HR: 0800h
AN: MR11A-0911    [Abstracts]
TI: Pressure dependence of (Mg,Fe)SiO3 ilmenite and perovskite determined by a multi-anvil apparatus with sintered diamond anvils
AU: * Yokoshi, S
EM: sho@misasa.okayama-u.ac.jp
AF: Institute for Study of the Earth's Interior, Okayama Univ., yamada 827, Misasa, Tottori, 682-0193 Japan
AU: Katsura, T
EM: tkatsura@misasa.okayama-u.ac.jp
AF: Institute for Study of the Earth's Interior, Okayama Univ., yamada 827, Misasa, Tottori, 682-0193 Japan
AU: Ito, E
EM: eiito@misasa.okayama-u.ac.jp
AF: Institute for Study of the Earth's Interior, Okayama Univ., yamada 827, Misasa, Tottori, 682-0193 Japan
AU: Okube, M
EM: makisan@misasa.okayama-u.ac.jp
AF: Institute for Study of the Earth's Interior, Okayama Univ., yamada 827, Misasa, Tottori, 682-0193 Japan
AU: Kawabe, K
EM: geo@misasa.okayama-u.ac.jp
AF: Institute for Study of the Earth's Interior, Okayama Univ., yamada 827, Misasa, Tottori, 682-0193 Japan
AU: Nozawa, A
EM: nozawa@spring8.or.jp
AF: Japan Synchrotoron Radiation Institute, Kouto, Mikazuki, Hyougo, 679-5198 Japan
AU: Funakoshi, K
EM: funakosi@spring8.or.jp
AF: Japan Synchrotoron Radiation Institute, Kouto, Mikazuki, Hyougo, 679-5198 Japan
AB: Geophysical observations such as the MT method suggest that the electrical conductivity increases from 1 to 10 S/m from the top to the bottom of the lower mantle (Olsen1999). Measurement of electrical conductivity of silicate perovskite under lower mantle conditions is indispensable to explain such geophysical observations, because the lower mantle is believed to be mainly composed of silicate perovskite. Many workers have conducted electrical conductivity measurements at high pressures and temperatures. Xu et al. (1998) measured electrical conductivity of silicate perovskite at 25 GPa and $1400-1600 \deg$C by using a multi-anvil apparatus. However, their pressure condition is limited to 25 GPa because of use of WC anvils, and therefore, they were not able to determine pressure dependence of electrical conductivity of silicate perovskite. In this study, we try to determine pressure dependence of electrical conductivity of mantle minerals, by using a multi-anvil apparatus with sintered diamond anvils, which allows us to measure electrical conductivity of minerals in a wide pressure range. We first measured electrical conductivity of (Mg$_{0.93}$Fe$_{0.07}$) SiO$_{3}$ ilmenite at pressures of 25, 30 and 35 GPa and temperatures of 300 to 1200 K. We obtained the activation energy and volume of 0.69(4) eV and -0.9(1) cm$^{3}$/mol, respectively. Thus electrical conductivity of ilmenite has large pressure dependence. For example, the ilmenite conductivity increases by 20 times at 500 K with increasing pressure from 25 to 35 GPa. Next, we conducted measurement for (Mg$_{0.93}$Fe$_{0.07}$) SiO$_{3}$ perovskite at pressures of 30 and 35 GPa and temperatures of 300 to 1400 K, showing the activation energy and volume of 0.39(4) eV, and -0.06(4) cm$^{3}$/mol, respectively. In contrast to ilmenite, electrical conductivity of perovskite has very small pressure dependence. We have calculated the electrical conductivity of the model lower mantle using the present experimental results, suggesting that it increases from 2.7 to 4.75 S/m from the top to the bottom of the model lower mantle. Thus it is difficult to explain the large increase in the electrical conductivity of the lower mantle shown by Olsen (1999) from the present experimental data.
DE: 7207 Core and mantle
DE: 3630 Experimental mineralogy and petrology
DE: 3900 MINERAL PHYSICS
DE: 3924 High-pressure behavior
DE: 0350 Pressure, density, and temperature
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting