Anomalous magnetic directions recorded by laboratory-induced chemical remanent magnetization

Abstract

It has been generally accepted that chemical remanent magnetization (CRM) is acquired either in the direction of the ambient field at the time of chemical alteration¹ or in the direction of a pre-existing natural remanent magnetization (CRM) ^2–4. We report here our experiments in which CRM is carried by magnetite formed during laboratory heating of titanomaghaemite in submarine basalts. This CRM is a stable, single component remanence, acquired in an intermediate direction between the ambient field and pre-existing NRM direction. The role of prior NRM in controlling the direction of CRM is suppressed by externally applied fields of ≈50 µT. (0.5 Oe) but is prominent in fields of ≈20 µT. Thus, stable, intermediate-direction CRMs acquired in past geomagnetic fields are a possibility.