TY - JOUR
T1 - Hydrogen diffusivity in wadsleyite and water distribution in the mantle transition zone
AU - Hae, Ryota
AU - Ohtani, Eiji
AU - Kubo, Tomoaki
AU - Koyama, Takao
AU - Utada, Hisashi
N1 - Funding Information:
We are grateful to T. Kondo, A. Suzuki, H. Terasaki, and A. Shimojuku for helpful discussions. This work was partially supported by the Grant-in-aid of Scientific Research of Priority Area (no. 16075202) and the grant-in-aid of Scientific Research (S) (no. 14102009) of Ministry of Education, Culture, Science, Sport, and Technology of Japanese Government to E.O. This work was conducted as a part of the 21st Century Center of Excellence program “Advanced Science and Technology Center of the Dynamic Earth” of Tohoku University.
PY - 2006/3/15
Y1 - 2006/3/15
N2 - The kinetics of the hydrogen diffusivity in synthesized polycrystalline wadsleyite was measured by IR spectroscopy in order to determine the diffusion coefficient of hydrogen in wadsleyite, the major constituent mineral in the mantle transition zone, with the composition of (Mg0.89Fe0.11)2SiO4. The hydration experiments were conducted at 15-16 GPa and temperature range from 900 to 1200 °C with Mg(OH)2 as the water source by Kawai-type multi-anvil apparatus. The diffusion rate obtained here is considered to be an effective diffusion coefficient with the grain size of ∼9 μm involving contributions both from the lattice diffusion and the grain boundary diffusion. The temperature dependence of diffusion of hydrogen in polycrystalline wadsleyite was determined to be DH = 9.6 × 10-6 exp [-123 (±32) (kJ mol-1)/RT] at 15 GPa. Hydrogen diffusion rate in wadsleyite is roughly consistent with the average diffusivity of hydrogen in olivine. In recent years, several authors have suggested a possibility of the hydrous transition zone, and the distribution and transport properties of water are still debated. On the basis of water-dependence of the electrical conductivity the water content in the mantle transition zone was estimated from the observed conductivity by using the Nernst-Einstein relation. The results obtained here show that the distribution of water should be quite heterogeneous throughout the mantle transition zone.
AB - The kinetics of the hydrogen diffusivity in synthesized polycrystalline wadsleyite was measured by IR spectroscopy in order to determine the diffusion coefficient of hydrogen in wadsleyite, the major constituent mineral in the mantle transition zone, with the composition of (Mg0.89Fe0.11)2SiO4. The hydration experiments were conducted at 15-16 GPa and temperature range from 900 to 1200 °C with Mg(OH)2 as the water source by Kawai-type multi-anvil apparatus. The diffusion rate obtained here is considered to be an effective diffusion coefficient with the grain size of ∼9 μm involving contributions both from the lattice diffusion and the grain boundary diffusion. The temperature dependence of diffusion of hydrogen in polycrystalline wadsleyite was determined to be DH = 9.6 × 10-6 exp [-123 (±32) (kJ mol-1)/RT] at 15 GPa. Hydrogen diffusion rate in wadsleyite is roughly consistent with the average diffusivity of hydrogen in olivine. In recent years, several authors have suggested a possibility of the hydrous transition zone, and the distribution and transport properties of water are still debated. On the basis of water-dependence of the electrical conductivity the water content in the mantle transition zone was estimated from the observed conductivity by using the Nernst-Einstein relation. The results obtained here show that the distribution of water should be quite heterogeneous throughout the mantle transition zone.
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U2 - 10.1016/j.epsl.2005.12.035
DO - 10.1016/j.epsl.2005.12.035
M3 - Article
AN - SCOPUS:33344464625
SN - 0012-821X
VL - 243
SP - 141
EP - 148
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 1-2
ER -