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

Abstract

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 (T mRM) given in 15.0 μ T, (2) 10 samples with artificial thermoremanent magnetization (TRM) given in 25.0 μ T and (3) 10 samples from the Kilauea 1970 lava. During the experiment, not laboratory TRMs but laboratory T mRMs 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 ± 0.6 μ T ( N = 4 ), 24.6 ± 1.9 μ T ( N = 5 ) and 39.1 ± 1.0 μ T ( 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 μ T (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.