HR: 1340h
AN: MR13C-1411    [Abstracts]
TI: Electrical conductivity variations of hydrous mineral and rocks associate with dehydration process
AU: * Fuji-ta, K
EM: fujita@fsao.eng.osaka-u.ac.jp
AF: Office for International Relations, Faculty of Enginering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan
AU: Katsura, T
EM: tkatsura@misasa.okayama-u.ac.jp
AF: Institute for Study of the Earth's Interior, Okayama University, 827 Yamada, Misasa, Tottori, 682-0193, Japan
AU: Matsuzaki, T
EM: takuya-m@misasa.okayama-u.ac.jp
AF: Institute for Study of the Earth's Interior, Okayama University, 827 Yamada, Misasa, Tottori, 682-0193, Japan
AU: Ichiki, M
EM: ichiki.m.aa@m.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8551, Japan
AU: Kobayashi, T
EM: kobayashi@kueps.kyoto-u.ac.jp
AF: Earth and Planetary Sciences, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto, 606-8502, Japan
AB: The electrical conductivity of rocks and minerals is an important parameter, because its value can help understanding subsurface conductivity structures. In particular, conductivity of hydrous mineral and rock contains hydrous mineral vary drastically due to the effect of water content and influence of ionic water. To detect electrical conductivity variations associate with dehydration process, we have conducted different types of laboratory measurements. Firstly, to observe dehydration reaction of brucite by electrical conductivity variation, we have developed a technique in a sealed condition. Electrical conductivity measurement of brucite was performed as a function of temperature while the confining pressure was kept at 1 GPa. As a result, two types of remarkable electrical conductivity variation of brucite could be seen. Below 700 K, conductivity of the sample seems to stabilize and show linear variation as expected from the Arrhenius equation. Once temperature was increased around dehydration boundary, brucite showed high conductivity. This may be because, coexisting solid and fluid phases, a mixed electronic and ionic conduction mechanism may operate in the sample. Secondly, electrical conductivity measurements of gneiss, basic rock and amphibolite were conducted using the conventional cell. The rock samples were not sealed in the high insulation assembly. The conductivity hysteresis of various rocks was plotted and examined. The systematic increase in conductivity up to 1000 K was observed. Above 1000 K, the conductivity of amphibolites does not vary linearly. As amphibolites contain much hydrous minerals, conductivity of the sample may be high after dehydration. From the successful experimental results, we found remarkable electrical conductivity variations associate with dehydrations. When temperature exceeds metamorphic condition or is near phase boundary condition, electrical conductivity of the sample increase drastically by 2 to 3 order of magnitude. For this phenomenon, we positively evaluate the effect of water and the influence of ionic fluid after dehydration, quantitatively. Even though small amount of H2O is formed after dehydration, bulk conductivity of the sample varies drastically. This increase of the conductivity associate with dehydration is often observed by EM soundings in and around the subduction zones in the Earth.
DE: 1515 Geomagnetic induction
DE: 3640 Igneous petrology
DE: 3660 Metamorphic petrology
DE: 5134 Thermal properties
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting