HR: 1340h
AN: GP53C-1373    [Abstracts]
TI: Development of the microwave LTD-DHT Shaw method for absolute paleointensity determination
AU: * Yamamoto, Y
EM: y.yamamoto@kochi-u.ac.jp
AF: Kochi University, B200 Monobe, Nankoku, Kochi, 783-8502, Japan
AU: Shaw, J
AF: University of Liverpool, Oliver Lodge Laboratories, Oxford Street, Liverpool, L69 7ZE, United Kingdom
AB: In the last decade, the microwave demagnetization and remagnetization techniques (Walton et al., 1992, 1993) have been successfully incorporated into the Thellier-type method for absolute paleointensity determination (e.g. Shaw et al., 1996; Hill and Shaw, 1999). In contrast to the conventional heating by electric ovens for laboratory acquisition of thermal remanent magnetization (TRM), laboratory alteration is significantly suppressed when microwaves are used to demagnetize/remagnetize the sample. As for the Shaw-type method, similar efforts should be made and thus we have tried to incorporate the microwave techniques into the LTD-DHT Shaw method (Tsunakawa and Shaw, 1994; Yamamoto et al., 2003). A series of preliminary experiments have been conducted on (1) four samples with artificial microwave TRM (TmRM) given in a field of 15.0 microtesla, (2) 10 samples with artificial TRM in 25.0 microtesla and (3) 10 samples from the Kilauea 1970 lava. During the experiment, laboratory TmRMs (not TRMs) are imparted by the applications of 80 W of microwave power for 5-10 seconds using the 14 GHz microwave demagnetizing-remagnetizing system. The `microwave LTD-DHT Shaw method' results in 15.2 +/- 0.6 microtesla (N=4), 24.6 +/- 1.9 microtesla (N=5) and 39.1 +/- 1.0 microtesla (N=4) for the experiments of (1), (2) and (3), respectively. Although the result of (3) is statistically different from the expected field of 35.8 microtesla (DGRF 1970), there is a reasonable explanation for this. We conclude that the microwave LTD-DHT Shaw method has been successful.
DE: 1521 Paleointensity
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting