Abstract

We consider two hypotheses for the origin of a linear trough extending ∼800 km eastward from the intersection of the Louisville seamount chain with the Tonga-Kermadec trench. An extinct spreading center origin is suggested by the trough's eastward termination at a depth discontinuity that resembles a fracture zone. The morphology of the trough, however, is inconsistent with the morphology of other extinct spreading centers, and these two features do not appear to be connected to a larger paleo-plate boundary on their eastern end. We consider an alternative hypothesis in which the trough may be a recent rift in the Pacific plate. Coupling between a large subducting seamount and the overriding Australian plate may serve as a mechanism to focus stresses and nucleate a rift in the subducting Pacific plate. In this model, the seamount would act as a rigid indenter producing tangential extension in the subducting plate about the region where it is coupled to the overriding plate. Impeded subduction is suggested by a prominent seismicity gap around the subducting seamount. The graben morphology of the trough is also consistent with an extensional origin. If hotspot volcanism can produce obstructions and local weaknesses conducive to plate coupling, stress localization, and nucleation of fractures, it may provide a mechanism for subduction-induced plate reorganizations.

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