Abstract

Nearly all linear island and seamount chains on the Pacific plate are parallel to small circles generated about either a Hawaiian pole at 72° N., 83° W. or an Emperor pole at 17° N., 107° W. The rates of rotation of the Pacific plate relative to the Hawaiian melting (hot) spot are calculated from age data from the Hawaiian-Emperor chain. Extrapolation of the known age progression along the Hawaiian chain yields a 27-m.y. estimate of the age of the Hawaiian-Emperor bend; however, recent radiometric ages from Koko seamount in the southern Emperor chain indicate that the Hawaiian-Emperor bend is 42 to 44 m.y. old. The Pacific plate apparently moved slowly, if at all, relative to the Hawaiian melting spot from about 20 to 42–44 m.y. ago. The rates of rotation calculated are 1.3° per m.y. about the Hawaiian pole (0 to 20–25 m.y.), < 0.5° per m.y. about a pole near the Hawaiian pole (20–25 to 42–44 m.y.), and 0.8° per m.y. about the Emperor pole (42–44 to 67–70 m.y.).

The proposed rotational motion of the Pacific plate relative to the Hawaiian melting spot can be used to predict ages of seamounts and islands in other chains if the various melting spots are fixed with respect to one another. Almost all ages from other chains are consistent with the rotational model except for two K-Ar ages from the Austral chain.

The proposed rotational motion of the Pacific plate can be used to reconstruct a paleomagnetic polar path of the Pacific plate if the melting spots are fixed with respect to the spin axis. The melting-spot polar path agrees well with the Late Cretaceous and limited Neogene paleomagnetic data. However, an extension of this polar path through the Late Cretaceous based on the Line Islands appears to be inconsistent with existing paleomagnetic data.

The assumption that melting spots are fixed relative to the spin axis (and therefore the equator) can be tested by comparing the equatorial belt of high sedimentation with the sediment distribution predicted by the rotational-plate motion model. Almost every Deep Sea Drilling Project (DSDP) site presently located just north of the equator has its highest sedimentation rate at the time when the melting-spot motion model predicts that it was located at the equator. An equatorial sedimentation model adapted after Winterer (1972) is combined with the melting-spot motion model to generate a predicted isopach map of the post-middle Eocene equatorial sediments. The resulting isopach map is remarkably similar to the Ewing and others (1968) map of actual isopachs determined by seismic profiling. No data at present require motion of the Hawaiian melting spot relative to the spin axis.

The tectonic histories of Japan and the Aleutians appear to reflect the proposed discontinuities of Pacific plate motion.

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