Investigation of rock magnetism in Aso Volcano
Nobukazu ITOH, Masahiro SAWADA, Teruaki YAMAMOTO and Nobuaki SHIGENO
Abstract
The magnetic properties of rock in the Mt.Aso volcano were investigated by collecting a total of 47 rock samples from three geological units that form an area near the Aso Nakadake crater: a Younge stpyroclastic cone; a Young volcanic edifice; and an old volcanic edifice. This was done with the objective of gathering basic magnetic petrology data for the volcano. The results of this investigation were as follows.
(１)
The remnant magnetization values of the samples collected near the Nakadake crater measured at room temperature ranged from the order of several A/m to several tens of A/m, suggesting that magnetically, the measured samples have basaltic properties. Further, the magnetization values tended to differ between the geological units and also vary from one rock type to another. We were also able to determine that rocks from the same outcrop do not necessarily present similar magnetization values.
(２)
Changes in the remnant magnetization were studied by progressive thermal demagnetization, and the results suggest that samples from different geological units exhibit different trends in thermal demagnetization.
(３)
We estimated the amount of induced magnetization by measuring the initial susceptibility, which was found to be about１ A/m for the samples from the Nakadake crater. It was also found that the initial susceptibility of some of the samples changes atabout 400°C. Furthermore, there tended to be a gradual increase in the initial susceptibility up to a
certain temperature, above which the initial susceptibility changed rapidly.
(Received 6 February 2009; received in revised form 13 March 2009; accepted 17 March 2009)
