Characteristic thermomagnetic curve in submarine basalts

Abstract

Thermomagnetic analyses at H=3,000 oe were carried out for 24 submarine rocks dredged from 10 sites mostly from seamounts in the Pacific Ocean. Most of the samples, which are believed to be in situ, show an irreversible increase of both Js and Curie temperature on heating both in air and in vacuum. This increase is explained as unmixing of the original titanomaghemite to magnetite and Ti-rich phases such as hemo-ilmenite and/or pseudo-brookite. The characteristic irreversible change in the thermomagnetic curve is almost sufficient to discriminate uniquely submarine basalts, erupted and preserved in the sea, from those erupted in air.