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Published October 15, 2015 | Accepted Version
Book Section - Chapter Open

The Pacific megagash: A future plate boundary?


Seismic anisotropy is an efficient way to investigate the deformation field within the upper mantle. In the framework of rigid tectonic plates, we make use of recent tomographic models of azimuthal anisotropy to derive the best rotation pole of the Pacific plate in the uppermost 200 km of the mantle. It is found to be in good agreement with current plate motion (NUVEL1, HS3, and NNR). However, when dividing the Pacific plate into two subplates separated by what we refer to as the megagash, an east-west low-velocity and low-anisotropy band extending across the Pacific plate from Samoa-Tonga to the Easter–Juan Fernández Islands, the rotation pole of northern Pacific is still in agreement with current plate motion but not the rotation pole of the southern part of the Pacific, far away from the "classical" rotation pole of the Pacific plate. This result suggests a differential motion between the North and South Pacific and an ongoing reorganization of plates in the Pacific Ocean. The megagash might be a future plate boundary between the North and South Pacific plates, associated with the intense volcanism along this band.

Additional Information

© 2015 Geological Society of America. Submitted on 23 September 2014. Accepted 10 February 2015. First published on September 4, 2015. This work benefited of constructive discussions with Mike Gurnis, Valerie Clouard, Muriel Gerbault at the beginning of the work, of Gael Burgos, and internships of several students, Estelle van Hauwaert, Nawal de Freslon. I also would like to thank Barbara Romanowicz and the second unknown reviewer for their critical and constructive reviews.

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