Mid-Arctic Ridge) northeast of Greenland southward to the Bouvet Triple Junction in the South Atlantic. Although the Mid-Atlantic Ridge is mostly an underwater feature, portions of it have enough elevation to extend above sea level. The section of the ridge that includes Iceland is known as the Reykjanes Ridge. The ridge has an average spreading rate of about 2.5 centimetres (0.98 in) per year.[1]

Atlantic bathymetry
A bathymetric map of the Mid-Atlantic Ridge

Discovery

Pangea animation 03
Pangaea's separation animated

A ridge under the Atlantic Ocean was first inferred by Matthew Fontaine Maury in 1850. The existence of the ridge was discovered during the expedition of HMS Challenger in 1872.[2] A team of scientists on board, led by Charles Wyville Thomson, discovered a large rise in the middle of the Atlantic while investigating the future location for a transatlantic telegraph cable.[3] The existence of such a ridge was confirmed by sonar in 1925[4] and was found to extend around Cape Agulhas into the Indian Ocean by the German Meteor expedition.[5]

In the 1950s, mapping of the Earth's ocean floors by Bruce Heezen, Maurice Ewing, Marie Tharp and others revealed that the Mid-Atlantic Ridge had a strange bathymetry of valleys and ridges,[6] with its central valley being seismologically active and the epicenter of many earthquakes.[7][8] Ewing, Heezen and Tharp discovered that the ridge is part of a 40,000-km-long essentially continuous system of mid-ocean ridges on the floors of all the Earth's oceans.[9] The discovery of this worldwide ridge system led to the theory of seafloor spreading and general acceptance of Wegener's theory of continental drift and expansion in the modified form of plate tectonics. The ridge is central to the breakup of the hypothetical supercontinent of Pangaea that began some 180 million years ago.

Notable features

In Iceland the Mid-Atlantic Ridge passes across the Þingvellir National Park, a popular destination for tourists

Iceland Mid-Atlantic Ridge Fig16
Iceland mid atlantic ridge

The Mid-Atlantic Ridge includes a deep rift valley that runs along the axis of the ridge along nearly its entire length. This rift marks the actual boundary between adjacent tectonic plates, where magma from the mantle reaches the seafloor, erupting as lava and producing new crustal material for the plates.

Near the equator, the Mid-Atlantic Ridge is divided into the North Atlantic Ridge and the South Atlantic Ridge by the Romanche Trench, a narrow submarine trench with a maximum depth of 7,758 m (25,453 ft), one of the deepest locations of the Atlantic Ocean. This trench, however, is not regarded as the boundary between the North and South American Plates, nor the Eurasian and African Plates.

Islands

The islands on or near the Mid-Atlantic Ridge, from north to south, with their respective highest peaks and location, are:

Northern Hemisphere (North Atlantic Ridge):

  1. Jan Mayen (Beerenberg, 2277 m (at 71°06′N 08°12′W / 71.100°N 8.200°W), in the Arctic Ocean
  2. Iceland (Hvannadalshnúkur at Vatnajökull, 2109.6 m (at 64°01′N 16°41′W / 64.017°N 16.683°W), through which the ridge runs
  3. Azores (Ponta do Pico or Pico Alto, on Pico Island, 2351 m, (at 38°28′0″N 28°24′0″W / 38.46667°N 28.40000°W)
  4. Saint Peter and Paul Rocks (Southwest Rock, 22.5 m, at 00°55′08″N 29°20′35″W / 0.91889°N 29.34306°W)

Southern Hemisphere (South Atlantic Ridge):

  1. Ascension Island (The Peak, Green Mountain, 859 m, at 07°59′S 14°25′W / 7.983°S 14.417°W)
  2. Saint Helena (Diana's Peak, 818 m at 15°57′S 5°41′W / 15.950°S 5.683°W)
  3. Tristan da Cunha (Queen Mary's Peak, 2062 m, at 37°05′S 12°17′W / 37.083°S 12.283°W)
  4. Gough Island (Edinburgh Peak, 909 m, at 40°20′S 10°00′W / 40.333°S 10.000°W)
  5. Bouvet Island (Olavtoppen, 780 m, at 54°24′S 03°21′E / 54.400°S 3.350°E)

Geology

Expl2286 - Flickr - NOAA Photo Library
Basaltic rocks of the MAR collected by the Hercules ROV during the 2005 Lost City Expedition.
For a general explanation of mid-oceanic ridges, see mid-oceanic ridge and seafloor spreading

The ridge sits atop a geologic feature known as the Mid-Atlantic Rise, which is a progressive bulge that runs the length of the Atlantic Ocean, with the ridge resting on the highest point of this linear bulge. This bulge is thought to be caused by upward convective forces in the asthenosphere pushing the oceanic crust and lithosphere. This divergent boundary first formed in the Triassic period, when a series of three-armed grabens coalesced on the supercontinent Pangaea to form the ridge. Usually, only two arms of any given three-armed graben become part of a divergent plate boundary. The failed arms are called aulacogens, and the aulacogens of the Mid-Atlantic Ridge eventually became many of the large river valleys seen along the Americas and Africa (including the Mississippi River, Amazon River and Niger River). The Fundy Basin on the Atlantic coast of North America between New Brunswick and Nova Scotia in Canada is evidence of the ancestral Mid-Atlantic Ridge.[10][11]

See also

References

  1. ^ USGS (5 May 1999). "Understanding plate motions". Retrieved 13 March 2011.
  2. ^ Hsü, Kenneth J. (1992). Challenger at Sea: A Ship That Revolutionized Earth Science. Princeton University Press. p. 57. ISBN 978-0-691-08735-1.
  3. ^ Redfern, R.; 2001: Origins, the Evolution of Continents, Oceans and Life, University of Oklahoma Press, ISBN 1-84188-192-9, p. 26
  4. ^ Alexander Hellemans and Brian Bunch, 1989, Timeline of Science, Sidgwick and Jackson, London
  5. ^ Stein, Glenn, A Victory in Peace: The German Atlantic Expedition 1925–27, June 2007
  6. ^ Ewing, W.M.; Dorman, H.J.; Ericson, J.N.; Heezen, B.C. (1953). "Exploration of the northwest Atlantic mid-ocean canyon". Bulletin of the Geological Society of America. 64 (7): 865–868. doi:10.1130/0016-7606(1953)64[865:eotnam]2.0.co;2.
  7. ^ Heezen, B. C.; Tharp, M. (1954). "Physiographic diagram of the western North Atlantic". Bulletin of the Geological Society of America. 65: 1261.
  8. ^ Hill, M.N.; Laughton, A.S. (1954). "Seismic Observations in the Eastern Atlantic, 1952". Proceedings of the Royal Society of London A: Mathematical and Physical Sciences. 222 (1150): 348–356. doi:10.1098/rspa.1954.0078.
  9. ^ Spencer, Edgar W. (1977). Introduction to the Structure of the Earth (2nd ed.). Tokyo: McGraw-Hill. ISBN 978-0-07-085751-3.
  10. ^ Burke, K.; Dewey, J. F. (1973). "Plume-generated triple junctions: key indicators in applying plate tectonics to old rocks" (PDF). The Journal of Geology. 81 (4): 406–433. doi:10.1086/627882. JSTOR 30070631.
  11. ^ Burke, K. (1976). "Development of graben associated with the initial ruptures of the Atlantic Ocean". Tectonophysics. 36 (1–3): 93–112. CiteSeerX 10.1.1.473.8997. doi:10.1016/0040-1951(76)90009-3.

Bibliography

External links

Aegir Ridge

The Aegir Ridge is an extinct segment of the Mid-Atlantic Ridge in the far-northern Atlantic Ocean. It marks the initial break-up boundary between Greenland and Norway, along which seafloor spreading was initiated at the beginning of the Eocene epoch to form the northern Atlantic Ocean. Towards the end of the Eocene, the newly forming Kolbeinsey Ridge propagated northwards from Iceland, splitting the Jan Mayen Microcontinent away from the Greenland Plate. As the Kolbeinsey Ridge formed, so activity on the Aegir Ridge reduced, ceasing completely at the end of the Oligocene epoch when the Kolbeinsey Ridge reached the Jan Mayen Fracture Zone.The relatively thin crust and short lifespan of the Aegir Ridge is anomalous given its proximity to the Iceland hotspot. Mantle hotspots deliver warm, actively-upwelling material to mid-ocean ridges, increasing mantle melting and crustal production. Likely, the stresses associated with plate tectonics and the mechanical structure of the lithosphere created a situation in which spreading at the Kolbeinsey Ridge was energetically favorable to spreading at the Aegir Ridge. As the Kolbeinsey Ridge began rifting, hotspot material would then draw out of the Aegir Ridge and flow preferentially towards the Kolbeinsey Ridge, leading to the ultimate extinction of the spreading center.

Atlantis Massif

The Atlantis Massif is a prominent undersea massif in the North Atlantic Ocean. It is a dome-shaped region approximately 10 miles (16 km) across and rising about 14,000 feet (4,267 m) from the sea floor. It is located at approximately 30°8′N latitude 42°8′W longitude; just east of the intersection of the Mid-Atlantic Ridge with the Atlantis Transform Fault. The highest point of the massif is around 700 metres (2,297 ft) beneath the surface.

It is believed that the massif was formed underneath the nearby Mid-Atlantic Ridge, but pulled from underneath the ridge during the movement of the plates, about 1.5 to 2 million years ago. Geologic studies of the massif have indicated that it is not composed of the black basalt typical of the ocean floor, but rather of dense green peridotite usually found in the mantle. The central dome is corrugated and striated in a way that is representative of an exposed ultramafic oceanic core complex.

An expedition to the area in 1996 made an important advance in the study of the ocean floor. It found that a steeply sloping detachment fault is associated with the oceanic core complex structure. The dome was caused by mantle material being extruded to the surface. Another expedition discovered the Lost City hydrothermal field near the summit of the ridge in 2000.

Another expedition in 2016, the IODP 357 expedition, targeted this massif, drilling cores.

Azores Plateau

The Azores Plateau or Azores Platform is an oceanic plateau encompassing the Azores archipelago and the Azores Triple Junction in the North Atlantic Ocean. It was formed by the Azores hotspot 20 million years ago and is still associated with active volcanism.The plateau consists of a roughly triangular-shaped large igneous province that lies less than 2,000 m (6,600 ft) below sea level.

Azores Triple Junction

The Azores Triple Junction (ATJ) is a geologic triple junction where the boundaries of three tectonic plates intersect: the North American Plate, the Eurasian Plate and the African Plate. This triple junction is located along the Mid-Atlantic Ridge (MAR) amidst the Azores islands, nearly due west of the Strait of Gibraltar. It is classed as a R-R-R triple junction of the T type (for its shape), as it is an intersection of the Mid-Atlantic Ridge running north-south and the Terceira Rift which runs east-southeast.

The spreading rate along the MAR does not change abruptly at the ATJ, instead decreasing from 22.9±0.1 mm/yr at 40°N to 19.8±0.2 mm/yr at 38°N. This means the ATJ is not a simple triple junction where three tectonic plates meet at a point. The transitional range of spreading rates instead indicates the presence of a microplate, commonly referred to as the Azores microplate, although the observed behaviour can also be explained in terms of a diffuse boundary. Its northern boundary intersects the MAR between 39.4°N and 40.0°N and its southern between 38.2°N and 38.5°N.

The microplate moves about 2 mm/yr east-northeast along its Nubian boundary.

Bouvet Island

Bouvet Island (Norwegian: Bouvetøya or Bouvet-øya, Urban East Norwegian: [bʊˈveːœʏɑ]) is an uninhabited subantarctic high island and dependency of Norway located in the South Atlantic Ocean at 54°25′S 3°22′E, thus locating it north of and outside the Antarctic Treaty System. It lies at the southern end of the Mid-Atlantic Ridge and is the most remote island in the world, approximately 1,700 kilometres (1,100 mi) north of the Princess Astrid Coast of Queen Maud Land, Antarctica, 1,160 kilometres (720 mi) east of the South Sandwich Islands and 2,600 kilometres (1,600 mi) south-southwest of the coast of South Africa.

The island has an area of 49 square kilometres (19 sq mi), of which 93 percent is covered by a glacier. The centre of the island is an ice-filled crater of an inactive volcano. Some skerries and one smaller island, Larsøya, lie along the coast. Nyrøysa, created by a rock slide in the late 1950s, is the only easy place to land and is the location of a weather station.

The island was first spotted on 1 January 1739 by Frenchman Jean-Baptiste Charles Bouvet de Lozier, on a French exploration mission in the South Atlantic with the ships Aigle and Marie. They did not make a landfall, and he mislabeled the coordinates for the island and the island was not sighted again until 1808, when the British whaler captain James Lindsay named it Lindsay Island. The first claim of landing, although disputed, was by American sailor Benjamin Morrell. In 1825, the island was claimed for the British Crown by George Norris, who named it Liverpool Island. He also reported Thompson Island as nearby, although this was later shown to be a phantom island. The first Norvegia expedition landed on the island in 1927 and claimed it for Norway. At this time the island was named Bouvet Island, or "Bouvetøya" in Norwegian. After a dispute with the United Kingdom, it was declared a Norwegian dependency in 1930. It became a nature reserve in 1971.

Bouvet Triple Junction

The Bouvet Triple Junction is a geologic triple junction of three tectonic plates located on the seafloor of the South Atlantic Ocean. It is named after Bouvet Island, which lies 275 kilometers to the east. The three plates which meet here are the South American Plate, the African Plate, and the Antarctic Plate. The Bouvet Triple Junction is an R-R-R type, that is, the three plate boundaries which meet here are mid-ocean ridges: the Mid-Atlantic Ridge (MAR), the Southwest Indian Ridge (SWIR), and the South American-Antarctic Ridge (SAAR).

Eurasian Plate

The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia. It also includes oceanic crust extending westward to the Mid-Atlantic Ridge and northward to the Gakkel Ridge.

The eastern side is a boundary with the North American Plate to the north and a boundary with the Philippine Sea Plate to the south and possibly with the Okhotsk Plate and the Amurian Plate. The southerly side is a boundary with the African Plate to the west, the Arabian Plate in the middle and the Indo-Australian Plate to the east. The westerly side is a divergent boundary with the North American Plate forming the northernmost part of the Mid-Atlantic Ridge, which is straddled by Iceland. All of the volcanic eruptions in Iceland, such as the 1973 eruption of Eldfell, the 1783 eruption of Laki, and the 2010 eruption of Eyjafjallajökull, are caused by the North American and the Eurasian Plates moving apart, which is a result of divergent plate boundary forces.

The geodynamics of central Asia is dominated by the interaction between the Eurasian and Indian Plates. In this area, many subplates or crust blocks have been recognized, which form the Central Asian and the East Asian transit zones.

Hydrothermal vents and seamounts of the Azores

The hydrothermal vents and seamounts of the Azores (Portuguese: fontes hidrotermais e montes submarinos dos Açores) are a series of Atlantic seamounts and hydrothermal vents that are part of the Mid-Atlantic Ridge system, giving rise to the archipelago and bathymetric region of the Azores. These geological structures, formed from masses of basalt (typical of mid-ocean regions), are of a geomorphological interest due to their rich deposits of ore. In addition it fosters a rich ecosystem of diverse subaquatic plant and animal life. There are food chains within this environment, for example, that are purely chemosynthetic, and do not need sunlight for photosynthesis.

Iceland hotspot

The Iceland hotspot is a hotspot which is partly responsible for the high volcanic activity which has formed the Iceland Plateau and the island of Iceland.

Iceland is one of the most active volcanic regions in the world, with eruptions occurring on average roughly every three years (in the 20th century there were 39 volcanic eruptions on and around Iceland). About a third of the basaltic lavas erupted in recorded history have been produced by Icelandic eruptions. Notable eruptions have included that of Eldgjá, a fissure of Katla, in 934 (the world's largest basaltic eruption ever witnessed), Laki in 1783 (the world's second largest), and several eruptions beneath ice caps, which have generated devastating glacial bursts, most recently in 2010 after the eruption of Eyjafjallajökull.

Iceland's location astride the Mid-Atlantic Ridge, where the Eurasian and North American Plates are moving apart, is partly responsible for this intense volcanic activity, but an additional cause is necessary to explain why Iceland is a substantial island while the rest of the ridge mostly consists of seamounts, with peaks below sea level.

As well as being a region of higher temperature than the surrounding mantle, it is believed to have a higher concentration of water. The presence of water in magma reduces the melting temperature, which may also play a role in enhancing Icelandic volcanism.

Kolbeinsey Ridge

The Kolbeinsey Ridge is a segment of the Mid-Atlantic Ridge located to the north of Iceland in the Arctic Ocean. It is bounded to the south by the Tjörnes Fracture Zone, which connects the submarine ridge to the on-shore Northern Volcanic Zone rifting center in eastern Iceland. The volcanic islands Kolbeinsey and Grímsey lie along the Kolbeinsey Ridge.

List of airports in Iceland

This is a list of airports in Iceland, sorted by location.

Iceland (Icelandic: Ísland) is a European island country located in the North Atlantic Ocean on the Mid-Atlantic Ridge. It has a population of about 320,000 and a total area of 103,000 km2 (39,769 sq mi). The capital and largest city is Reykjavík.

Mid-ocean ridge

A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of ~ 2,600 meters (8,500 ft) and rises about two kilometers above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a divergent plate boundary. The rate of seafloor spreading determines the morphology of the crest of the mid-ocean ridge and its width in an ocean basin. The production of new seafloor and oceanic lithosphere results from mantle upwelling in response to plate separation. The melt rises as magma at the linear weakness in the oceanic crust, and emerges as lava, creating new crust and lithosphere upon cooling. The Mid-Atlantic Ridge is a spreading center that bisects the North and South Atlantic basins; hence the origin of the name 'mid-ocean ridge'. Most oceanic spreading centers are not in the middle of their hosting ocean basis but regardless, are called mid-ocean ridges. Mid-ocean ridges around the globe are linked by plate tectonic boundaries and the outline of the ridges across the ocean floor appears similar to the seam of a baseball. The mid-ocean ridge system thus is the longest mountain range on Earth, reaching about 65,000 km (40,000 mi).

North American Plate

The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of 76,000,000 km2 (29,000,000 sq mi), it is the Earth's second largest tectonic plate, behind the Pacific Plate (which borders the plate to the west).

It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust. The interior of the main continental landmass includes an extensive granitic core called a craton. Along most of the edges of this craton are fragments of crustal material called terranes, which are accreted to the craton by tectonic actions over a long span of time. It is thought that much of North America west of the Rocky Mountains is composed of such terranes.

North Atlantic Current

The North Atlantic Current (NAC), also known as North Atlantic Drift and North Atlantic Sea Movement, is a powerful warm western boundary current within the Atlantic Ocean that extends the Gulf Stream northeastward.The NAC originates from where the Gulf Stream turns north at the Southeast Newfoundland Rise, a submarine ridge that stretches southeast from the Grand Banks. The NAC flows northward east of the Grand Banks, from 40°N to 51°N, before turning sharply east to cross the Atlantic. It transports more warm tropical water to northern latitudes than any other boundary current; more than 40 Sv in the south and 20 Sv as it crosses the Mid-Atlantic Ridge. It reaches speeds of 2 knots near the North American coast. Directed by topography, the NAC meanders heavily, but in contrast to the meanders of the Gulf Stream, the NAC meanders remain stable without breaking off into eddies.The colder parts of the Gulf Stream turn northward near the "tail" of the Grand Banks at 50°W where the Azores Current branches off to flow south of the Azores. From there the NAC flows northeastward, east of the Flemish Cap (47°N, 45°W). Approaching the Mid-Atlantic Ridge, it then turns eastward and becomes much broader and more diffuse. It then splits into a colder northeastern branch and a warmer eastern branch. As the warmer branch turns southward, most of the subtropical component of the Gulf Stream is diverted southward, and as a consequence, the North Atlantic is mostly supplied by subpolar waters, including a contribution from the Labrador Current recirculated into the NAC at 45°N.West of Continental Europe, it splits into two major branches. One branch goes southeast, becoming the Canary Current as it passes northwest Africa and turns southwest. The other major branch continues north along the coast of Northwestern Europe.

Other branches include the Irminger Current and the Norwegian Current. Driven by the global thermohaline circulation, the North Atlantic Current is part of the wind-driven Gulf Stream, which goes further east and north from the North American coast across the Atlantic and into the Arctic Ocean.

The North Atlantic Current, together with the Gulf Stream, have a long-lived reputation for having a considerable warming influence on European climate. However, the principal cause for differences in winter climate between North America and Europe seems to be winds rather than ocean currents (although the currents do exert influence at very high latitudes by preventing the formation of sea ice).

Oceanic basin

In hydrology, an oceanic basin may be anywhere on Earth that is covered by seawater but geologically ocean basins are large geologic basins that are below sea level. Geologically, there are other undersea geomorphological features such as the continental shelves, the deep ocean trenches, and the undersea mountain ranges (for example, the mid-Atlantic ridge and the Emperor Seamounts) which are not considered to be part of the ocean basins; while hydrologically, oceanic basins include the flanking continental shelves and shallow, epeiric seas.

Pyrolobus fumarii

Pyrolobus fumarii, (literally the "firelobe of the chimney"), is a species of archaea known for its ability to live at extremely high temperatures that kill most organisms.It was first discovered in 1997 in a black smoker hydrothermal vent at the Mid-Atlantic Ridge, setting the upper temperature threshold for known life to exist at 113°C (235.4°F), but more recently Methanopyrus kandleri has been discovered which can survive temperatures up to 122°C. (251.6°F) The species "freezes" or solidifies and ceases growth at temperatures of 90°C (194°F) and below.Strain 121, a microbe from the same family found at a vent in the Pacific Ocean, survived and multiplied during a 10-hour interval spent at 121°C (294.8°F) in an autoclave.

Romanche Trench

The Romanche Trench, also called the Romanche Furrow or Romanche Gap, is the third deepest of the major trenches of the Atlantic Ocean, after the Puerto Rico Trench and the South Sandwich Trench. It bisects the Mid-Atlantic Ridge (MAR) just north of the equator at the narrowest part of the Atlantic between Brazil and West Africa, extending from 2°N to 2°S and from 16°W to 20°W. The trench has been formed by the actions of the Romanche Fracture Zone, a portion of which is an active transform boundary offsetting sections of the Mid-Atlantic Ridge.It was named after the French navy ship La Romanche, commanded by captain Louis-Ferdinand Martial which on 11 October 1883 made soundings that revealed the trench. The boat was coming to France after a few months scientific mission near cape Horn, part of the first International Polar Year.

South American Plate

The South American Plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African Plate, with which it forms the southern part of the Mid-Atlantic Ridge.

The easterly edge is a divergent boundary with the African Plate; the southerly edge is a complex boundary with the Antarctic Plate, the Scotia Plate, and the Sandwich Plate; the westerly edge is a convergent boundary with the subducting Nazca Plate; and the northerly edge is a boundary with the Caribbean Plate and the oceanic crust of the North American Plate. At the Chile Triple Junction, near the west coast of the Taitao–Tres Montes Peninsula, an oceanic ridge known as the Chile Rise is actively subducting under the South American Plate.

Geological research suggests that the South American Plate is moving westward away from the Mid-Atlantic Ridge: "Parts of the plate boundaries consisting of alternations of relatively short transform fault and spreading ridge segments are represented by a boundary following the general trend." As a result, the eastward-moving and more dense Nazca Plate is subducting under the western edge of the South American Plate, along the continent's Pacific coast, at a rate of 77 mm (3.0 in) per year. The collision of these two plates is responsible for lifting the massive Andes Mountains and for creating the numerous volcanoes which are strewn throughout them.

South Greenland Triple Junction

The South Greenland Triple Junction was a geologic triple junction in the North Atlantic Ocean that divided the North American, Greenland and Eurasian plates. It existed during the Paleogene and consisted of the Mid-Labrador and Mid-Atlantic ridges. The triple junction became extinct when seafloor spreading along the Mid-Labrador Ridge ceased during the Eocene.

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