The Scotia Plate () is a
tectonic plate
Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...
on the edge of the
South Atlantic
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 an ...
and
Southern oceans. Thought to have formed during the early
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'', " ...
with the opening of 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 ...
that separates South America from Antarctica, it is a minor plate whose movement is largely controlled by the two major plates that surround it: the
South American Plate and the
Antarctic Plate
The Antarctic Plate is a tectonic plate containing the continent of Antarctica, the Kerguelen Plateau, and some remote islands in the Southern Ocean and other surrounding oceans. After breakup from Gondwana (the southern part of the superconti ...
. The Scotia Plate takes its name from the
steam yacht
A steam yacht is a class of luxury or commercial yacht with primary or secondary steam propulsion in addition to the sails usually carried by yachts.
Origin of the name
The English steamboat entrepreneur George Dodd (1783–1827) used the term ...
''Scotia'' of the
Scottish National Antarctic Expedition
The Scottish National Antarctic Expedition (SNAE), 1902–1904, was organised and led by William Speirs Bruce, a natural scientist and former medical student from the University of Edinburgh. Although overshadowed in terms of prestige by Rob ...
(1902–04), the expedition that made the first
bathymetric
Bathymetry (; ) is the study of underwater depth of ocean floors (''seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water d ...
study of the region.
Roughly rhomboid, extending between and , the plate is wide and long. It is moving
WSW at /year and the
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 ...
is moving east at /year in an absolute reference frame.
The Scotia Plate is made of
oceanic crust
Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic ...
and
continental
Continental may refer to:
Places
* Continent, the major landmasses of Earth
* Continental, Arizona, a small community in Pima County, Arizona, US
* Continental, Ohio, a small town in Putnam County, US
Arts and entertainment
* ''Continental'' ( ...
fragments now distributed around 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 ...
. Before the formation of the plate began (40Ma), these fragments formed a continuous landmass from
Patagonia
Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...
to the
Antarctic Peninsula along an active subduction margin.
At present, the plate is almost completely submerged, with only the small exceptions of
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 ...
on its northeastern edge and the southern tip of South America.
Tectonic setting
![East Scotia Ridge vents map](https://upload.wikimedia.org/wikipedia/commons/a/ae/East_Scotia_Ridge_vents_map.png)
Together with the Sandwich Plate, the Scotia Plate joins the southernmost Andes to the Antarctic Peninsula, just like the
Caribbean Plate
The Caribbean Plate is a mostly oceanic tectonic plate underlying Central America and the Caribbean Sea off the north coast of South America.
Roughly 3.2 million square kilometers (1.2 million square miles) in area, the Caribbean Plate borders ...
joins the northernmost Andes to North America, and these two plates are comparable in several ways. Both have
volcanic arc
A volcanic arc (also known as a magmatic arc) is a belt of volcanoes formed above a subducting oceanic tectonic plate,
with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc lo ...
s at their eastern ends, the
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 ...
on the Sandwich Plate and the
Lesser Antilles
The Lesser Antilles ( es, link=no, Antillas Menores; french: link=no, Petites Antilles; pap, Antias Menor; nl, Kleine Antillen) are a group of islands in the Caribbean Sea. Most of them are part of a long, partially volcanic island arc bet ...
on the Caribbean Plate, and both plates also had a major impact on global climate when they closed the two major gateways between the Pacific and Atlantic Oceans during the
Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
and
Cenozoic.
North Scotia Ridge
The northern edge of the Scotia Plate is bounded by the South American Plate, forming the North Scotia Ridge. The North Scotia ridge is a left-lateral, or sinistral, transform boundary with a transform rate of roughly 7.1 mm/yr.
The
Magallanes–Fagnano Fault
The Magallanes–Fagnano Fault () is a continental transform fault. The fault marks a transform boundary between the Scotia Plate and the South American Plate, cutting across continental crust. It runs under the Strait of Magellan's western arm, A ...
is passing through
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 northern ridge stretches from
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 ...
off
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 ...
in the west to the
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 ...
South Georgia in the east, with a series of shallow banks in between:
Burdwood, Davis, Barker, and
Shag Rocks. North of the ridge is the deep
Falkland Trough.
South Georgia microcontinent
Experts in plate tectonics have been unable to determine whether the South Georgian Islands are part of the Scotia Plate or have been recently accreted to the South American Plate. Surface expressions of the plate boundary are found north of the islands suggesting a long-term presence of the transform fault there. Yet
seismic studies have identified strain and thrusting south of the islands indicating the possible shift of the transform fault to an area south of the island. It has also been suggested that the plate bearing the islands may have broken off from the Scotia Plate, forming a new independent South Georgia microplate, yet there is little evidence to make this conclusion.
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 ...
was originally connected to the Roca Verdes
back-arc basin (southernmost
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 ...
) until the
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'', " ...
. Before that, this basin went through a series of geological transformations during the
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 ...
, through which South Georgia was first buried, then made a topographic feature again by the Late Cretaceous. At about 45 Ma, South Georgia, still part of the
South American Plate, got buried again and something, possibly rotation of the Fuegian Andes, completed the break-up and allowed South Georgia a second
exhumation
Burial, also known as interment or inhumation, is a method of final disposition whereby a dead body is placed into the ground, sometimes with objects. This is usually accomplished by excavating a pit or trench, placing the deceased and objec ...
. During the
Oligocene (34–23 Ma) South Georgia was reburied again as seafloor spreading took place in the West Scotia Sea. 10 Ma, finally, the South Georgia microcontinent was uplifted as a result of the collision 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. ...
.
South Scotia Ridge
The southern edge of the plate is bordered by the Antarctic Plate, forming the South Scotia Ridge, a left-lateral
transform boundary
A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subductio ...
sliding at a rate of roughly 7.4–9.5 mm/yr that occupies the southern half of the Antarctic-Scotia plate boundary.
The relative motion between the Scotia Plate and the Antarctic Plate on the western boundary is 7.5–8.7 mm/yr.
Though the South Scotia Ridge is overall a transform fault, small sections of the ridge are spreading to make up for the somewhat jagged shape of the boundary.
At the eastern tip of the
Antarctic Peninsula, the beginning of South Scotia Ridge, a small and heavily dissected bank degenerates into several outcrops dominated by Paleozoic and Cretaceous rocks. A small basin, Powel Basin, separates this cluster from the
South Orkney
The South Orkney Islands are a group of islands in the Southern Ocean, about north-east of the tip of the Antarctic Peninsula[Scotia Arc
The Scotia Arc is the island arc system forming the north, east and south border of the Scotia Sea. The northern border, the North Scotia Ridge, comprises (from west to east) Isla de los Estados at the tip of Tierra del Fuego, the Burdwood, Davis, ...]
east of the
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 ...
, are the
South Sandwich 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 ...
and
trench
A trench is a type of excavation or in the ground that is generally deeper than it is wide (as opposed to a wider gully, or ditch), and narrow compared with its length (as opposed to a simple hole or pit).
In geology, trenches result from ero ...
. This volcanic active island arc has submerged ancestors in Jane and Discovery banks in the southern ridge.
Shackleton Fracture Zone
The western edge of the plate is bounded by the Antarctic Plate, forming the Shackleton Fracture Zone and the southern
Chile Trench. The Southern Chile Trench is a southern extension of the subduction of the Antarctic and Nazca plates below South America. Heading south along the ridge, the subduction rate decreases until its remaining oblique motion evolves into the Shackleton Fracture Zone transform boundary. The south-western edge of the plate is bounded by the
Shetland microplate separating the Shackleton Fracture Zone and the South Scotia Ridge.
North of
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 along the southern half of the Shackleton Fracture Zone is the remnant 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 ...
(also known as Drake or Aluk Plate). Around 47 Ma the subduction of the Phoenix Plate started as the propagation of the
Pacific-Antarctic Ridge
The Pacific-Antarctic Ridge (PAR) is a divergent tectonic plate boundary located on the seafloor of the South Pacific Ocean, separating the Pacific Plate from the Antarctic Plate. It is regarded as the southern section of the East Pacific Rise ...
continued. The last collision between Phoenix ridge segments and the subduction zone was 6.5 Ma and at 3.3 Ma movements had stopped and the remnants of the Phoenix Plate was incorporated into the Antarctic Plate. The southern part of the Shackleton Fracture Zone is the former eastern edge of the Phoenix Plate.
East Scotia Ridge
The eastern edge of the Scotia Plate is a spreading ridge bounded by the
South Sandwich microplate, forming the East Scotia Ridge. The East Scotia Ridge is a
back-arc spreading ridge that formed due to subduction of the South American Plate below the South Sandwich Plate along the South Sandwich Island arc. Exact spreading rates are still being disputed in the literature, but it has been agreed that rates range between 60 and 90 mm/yr.
The banks of northern Central Scotia Sea are superposed on oceanic basement and the spreading centre of the West Scotia Sea. Analyses of samples of
volcaniclastic
Volcaniclastics are geologic materials composed of broken fragments ( clasts) of volcanic rock. These encompass all clastic volcanic materials, regardless of what process fragmented the rock, how it was subsequently transported, what environment it ...
rocks from these sites indicate they are constructs of a continental arc and in some cases oceanic arc similar to those being formed in the currently active South Sandwich Arc. The oldest volcanic arc activity in the central and eastern regions of the Scotia Sea are 28.5 Ma. The South Sandwich forarc originated in the Central Scotia Sea at that time but has since been translated eastward by the back-arc spreading centre of the East Scotia Ridge.
Timeline
The timing of the formation of the Scotia Plate and opening of 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 ...
have long been the subject of much debate due to the important implications for changes in ocean currents and shifts in
paleoclimate. The thermal isolation of
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
, engendering the formation of the
Antarctic ice sheet, has largely been attributed to the opening of the Drake Passage.
Formation
The Scotia Plate originated about (Ma), during the late
Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
at the
Panthalassic margins of the
Gondwana supercontinent between two Precambrian cratons, the
Kalahari
The Kalahari Desert is a large semi-arid sandy savanna in Southern Africa extending for , covering much of Botswana, and parts of Namibia and South Africa.
It is not to be confused with the Angolan, Namibian, and South African Namib coasta ...
and
East Antarctic Cratons, now located in Africa and Antarctica. Its development was also influenced by the
Río de la Plata Craton
The Rio de la Plata Craton (RPC) is a medium-sized continental block found in Uruguay, eastern Argentina and southern Brazil. During its complex and protracted history it interacted with a series other blocks and is therefore considered importan ...
in South America. The initial cause for its formation was the break-up of Gondwana in what became the south-west Indian Ocean.
The earliest marine fossils found on the
Maurice Ewing Bank, on the eastern end of the
Falkland Plateau, are associated with the Indian and
Tethys Ocean
The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean that covered most of the Earth during much of the Mesozoic Era and early Cenozoic Era, located between the ancient continents ...
s and probably slightly more than 150 Ma. The
Weddell Sea
The Weddell Sea is part of the Southern Ocean and contains the Weddell Gyre. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. The easternmost point is Cape Norvegia at Princess Martha ...
opened and spread along the southern margin of the Falkland Plateau and into the Rocas Verdes back-arc basin which extends from South Georgia and along the Patagonian Andes. Fragments of the inverted oceanic
basement of this basin are preserved as
ophiolitic complexes in this area, including the
Larsen Harbour
Larsen Harbour ( es, Bahía Larsen) is a narrow long inlet of indenting volcanic rocks and sheeted dykes known as the Larsen Harbour Formation. It is a branch of Drygalski Fjord, entered west-northwest of Nattriss Head, at the southeast end of ...
complex on South Georgia. This makes it possible to restore the original position of the South Georgia microcontinent south of the Burdwood Bank on the western North Scotia Ridge south of the Falkland Islands.
The Rocas Verdes basin was filled with
turbidite
A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean.
Sequencing
Turbidites wer ...
s derived from the volcanic arc on its Pacific margin and partly from its continental margin. The Weddell Sea continued to expand which led to the extension between the Patagonian Andes and the Antarctic Peninsula. In the Mid-Cretaceous (100 Ma) the spreading rate in South Atlantic increased significantly and the
Mid-Atlantic Ridge
The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent 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, the ridge separates the North ...
grew from 1200 km to 7000 km. This led to compressional deformations along the western margin of the South American Plate and the
obduction
Obduction is a geological process whereby denser oceanic crust (and even upper mantle) is scraped off a descending ocean plate at a convergent plate boundary and thrust on top of an adjacent plate. When oceanic and continental plates converge ...
of the Rocas Verdes basement onto this margin. Structures associated with this obduction are found from Tierra del Fuego to South Georgia.
The acceleration of the westward motion of South America and the inversion of the Rocas Verde Basin finally lead to the initiation of the Scotia Arc. This inversion had a strike-slip component which can be seen in the
Cooper Bay
Cooper Island is a small island, long, which lies at the north side of the entrance to Drygalski Fjord, off the southeast end of South Georgia. It was discovered by a British expedition under James Cook in 1775, and named for Lieutenant Robe ...
dislocation on South Georgia. This geological regime lead to the uplift and elongation of the Andes and the embryonic North Scotia Ridge, which resulted in the initial eastward relocation of the South Georgia microcontinent and formation of the Central Scotia Sea.
Opening of Drake Passage
Between the Late Cretaceous and the Early Oligocene (90–30 Ma) little changed in the region, except for the subduction of the Phoenix Plate along the Shackleton Fracture Zone. The Late Paleocene and Early Eocene (60–50 Ma) saw the formation of South Scotia Sea and South Scotia Ridge — the first sign of separation of the southern Andes and the Antarctic Peninsula — which resulted in seafloor spreading in the West Scotia Sea and hence the initial opening of a deep Drake Passage. The ongoing lengthening of the North Scotia Ridge beyond the Burdwood Bank caused South Georgia to move further east. The banks of the North Scotia Ridge contain volcanic rocks similar to those found in Tierra del Fuego, including on
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 ...
on the easternmost tip.
During the early Eocene (50 Ma), the Drake Passage between the southern tip of South America at
Cape Horn
Cape Horn ( es, Cabo de Hornos, ) is the southernmost headland of the Tierra del Fuego archipelago of southern Chile, and is located on the small Hornos Island. Although not the most southerly point of South America (which are the Diego Ramí ...
and the South Shetland Islands of Antarctica was a small opening with limited circulation. A change in relative motion between the South American Plate and the Antarctic Plate would have severe effects, causing seafloor spreading and the formation of the Scotia Plate.
Marine geophysical data indicates that motion between the South American Plate and the Antarctic Plate shifted from N-S to WNW-ESE accompanied by an eightfold increase in the separation rate. This shift in spreading initiated crustal thinning and by 30–34 Ma, the West Scotia Ridge formed.
One of the most prominent features in the Scotia Plate itself is the
median valley known as the West Scotia Ridge. It was produced by two plates that are no longer independently active: the Magallanes and Central Scotia Plates. The ridge consists of seven segments separated by right-lateral transform offsets of various lengths. The western region of the Scotia Plate can be dated to 26–5.5 Ma.
A complex pattern of spreading prior to 26 Ma is probably present in the oldest parts of this spreading regime; i.e. west of Terror Rise (north of
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 ...
) and on the shelf slope of Tierra del Fuego. Until 17 Ma the Central Scotia Plate moved quickly eastwards, fuelled by the eastern trench migration, but both plates have moved very slowly since.
References
Notes
Sources
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{{Coord, 57, S, 46, W, display=title
Tectonic plates
Geology of the Atlantic Ocean
Geology of Argentina
Geology of Magallanes Region