Northeast Georgia Rise | |
---|---|
Summit depth | 2 km (1.2 mi) |
Height | 3 km (1.9 mi) |
Summit area | 400 km × 400 km (250 mi × 250 mi) [1] |
Location | |
Location | Northeast of South Georgia Island |
Coordinates | 52°30′S31°00′W / 52.5°S 31.0°W |
Country | International |
Geology | |
Type | LIP, hotspot volcano |
Age of rock | 100 to 94 Ma |
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.
The rise is separated from South Georgia Island by the Northeast Georgia Passage. The Georgia Basin surrounds the northern end of the rise. [2] The Agulhas-Falkland Fracture Zone (AFFZ) stretches across the Atlantic north of the Northeast Georgia Rise. A group of small seamounts north of the rise are aligned with a gap in the AFFZ. East of this gap the AFFZ is a single ridge with an average height of 2,500 m (8,200 ft) but west of the gap the AFFZ is a double ridge with an average height of 1,500 m (4,900 ft). [3]
On the eastern flank of the rise is a prominent ridge, the Soledad Ridge, about 1,000 m (3,300 ft) tall. It has the same orientation as the southeastern part of the rise. It is a basement-feature in which bottom-water have scoured a channel. Both the Northeast Georgia Rise and the Islas Orcadas Rise east of it, are seemingly dissected by transverse valleys that extend to the fracture zones of the Mid-Atlantic Ridge. [3]
The Northeast Georgia Rise is made of oceanic crust that formed when Africa and South America spread apart after the Gondwana breakup. [1] 100 Ma the Northeast Georgia Rise was part of the Agulhas Plateau-Northeast Georgia Rise-Maud Rise large igneous province (LIP) in what today is the southwesternmost Indian Ocean south of South Africa. This LIP, often called the southeast African LIP, formed at the triple junction where Gondwana passed over the Bouvet Hotspot and broke-up into Antarctica, South America, and Africa. This volcanism lasted until 94 Ma after which seafloor spreading detached the Northeast Georgia Rise and Maude Rise from the Agulhas Plateau and the Northeast Georgia Rise migrated westward to its current location and Maud Rise south towards the Weddell Sea. [4]
Northeast Georgia Rise and the Agulhas Plateau were always located on different tectonic plates, the South American and African plates respectively. Because of this, these two plateaus can be used to reconstruct the movements of the two plates from the formation of the southeast African LIP. [5]
Northeast Georgia rise collided with the South Georgia microcontinental block about 10 Ma which caused the uplift of this block and the creation of the present islands. The collision coincided with the termination of spreading at the West Scotia Sea and resulted in a bathymetric obstacle that still steers the Antarctic Circumpolar Current northward. [6]
Two or more episodes of deformation have modified the topography of the ridge. Late Oligocene faulting coincides with the opening of the Scotia Sea; the western part of the Northeast Georgia Rise was uplifted by 0.5–1 km (0.31–0.62 mi) during the Neogene (23-3 Ma); the topography of the southwestern part of the rise may have formed by interaction with the advancing South Sandwich Trench or the South Sandwich block. [1]
As a part of the Scotia Plate, the South Georgia block has been moving eastward. It is possible that when Northeast Georgia Rise, with its thickened, buoyant crust, reached the convergent South American-Scotia margin, the rise stopped the South Georgia block, transformed it into a series of fault blocks, and forced the margin to relocate south of the South Georgia block — effectively making it part of the South American Plate. [7]
In the Scotia Sea the Antarctic Circumpolar Current (ACC) is deflected north by the South Scotia Ridge. It then widens extensively before passing over the North Scotia Ridge. North of South Georgia the southern boundary of the ACC is retroflected around the Northeast Georgia Rise. [2] The Southern Antarctic Circumpolar Current Front (SACCF) meanders across the Scotia Sea from the western shelf of the Antarctic Peninsula to the southwestern side of South Georgia. From there SACCF wraps the island anti-cyclonically, retroflects north of it, and flows across the Northeast Georgia Rise before looping cyclonically into the South Atlantic. The retroflection north of the island and across the rise shows a strong seasonal variability but SACCF remains constrained by these bathymetric obstacles. [8]
Weddell Sea Deep Water (WSDW) circulates cyclonically in the Weddell Gyre from where it escapes through gaps in the South Scotia Ridge, such as the South Sandwich Trench. It then flows across the Scotia Sea which it can only escape through the Georgia Passage. WSDW can reach the Georgia Basin by two routes: either by circumnavigating the Northeast Georgia Rise on its eastern side or by passing through the Northeast Georgia Passage. [9] [10]
The Antarctic Circumpolar Current (ACC) is an ocean current that flows clockwise from west to east around Antarctica. An alternative name for the ACC is the West Wind Drift. The ACC is the dominant circulation feature of the Southern Ocean and has a mean transport estimated at 100–150 Sverdrups, or possibly even higher, making it the largest ocean current. The current is circumpolar due to the lack of any landmass connecting with Antarctica and this keeps warm ocean waters away from Antarctica, enabling that continent to maintain its huge ice sheet.
The Drake Passage is the body of water between South America's Cape Horn, Chile, Argentina and the South Shetland Islands of Antarctica. It connects the southwestern part of the Atlantic Ocean with the southeastern part of the Pacific Ocean and extends into the Southern Ocean. The passage is named after the 16th-century English explorer and privateer Sir Francis Drake.
The African Plate, also known as the Nubian Plate, is a major tectonic plate that includes much of the continent of Africa and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plate to the west ; the Arabian Plate and Somali Plate to the east; the Eurasian Plate, Aegean Sea Plate and Anatolian Plate to the north; and the Antarctic Plate to the south.
The Scotia Plate is a tectonic plate on the edge of the South Atlantic and Southern oceans. Thought to have formed during the early Eocene with the opening of the Drake Passage 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 Scotia Plate takes its name from the steam yacht Scotia of the Scottish National Antarctic Expedition (1902–04), the expedition that made the first bathymetric study of the region.
The Kerguelen Plateau, also known as the Kerguelen–Heard Plateau, is an oceanic plateau and large igneous province (LIP) located on the Antarctic Plate, in the southern Indian Ocean. It is about 3,000 km (1,900 mi) to the southwest of Australia and is nearly three times the size of California. The plateau extends for more than 2,200 km (1,400 mi) in a northwest–southeast direction and lies in deep water.
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The Agulhas Bank is a broad, shallow part of the southern African continental shelf which extends up to 250 km (160 mi) south of Cape Agulhas before falling steeply to the abyssal plain.
The Antarctic bottom water (AABW) is a type of water mass in the Southern Ocean surrounding Antarctica with temperatures ranging from −0.8 to 2 °C (35 °F) and absolute salinities from 34.6 to 35.0 g/kg. As the densest water mass of the oceans, AABW is found to occupy the depth range below 4000 m of all ocean basins that have a connection to the Southern Ocean at that level.
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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 Isla de los Estados at the tip of Tierra del Fuego, the Burdwood, Davis, and Aurora Banks; the Shag, South Georgia Island and Clerke Rocks. The eastern border comprises the volcanic South Sandwich Islands flanked by the South Sandwich Trench. The southern border, the South Scotia Ridge, comprises Herdman, Discovery, Bruce, Pirie, and Jane Banks; the South Orkney Islands and Elephant Island. The Bransfield Strait, finally, separates the arc from the South Shetland Islands and James Ross Island flanking the tip of the Antarctic Peninsula.
The South American–Antarctic Ridge or simply American-Antarctic Ridge is the tectonic spreading center between the South American Plate and the Antarctic Plate. It runs along the sea-floor from the Bouvet Triple Junction in the South Atlantic Ocean south-westward to a major transform fault boundary east of the South Sandwich Islands. Near the Bouvet Triple Junction the spreading half rate is 9 mm/a (0.35 in/year), which is slow, and the SAAR has the rough topography characteristic of slow-spreading ridges.
The Weddell Gyre is one of the two gyres that exist within the Southern Ocean. The gyre is formed by interactions between the Antarctic Circumpolar Current (ACC) and the Antarctic Continental Shelf. The gyre is located in the Weddell Sea, and rotates clockwise. South of the ACC and spreading northeast from the Antarctic Peninsula, the gyre is an extended large cyclone. Where the northeastern end ends at 30°E, which is marked by the southward turn of the ACC, the northern part of the gyre spreads over the Southern Scotia Sea and goes northward to the South Sandwich Arc. Axis of the gyre is over the southern flanks of the South Scotia, America-Antarctic, and Southwest Indian Ridges. In the southern part of the gyre, the westward return flow is about 66 sverdrup (Sv), while in the northern rim current, there is an eastward flow of 61 Sv.
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The Agulhas Plateau is an oceanic plateau located in the south-western Indian Ocean about 500 km (310 mi) south of South Africa. It is a remainder of a large igneous province (LIP), the Southeast African LIP, that formed 140 to 95 million years ago (Ma) at or near the triple junction where Gondwana broke-up into Antarctica, South America, and Africa. The plateau formed 100 to 94 Ma together with Northeast Georgia Rise and Maud Rise when the region passed over the Bouvet hotspot.
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