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 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 finally to the south it is bounded by the Nazca plate.
The Cocos Plate was created by sea floor spreading along the East Pacific Rise and the Cocos Ridge, specifically in a complicated area geologists call the Cocos-Nazca spreading system. From the rise the plate is pushed eastward and pushed or dragged (perhaps both) under the less dense overriding Caribbean Plate, in the process called subduction. The subducted leading edge heats up and adds its water to the mantle above it. In the mantle layer called the asthenosphere, mantle rock melts to make magma, trapping superheated water under great pressure. As a result, to the northeast of the subducting edge lies the continuous arc of volcanos —also known as the Central America Volcanic Arc— stretching from Costa Rica to Guatemala, and a belt of earthquakes that extends farther north, into Mexico.
The northern boundary of the Cocos Plate is the Middle America Trench. The eastern boundary is a transform fault, the Panama Fracture Zone. The southern boundary is a mid-oceanic ridge, the Galapagos Rise. The western boundary is another mid-ocean ridge, the East Pacific Rise.
An earthquake that occurred in Mexico city in 1985 resulted in the subduction of the Cocos Plate. The Cocos plate has been subducting under the North American plate along the Middle America Trench located under the Caribbean plate which is the major subduction zone, currently one of the largest trenches.The Southern boundary of the Cocos Plate is a mid oceanic ridge that is a divergent boundary. There is an ongoing volcanic belt that extends from Guatemala to Costa Rica caused by the melting of mantle rock to make magma. The volcanic front of the Mexican volcanic belt is located far away from the trench at a distance of 220 km in the West to 450 km in the east along the volcanic belt. Widespread volcanism occurs throughout southern Mexico,in specific along the east trending Mexican volcanic belt. To overcome the problem, there was a proposal of subducting the Cocos Plate to greater depths (Pardo and Suarez,1995) but was proven to be controversial by Velma,2001.
The Rivera Plate north of the Cocos Plate is thought to have separated from the Cocos Plate 5–10 million years ago. The boundary between the two plates appears to lack a definite transform fault, yet they are regarded as distinct. After its separation from the Cocos Plate, the Rivera Plat started acting as an independent microplate.
The devastating 1985 Mexico City earthquake was a result of the subduction of the Cocos Plate beneath the North American Plate. The also devastating 2001 El Salvador earthquakes were generated in the subduction of this plate on the Caribbean Plate.
5 Influence of Rivera-Cocos plate boundary geodynamics on earthquake intensity patterns; the 9 October 1995 (Mw 8.0) and 21 (22) January 2003 (Mw 7.5) earthquakes
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