Abstract

The Hawaiian Ridge and Emperor Seamounts appear to form a single chain of tholeiitic shield volcanoes that erupted sequentially on the sea floor of the central Pacific Ocean during Tertiary and Quaternary time. The chain cuts obliquely across the older Cretaceous structural patterns of that sea floor. While the pattern of the chain as a whole is linear, the individual volcanoes lie on short, sigmoidal, en echelon loci that are subparallel with respect to each other and that may represent extensional features in the crust and upper mantle. In general, the order of eurption progressed from northwest to southeaśt along the chain, but the rate of progression of volcanism along individual loci is nonlinear where best studied in the southeastern part of the chain. Furthermore, simultaneous eruptions appear to have occurred within a distance along the chain of about 200 to 400 km. The available data are consistent with a genesis related to the motion of the Pacific crust over a melting spot in the mantle. This melting spot, which may be due to either excess heat or pressure release, appears to have a diameter of about 300 km and is presently centered slightly north of the island of Hawaii. We concur with the idea that the bend in the Hawaiian-Emperor chain probably reflects a significant change in the motion of the Pacific plate. Our best estimate of the age of the Hawaiian-Emperor bend, based on the existing radiometric data, is 24.6 ± 2.5 m.y., which correlates with a time of increased tectonic activity in the western Pacific island arcs and along the northern and eastern boundaries of the Pacific plate. The vector change in the motion of the Pacific plate (with respect to the melting spot) that is required to produce the bend is about 12 cm/yr in a west-southwest-ward direction.

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