HR: 14:55h
AN: MR13A-06 INVITED     [Abstracts]
TI: Use of Kawai-type Apparatus Combined with Synchrotron X-ray Radiation for Study of Kinetics of Phase Transformations in Mantle Minerals
AU: * Ohtani, E
EM: ohtani@mail.tains.tohoku.ac.jp
AF: Tohoku university , Aza-Aoba, Aramaki Aoba-ku, Sendai, 980-8578 Japan
AU: Kubo, T
EM: kubotomo@geo.kyushu-u.ac.jp
AF: Kyushu University , Hakozaki, Higaashi-ku, Fukuoka, 812-8581 Japan
AU: Hosoya, T
EM: hosoya@ganko.tohoku.ac.jp
AF: Tohoku university , Aza-Aoba, Aramaki Aoba-ku, Sendai, 980-8578 Japan
AU: Funakoshi, K
EM: funakosi@spring8.or.jp
AF: Japan Synchrotron Research Institute, Kouto, Mikazuki-cho, Sayo-gun, Hyogo-ken, 679-5198 Japan
AB: Kawai type multianvil apparatus combined with the intense X-ray from synchrotron radiation is a useful tool for study of the reaction kinetics of the phase transformations of mantle minerals. MAX-III installed at Photon Factory and SPEED 1500 at SPring-8 are used for the experiments. We used sintered diamond composites of 10mm or 14 mm cubes with a 2 mm truncation for the experiments made above 30 GPa. We conducted studies on reaction kinetics of several phase transformations of mantle minerals. Decomposition of ringwoodite is the most important phase transformation which corresponds to the 660 km discontinuity. Metastable coexistence of periclase + stishovite, or periclase + ilmenite was observed in the initial stage of the transformation in the low temperature range. The metastable assembly disappears eventually after about 10 minutes. A kinetics study of the post-garnet transformation revealed that the post-garnet transformation is significantly sluggish compared to the decomposition reaction of ringwoodite. The reaction kinetics of the transformation of MgSiO3 from enstatite to wadsleyite + stishovite, ringwoodite + stishovite, and to ilmenite were studied. The enstatite-ilmenite phase transformation is much faster than the decomposition reactions. This suggests that a decomposition of enstatite may not occur but enstatite transforms directly to ilmentite in the cold subducting slabs. The experiments on the olivine-wadsleyite transformation kinetics in Mg2SiO4 under the dry and wet conditions with 0.5 wt. % water indicate remarkable enhancement of the phase transformation kinetics by existence of water. Seismic observations indicate that metastable olivine regions are not detected in the slabs, rather the elevation of the 410 km discontinuity, which is consistent with the equilibrium boundary, has been observed. The seismic reflectors, which were reported in the lower mantle, imply a density increase associated with the anomaly (e.g., Niu et al., 2003), suggesting existence of the basaltic crust with a perovskite assemblage in the lower mantle. These seismic data imply existence of equilibrium assemblies even in the cold slabs in the transition zone and lower mantle, which may be consistent with the wet slabs where the phase transformation kinetics are enhanced under the wet conditions.
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
DE: 3994 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting