HR: 0800h
AN: V41A-1355    [Abstracts]
TI: Viscosity Measurement of a Hydrous MORB Melt at High Pressure
AU: * Kato, S
EM: kato_sck@ganko.touku.ac.jp
AF: Institute of Mineralogy and Petrology and Economic Geology, Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Ohtani, E
EM: ohtani@mail.tains.tohoku.ac.jp
AF: Institute of Mineralogy and Petrology and Economic Geology, Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Suzuki, A
EM: a-suzuki@mail.tains.tohoku.ac.jp
AF: Institute of Mineralogy and Petrology and Economic Geology, Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Ando, R
EM: andou_rt@ganko.tohoku.ac.jp
AF: Institute of Mineralogy and Petrology and Economic Geology, Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Funakoshi, K
EM: funakosi@spring8.or.jp
AF: Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto Mikazuki-cho Sayo-gun, Hyogo, 679-5198 Japan
AB: Viscosity of silicate melt is a fundamental property for understanding the chemical differentiation of the Earth. The change of viscosity with temperature and pressure reflects the change of the structure of the melt. Therefore, it is important to measure the viscosity of silicate melt at high pressure. The viscosity of many silicate melts has been investigated to date, such as the basalt melt (Fujii and Kushiro, 1977; Ando et al., 2003). The influence of volatile component on viscosity of silicate melt is a matter of debate. Therefore, we measured the viscosity of a hydrous MORB melt at high pressure. The viscosity was measured by the in situ falling sphere viscometry using X-ray radiography at SPring-8 synchrotron facility (BL04B1) in Japan. We used the synthetic glass powder of MORB plus gibbsite of which composition was simplified to a 7-component system, SiO2-Al2O3-FeO-MgO-CaO-Na2O-H2O. Water content was 8 wt%. Experiments were carried out in the temperature range of 1463 to 1752 K, and in the pressure range of 0.7 to 5.1 GPa. It is turned out that the viscosity of a hydrous MORB melt has a weaker temperature dependency than the olivine tholeiite melt (Fujii and Kushiro, 1977) at about 0.7GPa. Generally, the more polymerized melt has a larger temperature dependency of viscosity. This result suggests that water depolymerizes the structure of the silicate melt. This is consistent with the viscosity of the melt in the albite-water system (Dingwell, 1987).The viscosity of the hydrous MORB melt is smaller than that of anhydrous MORB (Ando et al., 2003) at the same pressure and the temperature, due to incorporation of water in the silicate melt structure. The effect of water is less remarkable than that in the albite-water system (Dingwell, 1987) because the structure of hydrous MORB melt is depolymerized. The viscosity of anhydrous MORB decreases with pressure up to ca. 2.5 GPa, but it increases with pressure at above 2.5 GPa (Ando et al., 2003). The viscosity of the hydrous MORB melt, on the other hand, increase with increasing pressure like other depolymerized melt, such as diopside (Reid et al., 2003).
DE: 3924 High-pressure behavior
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting