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-yearold
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.

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