HR: 0800h
AN: MR41A-0914    [Abstracts]
TI: High-pressure and high-temperature stability field of hydrous phase delta-AlOOH
AU: * Sano, A
EM: sano@ganko.tohoku.ac.jp
AF: Tohoku University, Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Aramaki Aza Aoba, Aoba-ku, Sendai, Miyagi, 980-8578 Japan
AU: Ohtani, E
EM: ohtani@mail.tains.tohoku.ac.jp
AF: Tohoku University, Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Aramaki Aza Aoba, Aoba-ku, Sendai, Miyagi, 980-8578 Japan
AU: Kondo, T
EM: tdskondo@mail.tains.tohoku.ac.jp
AF: Tohoku University, Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Aramaki Aza Aoba, Aoba-ku, Sendai, Miyagi, 980-8578 Japan
AU: Hirao, N
EM: hirao@sci.u-hyogo.ac.jp
AF: University of Hyogo, 3-2-1 Kouto, Kamigori-cho, Ako-gun, Hyogo, 678-1297 Japan
AU: Sone, T
EM: sone@ganko.tohoku.ac.jp
AF: Tohoku University, Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Aramaki Aza Aoba, Aoba-ku, Sendai, Miyagi, 980-8578 Japan
AU: Kikegawa, T
EM: takumi.kikegawa@kek.jp
AF: High Energy Accelerator Reaserch Organization, Photon Factory, 1-1 Oho, Tsukuba, Ibaraki, 305-0801 Japan
AU: Sata, N
EM: sata@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Natsushima-cho, Yokosuka, Kanagawa, 237-0061 Japan
AU: Ohishi, Y
EM: ohishi@spring8.or.jp
AF: Japan Synchrotron Radiation Research Institute, Mikazuki-cho, Sayo-gun, Hyogo, 679-5198 Japan
AB: Stability field of hydrous phases is a key for understanding water concentration in the earth's mantle. δ-AlOOH is a high-pressure polymorph of diaspore (α-AlOOH) and boehmite (γ-AlOOH). The space group of this phase is Pnn2 and it is similar to CaCl₂-type SiO₂ which is a high-pressure polymorph of stishovite; edge-sharing Al-O octahedra make single-chain along c-axis. Although it has a large stability field in pressure range from 18 GPa to 32 GPa and temperature of up to 1473 K, the high-pressure stability limits has not yet clarified. In this study, we investigated the stability field of δ-AlOOH up to 130 GPa.
The high-pressure experiments were performed using a laser-heated diamond-anvil cell. Starting material was gibbsite (Al(OH)₃) powder mixed with platinum black as a laser absorber. The sample was sandwiched by pure gibbsite layers and loaded into a rhenium gasket. Pressures were measured with ruby-fluorescence technique before and after heating. The sample was heated from both sides by a Nd:YAG laser operated in multimode. After experiment, stable phase in each condition was determined using the X-ray diffraction and Raman spectroscopy method. We also conducted in-situ X-ray diffraction experiments under high-pressure and temperature conditions together with the X-ray diffraction of the recovered samples both at BL10XU in SPring-8 and BL-13A in Photon Factory. In these runs, pressures were also calculated using the equation of state of platinum.
The experimental conditions were in the pressures between 50-130 GPa and temperatures to 1800 K. X-ray analysis shows the sample recovered from the pressure and temperature range from 40 GPa and 1577 K to 130 GPa and 1800 K consists of δ-AlOOH. In the in-situ experiments, crystallization of δ-AlOOH was observed at 65 GPa and 1300 K and it was stable up to 1700 K. δ-AlOOH is stable in the large pressure range with a dehydration temperature around 1800K. It can be a water reservoir in subducting slabs in the deep lower mantle conditions beyond the dehydration conditions of the other hydrous phases such as dense hydrous magnesium silicates.
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005