Hydrogen diffusivity in wadsleyite and water distribution in the mantle transition zone

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doi: 10.1016/j.epsl.2005.12.035
Authors:Hae, Ryota; Ohtani, Eiji; Kubo, Tomoaki; Koyama, Takao; Utada, Hisashi
Author Affiliations:Primary:
Tohoku University, Institute of Mineralogy, Petrology, and Economic Geology, Sendai, Japan
Other:
Kyushu University, Japan
Japan Agency for Marine-Earth Science and Technology, Japan
University of Tokyo, Japan
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 243(1-2), p.141-148. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:2006
Note:In English. 34 refs.; illus., incl. 1 table
Summary: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. 410 km discontinuity: An experimental study, Geophys. Res. Lett. 29 (2002) doi:10.1029/2001GL014418.], and the distribution and transport properties of water are still debated [e.g., D. R. Bell, G. R. Rossman, Water in Earth's mantle: The role of nominally anhydrous minerals, Science 255 (1992) 1391-1397; N. Bolfan-Casanova, H. Keppler, D. C. Rubie, Water partitioning between nominally anhydrous minerals in the MgO-SiO2-H2O system up to 24 GPa: implications for the distribution of water in Earth's mantle, Earth Planet. Sci. Lett. 182 (2000) 209-221; J. Ingrin, H. Skogby, Hydrogen in nominally anhydrous upper mantle minerals: concentration levels and implications, Eur. J. Mineral. 12 (2000) 543-570; G. Richard, M. Monnereau, J. Ingrin, Is the transition zone an empty water reservoir? Inferences from numerical model of mantle dynamics, Earth Planet. Sci. Lett. 205 (2002) 37-51; E. Ohtani, K. Litasov, T. Hosoya, T. Kubo, T. Kondo, Water transport into the deep mantle and formation of a hydrous transition zone, Phys. Earth Planet. Inter. 143 (2004) 255-269.]. On the basis of water-dependence of the electrical conductivity [S. Karato, The role of hydrogen in the electrical conductivity of the upper mantle, Nature 347 (1990) 272-273.] 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. Abstract Copyright (2006) Elsevier, B.V.
Sections:Experimental mineralogy
Subsections:Silicates
Subjects:Diffusion; Diffusivity; Distribution; Electrical conductivity; Experimental studies; High pressure; High temperature; Hydration; Hydrogen; Infrared spectra; Mantle; Nesosilicates; Olivine; Olivine group; Orthosilicates; Pressure; Silicates; Spectra; Temperature; Transition zones; Wadsleyite; Water; Water content
Abstract Numbers:06M/1555
Record ID:2007116150
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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