4:45 PM - 5:00 PM
[SVC39-10] Volcanic Rocks Evaluation Using Magnetic Susceptibility
Keywords:nanolite, pyroclast, magnetite
Magnetic susceptibility measurement was conducted using SM-30 (ZH Instruments) which is the handy type and MS3-MS2B and MS3-MS2G (Bartington Instruments Ltd.) which are laboratory instruments. All the samples were pulverized using a Multi-Beads Shocker (Yasui Kikai, Co.) with 3000 rpm in 10 seconds, then stored in the standard box. The measurement using SM-30 requires ~150 g samples packed into circle plate (96.25 cm3), while MS2B sensor requires ~20 g samples packed into the circle box (10 ml volume) and MS2G sensor requires ~2 g packed into the cylinder tube (1 ml volume). MS3 meter connected to Bartsoft software during the measurement process which can measure both κ and χ, whereas SM-30 is only κ. The MS2B sensor records low-frequency (κLF) and high-frequency (κHF) which are considered to find frequency dependence of the samples (κFD). The measurement processes conducted in the same place.
Relative tendencies of susceptibility of samples were similar in SM-30 and MS3. Compared to MS3, susceptibility measured with SM-30 is ~30 % lower. Instrumental reproducibility (2σ) of MS2B and MS2G are ~5 x 10-6 and ~7 x 10-6 (κ; dimensionless), respectively. When different grain size measured, volume susceptibility (κ) varied, but mass susceptibility (χ) shows the same value. Thus, mass-specific correction must be acceptable for volcanic rocks powder measurement because the correction rectifies the error by density variance. Mass susceptibility value from mixing andesite (8.6 x 10-6 m3/kg) and rhyolite (0.3 x 10-6 m3/kg) with equal amounts resulted in roughly intermediate (4.2 x 10-6 m3/kg) between them. Mass susceptibility value shows proportional dependency to the Fe-oxides mass. When the andesite heated in the air, susceptibility decreased with the increase of heating time accompanied by increasing its frequency dependence. The changes of mineral structure, from ferromagnetic to paramagnetic due to the heating process may cause a drop in susceptibility. The susceptibility decreased as the order of andesite (Sakurajima-Taisho pumices), basalt (Fuji-Hoei scoria) and rhyolite (Wadatoge obsidian). It is necessary to clarify the influence on the magnetic susceptibility of magnetite nanolite and ultrananolite.