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The 'Cocos Plate' (Chocos 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.
The Cocos Plate is created by sea floor spreading along the East Pacific Rise, 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. As a result, to the northeast of the subducting edge lies the continuous arc of volcanos stretching from Costa Rica to Guatemala and a belt of earthquakes that extends farther north, into Mexico.

The northeastern and eastern sides are convergent boundaries subducting under the North American Plate, the Caribbean Plate, and the South American Plate. The Cocos Plate is bounded by divergent boundaries to the south with the Nazca Plate and to the west with the Pacific Plate.
The Cocos and Nazca Plates are the remnants of the former Farallon Plate, which broke up about 23 million years ago. The boundary between the plates is marked by a hotspot under the Galapagos Islands.
The subducting Rivera Plate north of the Cocos Plate, is thought to have separated from the Cocos Plate 5-10 million years ago.
The devastating 1985 Mexico City earthquake was caused by seismic activity in the Cocos Plate.

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★ the volcanic arc

★ Martin Meschede and Udo Barckhausen, "Plate tectonic evolution of the Cocos-Nazca plate": reconstructing its geological evolution