Structural and temporal requirements for geomagnetic field reversal deduced from lava flows

Details Structural and temporal requirements for geomagnetic field reversal deduced from lava flows Structural and temporal requirements for geomagnetic field reversal deduced from lava flows

Mar 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005natur.434..633s&link_type=abstract

Nature, Volume 434, Issue 7033, pp. 633-636 (2005).

Astronomy and Astrophysics

Astronomy

30

Scientific paper

Reversals of the Earth's magnetic field reflect changes in the geodynamo-flow within the outer core-that generates the field. Constraining core processes or mantle properties that induce or modulate reversals requires knowing the timing and morphology of field changes that precede and accompany these reversals. But the short duration of transitional field states and fragmentary nature of even the best palaeomagnetic records make it difficult to provide a timeline for the reversal process. 40Ar/39Ar dating of lavas on Tahiti, long thought to record the primary part of the most recent `Matuyama-Brunhes' reversal, gives an age of 795 +/- 7kyr, indistinguishable from that of lavas in Chile and La Palma that record a transition in the Earth's magnetic field, but older than the accepted age for the reversal. Only the `transitional' lavas on Maui and one from La Palma (dated at 776 +/- 2kyr), agree with the astronomical age for the reversal. Here we propose that the older lavas record the onset of a geodynamo process, which only on occasion would result in polarity change. This initial instability, associated with the first of two decreases in field intensity, began ~18kyr before the actual polarity switch. These data support the claim that complete reversals require a significant period for magnetic flux to escape from the solid inner core and sufficiently weaken its stabilizing effect.

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