HR: 0800h
AN: MR41A-0904    [Abstracts]
TI: High pressure and high temperature stability and the equation of state of superhydrous phase B by in situ X-ray diffraction
AU: * Inoue, T
EM: inoue@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, Bunkyo-cho 2-5, Matsuyama, 790-8577 Japan
AU: Ueda, T
EM: inoue@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, Bunkyo-cho 2-5, Matsuyama, 790-8577 Japan
AU: Higo, Y
EM: higo@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, Bunkyo-cho 2-5, Matsuyama, 790-8577 Japan
AU: Yamada, A
EM: a-yamada@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, Bunkyo-cho 2-5, Matsuyama, 790-8577 Japan
AU: Irifune, T
EM: irifune@dpc.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, Bunkyo-cho 2-5, Matsuyama, 790-8577 Japan
AU: Funakoshi, K
EM: funakosi@spring8.or.jp
AF: Japan Synchrotron Radiation Institute, Mikazuki-cho, Kouto 1-1-1, Sayo, Hyogo, 679-5198 Japan
AB: We have determined the stability and the equation of state of superhydrous phase B (Mg₁₀Si₃ O₁₈H₄) by in situ X-ray diffraction measurements using a metal capsule. The experiments were conducted at SPring-8 in a pressure range between 13 and 23 GPa and at temperatures up to 1673 K. A high temperature X-ray diffraction measurement was also conducted to determine the thermal expansion coefficient at the atmospheric pressure. Superhydrous phase B was found to melt incongruently into wadsleyite+liquid at 1273 K and 13 GPa, whereas it melted incongruently into ringwoodite+liquid at 1473 K and 20 GPa. The isothermal bulk modulus (K₀) and its temperature derivative (dK/dT) of superhydrous phase B were determined as 132 GPa and -2.5×10^-2 GPa/K, respectively, while the thermal expansion coefficient was 37.6×10^-6 K^-1. The phase relations imply that superhydrous phase B may be stable in relatively low temperature regions of the mantle transition zone, such as in subducted slabs, but not in the surronding mantle. The density difference between model subducted hydrous slabs and the surrounding mantle was calculated at 20 GPa as functions of water content and temperature in the slab using the present results, which demonstrates that the superhydrous phase B bearing slabs with H₂O contents of 0.5 wt% , 1.0 wt% and 1.5 wt% are denser than the surrounding mantle at temperatures below 1473 K, 1173 K and 873 K, respectively. This implies that the possible penetration of a hydrous slab into the deeper mantle strongly depends on its water content and temperature profile.
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3621 Mantle processes (1038)
DE: 3630 Experimental mineralogy and petrology
DE: 3919 Equations of state
DE: 3949 Thermal expansivity
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005