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Nazca Plate: Map

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The Nazca Plate, named after the Nazcamarker region of southern Perumarker, is an oceanic tectonic plate in the eastern Pacific Oceanmarker basin off the west coast of South America. The ongoing subduction along the Peru-Chile Trenchmarker of Nazca Plate under the South American Plate is largely responsible for the Andean orogeny. Nazca Plate bound to west to the Pacific Plate and to south with the Antarctic Plate throught the East Pacific Rise and the Chile Rise respectively. The movement of Nazca Plate under several hotpots have created some volcanic island as well as east-west running seamount chains the subduct under South America. Nazca is relatively young plate both in terms of age of rocks and existence as independent plate.

Seafloor speading

Yet another triple junction, the Chile Triple Junction, occurs on the seafloor of the Pacific Oceanmarker off Taitao and Tres Montes Peninsula at the southern coast of Chilemarker. Here three tectonic plates meet: the Nazca Plate, the South American Plate, and the Antarctic Plate.

Subduction

The eastern margin is a convergent boundary subduction zone under the South American Plate and the Andes Mountains, forming the Peru-Chile Trenchmarker. 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.

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 Trenchmarker.

The subdubduction of Nazca plate under southern Chile has produced the largest recorded earthquake; the moment magnitude 9.5 1960 Valdivia earthquakemarker.

Hotspots

A triple junction occurs at the northwest corner of the plate where the Nazca, Cocos, and Pacific Plates all join off the coast of Colombiamarker. A second triple junction occurs at the southwest corner at the intersection of the Nazca, Pacific, and Antarctic Plates off the coast of southern Chilemarker. 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 Islandmarker.

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 archipelagomarker at its western end. It is being subducted under South American with the rest of the Nazca Plate.

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 volcanic Andes Mountain Range. Deformation of the Nazca Plate even affects the geography of Boliviamarker, far to the east (Tinker et al.). It was on the Nazca Plate that the 1994 Bolivia earthquakemarker 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 Islandsmarker is an exception.

Geologic history

The precursor of the Nazca Plate and the Cocos Plate to its north was the Farallon Plate, which split in late Oligocene times, about 22.8 Mya, a date arrived at by interpreting magnetic anomalies.

Notes

  1. http://www.nsm.buffalo.edu/courses/gly481-581/McGuire05_2.pdf Tectonics of South America: Chile Triple Junction


References




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