The Phoenix Plate was an ancient tectonic plate that existed during the mid-Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 through early Tertiary

Tertiary

The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...

 time. The Phoenix Plate began subducting under the Antarctic Plate

Antarctic Plate

The 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...

. The Phoenix Ridge

Phoenix Ridge

The Phoenix Ridge was an ancient mid-ocean ridge that existed between the Phoenix Plate and the Pacific Plate. The Phoenix Ridge consisted of three ridges and had a spreading rate of 18–20 cm per year until around 84 Ma. A major decrease in spreading rate, and the convergence rate with the...

, a mid-oceanic ridge between the Pacific

Pacific Plate

The 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 the Phoenix Plates which had a spreading rate of 18-20 cm per year until around 84 Ma. A major decrease in spreading rate, and the convergence rate with the Antarctic Plate occurred around 52.3 Ma. During the Late Cretaceous

Late Cretaceous

The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...

, the Phoenix Plate fragmented into the Charcot Plate

Charcot Plate

The Charcot Plate was a fragment of the Phoenix Plate. The Charcot Plate is subducting under West Antarctica. The subduction of the Charcot Plate stopped before 83 Ma, and became fused onto the Antarctic Peninsula. There are remnants of the western part of the Charcot Plate in the Bellingshausen Sea....

, much in the same way in which the Rivera

Rivera Plate

The Rivera Plate is a small tectonic plate located off the west coast of Mexico, just south of the Baja California Peninsula. It is bounded on the northwest by the East Pacific Rise, on the southwest by the Rivera Transform Fault, on the southeast by a deformation zone, and on the northeast by...

 and the Cocos Plate

Cocos Plate

The 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:...

 were formed by the fragmentation of the Farallon Plate

Farallon Plate

The 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...

.