Japan Geoscience Union Meeting 2016

Presentation information

International Session (Oral)

Symbol S (Solid Earth Sciences) » S-GC Geochemistry

[S-GC16] Volatile Cycles in the Deep Earth - from Subduction Zones to the Mantle and Core

Wed. May 25, 2016 3:30 PM - 5:00 PM 304 (3F)

Convener:*Hirochika Sumino(Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo), Takeshi Hanyu(Japan Agency for Marine-Earth Science and Technology, Department of Solid Earth Geochemistry), Yuji Sano(Division of Ocean and Earth Systems, Atmosphere and Ocean Research Institute, University of Tokyo), Colin Jackson(Geophysical Laboratory, Carnegie Institution of Washington), Chair:Hirochika Sumino(Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo), Takeshi Hanyu(Japan Agency for Marine-Earth Science and Technology, Department of Solid Earth Geochemistry)

3:30 PM - 3:45 PM

[SGC16-07] Hydrous bridgmanite: Water storage capacity in the lower mantle

★Invited papers

*Toru Inoue1, Sho Kakizawa1, Kiyoshi Fujino1, Takahiro Kuribayashi2, Toshiro Nagase2, Steeve Greaux1, Yuji Higo3, Naoya Sakamoto4, Hisayoshi Yurimoto4, Takanori Hattori5, Asami Sano5 (1.Geodynamics Research Center, Ehime University, 2.Tohoku University, 3.JASRI, SPring-8, 4.Hokkaido University, 5.JAEA)

Keywords:hydrous bridgmanite, lower mantle, Synchrotron X-ray in situ experiment, neutron diffraction, elastic property

Recently hydrous ringwoodite was found in a natural diamond inclusion, which includes ~1.5 wt% H2O. In addition, the experimental studies show that wadsleyite and ringwoodite, which are the most abundant minerals in the mantle transition zone, can contain water up to 2.2–2.7 wt% [e.g. Inoue et al., 1995, 1998, Kohlstedt et al., 1996]. These results show that the mantle transition zone is a strong water reservoir in the Earth’s interior, and at least locally, hydrous. On the other hand, the water storage capacity in the lower mantle is a matter of debate.
We have been conducting the study for the stability and water solubility of hydrous and nominally anhydrous minerals, and the recent target is the effect of Al. In this process, we found that Al-bearing bridgmanite (Mg-silicate perovskite) can contain significant amount of water. The possible H substitution mechanism can be proposed by means of chemical compositional relationship between Mg, Si, Al and H. In addition, we clarified the possible H position in the bridgmanite by means of the powder neutron diffraction analysis in J-PARC, together with the single crystal X-ray structural analysis in PF. This shows that the significant amount of H (water) can be stored in the Earth’s lower mantle.
Because of the H in the bridgmanite, the physical properties of the bridgmanite can be changed. The information is very important to discuss the water content and the composition in the lower mantle. We have also conducted the equation of state and the ultrasonic wave velocity measurements of hydrous bridgmanite in BL04B1, SPring-8 to determine the elastic wave velocities and the elastic properties under high pressure and temperature condition. In this talk, I will introduce about our “hydrous bridgmanite” project.