GEOLOGY: A Quick Turn to the Left

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Science  09 Aug 2002:
Vol. 297, Issue 5583, pp. 899a
DOI: 10.1126/science.297.5583.899a

The Fiji Islands sit in an area of almost byzantine tectonic complexity—a zone of seafloor spreading and transform faulting between the Tonga and Vanuatu trenches in an offset section of the Pacific-Australian convergent plate boundary. Understanding this region's history can help in interpreting the geologic evolution of more ancient arc and back-arc settings, such as those thought to have characterized parts of the western margin of North America and the Mediterranean region.

Paleomagnetic results indicate that the Fiji platform itself has rotated substantially (21° to 135° counterclockwise) during the late Cenozoic. Begg and Gray have placed new constraints on the timing and magnitude of the rotation by supplementing the paleomagnetic studies with analyses of the progressive changes in the orientation of age-dated lava-filled dikes and in the slip direction of faults in Tavua, a Pliocene volcano on the island of Viti Levu. Assuming a roughly constant direction of regional compressive stress, they find that the Fiji platform rotated by approximately 50° in the brief interval from 5 to 3 million years ago. — SW

Tectonics 21, 10.1029/2000TC001259 (2002).

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