Permanent Aspects of the Earth's Non-dipole Magnetic Field over Upper Tertiary Times

Investigation of collected palaeomagnetic results from continental igneous rocks and from oceanic sediment-cores, shows a persistent off-centre displacement of the effective dipole source of the main field over Quaternary and Recent times (about the past two million years). This dipole displacement is 191±38 km northward along the rotational axis. Further evidence suggests a similar enduring displacement during all of Upper Tertiary time. The effect of this result on palaeomagnetic interpretations is discussed. The evidence also suggests that we might search for significant differences between the time-average normal and reversed field configurations, and for other internal manifestations of the north-south asymmetry. A consistently world-wide eastward declination of 3.3±1.0° has been found for the time-average Upper Tertiary and later field, but no satisfactory explanation has been proposed.