Investigation of the Large Scale Palaeomagnetic Field over the past 25 million years. Eastward Shift of the Icelandic Spreading Ridge

Abstract

An up‐to‐date appraisal of 291 late Tertiary and Quaternary palaeomagnetic pole positions shows that they cannot be explained by accepted rates and directions of rigid plate movements (although such movements are not disputed). The pole positions are thus believed to reflect in large part the behaviour of the geomagnetic field itself. The mean late Tertiary best‐fitting field source is an axial dipole, displaced north of the equatorial plane by 325 ± 57 km. However, there has been a slow rate of change of this parameter during the late Tertiary. Icelandic data, when examined in detail, also show evidence of long‐term geomagnetic field variations and further suggest that the hypothesis of an eastward shift of the Icelandic spreading ridge during the Pliocene is correct. A consequence of these long‐term geomagnetic field variations, spanning at least several years, is that it may not be possible to define palaeomagnetic pole positions with an accuracy better than about 5°. Copyright © 1974, Wiley Blackwell. All rights reserved