New paleomagnetic data invite reassessment of the breakup history of parts of the Pacific margin of Gondwana due to the Mesozoic opening of the southern ocean basins. These data indicate clockwise rotation of the Antarctic Peninsula relative to East Antarctica between ∼175 and ∼155 Ma that would have created as much as 1000 km of pre-anomaly M25 ocean floor in the Weddell Sea basin. The paleomagnetic data also suggest that between ∼155 and ∼130 Ma, the Antarctic Peninsula rotated counterclockwise relative to East Antarctica, rotation that, along with the southward motion of East Antarctica, would have caused subduction of the newly created Weddell Sea ocean floor beneath the southern Antarctic Peninsula. East-vergent folding and thrusting of Jurassic back-arc basin rocks along the southeastern Antarctic Peninsula, known as the Palmer Land event, probably resulted from deformation along this newly created convergent margin. The presence of Jurassic Weddell Sea floor would have isolated eastern Gondwana (East Antarctica, Australia, and India) from the Antarctic Peninsula and western Gondwana (Africa and South America), encouraging increased marine faunal connections between the Pacific and Weddell Sea- Mozambique-Somali ocean basins during the ∼175 to ∼130 Ma interval. After ∼130 Ma, the Antarctic Peninsula would have been connected to East Antarctica via the other West Antarctic terranes, thereby facilitating land migrations between eastern and western Gondwana.

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