The
Nazca Plate, named after the
NazcaNazca is a system of valleys on the southern coast of Peru, and the name of the region's largest existing town in the Nazca Province. It is also the name applied to the Nazca culture that flourished in the area between 300 BC and AD 800...
region of southern
PeruPeru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
, is an oceanic tectonic plate in the eastern
Pacific OceanThe Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
basin off the west coast of
South AmericaSouth America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. The ongoing
subductionIn geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
along the
Peru-Chile TrenchThe Peru-Chile Trench, also known as the Atacama Trench, is an oceanic trench in the eastern Pacific Ocean, about 160 kilometres off the coast of Peru and Chile...
of the Nazca Plate under the
South American PlateThe South American Plate is a continental tectonic plate which includes the continent of South America and also a sizeable region of the Atlantic Ocean seabed extending eastward to the Mid-Atlantic Ridge....
is largely responsible for the
Andean orogenyThe Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...
. The Nazca Plate is bound to the west to the
Pacific PlateThe Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
and to the south with the
Antarctic PlateThe Antarctic Plate is a tectonic plate covering the continent of Antarctica and extending outward under the surrounding oceans. The Antarctic Plate has a boundary with the Nazca Plate, the South American Plate, the African Plate, the Indo-Australian Plate, the Scotia Plate and a divergent boundary...
through the
East Pacific RiseThe East Pacific Rise is a mid-oceanic ridge, a divergent tectonic plate boundary located along the floor of the Pacific Ocean. It separates the Pacific Plate to the west from the North American Plate, the Rivera Plate, the Cocos Plate, the Nazca Plate, and the Antarctic Plate...
and the
Chile RiseThe Chile Rise or Chile Ridge is an oceanic ridge, a tectonic divergent plate boundary between the Nazca and Antarctic Plates. Its eastern end is the Chile Triple Junction where the Chile Rise is being subducted below the South American Plate in the Peru-Chile Trench...
respectively. The movement of the Nazca Plate over several
hotspotsThe places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them...
has created some volcanic islands as well as east-west running
seamountA seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
chains that subduct under South America. Nazca is a relatively young plate both in terms of age of rocks and existence as independent plate.
East Pacific and Chile Rise
A
triple junctionA triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction a boundary will be one of 3 types - a ridge, trench or transform fault - and triple junctions can be described according to the types of plate margin that meet at them...
, the
Chile Triple JunctionThe Chile 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...
, occurs on the seafloor of the
Pacific OceanThe Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
off
TaitaoThe Taitao Peninsula is a westward projection of the mainland of Chile, with which it is connected by the narrow Isthmus of Ofqui, over which the natives and early missionaries were accustomed to carry their boats between the Moraleda Channel and Gulf of Penas...
and
Tres Montes PeninsulaThe Tres Montes Peninsula is a southwestward projection of Taitao Peninsula which in turn connects to the mainland of Chile by the narrow Isthmus of Ofqui. The peninsula is situated in Aisén Region close to the Chile Triple Junction of the Nazca, Antarctic and South American Plate....
at the southern coast of
ChileChile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
. Here three
tectonicTectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
plates meet: the Nazca Plate, the
South American PlateThe South American Plate is a continental tectonic plate which includes the continent of South America and also a sizeable region of the Atlantic Ocean seabed extending eastward to the Mid-Atlantic Ridge....
, and the
Antarctic PlateThe Antarctic Plate is a tectonic plate covering the continent of Antarctica and extending outward under the surrounding oceans. The Antarctic Plate has a boundary with the Nazca Plate, the South American Plate, the African Plate, the Indo-Australian Plate, the Scotia Plate and a divergent boundary...
.
Peru-Chile Trench
The eastern margin is a
convergent boundaryIn plate tectonics, a convergent boundary, also known as a destructive plate boundary , is an actively deforming region where two tectonic plates or fragments of lithosphere move toward one another and collide...
subduction zone under the South American Plate and the Andes Mountains, forming the
Peru-Chile TrenchThe Peru-Chile Trench, also known as the Atacama Trench, is an oceanic trench in the eastern Pacific Ocean, about 160 kilometres off the coast of Peru and Chile...
. The southern side is a
divergent boundaryIn plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts which produce rift valleys...
with the Antarctic Plate, the
Chile RiseThe Chile Rise or Chile Ridge is an oceanic ridge, a tectonic divergent plate boundary between the Nazca and Antarctic Plates. Its eastern end is the Chile Triple Junction where the Chile Rise is being subducted below the South American Plate in the Peru-Chile Trench...
, where
seafloor spreadingSeafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Seafloor spreading helps explain continental drift in the theory of plate tectonics....
permits
magmaMagma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
to rise. The western side is a divergent boundary with the
Pacific PlateThe Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
, forming the
East Pacific RiseThe East Pacific Rise is a mid-oceanic ridge, a divergent tectonic plate boundary located along the floor of the Pacific Ocean. It separates the Pacific Plate to the west from the North American Plate, the Rivera Plate, the Cocos Plate, the Nazca Plate, and the Antarctic Plate...
. The northern side is a divergent boundary with the
Cocos PlateThe Cocos Plate is an oceanic tectonic plate beneath the Pacific Ocean off the west coast of Central America, named for Cocos Island, which rides upon it.-Geology:...
, the
Galapagos RiseThe Galapagos Rise is a divergent boundary located between the South American coast and the triple junction of the Nazca Plate, the Cocos Plate, and the Pacific Plate. The volcanically active Galapagos Islands exist on the Galápagos hotspot above 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 magnitudeThe moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...
9.5 1960 Valdivia earthquake.
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
ColombiaColombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...
. Yet another triple junction occurs at the southwest corner at the intersection of the Nazca, Pacific, and Antarctic Plates off the coast of southern
ChileChile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
. At each of these triple junctions an
anomalousAnomaly may refer to:-Astronomy and celestial mechanics :* In astronomy, an anomaly is a quantity measured with respect to an apsis, usually the periapsis...
microplate exists, the
Galapagos MicroplateThe Galapagos Microplate is a small tectonic plate off the west coast of South America near the Galapagos Islands. It differs from most other crustal plates in that it is rotating clockwise between three much larger crustal plates around it, the Nazca, Cocos and Pacific Plates...
at the northern junction and the
Juan Fernandez MicroplateThe Juan Fernández Plate is a small tectonic plate located at the triple junction between the Nazca Plate, Antarctic Plate and the Pacific Plate. It is moving in a clockwise direction. The Juan Fernández Islands of Chile are not carried on this plate as may be suggested by the name.-References:*...
at the southern junction. The
Easter Island MicroplateThe Easter Plate is a small tectonic plate or microplate in the southeastern Pacific. The plate is bounded on the west by the Pacific Plate, and the east by the Nazca Plate. The entire plate is covered by the Pacific Ocean...
is a third microplate that is located just north of the Juan Fernandez Microplate and lies just west of
Easter IslandEaster Island is a Polynesian island in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian triangle. A special territory of Chile that was annexed in 1888, Easter Island is famous for its 887 extant monumental statues, called moai, created by the early Rapanui people...
.
Aseismic ridges
The
Carnegie Ridge is a 1350-km-long and up to 300-km-wide feature on the ocean floor of the northern Nazca Plate that includes the
Galápagos archipelagoThe Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...
at its western end. It is being subducted under South America with the rest of the Nazca Plate.
Fracture zones
Darwin Gap is the area between the Nazca Plate and the coast of Chile, where
Charles DarwinCharles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
experienced the
earthquake of 1835The 1835 Concepción earthquake occurred near the neighboring cities of Concepción and Talcahuano in Chile on February 20 at 15:30 local time and has an estimated magnitude of 8.2 Mfa or 8.1 Ml. The earthquake triggered a tsunami which caused the destruction of Talcahuano. A total of at least 50...
. It is expected that this area will be the epicenter of a major quake in the near future.
[Darwin Gap quake will shake Chile again http://www.newscientist.com/article/dn20048-darwin-gap-quake-will-shake-chile-again.html, New Scientist, 30 Jan 2011, accessed 8 Feb 2011.]
Plate motion
The absolute motion of the Nazca Plate has been calibrated at 3.7 cm/yr east motion (88°), some of the fastest absolute motion 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
volcanic2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
AndesThe Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...
Mountain Range. Deformation of the Nazca Plate even affects the geography of
BoliviaBolivia officially known as Plurinational State of Bolivia , is a landlocked country in central South America. It is the poorest country in South America...
, far to the east (Tinker et al.). It was on the Nazca Plate that the
1994 Bolivia earthquakeThe 1994 Bolivia earthquake occurred on June 9, 1994. The epicenter was located in a sparsely populated region in the Amazon jungle, about 200 miles from La Paz....
occurred, measuring a magnitude MW of 8.2 and the strongest earthquake occurring deeper than 300 km.
Luckily, very few islands are there to suffer the earthquakes that are a result of complicated movements at these junctions.
Juan Fernández IslandsThe Juan Fernández Islands are a sparsely inhabited island group reliant on tourism and fishing in the South Pacific Ocean, situated about off the coast of Chile, and is composed of three main volcanic islands; Robinson Crusoe Island, Alejandro Selkirk Island and Santa Clara Island, the first...
is an exception.
Geologic history
The precursor of the Nazca Plate and the
Cocos PlateThe Cocos Plate is an oceanic tectonic plate beneath the Pacific Ocean off the west coast of Central America, named for Cocos Island, which rides upon it.-Geology:...
to its north was the
Farallon PlateThe Farallon Plate was an ancient oceanic plate, which began subducting under the west coast of the North American Plate— then located in modern Utah— as Pangaea broke apart during the Jurassic Period...
, which split in late
OligoceneThe Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
times, about 22.8 Mya, a date arrived at by interpreting magnetic anomalies.