Magnetic properties of zero‐age oceanic crust; A new submarine lava flow on the Juan de Fuca Ridge

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Abstract
A volcanic eruption that occurred in October, 1993 on the Juan de Fuca Ridge shows unusually high magnetization when compared with older samples from the off‐axis Juan de Fuca Ridge and other Pacific sites. These data, plus data from other young oceanic basalts, indicate that oceanic crustal magnetization may decay rapidly, by 10% in the first year. The considerably slower decrease in magnetization for rocks from older, off‐axis sites agrees with previous models of progressive low temperature oxidation of the mineral titanomagnetite. The magnetization for newly erupted submarine basalts, however, is not consistent with the exponential decay predicted from older sites, indicating that oxidation may not be the sole process responsible for the short‐term decay. Similarly, weak field magnetic susceptibility of the younger rocks does not show an obvious corresponding decrease with increasing age, as expected for the oxidation of titanomagnetite to titanomaghemite. These preliminary results indicate that decay of magnetization of oceanic crustal rocks with time may have two distinct stages, with only the later stage being due to the progressive oxidation of the magnetic minerals.

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