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Steens Mountain—Reversal


Record of Steens Mountain reversal cast in terms of virtual geomagnetic poles (VGPs). Compare with VGP path for the second reversal of the tomographic simulation, depicted below under Simulations.

Record of the Steens Mountain reversal showing the path of directions traversed by the field as polarity progressed from reversed to normal. Successive lavas with essentially the same direction are averaged to give a directional group (DG), and indicated as numbered circles along the path. The first attempt of the field to reverse was unsuccessful; although it attained normal polarity by DG30, it soon returned to intermediate directions and only achieved stable normal polarity after DG15.

The big gaps in direction between DG31 and 30, 22 and 21, and 21 and 20 are striking. In both the first and second gap there is a lava flow with individual sample directions smeared along the path in such a way as to suggest that the field may have been changing extremely fast during the time the flow was cooling and becoming magnetized. If this interpretation is correct, it has significant implications for fluid velocities in the core, functioning of the geodynamo, and, as an aside, the mean conductivity of the mantle. If the smeared directions are an artifact, they signal a virtually invisible remagnetization mechanism that paleomagnetists must strive to understand and guard against.


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Last Modified 12/14/01
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