The supercontinent Rodinia began to break-up 870–845  probably as a consequence of a superplume caused by mantle slab avalanches along the margins of the supercontinent. In a second episode 750  the western half of Rodinia started to rift apart: western Kalahari and South China broke away from the western margins of Laurentia; and by 720  Australia and East Antarctica had also separated. In the Early Jurassic the Pacific Plate opened originating from a triple junction between the Panthalassic Farallon, Phoenix, and Izanagi plates. Panthalassa can be reconstructed based on magnetic lineations and fracture zones preserved in the western Pacific.