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Detailed Reference Information |
Valet, J., Brassart, J., Quidelleur, X., Soler, V., Gillot, P. and Hongre, L. (1999). Paleointensity variations across the last geomagnetic reversal at La Palma, Canary Islands, Spain. Journal of Geophysical Research 104: doi: 10.1029/1998JB900099. issn: 0148-0227. |
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A detailed volcanic record of absolute paleointensity has been obtained for the period encompassing the last geomagnetic reversal, from a succession of 69 distinct lava flows in two adjacent sections on the island of La Palma. The correlation between the two sections relies on the positions of the Brunhes-Matuyama boundary and on the flow chronology obtained by a refined potassium/argon (K/Ar) dating technique. Several pretransitional flows exhibit very shallow paleomagnetic inclinations, but they cannot be considered as really transitional. Paleointensity experiments conducted on 288 specimens provided 168 successful determinations (14 were obtained after correction) for 50 lava flows that were considered to represent 45 distinct units. The evolution of the paleofield intensity can be constructed by assuming uniform extrusion rates between three dated lava flows. The period preceding the transition is characterized by large fluctuations with typical peak to peak amplitudes between 20 and 40 μT which decrease down to 7 μT prior to the transition. The 100 kyr- long interval following the reversal is associated with field intensities as high as 60 μT and depict a strong and rapid restoration of the dipole field. The virtual dipole moments (VDMs) have been compared with sedimentary VDMs generated from the record of relative paleointensity from Ocean Drilling Program site 851, to which have been added non dipole components similar to the present geomagnetic field. A reasonable fit can be made between the two curves which implies variations in the eruption rates but not incompatible with the uncertainties in the K-Ar age determinations. Thus these results can support but do not fully demonstrate the existence of asymmetrical saw-toothed variations in field intensity. ¿ 1999 American Geophysical Union |
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Keywords
Geomagnetism and Paleomagnetism, Paleointensity, Geomagnetism and Paleomagnetism, Reversals (process, timescale, magnetostratigraphy), Geomagnetism and Paleomagnetism, Core processes, Geomagnetism and Paleomagnetism, Rock and mineral magnetism |
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Publisher
American Geophysical Union 2000 Florida Avenue N.W. Washington, D.C. 20009-1277 USA 1-202-462-6900 1-202-328-0566 service@agu.org |
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