Letter abstract

Nature Geoscience 2, 713 - 717 (2009)
Published online: 13 September 2009 | Corrected online: 13 April 2010 | doi:10.1038/ngeo622

There is a Corrigendum (May 2010) associated with this Letter.

Subject Category: Geomagnetism, palaeomagnetism and core processes

No asymmetry in geomagnetic reversals recorded by 1.1-billion-year-old Keweenawan basalts

Nicholas L. Swanson-Hysell1, Adam C. Maloof1, Benjamin P. Weiss2 & David A. D. Evans3


Interpreting the past latitude and geography of the continents from palaeomagnetic data relies on the key assumption that Earth’s geomagnetic field behaves as a geocentric axial dipole. The axial dipolar field model implies that all geomagnetic reversals should be symmetric. However, palaeomagnetic data from volcanic rocks produced by the 1.1-billion-year-old Keweenawan Rift system in North America have been interpreted to show asymmetric reversals, which had led to the suggestion that there was a significant non-axial dipole contribution to the magnetic field during this time1, 2. Here we present high-resolution palaeomagnetic data that span three geomagnetic field reversals from a well-described series of basalt flows at Mamainse Point, Ontario, in the Keweenawan Rift. Our data show that each reversal is symmetric. We thus conclude that the previously documented reversal asymmetry is an artefact of the rapid motion of North America during this time. Comparisons of reversed and normal populations that were time-averaged over entire polarity intervals, or from sites not directly on either side of a geomagnetic reversal, have previously led to the appearance of reversal asymmetry.

  1. Department of Geosciences, Princeton University, Guyot Hall, Washington Road, Princeton, New Jersey 08544, USA
  2. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
  3. Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, Connecticut 06520, USA

Correspondence to: Nicholas L. Swanson-Hysell1 e-mail: nswanson@princeton.edu

* In the version of this Letter originally published, Supplementary Tables S2, S3 and S4 contained several errors. Consequently, the estimates of the rate of motion on page 716 should have read: "The estimates for the rate of motion from 1,108Myr to 1,097Myr range between 21.5±7.1cmyr−1 for Osler Volcanics reversed→North Shore normal, to 33.6±3.5cmyr−1 for Coldwell Complex reversed→North Shore normal." Furthermore, the position of the Duluth Complex reversed pole in Fig. 3a and the positions of the lower normal and upper normal palaeopoles in Fig. 3b were slightly incorrect. These errors have been corrected in the HTML and PDF versions of the text.


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