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The Scotia Arc is the
island arc Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle alon ...
system forming the north, east and south border of the
Scotia Sea The Scotia Sea is a sea located at the northern edge of the Southern Ocean at its boundary with the South Atlantic Ocean. It is bounded on the west by the Drake Passage and on the north, east, and south by the Scotia Arc, an undersea ridge and ...
. The northern border, the North Scotia Ridge, comprises (from west to east)
Isla de los Estados Isla de los Estados (English: Staten Island, from the Dutch ''Stateneiland'') is an Argentine island that lies off the eastern extremity of Tierra del Fuego, from which it is separated by the Le Maire Strait. It was named after the Netherlands ...
at the tip of
Tierra del Fuego Tierra del Fuego (, ; Spanish for "Land of the Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of the main island, Isla ...
, the Burdwood, Davis, and Aurora Banks; the
Shag Shag, or Shagged, or Shagger, or Shagging, or Shags may refer to: Animals * Shag or cormorant, a bird family ** European shag, a specific species of the shag or cormorant family ** Great cormorant another species of the family People Pseudonym ...
,
South Georgia Island South Georgia ( es, Isla San Pedro) is an island in the South Atlantic Ocean that is part of the British Overseas Territory of South Georgia and the South Sandwich Islands. It lies around east of the Falkland Islands. Stretching in the east†...
and Clerke Rocks. The eastern border comprises the volcanic
South Sandwich Islands ) , anthem = "God Save the King" , song_type = , song = , image_map = South Georgia and the South Sandwich Islands in United Kingdom.svg , map_caption = Location of South Georgia and the South Sandwich Islands in the southern Atlantic Oce ...
flanked by the
South Sandwich Trench The South Sandwich Trench is a deep arcuate trench in the South Atlantic Ocean lying to the east of the South Sandwich Islands. It is the deepest trench of the Southern Atlantic Ocean, and the second deepest of the Atlantic Ocean after the Puert ...
. The southern border, the South Scotia Ridge, (east to west) comprises Herdman,
Discovery Discovery may refer to: * Discovery (observation), observing or finding something unknown * Discovery (fiction), a character's learning something unknown * Discovery (law), a process in courts of law relating to evidence Discovery, The Discover ...
,
Bruce The English language name Bruce arrived in Scotland with the Normans, from the place name Brix, Manche in Normandy, France, meaning "the willowlands". Initially promulgated via the descendants of king Robert the Bruce (1274−1329), it has been ...
, Pirie, and Jane Banks; the South Orkney Islands and
Elephant Island Elephant Island is an ice-covered, mountainous island off the coast of Antarctica in the outer reaches of the South Shetland Islands, in the Southern Ocean. The island is situated north-northeast of the tip of the Antarctic Peninsula, west-so ...
. The
Bransfield Strait Bransfield Strait or Fleet Sea ( es, Estrecho de Bransfield, Mar de la Flota) is a body of water about wide extending for in a general northeast – southwest direction between the South Shetland Islands and the Antarctic Peninsula. History ...
, finally, separates the arc from the
South Shetland Islands The South Shetland Islands are a group of Antarctic islands with a total area of . They lie about north of the Antarctic Peninsula, and between southwest of the nearest point of the South Orkney Islands. By the Antarctic Treaty of 1 ...
and
James Ross Island James Ross Island is a large island off the southeast side and near the northeastern extremity of the Antarctic Peninsula, from which it is separated by Prince Gustav Channel. Rising to , it is irregularly shaped and extends in a north–south ...
flanking the tip of the Antarctic Peninsula. The Scotia Arc surrounds the small
Scotia Scotia is a Latin placename derived from ''Scoti'', a Latin name for the Gaels, first attested in the late 3rd century.Duffy, Seán. ''Medieval Ireland: An Encyclopedia''. Routledge, 2005. p.698 The Romans referred to Ireland as "Scotia" around ...
and
South Sandwich Plate The South Sandwich Plate or Sandwich Plate is a minor tectonic plate bounded by the subducting South American Plate to the east, the Antarctic Plate to the south and the Scotia Plate to the west. The plate is separated from the Scotia Plate by th ...
s. The arc is formed by
continental fragment Continental crustal fragments, partly synonymous with microcontinents, are pieces of continents that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin. Cau ...
s that once formed a land bridge between South America and Antarctica, once part of the subduction margin that still forms the
Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
. An ancestral arc, which formed a separate subduction system, broke through this land bridge and started to form the Scotia Sea by eastward back-arc extension driven by subduction of the South American Plate (also located east of the Scotia Arc). Today, the Scotia Arc forms a discontinuous link between South America and Antarctica, it is considered a continuation of the Andes, and the antarctic part of the mountain range is called
Antarctandes The Antarctandes (''Antartandes'' in Spanish), also known as the Antarctic Peninsula cordillera,http://archives.datapages.com/data/meta/circ_pac/0012/0013_f_firstpage.pdf is the mountain range that is located on the northern Antarctic Peninsula, ...
. It is also an important barrier between the Pacific and Atlantic Oceans, and therefore for the Antarctic Circumpolar Current.


Geology

The formation of the Scotia Arc was initiated by an acceleration in South America's westward migration in the mid-
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
(, Ma) which led to the uplift of the Fuegan
Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
and the then adjacent and embryonic North Scotia Ridge. The uplift of the ridge initiated the eastward migration of the South Georgia
microcontinent Continental crustal fragments, partly synonymous with microcontinents, are pieces of continents that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin. Caus ...
from Tierra del Fuego towards its current location. In the Late Cretaceous South America started to move west relative to Antarctica. Little changed in the region between the Late Cretaceous and Oligocene (90-30 Ma) except for the subduction of the
Phoenix Plate The Phoenix Plate (also known as the Aluk Plate or Drake Plate) was a tectonic plate that existed during the early Paleozoic through late Cenozoic time. It formed a triple junction with the Izanagi and Farallon plates in the Panthalassa Ocean as ...
on the Pacific margin of the land bridge that still connected South America and Antarctica â€” what would become the
Drake Passage The Drake Passage (referred to as Mar de Hoces Hoces Sea"in Spanish-speaking countries) is the body of water between South America's Cape Horn, Chile and the South Shetland Islands of Antarctica. It connects the southwestern part of the Atla ...
was at this time a cusp on the Pacific side of the land bridge. The
Late Paleocene The Thanetian is, in the ICS Geologic timescale, the latest age or uppermost stratigraphic stage of the Paleocene Epoch or Series. It spans the time between . The Thanetian is preceded by the Selandian Age and followed by the Ypresian Age (p ...
to the Early Eocene (55 Ma) saw rift basin formation in the Fuegan Andes which led to crustal extension: the first sign of separation between the two continents and the formation of the South Scotia Sea and South Scotia Ridge. Spreading in the West Scotia Sea led to the further lengthening of the North Scotia Ridge and South Georgia moving further east. Spreading in the West Scotia Sea finally led to the rifting of the South Orkney microcontinent from the tip of the Antarctic Peninsula. This event initiated the South Scotia Ridge. The banks of the South Scotia Ridge are made of continental crust that rifted off the land bridge 40-30 Ma. The banks on the northern Central Scotia Sea, on the other hand, are volcanic constructs overlaying an oceanic basement parts of which is the spreading centre of the separation between South America and Antarctica. Seafloor spreading in the West Scotia Sea continued until 6.6-5.9 Ma. The oldest volcanic activity in Central and Eastern Scotia Sea, i.e. the first signs of a volcanic arc, has been dated to 28.5 Ma. The South Sandwich Islands fore-arc originated in the Central Scotia Sea and was translated eastward by the
back-arc A back-arc basin is a type of geologic basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most o ...
spreading centre in the East Scotia Sea, i.e. the East Scotia Ridge. South Georgia's eastward migration ended about 9 Ma when the microcontinent collided with the
Northeast Georgia Rise The Northeast Georgia Rise is an oceanic plateau located in the South Atlantic Ocean northeast of South Georgia Island and west of the Falkland Plateau. Bathymetry The rise is separated from South Georgia Island by the Northeast Georgia Passage. ...
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 ...
on the South American Plate north-east of South Georgia. A submerged equivalent to the current South Sandwich Arc was relocated westward by the same spreading centre. After, and probably because of, the collision, the East Scotia Sea spreading centre split the ancestral South Sandwich Arc leaving a remnant arc under the Central Scotia Sea. The collision also produced the rugged
Allardyce Range The Allardyce Range ( es, Cordillera de San Telmo) is a mountain range rising south of Cumberland Bay and dominating the central part of South Georgia, a UK overseas territory. It extends for from Mount Globus in the northwest to Mount Brooke ...
on South Georgia, making the -high range three times higher than the conjugate rocks on
Navarino Island Navarino Island () is a Chilean island located between Isla Grande de Tierra del Fuego, to the north, and Cape Horn, to the south. The island forms part of the Commune of Cabo de Hornos, the southernmost commune in Chile and in the world, belong ...
in Tierra del Fuego. The driving mechanism behind the formation of the arc, as proposed by , is a mantle return-flow from the Pacific to the Atlantic.


References


Notes


Sources

* * * {{coord, 57, 30, S, 40, 00, W, scale:20000000, display=title Volcanism of Antarctica Volcanic arc islands