Shetland Plate

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Shetland Plate
ShetlandPlate.png
Shetland Plate shaded in red.
Type Minor
Coordinates 62°10′S61°00′W / 62.167°S 61.000°W / -62.167; -61.000 Coordinates: 62°10′S61°00′W / 62.167°S 61.000°W / -62.167; -61.000
Movement1Northwest
Speed11 to 2 cm (0.39 to 0.79 in)/yr
Features South Shetland Islands, Southern Ocean
1Relative to the African Plate

The Shetland Plate, or South Shetland Plate, is a tectonic microplate located off the tip of the Antarctic Peninsula that contains the South Shetland Islands. [1] The plate is bordered on three sides by the Antarctic Plate, while 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 a 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]

Contents

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

Boundaries and bathymetry of the Shetland Plate. Shetland Plate Boundries.png
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 Deception Island and Penguin Island. Plutons of calc-alkaline compositions, formed from a type of magma created 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 indicate that subduction is still occurring at the Shetland Trench. [8]

Related Research Articles

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The Ring of Fire is a region around much of the rim of the Pacific Ocean where many volcanic eruptions and earthquakes occur. The Ring of Fire is a horseshoe-shaped belt about 40,000 km (25,000 mi) long and up to about 500 km (310 mi) wide.

Island arc Arc-shaped archipelago formed by intense seismic activity of long chains of active volcanoes

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 along the subduction zone. They are the principal way by which continental growth is achieved.

Antarctic Plate Tectonic plate containing the continent of Antarctica and extending outward under the surrounding oceans

The Antarctic Plate is a tectonic plate containing the continent of Antarctica, the Kerguelen Plateau and extending outward under the surrounding oceans. After breakup from Gondwana, the Antarctic plate began moving the continent of Antarctica south to its present isolated location causing the continent to develop a much colder climate. The Antarctic Plate is bounded almost entirely by extensional mid-ocean ridge systems. The adjoining plates are the Nazca Plate, the South American Plate, the African Plate, the Somali Plate, the Indo-Australian Plate, the Pacific Plate, and, across a transform boundary, the Scotia Plate.

African Plate A major tectonic plate underlying Africa west of the East African Rift

The African Plate is a major tectonic plate straddling the Equator as well as the prime meridian. It includes much of the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges. Between 60 million years ago and 10 million years ago, the Somali Plate began rifting from the African Plate along the East African Rift. Since the continent of Africa consists of crust from both the African and the Somali plates, some literature refers to the African Plate as the Nubian Plate to distinguish it from the continent as a whole.

Scotia Plate Minor oceanic tectonic plate between the South American and Antarctic Plates

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.

Penguin Island (South Shetland Islands)

Penguin Island is one of the smaller of the South Shetland Islands of Antarctica.

South Shetland Trough

The South Shetland Trough is an undersea trough located north of the South Shetland Islands. It 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 South Shetland Islands.

West Antarctic Rift System

The West Antarctic Rift System is a series of rift valleys between East and West Antarctica. It encompasses the Ross Embayment, the Ross Sea, the area under the Ross Ice Shelf and a part of Marie Byrd Land in West Antarctica, reaching to the base of the Antarctic Peninsula. It has an estimated length of 3,000 km (1,900 mi) and a width of approximately 700 km (430 mi). Its evolution is due to lithospheric thinning of an area of Antarctica that resulted in the demarcation of East and West Antarctica. The scale and evolution of the rift system has been compared to that of the Basin and Range Province of the Western United States.

Phoenix Plate Tectonic plate that existed during the mid-Jurassc through late-Cenozoic time

The Phoenix 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 early as 410 million years ago, during which time the Phoenix Plate was subducting under eastern Gondwana.

Back-arc basin Submarine features associated with island arcs and subduction zones

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Seal Nunataks

The Seal Nunataks are a group of 16 islands called nunataks emerging from the Larsen Ice Shelf east of Graham Land, Antarctic Peninsula. The Seal Nunataks have been described as separate volcanic vents of ages ranging from Miocene to Pleistocene. There are unconfirmed reports of Holocene volcanic activity.

Izu–Bonin–Mariana Arc

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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 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.

Caroline Plate Minor oceanic tectonic plate north of New Guinea

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Mariana Plate Small tectonic plate west of the Mariana Trench

The Mariana Plate is a micro tectonic plate located west of the Mariana Trench which forms the basement of the Mariana Islands which form part of the Izu–Bonin–Mariana Arc. It is separated from the Philippine Sea Plate to the west by a divergent boundary with numerous transform fault offsets. The boundary between the Mariana and the Pacific Plate to the east is a subduction zone with the Pacific Plate subducting beneath the Mariana. This eastern subduction is divided into the Mariana Trench, which forms the southeastern boundary, and the Izu–Ogasawara Trench the northeastern boundary. The subduction plate motion is responsible for the shape of the Mariana plate and back arc.

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This is a list of articles related to plate tectonics and tectonic plates.

The Antarctic Peninsula, roughly 1,000 kilometres (650 mi) south of South America, is the northernmost portion of the continent of Antarctica. Like the associated Andes, the Antarctic Peninsula is an excellent example of ocean-continent collision resulting in subduction. The peninsula has experienced continuous subduction for over 200 million years, but changes in continental configurations during the amalgamation and breakup of continents have changed the orientation of the peninsula itself, as well as the underlying volcanic rocks associated with the subduction zone.

Geology of the Pacific Ocean Overview about the geology of the Pacific Ocean

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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 from Smith Island 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 long by 70 kilometres wide with a depth of 1.3 kilometres, the Central basin is 230 kilometres long by 60 kilometres wide with a depth of 1.9 kilometres, and the Eastern basin is 150 kilometres long by 40 kilometres wide with a depth of over 2.7 kilometres. 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 deep.

References

  1. 1 2 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. 1 2 3 4 5 Bird, Peter (March 2003). "An updated digital model of plate boundaries". Geochemistry, Geophysics, Geosystems . 4 (3). doi: 10.1029/2001gc000252 . ISSN   1525-2027.
  3. 1 2 3 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. 1 2 3 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. 1 2 3 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.
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