 During the Late Cretaceous or early Cenozoic, the southwestern part of the Phoenix Plate fragmented into the Charcot Plate, much in the same way in which the Rivera and Cocos plates were formed by the fragmentation of the Farallon Plate.The Antarctic-Phoenix Ridge, a mid-oceanic ridge between the Antarctic and Phoenix plates, initiated following Late Cretaceous to early Cenozoic times when the Phoenix Plate had divergent boundaries with the Bellingshausen and Pacific plates in the southwestern Pacific Ocean.A major decrease in spreading rate of the Antarctic-Phoenix Ridge and the convergence rate of the Phoenix Plate with the Antarctic Plate occurred around 52.3 million years ago, followed by subduction of a segment of the Antarctic-Phoenix Ridge between 50 and 43 million years ago.