HR: 09:45h
AN: GP41A-08    [Abstracts]
TI: Testing paleosecular variation field models in the Pre-Cambrian
AU: * Fields, R
EM: rfields@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD, La Jolla, CA 92092-0220, United States
AU: Tauxe, L
EM: ltauxe@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD, La Jolla, CA 92092-0220, United States
AU: Kodama, K P
EM: kpk0@lehigh.edu
AF: LeHigh, Dept Earth & Environmental Sci 31 Williams Dr, Bethlehem, PA 18015-3188, United States
AB: One of the most useful assumptions in paleomagnetism is that the geomagnetic field is on average close to that of a geocentric axial dipole (GAD). The assumption that the time-averaged geomagnetic field closely approximates that of a geocentric axial dipole (GAD) is valid for at least the last 5 million years and most paleomagnetic studies make this implicit assumption. Following the seminal work of Constable and Parker (1988), Tauxe and Kent (2004) developed a simple statistical model for the geomagnetic field, which allows prediction of the distribution of directions (and intensities) for any given latitude. They found a simple relationship between the North-South elongation of directions and the inclination. If the field model is approximately valid in the past, comparison of observed directions with predicted distributions allows paleomagnetists to assess the reliability of the observed directions in a novel way and in some cases allows data to be corrected for anomalous inclination shallowing, for example. While the model fits the published data for the last 5 million years reasonably well, it is unknown how far back in time the model is even approximately valid. The key objectives of this study were 1) to sample a sequence of lava flows that are some 1.2 Ga, exposed on the western side of Lake Superior and 2) to obtain paleomagnetic directions from them as a test of the statistical field model in the past. We will present results from 80 ancient lava flows sampled from the North Shore Volcanics.
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 1532 Reference fields: regional, global
DE: 1594 Instruments and techniques
DE: 1599 General or miscellaneous
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting