Shetland Plate

The Shetland Plate is a tectonic microplate located off the tip of the Antarctic Peninsula and contains the South Shetland Islands.[1] The plate is bordered on three sides by the Antarctic Plate and the fourth side is bordered by the Scotia Plate. The northwestern border is defined by the South Shetland Trench separating the Shetland Plate to the south from the Antarctic Plate to the north. This trench is the remnant of a subduction zone where the defunct Phoenix Plate, now part of the Antarctic Plate, subducted under the Antarctic Peninsula and the Shetland Islands. The southeastern border is rift zone with the Antarctic Plate creating the Bransfield Basin.[2] The southwestern and northeastern boundaries are each part of larger fracture zones. The southwestern border is the Hero Fracture Zone and separates the Antarctic Plate to the southwest from the Shetland Plate to the northeast. The northeastern boundary is the Shackleton Fracture Zone and separates the Shetland Plate to the southwest from the Scotia Plate.[1]

Shetland Plate
ShetlandPlate
Shetland Plate shaded in red.
TypeMinor
Coordinates62°10′S 61°00′W / 62.167°S 61.000°WCoordinates: 62°10′S 61°00′W / 62.167°S 61.000°W
Movement1Northwest
Speed11 to 2 cm (0.39 to 0.79 in)/yr
FeaturesSouth Shetland Islands, Southern Ocean
1Relative to the African Plate

Geologic history

The Shetland Plate started forming 3 to 4 million years ago.[2] Prior to formation, the Shetland Plate was part of the Antarctic Plate adjacent to the Antarctic Peninsula. During this period, the Phoenix Plate to the northwest, was subducting under the Antarctic Peninsula and the South Shetland Islands, which created the South Shetland Trench.[3] Approximately 3 million years ago spreading stopped at the Antarctic-Phoenix spreading center in Drake Passage. The Phoenix Plate is now considered part of the larger Antarctic Plate due to a lack of relative movement between the two since spreading ceased.[3] However, subduction in the South Shetland Trench did not cease. Slab rollback of the former Phoenix Plate underneath the South Shetland Islands caused rifting to develop in the Antarctic Peninsula creating the Shetland Plate and the Bransfield Basin. Rifting centers in the Bransfield Basin continue to separate the Shetland Plate from the Antarctic Peninsula.[4]

Tectonic setting

South Shetland Trench

The South Shetland Trench forms the northwest border of the Shetland Plate. The trench is formed by the subduction of the Antarctic Plate in the north under the Shetland Plate in the south.[2] Subduction along this trench has slowed significantly over time, from 4 to 6 centimetres (1.6 to 2.4 in) per year over the last 30 million years to 1 to 2 centimetres (0.39 to 0.79 in) per year in the last 6 million years.[3][5] Current subduction is caused by the movement of the Shetland Plate northward, as well as, slab rollback of the former Phoenix Plate.

Bransfield Basin

Shetland Plate Boundries
Boundaries and bathymetry of the Shetland Plate.

The Bransfield Basin forms the southeast border of the Shetland Plate. The basin separates the Shetland Plate on the north and the Antarctic Plate to the south. The basin is a back-arc rift basin.[2] The basin ranges from 1,300 metres (4,300 ft) to more than 2,700 metres (8,900 ft) deep.[6]

Fracture Zones

The Shackleton Fracture Zone is the northeast border of the Shetland Plate.[5] The fracture zone is a series of parallel transform faults separating the Scotia Plate from the Shetland Plate. This border with the Scotia Plate is the only Shetland Plate boundary that is not with the Antarctic Plate.[2]

The Hero Fracture Zone is the southwest boundary of the Shetland Plate. This feature separates the Shetland Plate from the Antarctic Plate. These parallel faults connect the Bransfield Basin in the south to the South Shetland Trench in the north.[5]

Volcanism

Absolute K-Ar ages indicate volcanism has been active from the Cenozoic to the present. Current volcanism can be seen at places like Deception Island and Penguin Island. Calc-alkaline plutons, a type of magma seen above subduction zones, date from the Cenozoic to the Miocene and is coincident with the active subduction of the Phoenix plate under Antarctica. More recent Pliocene dated volcanism in the Bransfield basin has transitional chemistry between subduction zone calc-alkaline and mid ocean ridge tholeiitic magmas. The transitional chemistry can be explained by back-arc rifting in the Bransfield Basin.[7][8]

Earthquakes

Since the early 1980s earthquakes have been recorded in the Shetland Plate. The amount of data has been limited by remoteness, severe weather, and a lack of permeant seismic stations in the area.[8][9] Intermediate depth earthquakes (35–55 km) under the South Shetland Islands indicates that subduction is still occurring at the Shetland Trench.[8]

References

  1. ^ a b Berrocoso, M.; Fernández-Ros, A.; Prates, G.; García, A.; Kraus, S. (January 2016). "Geodetic implications on block formation and geodynamic domains in the South Shetland Islands, Antarctic Peninsula". Tectonophysics. 666: 211–219. doi:10.1016/j.tecto.2015.10.023. hdl:10400.1/9659.
  2. ^ a b c d e Bird, Peter (March 2003). "An updated digital model of plate boundaries". Geochemistry, Geophysics, Geosystems. 4 (3). doi:10.1029/2001gc000252. ISSN 1525-2027.
  3. ^ a b c Vérard, Christian; Flores, Kennet; Stampfli, Gérard (January 2012). "Geodynamic reconstructions of the South America–Antarctica plate system". Journal of Geodynamics. 53: 43–60. doi:10.1016/j.jog.2011.07.007.
  4. ^ Solari, M. A.; Hervé, F.; Martinod, J.; Roux, J. P. Le; Ramírez, L. E.; Palacios, C. (April 2008). "Geotectonic evolution of the Bransfield Basin, Antarctic Peninsula: insights from analogue models". Antarctic Science. 20 (2): 185–196. doi:10.1017/s095410200800093x. ISSN 1365-2079.
  5. ^ a b c Jin, Young Keun; Lee, Joohan; Hong, Jong Kuk; Nam, Sang Heon (March 2009). "Is subduction ongoing in the South Shetland Trench, Antarctic Peninsula?: new constraints from crustal structures of outer trench wall". Geosciences Journal. 13 (1): 59–67. doi:10.1007/s12303-009-0005-5. ISSN 1226-4806.
  6. ^ Gràcia, Eulàlia; Canals, Miquel; Farràn, Marcel Lí; Prieto, Maria José; Sorribas, Jordi; Team, Gebra (June 1996). "Morphostructure and evolution of the central and Eastern Bransfield Basins (NW Antarctic Peninsula)". Marine Geophysical Researches. 18 (2–4): 429–448. doi:10.1007/BF00286088. ISSN 0025-3235.
  7. ^ González-Ferrán, O. (April 1985). "Volcanic and tectonic evolution of the Northern Antarctic Peninsula—Late Cenozoic to recent". Tectonophysics. 114 (1–4): 389–409. doi:10.1016/0040-1951(85)90023-x.
  8. ^ a b c Pelayo, Aristeo M.; Wiens, Douglas A. (1989). "Seismotectonics and relative plate motions in the Scotia Sea region". Journal of Geophysical Research. 94 (B6): 7293. doi:10.1029/jb094ib06p07293. ISSN 0148-0227.
  9. ^ Ibáñez, J. M.; Morales, J.; Alguacil, G.; Almendros, J.; Oritz, R.; Pezzo, E. Del (March 1997). "Intermediate-focus earthquakes under South Shetland Islands (Antarctica'". Geophysical Research Letters. 24 (5): 531–534. doi:10.1029/97gl00314. ISSN 1944-8007.
7 Continents Club

People who choose to run a marathon on all seven continents are generally considered to be a part of the 7 continents club. However, there is some dispute over what counts for each continent, with specific issue being taken due to races being run in "Antarctica" that actually take place on outlying islands of the continent and not within the continent itself.

Due to the extreme weather conditions in Antarctica, not all races are completed as promised. A notable example is 2001, the Antarctica Marathon in Antarctica had to be held on a boat.

Bransfield Basin

The Bransfield Basin is a back-arc rift basin located off the Northern tip of the Antarctic Peninsula. The basin lies within a Northeast and Southwest trending strait that separates the peninsula from the nearby South Shetland Islands to the Northwest. The basin extends for more than 500 kilometres (310 miles) from Smith Island (South Shetland Islands) to a portion of the Hero Fracture Zone. The basin can be subdivided into three basins: Western, Central, and Eastern. The Western basin is 130 kilometres (81 miles) long by 70 kilometres (43 miles) wide with a depth of 1.3 kilometres (1,400 yards), the Central basin is 230 kilometres (140 miles) long by 60 kilometres (37 miles) wide with a depth of 1.9 kilometres (2,100 yards), and the Eastern basin is 150 kilometres (93 miles) long by 40 kilometres (25 miles) wide with a depth of over 2.7 kilometres (3,000 yards). The three basins are separated by the Deception Island and Bridgeman Island. The moho depth in the region has been seismically interpreted to be roughly 34 kilometres (21 miles) deep.

List of tectonic plates

This is a list of tectonic plates on the Earth's surface. Tectonic plates are pieces of Earth's crust and uppermost mantle, together referred to as the lithosphere. The plates are around 100 km (62 mi) thick and consist of two principal types of material: oceanic crust (also called sima from silicon and magnesium) and continental crust (sial from silicon and aluminium). The composition of the two types of crust differs markedly, with mafic basaltic rocks dominating oceanic crust, while continental crust consists principally of lower-density felsic granitic rocks.

Scotia Plate

The Scotia Plate (Spanish: Placa Scotia) is a tectonic plate on the edge of the South Atlantic and Southern Ocean. 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 Antarctic Plate.Roughly rhomboid, extending between 50°S 70°W and 63°S 20°W, the plate is 800 km (500 mi) wide and 3,000 km (1,900 mi) long. It is moving WSW at 2.2 cm (0.87 in)/year and the South Sandwich Plate is moving east at 5.5 cm (2.2 in)/year in an absolute reference frame. It 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 Scotia Plate is made of oceanic crust and continental fragments now distributed around the Scotia Sea. Before the formation of the plate began 40 million years ago (40Ma), these fragments formed a continuous landmass from Patagonia to the Antarctic Peninsula along an active subduction margin. At present the plate is almost completely submerged, with only the small exceptions of the South Georgia Islands on its northeastern edge and the southern tip of South America.

South Shetland Islands

The South Shetland Islands are a group of Antarctic islands with a total area of 3,687 square kilometres (1,424 sq mi). They lie about 120 kilometres (75 mi) north of the Antarctic Peninsula, and between 430 kilometres (270 mi) to 900 kilometres (560 mi) south-west from the nearest point of the South Orkney Islands. By the Antarctic Treaty of 1959, the islands' sovereignty is neither recognized nor disputed by the signatories and they are free for use by any signatory for non-military purposes.

The islands have been claimed by the United Kingdom since 1908 and as part of the British Antarctic Territory since 1962. They are also claimed by the governments of Chile (since 1940, as part of the Antártica Chilena province) and by Argentina (since 1943, as part of Argentine Antarctica, Tierra del Fuego Province).

Several countries maintain research stations on the islands. Most of them are situated on King George Island, benefitting from the airfield of the Chilean base Eduardo Frei.

There are sixteen research stations to date in different parts of the islands, with Chilean stations being the greatest in number.

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