Seamount chains formed near the crest of Juan de Fuca Ridge, northeast Pacific Ocean

Abstract

Heck and Heckle are seamount chains trending approximately northwest on the western flank of Juan de Fuca Ridge near its northern end. Evidence from magnetic anomalies and from chemistry and relative ages of dredged basalt suggests that the seamounts in these chains are produced near the spreading centre on Juan de Fuca Ridge and do not continue to grow as they are carried away by sea-floor spreading. Their development is possibly related to transverse fractures on Juan de Fuca Ridge resulting from reorientation of the ridge from north to north-northeast which began about 8 m.y. ago, combined with tension in the Pacific Plate. In contrast the Eickelberg Chain to the south may have been produced by a fixed-mantle plume now located near Juan de Fuca Ridge, as suggested by limited basalt geochemistry and by the long and productive life of that chain. The Pratt-Welker Chain may also have been produced by a mantle plume, but most other seamounts on the western flanks of Juan de Fuca and Explorer ridges are thought to have formed at crustal fractures near the spreading centres in the same way as the seamounts of the Heck and Heckle chains.