Remanent Magnetization and the Interpretation of Magnetic Anomalies

Lavas and intrusives are often permanently magnetized in a direction different from the direction of the present geomagnetic field and this can make the interpretation of a magnetic intensity map difficult. However, the profiles over a permanently magnetized body are identical with the profiles over an inductively magnetized body of the same shape provided the direction and dip of the geomagnetic field in the induced case is appropriately changed. In which case, the shape of the body can be deduced by the well‐known methods of interpretation of induced anomalies. Examples of the application of this method to Australian Kainozoic basalts, Tertiary basalts from Australia and Tasmania, and the classical Pilansberg dykes have been worked out. This article stresses the fact that the apparently confused patterns obtained by magnetic surveys over volcanic rocks can often be explained with little difficulty as the juxtaposition of normal and reversely magnetized rocks.