The alignment and age progression of volcanoes produced as a tectonic plate moves over a mantle plume can be used to reconstruct both the direction and rate of past plate motion assuming the plume remains in a fixed location. New 40Ar/39Ar dates for lavas from 15 volcanoes spanning the entire length (∼2800 km) of the Northwest Hawaiian Ridge (NWHR) facilitate improved age-distance relationships. These are used to constrain a significant kink in the NWHR at 25.3 ± 0.5 Ma as the Pacific plate experienced a brief episode of more northerly motion and rotated counter-clockwise. The age progression (i.e., velocity of the Pacific plate) increased markedly from 57 to 87 km/Ma following the plate motion change. This mid-Cenozoic tectonic reorganization has been previously identified in plate motion models, but has been poorly constrained temporally. We demonstrate that this event affected four seamount trails within the Pacific Basin, and had a significant impact on all circum-Pacific volcanic arcs.

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