Nazca Plate

The Nazca 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 both in terms of the age of its rocks and its existence as an independent plate having been formed from the break-up of the Farallon Plate about 23 million years ago. The oldest rocks of the plate are about 50 million years old.[2]

Nazca Plate
The Nazca Plate
TypeMinor
Approximate area15,600,000 km2[1]
Movement1north-east
Speed140-53mm/year
FeaturesPacific Ocean
1Relative to the African Plate

Boundaries

East Pacific and Chile Rise

A triple junction, the Chile Triple Junction,[3] occurs on the seafloor of the Pacific Ocean off Taitao and Tres Montes Peninsula at the southern coast of Chile. Here three tectonic plates meet: the Nazca Plate, the South American Plate, and the Antarctic Plate.

Peru–Chile Trench

The eastern margin is a convergent boundary subduction zone under the South American Plate and the Andes Mountains, forming the Peru–Chile Trench. The southern side is a divergent boundary with the Antarctic Plate, the Chile Rise, where seafloor spreading permits magma to rise. The western side is a divergent boundary with the Pacific Plate, forming the East Pacific Rise. The northern side is a divergent boundary with the Cocos Plate, the Galapagos Rise.

The subduction of the Nazca plate under southern Chile has a history of producing massive earthquakes, including the largest ever recorded on earth, the moment magnitude 9.5 1960 Valdivia earthquake.

Intraplate features

Hotspots

A second triple junction occurs at the northwest corner of the plate where the Nazca, Cocos, and Pacific Plates all join off the coast of Colombia. Yet another triple junction occurs at the southwest corner at the intersection of the Nazca, Pacific, and Antarctic Plates off the coast of southern Chile. At each of these triple junctions an anomalous microplate exists, the Galapagos Microplate at the northern junction and the Juan Fernandez Microplate at the southern junction. The Easter Island Microplate is a third microplate that is located just north of the Juan Fernandez Microplate and lies just west of Easter Island.

Aseismic ridges

The Carnegie Ridge is a 1,350-km-long and up to 300-km-wide feature on the ocean floor of the northern Nazca Plate that includes the Galápagos archipelago at its western end. It is being subducted under South America with the rest of the Nazca Plate.

Fracture zones

The Darwin Gap is the area between the Nazca Plate and the coast of Chile, where Charles Darwin experienced the earthquake of 1835. It is expected that this area will be the epicenter of a major quake in the near future.[4]

Plate motion

The absolute motion of the Nazca Plate has been calibrated at 3.7 cm/yr east motion (88°), one of the fastest absolute motions of any tectonic plate. The subducting Nazca Plate, which exhibits unusual flat-slab subduction, is tearing as well as deforming as it is subducted (Barzangi and Isacks). The subduction has formed, and continues to form, the volcanic Andes Mountain Range. Deformation of the Nazca Plate even affects the geography of Bolivia, far to the east (Tinker et al.). The 1994 Bolivia earthquake occurred on the Nazca Plate; this had a magnitude of 8.2 , which at that time was the strongest instrumentally recorded earthquake occurring deeper than 300 km.

Aside from the Juan Fernández Islands, this area has very few other islands that are affected by the earthquakes that are a result of complicated movements at these junctions.

Geologic history

The precursor of both the Nazca Plate and the Cocos Plate (to its north) was the Farallon Plate, which split in the late Oligocene, about 22.8 Mya, a date arrived at by interpreting magnetic anomalies. Subduction under the South American continent began about 140 Mya, although the formation of the high parts of the Central Andes and the Bolivian orocline did not occur until 45 Mya. It has been suggested that the mountains were forced up by the subduction of the older and heavier parts of the plate, which sank more quickly into the mantle.[5]

See also

References

  1. ^ "Sizes of Tectonic or Lithospheric Plates". About.com Geology. Retrieved 4 January 2016.
  2. ^ Dutch, Steven. "Sea Floor Spreading in the Pacific".
  3. ^ Kelly McGuire (8 April 2004). "Tectonics of South America: Chile Triple Junction" (PDF). Retrieved 27 February 2016.
  4. ^ Darwin Gap quake will shake Chile again [1], New Scientist, 30 Jan 2011, accessed 8 Feb 2011.
  5. ^ "Mountains on a plate form the Andes" (Issue No:214). University World News. 25 March 2012. Retrieved 8 February 2016.
Bibliography

Coordinates: 15°00′00″S 85°00′00″W / 15.00000°S 85.00000°W

Antarctic Plate

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 southern part of the supercontinent Pangea), 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.

The Antarctic Plate has an area of about 60,900,000 km2 (23,500,000 sq mi). It is the Earth's fifth-largest plate.

The Antarctic Plate's movement is estimated to be at least 1 cm (0.4 in) per year towards the Atlantic Ocean

Cachet Fault

Cachet Fault is a dextral strike-slip fault in Aysén Region, Chile. The fault runs in north-south direction right to the east of the Northern Patagonian Ice Field. Various west-east glacial valleys have been displaced the movement of the fault. The existence of the fault and its movement has been linked to the Chile Triple Junction and the oblique subduction of Nazca Plate. The fault exhibits present-day seismicity. Together, Exploradores Fault Zone and Liquiñe-Ofqui Fault Zone and Cachet Fault makes up the boundaries of a crustal block that has been uplifted hosting at present the Northern Patagonian Ice Field.

Carnegie Ridge

The Carnegie Ridge is an aseismic ridge on the Nazca Plate that is being subducted beneath the South American Plate. The ridge is thought to be a result of the passage of the Nazca Plate over the Galapagos hotspot. It is named for the research vessel Carnegie, which discovered it in 1929.

Chile Triple Junction

The Chile Triple Junction (or Chile Margin Triple Junction) is a geologic triple junction located on the seafloor of the Pacific Ocean off Taitao and Tres Montes Peninsula on the southern coast of Chile. Here three tectonic plates meet: the South American Plate, the Nazca Plate, and the Antarctic Plate. This triple junction is unusual in that it consists of a mid-oceanic ridge, the Chile Rise, being subducted under the South American Plate at the Peru–Chile Trench.

The Antarctic Plate started to subduct beneath South America 14 million years ago in the Miocene epoch forming the Chile Triple Junction. At first the Antarctic Plate subducted only in the southernmost tip of Patagonia, meaning that the Chile Triple Junction lay near the Strait of Magellan. As the southern part of Nazca Plate and the Chile Rise became consumed by subduction the more northerly regions of the Antarctic Plate begun to subduct beneath Patagonia so that the Chile Triple Junction advanced gradually to its present position in front of Taitao Peninsula at 46°15’.Taitao Peninsula lies near the triple junction and various geological features, such as the Taitao ophiolite, are related to the dynamics of the triple junction.

Cocos Plate

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 by several different plates. To the northeast it is bounded 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.

Coiba Plate

The Coiba Plate is a small tectonic plate (a microplate) located off the coasts south of Panama and northwestern Colombia. It is named after Coiba, the largest island of Central America, just north of the plate offshore southern Panama. It is bounded on the west by the Cocos Plate, on the south by the Malpelo Plate, on the east by the North Andes Plate, and on the north by the Panama Plate. This microplate was previously assumed to be part of the Nazca Plate, forming the northeastern tongue of the Nazca Plate together with the Malpelo Plate. Bordering the Coiba Plate on the east are the north-south striking Bahía Solano Fault and east of that, the Serranía de Baudó, an isolated mountain chain in northwestern Chocó, Colombia.

Easter Microplate

Easter Plate is located to the west of Easter Island off the west coast of South America in the middle of the Pacific Ocean, bordering the Nazca plate to the east and the Pacific plate to the west. It was discovered from looking at earthquake distributions that were offset from the previously perceived Nazca-Pacific Divergent boundary. This young plate is 5.25 million years old and is considered a microplate because it is small with an area of approximately 160,000 km2. Seafloor spreading along the Easter microplate's borders have some of the highest global rates, ranging from 50 to 140 mm/yr.

Galápagos Microplate

The Galapagos Microplate (GMP) is a geological feature of the oceanic crust located at 1°50' N, offshore of the west coast of Colombia. The GMP is collocated with the Galapagos Triple Junction, which is an atypical ridge-ridge-ridge triple junction. At the Galapagos Triple Junction, the Pacific Plate, Cocos Plate, and Nazca Plate meet incompletely, forming two counter-rotating microplates at the junction of the Cocos-Nazca, Pacific-Cocos, and Pacific-Nazca spreading ridges.

Geology of Colombia

Geology of Colombia refers to the geological composition of the Republic of Colombia that determines its geography. Most of the emerged territory of Colombia covers vast areas within the South American plate, whereas much submerged territory lies within the Caribbean plate and the Nazca plate.

Juan Fernández Plate

The Juan Fernandez Plate is a microplate in the Pacific Ocean. With a surface area of approximately 105 km2, the microplate is located between 32° and 35°S and 109° and 112°W. The plate is located at a triple junction between the Pacific Plate, Antarctic Plate, and Nazca Plate. Approximately 2000 km to the west of South America, it is, on average, 3000 meters deep with its shallowest point coming to approximately 1600 meters, and its deepest point reaching 4400 meters.

Juan Fernández Ridge

The Juan Fernández Ridge is a volcanic island and seamount chain on the Nazca Plate. It runs in a west–east direction from the Juan Fernández hotspot to the Peru–Chile Trench at a latitude of 33° S near Valparaíso. The Juan Fernández Islands are the only seamounts that reach the surface.

Subduction of the ridge beneath South America is thought to have caused the Pampean flat-slab and its associated inland tectonic deformation and reduced magmatic acticity.

Malpelo Plate

The Malpelo Plate is a small tectonic plate (a microplate) located off the coasts west of Ecuador and Colombia. It is the 57th plate to be identified. It is named after Malpelo Island, the only emerged part of the plate. It is bounded on the west by the Cocos Plate, on the south by the Nazca Plate, on the east by the North Andes Plate, and on the north by the Coiba Plate, separated by the Coiba Transform Fault (CTF). This microplate was previously assumed to be part of the Nazca Plate. The Malpelo Plate borders three major faults of Pacific Colombia, the north to south striking Bahía Solano Fault in the north and the Naya-Micay and Remolino-El Charco Faults in the south.

Megathrust earthquake

Megathrust earthquakes occur at subduction zones at destructive convergent plate boundaries, where one tectonic plate is forced underneath another, caused by slip along the thrust fault that forms the contact between them. These interplate earthquakes are the planet's most powerful, with moment magnitudes (Mw) that can exceed 9.0. Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes. No other type of known terrestrial source of tectonic activity has produced earthquakes of this scale.

Nazca Ridge

The Nazca Ridge is a submarine ridge, located on the Nazca Plate off the west coast of South America. This plate and ridge are currently subducting under the South American Plate at a convergent boundary known as the Peru-Chile Trench at approximately 7.7 cm/yr. The Nazca Ridge began subducting obliquely to the collision margin at 11°S, approximately 11.2 Ma, and the current subduction location is 15°S. The ridge is composed of abnormally thick basaltic ocean crust, averaging 18 ±3 km thick. This crust is buoyant, resulting in flat slab subduction under Peru. This flat slab subduction has been associated with the uplift of Pisco Basin and the cessation of Andes volcanism and the uplift of the Fitzcarrald Arch on the South American continent approximately 4 Ma.

North Andes Plate

The North Andes Plate is a small tectonic plate located in the northern Andes. It is squeezed between the faster moving South American Plate and the Nazca Plate. Due to the subduction of the Nazca Plate this area is very prone to volcanic and seismic activity.

Panama Plate

The Panama Plate is a small tectonic plate sandwiched between the Cocos Plate and Nazca Plate to the south and the Caribbean Plate to the north. Most of its borders are convergent boundaries including a subduction zone to the west. It consists, for the most part, of the nations of Panama and Costa Rica.

Peru–Chile Trench

The Peru–Chile Trench, also known as the Atacama Trench, is an oceanic trench in the eastern Pacific Ocean, about 160 kilometres (100 mi) off the coast of Peru and Chile. It reaches a maximum depth of 8,065 meters (26,460 ft) below sea level in Richards Deep (23°10′45″S 71°18′41″W) and is approximately 5,900 kilometres (3,666 mi) long; its mean width is 64 kilometres (40 mi) and it covers an expanse of some 590,000 square kilometres (228,000 mi²).

The trench delineates the boundary between the subducting Nazca Plate and the overriding South American Plate.

South American Plate

The South American Plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African Plate, with which it forms the southern part of the Mid-Atlantic Ridge.

The easterly edge is a divergent boundary with the African Plate; the southerly edge is a complex boundary with the Antarctic Plate, the Scotia Plate, and the Sandwich Plate; the westerly edge is a convergent boundary with the subducting Nazca Plate; and the northerly edge is a boundary with the Caribbean Plate and the oceanic crust of the North American Plate. At the Chile Triple Junction, near the west coast of the Taitao–Tres Montes Peninsula, an oceanic ridge known as the Chile Rise is actively subducting under the South American Plate.

Geological research suggests that the South American Plate is moving westward away from the Mid-Atlantic Ridge: "Parts of the plate boundaries consisting of alternations of relatively short transform fault and spreading ridge segments are represented by a boundary following the general trend." As a result, the eastward-moving and more dense Nazca Plate is subducting under the western edge of the South American Plate, along the continent's Pacific coast, at a rate of 77 mm (3.0 in) per year. The collision of these two plates is responsible for lifting the massive Andes Mountains and for creating the numerous volcanoes which are strewn throughout them.

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