Japan Geoscience Union Meeting 2019

Presentation information

[E] Oral

S (Solid Earth Sciences ) » S-IT Science of the Earth's Interior & Techtonophysics

[S-IT21] Interaction and Coevolution of the Core and Mantle in the Earth and Planets

Mon. May 27, 2019 1:45 PM - 3:15 PM A10 (TOKYO BAY MAKUHARI HALL)

convener:Kenji Kawai(Department of Earth and Planetary Science, School of Science, University of Tokyo), Tsuyoshi Iizuka(University of Tokyo), Kenji Ohta(Department of Earth and Planetary Sciences, Tokyo Institute of Technology), Taku Tsuchiya(Geodynamics Research Center, Ehime University), Chairperson:Hitoshi Gomi, Tsuyoshi Iizuka

2:15 PM - 2:30 PM

[SIT21-15] Ultralow-velocity zones possibly explained by light element-enriched iron compounds

*Liang Yuan1, Eiji Ohtani1, Xiang Wu2, Shengxuan Huang3, Daijo Ikuta1, Tatsuya Sakamaki1, Seiji Kamada1, Hiroshi Fukui4,5, Satoshi Tsutsui6, Hiroshi Uchiyama6, Daisuke Ishikawa5,6, Naohisa Hirao6, Alfred Q. R. Baron5 (1.Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan, 2.State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China, 3.Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, Peking University and School of Earth and Space Sciences, Peking University, Beijing 100871, China, 4.Center for Novel Material Science under Multi-Extreme Conditions, Graduate School of Material Science, University of Hyogo, Hyogo 678-1297, Japan, 5.Materials Dynamics Laboratory, RIKEN SPring-8 Center, Hyogo 679-5148, Japan, 6.Japan Synchrotron Radiation Research Institute (JASRI), SPring-8, Hyogo, 679-5198, Japan)

Keywords:Core–mantle boundary, Ultralow-velocity zones, Light elements, Iron compounds

The core–mantle boundary (CMB) is the most fundamental chemical discontinuity in the Earth. Recent experiments showed that, when water meets iron at the CMB, hydrogen-bearing iron peroxide FeO2Hx can be produced. The results indicate that water can interact with iron metal very differently than it does on the surface of the earth. Seismic waves speeds in this hydrogen bearing iron peroxide are much slower compared with lower-mantle silicate solid phases, and therefore it may help explain the seismic anomalies at the CMB.

Given the steep geothermal gradient across the CMB, the hydrogen-bearing iron peroxide FeO2Hx likely undergoes high-temperature decomposition into anhydrous iron oxides (e.g., Fe2O3) and fluids. We measured the sound velocity of Fe2O3 post-perovskite (ppv) through inelastic X-ray scattering up to 132 GPa and 1,800 K, relevant to the lowermost mantle. Combined with first-principles investigations, we are able to show that Fe2O3 ppv has very low sound velocities and strong anisotropy with respect to lower-mantle silicates. Therefore, both hydrogen-bearing iron peroxide FeO2Hx and post-perovskite Fe2O3 are candidate phases for ultralow-velocity zones at the CMB.

Funding acknowledgment: This work was supported by the JSPS Japanese–German Graduate Externship.