Nazca Plate
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     The Nacza plate, shown in light blue

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 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. A triple junction occurs at the northwest corner of the plate where the Nazca, the Cocos, and the Pacific plates all join off the coast of Colombia.

A second junction, the Chile Triple Junction, occurs at the southwest corner at the intersection with the Nazca, the Pacific, and the 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.

Yet another triple junction, the Chile Triple Junction,^[1] 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. 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. This triple junction has been considered to be related to the moment magnitude 9.5, 1960 megathrust earthquake known as the Great Chilean Earthquake.

Luckily, very few islands are there to suffer the earthquakes that are a result of complicated movements at these junctions. Juan Fernández Islands is an exception.

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

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) 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 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 My, a date arrived at by interpreting magnetic anomalies.

Notes

References

• Extreme Science site: "A Lesson in Plate tetonics" The basics explained.
• Galapagos rise junction (map)
• Juan Fernandez and Easter microplate (map)
• Muawia Barazangi and Bryan L. Isacks, "Spatial distribution of earthquakes and subduction of the Nazca plate beneath South America" in Geology Vol. 4, No. 11, pp. 686–692. Abstract
• Mark Andrew Tinker, Terry C. Wallace, Susan L. Beck, Stephen Myers, and Andrew Papanikolas, "Geometry and state of stress of the Nazca plate beneath Bolivia and its implication for the evolution of the Bolivian orocline" in Geology 24(5), pp. 387–390 Abstract
• Cahill, T. and B. Isacks (1992). "Seismicity and shape of the subducted Nazca plate." Journal Geophysical Research 97 (12)
• James, D. (1978). "Subduction of the Nazca plate beneath Central Peru." Geology 6 (3) pp 174 – 178
• Martin Meschede and Udo Barckhausen, "Plate tectonic evolution of the Cocos-Nazca spreading center" (pdf file)

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