Palaeomagnetic Secular Variation for Recent Normal and Reversed Epochs, from the Newer Volcanics of Victoria, Australia

Abstract

Summary Palaeomagnetic studies were carried out on 46 sites in basalts from the Newer Volcanics of Victoria, which range in age from Recent to at least 4.5 My. After magnetic cleaning the 25 normal and 21 reversed sites show a marked improvement in precision compared with a previous investigation of 32 sites in which only NRM directions were considered, and give a palaeomagnetic pole at 86.6° S, 266.3° E with A95= 1.9°. The small departure from the present south geographic pole is in the correct sense required by sea-floor spreading south of Australia. The between-site scattering of the mean directions and mean poles (VGPs), as a measure of secular variation, indicated no significant difference between the normal and reversed epochs. The overall values of the between-site angular standard deviation with respect to directions was 8.9°, and with respect to VGPs was 11.4°. The latter is significantly lower than expected on Cox's model, but not significantly different from results from New Zealand and the Western U.S.A., which have similar latitudes to the Newer Volcanics. Comparison of the angular dispersion due to directions with Creer's model suggests that the hemispherical asymmetry of the non-dipole field has persisted over the past few million years, and that the contribution of dipole wobble to the secular variation must have been small over the same period.