![Scotia Sea NOAA](https://upload.wikimedia.org/wikipedia/commons/2/2e/Scotia_Sea_NOAA.jpg)
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 i ...
. 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 G ...
, 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 Clerke Rocks are a group of small rocky islands some southeast of South Georgia that extend from east to west. The Clerke Rocks include The Office Boys () at the northeastern end and Nobby (Spanish: ''Islote Llamativo'' or ''Roca Notable ...
. 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 Discovery ...
,
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 a ...
,
Pirie, and
Jane Banks; the
South Orkney Islands
The South Orkney Islands are a group of islands in the Southern Ocean, about north-east of the tip of the Antarctic Peninsula[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 195 ...
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 Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San MartÃn in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...
.
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 t ...
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.
Caus ...
s that once formed a land bridge between South America and Antarctica, once part of the
subduction
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...
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
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-A ...
(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
The Antarctic Circumpolar Current (ACC) is an ocean current that flows clockwise (as seen from the South Pole) from west to east around Antarctica. An alternative name for the ACC is the West Wind Drift. The ACC is the dominant circulation feat ...
.
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 th ...
(, Ma) which led to the
uplift
Uplift may refer to: Science
* Geologic uplift, a geological process
** Tectonic uplift, a geological process
* Stellar uplift, the theoretical prospect of moving a stellar mass
* Uplift mountains
* Llano Uplift
* Nemaha Uplift
Business
* Uplif ...
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
The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
(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 — 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 International Commission on Stratigraphy, ICS Geologic timescale, the latest age (geology), age or uppermost stage (stratigraphy), stratigraphic stage of the Paleocene epoch (geology), Epoch or series (stratigraphy), Serie ...
to the
Early Eocene
In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by the Eocene Lutetian Age. The Ypresian i ...
(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
A basement or cellar is one or more floors of a building that are completely or partly below the ground floor. It generally is used as a utility space for a building, where such items as the furnace, water heater, breaker panel or fuse box, ...
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
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Volcanism of Antarctica
Volcanic arc islands