Linear volcanic chains — recording plate motions?

Abstract

Volcanic island chains, showing a progression from high volcanic cone to coral atoll, are especially well developed in the Pacific Ocean, well removed from the active plate margins. These chains include the Hawaiian, Marquesas, Society and Austral Islands, all of which are subparallel and approximately perpendicular to the axis of the East Pacific Rise. Potassium—argon age measurements made a decade ago demonstrated that the locus of volcanism in the Hawaiian chain has migrated toward the southeast in a regular manner, confirming what James Dana suggested more than a century ago. Regression of available K-Ar data on the age of shield building volcanism for sixteen volcanoes of the Hawaiian chain against distance from the site of present activity at Kilauea show a strong linear correlation, yielding an average migration rate for the volcanism of 9.66 (±0.27) cm/yr over the last 27 m.y. This analysis indicates that non-linear models for the migration of volcanism in the Hawaiian chain are unnecessary. A similar monotonic decrease in age of volcanism toward the southeast occurs in the Marquesas, Society and Austral Islands in the South Pacific, with rates of migration in the order of 11 cm/yr. These results together with those from the Hawaiian Islands, the Pitcairn—Gambier Islands and the Pratt-Welker Seamounts are consistent with movement of the Pacific lithospheric plate over magma sources that are fixed in the upper mantle relative to one another. A virtually perfect fit of all the data is obtained for a Pacific plate rotation pole located at 70°N 101°W and a rate of rotation of the Pacific plate about this pole of 1.00 (±0.02)°/m.y. over at least the last 10 m.y. of geological time. These data from the Pacific provide strong support for the Wilson-Morgan hot spot or plume model for the origin of island chains, although the means by which the thermal anomaly underlying each volcanic chain in maintained within the mantle still remains unclear.