Magnetic measurements over the Hawaiian ridge and their vulcanological implications

Abstract

The results of an aeromagnetic survey of the Hawaiian Islands are studied in terms of the local magnetic anomalies defined and their relation to known centers of vulcanism. A quantitative analysis as to the depth of origin of the anomalies indicates that in nearly all cases they can be attributed to sub-surface intrusive rock masses at depths of the order of 2 to 6 kilometers. That the intrusive rocks defined are probably related to intrusions of magma derived from the underlying mantle is indicated by both quantitative studies of associated gravity anomalies and seismic refraction crustal measurements. On the basis of these integrated geophysical studies, it appears that there has been extensive intrusion of mantle-derived magma into the crust along the East-West trending submarine Molokai Fracture Zone and that where this fracture system intersected a Northwest-Southeast zone of tectonic weakness or fracture there was vulcanism that led to the formation of the Hawaiian Islands. Although magnetic data are lacking as yet over the entire Hawaiian Ridge from Hawaii to Midway Island, it is not an unreasonable hypothesis that the Ridge as a whole developed in a similar manner over its entire length as a progressive feature with time, in response to a secular shift in crustal stress pattern at the intersection of two major translational fault systems.