Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second plate, the heavier plate dives beneath the other and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with rates of convergence as high as 11 cm/year.
Obduction is a geological process whereby denser oceanic crust 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, normally the denser oceanic crust sinks under the continental crust in the process of subduction. Obduction, which is less common, normally occurs in plate collisions at orogenic belts or back-arc basins.
A convergent boundary is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a plane where many earthquakes occur, called the Wadati–Benioff zone. These collisions happen on scales of millions to tens of millions of years and can lead to volcanism, earthquakes, orogenesis, destruction of lithosphere, and deformation. Convergent boundaries occur between oceanic-oceanic lithosphere, oceanic-continental lithosphere, and continental-continental lithosphere. The geologic features related to convergent boundaries vary depending on crust types.
The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru–Chile Trench, of the Nazca plate under the South American plate is largely responsible for the Andean orogeny. The Nazca plate is bounded on the west by the Pacific plate and to the south by the Antarctic plate through the East Pacific Rise and the Chile Rise, respectively. The movement of the Nazca plate over several hotspots has created some volcanic islands as well as east–west running seamount chains that subduct under South America. Nazca is a relatively young plate in terms of the age of its rocks and its existence as an independent plate, having been formed from the breakup of the Farallon plate about 23 million years ago. The oldest rocks of the plate are about 50 million years old.
The Cocos plate is a young oceanic tectonic plate beneath the Pacific Ocean off the west coast of Central America, named for Cocos Island, which rides upon it. The Cocos plate was created approximately 23 million years ago when the Farallon plate broke into two pieces, which also created the Nazca plate. The Cocos plate also broke into two pieces, creating the small Rivera plate. The Cocos plate is bounded to the northeast by the North American plate and the Caribbean plate. To the west it is bounded by the Pacific plate and to the south by the Nazca plate.
The Australian plate is a major tectonic plate in the eastern and, largely, southern hemispheres. Originally a part of the ancient continent of Gondwana, Australia remained connected to India and Antarctica until approximately 100 million years ago when India broke away and began moving north. Australia and Antarctica had begun rifting by 96 million years ago and completely separated a while after this, some believing as recently as 45 million years ago, but most accepting presently that this had occurred by 60 million years ago.
The Scotia plate is a minor 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 Antarctica and South America, it is a minor plate whose movement is largely controlled by the two major plates that surround it: the Antarctic plate and the South American 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 Izu–Bonin–Mariana (IBM) arc system is a tectonic plate convergent boundary in Micronesia. The IBM arc system extends over 2800 km south from Tokyo, Japan, to beyond Guam, and includes the Izu Islands, the Bonin Islands, and the Mariana Islands; much more of the IBM arc system is submerged below sealevel. The IBM arc system lies along the eastern margin of the Philippine Sea plate in the Western Pacific Ocean. It is the site of the deepest gash in Earth's solid surface, the Challenger Deep in the Mariana Trench.
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. Finally, the Bransfield Strait 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 1,600 kilometres (990 mi) long Macquarie fault zone is a major right lateral-moving transform fault along the seafloor of the south Pacific Ocean which runs from New Zealand southwestward towards the Macquarie triple junction. It is also the tectonic plate boundary between the Australian plate to the northwest and the Pacific plate to the southeast. As such it is a region of high seismic activity and recorded the largest strike-slip event on record up to 23 May 1989, of at least 8.0
The Pacific-Farallon Ridge was a spreading ridge during the Late Cretaceous that extended 10,000 km in length and separated the Pacific Plate to the west and the Farallon Plate to the east. It ran south from the Pacific-Farallon-Kula triple junction at 51°N to the Pacific-Farallon-Antarctic triple junction at 43°S. As the Farallon Plate subducted obliquely under the North American Plate, the Pacific-Farallon Ridge approached and eventually made contact with the North American Plate about 30 million years ago. On average, this ridge had an equatorial spreading rate of 13.5 cm per year until its eventual collision with the North American Plate. In present day, the Pacific-Farallon Ridge no longer formally exists since the Farallon Plate has been broken up or subducted beneath the North American Plate, and the ridge has segmented, having been mostly subducted as well. The most notable remnant of the Pacific-Farallon Ridge is the 4000 km Pacific-Nazca segment of the East Pacific Rise.
The Caroline plate is a minor tectonic plate that straddles the Equator in the eastern hemisphere located north of New Guinea. It forms a subduction zone along the border with the Bird's Head plate and other minor plates of the New Guinea region to the south. A transform boundary forms the northern border with the Pacific plate. Along the border with the Philippine Sea plate is a convergent boundary that transitions into a rift.
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.
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. 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. 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.
The Pacific Ocean evolved in the Mesozoic from the Panthalassic Ocean, which had formed when Rodinia rifted apart around 750 Ma. The first ocean floor which is part of the current Pacific plate began 160 Ma to the west of the central Pacific and subsequently developed into the largest oceanic plate on Earth.
The Woodlark Basin is a young geologic structural basin located in the southwestern Pacific Ocean, found to the southeast of the island country of Papua New Guinea. The basin is an extensional basin that is actively spreading and has a seafloor spreading center. The basin formed between the then Indo-Australian plate and the Solomon microplate creating the presently independent Woodlark plate. The Woodlark Basin has a complex geologic history dating back twenty million years to the initial opening of the basin but most of the spreading has happened in the last 3.6 million years.
Subduction polarity reversal is a geologic process in which two converging plates switch roles: The over-lying plate becomes the down-going plate, and vice versa. There are two basic units which make up a subduction zone. This consists of an overriding plate and the subduction plate. Two plates move towards each other due to tectonic forces. The overriding plate will be on the top of the subducting plate. This type of tectonic interaction is found at many plate boundaries.
The Chile Ridge, also known as the Chile Rise, is a submarine oceanic ridge formed by the divergent plate boundary between the Nazca plate and the Antarctic plate. It extends from the triple junction of the Nazca, Pacific, and Antarctic plates to the Southern coast of Chile. The Chile Ridge is easy to recognize on the map, as the ridge is divided into several segmented fracture zones which are perpendicular to the ridge segments, showing an orthogonal shape toward the spreading direction. The total length of the ridge segments is about 550–600 km.
