Demagnetization of igneous rocks by alternating magnetic fields

Abstract

Abstract The presence of secondary components of magnetization in basalts often limits the usefulness of their directions of natural remanent megnetization for palaeomagnetic work. Them secondary components may be removed by alternating magnetic fields. The procedures for doing this are described end tests based on the internal consistency of the results re devised to judge their reliability. Them are supplied successfully to a series of results from specimens collected from the Tertiary basalts of New South Wales. Australia. and a determination of the geomegnetic field in S.E. Australia during the Lower Tertiary is obtained. A study of the behaviour of these basalts in high alternating fields suggests that most of the iron mineral grains have a multi-domain character, and contain a hard end soft component in the ratio of about 1:10.