Panthalassic Ocean

Panthalassa, also known as the Panthalassic or Panthalassan Ocean, (from Greek "all" and "sea"), was the superocean that surrounded the supercontinent Pangaea. During the Paleozoic—Mesozoic transition c. 250 Ma it occupied almost 70% of Earth's surface. Its ocean-floor has completely disappeared because of the continuous subduction along the continental margins on its circumference. Panthalassa is also referred to as the Paleo-Pacific ("old Pacific") or Proto-Pacific because the Pacific Ocean developed from its centre in the Mesozoic to the present.

The supercontinent Rodinia began to break-up 870–845 Ma probably as a consequence of a superplume caused by mantle slab avalanches along the margins of the supercontinent. In a second episode c. 750 Ma the western half of Rodinia started to rift part: western Kalahari and South China) broke away from the western margins of Laurentia; and by 720 Ma Australia and East Antarctica had also separated. In the Late 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.

In western Laurentia (North America), a tectonic episode that preceded this rifting produced failed rifts that harboured large depositional basins in Western Laurentia. The global ocean of Mirovia, an ocean that surrounded Rodinia, started to shrink as the Pan-African ocean and Panthalassa expanded.

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