Development of the microwave LTD-DHT Shaw method for absolute paleointensity determination

In the last decade, the microwave demagnetization and remagnetization techniques have been successfully incorporated into the Thellier-type method for absolute paleointensity determination. As for the Shaw-type method, similar efforts should be made and thus we have tried to incorporate the microwave techniques into the low temperature demagnetization (LTD)-double heating test (DHT) Shaw method. A series of preliminary experiments have been conducted on (1) four samples with artificial microwave thermoremanent magnetization (TmRM) given in 15.0 μT, (2) 10 samples with artificial thermoremanent magnetization (TRM) given in 25.0 μT and (3) 10 samples from the Kilauea 1970 lava. During the experiment, not laboratory TRMs but laboratory TmRMs are imparted by the applications of 80 W of microwave power for 5-10 s using the 14 GHz microwave demagnetizing-remagnetizing system. The 'microwave LTD-DHT Shaw method' results were 15.2±0.6μ T (N=4), 24.6±1.9μ T (N=5) and 39.1±1.0 μT (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 μT (DGRF 1970), there is a reasonable explanation for this. We conclude that the microwave LTD-DHT Shaw method has been successful, though experimental conditions should be further investigated in future studies in order to increase success rates.