| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1995: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1994: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Research Abstract |
Paleointensity study of geomagnetic excursion is very scarce, especially for the data from volcanic rocks, which have methods of paleointensity determination with firm theoretical basis. It is because there were very few, only two, reports of excursions from volcanic rocks young enough to distinguish from ordinary reversals. One is from lake Mungo, Australia, by Barbetti and McElhinny (1976). Their results showed that the intensity is stronger in excursion than usual. This result is, however, critisized to be an artifact due to lightning. Their samples were from archeological fireplace and can not be re-sampled for examination. The other is from the Laschamp excursion (Roperch et al., 1988). It shows that the paleointensity at the excursion is significantly weaker (7.7muT) than the present geomagnetic field. In order to add paleointensity data in excursion, we carried out Thellier method experiments of the Auckland excursion, which we have reported as an excursion younger than 50ka fro
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m Auckland volcanic field New Zealand (Shibuya et al., 1992).
The experiments were carried out Coe's version of Thellier method. At each temperature stage, the samples were heated twice in air. In each heating, samples were situated in the furnace in room temperature then the furnace was heated to the arranged temperature within 15min.and stayd at the temperature for 15min. Special care was taken for the reproducibility of the heating cycle, so that the reproducibility of the temperature of the two heatings is less than 1ﾟC.The first heating cycle was done in null magnetic field to determine the residual portion of the NRM and the second was done in a known magnetic field to produce a laboratory partial TRM.
Twenty four samples from 18 sites, 11 sites of intermediate and 7 of normal direction, have been submitted to the experiments. Five samples from the normal sites ranged from 4 to 50muT,while 14 samples from the intermediate sites ranged from 3 to 14muT,and other 5 samples did not show straight relation between NRM and TRM.This result is concordant to the result from Laschamp excursion as well as general expectation. Less
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