HR: 1340h
AN: GP33A-0919    [Abstracts]
TI: The reliability of paleomagnetic directions
AU: Deenen, M H
EM: deenen@geo.uu.nl
AF: Paleomagnetic Laboratory 'Fort Hoofddijk', Faculty of Earth Sciences, Utrecht University, Budapestlaan 17, Utrecht, 3584 CD, Netherlands
AU: * van Hinsbergen, D J
EM: hins@geo.uu.nl
AF: Paleomagnetic Laboratory 'Fort Hoofddijk', Faculty of Earth Sciences, Utrecht University, Budapestlaan 17, Utrecht, 3584 CD, Netherlands
AU: Langereis, C G
EM: langer@geo.u.nl
AF: Paleomagnetic Laboratory 'Fort Hoofddijk', Faculty of Earth Sciences, Utrecht University, Budapestlaan 17, Utrecht, 3584 CD, Netherlands
AB: Reliable paleomagnetic poles are vital for plate tectonic reconstructions. Several authors have proposed reliability criteria for paleomagnetic data but the most commonly used were proposed by van der Voo (1990) who introduced seven criteria to reliable determine a paleomagnetic pole. To average paleosecular variation (PSV) of the geomagnetic field van der Voo proposed to average at least 24 samples with a precision parameter, k (or K for virtual geomagnetic poles (VGPs)) of at least 10.0 and a maximum of 16 degrees for the a95 (or A95). These criteria apply for statistics derived from sets of directions as well as from VGPs. A problem that is largely ignored in paleomagnetism is the use of Fisher statistics (Fisher, 1953) on directions (a95 and k) instead of on VGPs (A95 and K). As was proposed decades ago and recently stressed by Tauxe and Kent (2004), the observed geomagnetic field behaviour fits better with the Virtual Geomagnetic Poles (VGPs) to be Fisherian rather than distributions of measured directions, which are consequently elongated in a north-south direction, especially at low and mid latitudes. We argue that it is more correct to use general Fisher statistics on the VGPs, and so consequently look at deviations from the mean in declination and inclination separately. Furthermore, we use a modified statistical model for the geomagnetic field for the last 5 Ma from Tauxe and Kent (2004) and a set of purely Fisherian VGPs to predict reasonable values for A95 and K as a function of N (amount of samples/sites). These simulations are used as well to give restrictions on the number of samples needed to average out PSV of the geomagnetic field within a certain error. R.van der Voo, 1990. The reliability of paleomagnetic data. Tectonophysics, 184: 1-9 L. Tauxe, D.V. Kent, 2004. A simplified statistical model for the geomagnetic field and the detection of shallow bias in paleomagnetic inclinations: was the ancient magnetic field dipolar? Timescales of the Paleomagnetic Field. Geophys. Monogr. Am. Geophys. Union, 145: 101- 115.
DE: 1522 Paleomagnetic secular variation
DE: 1525 Paleomagnetism applied to tectonics: regional, global
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting