TY - JOUR
T1 - Supercritical fluid in the mantle transition zone deduced from H–D interdiffusion of wadsleyite
AU - Sun, Wei
AU - Yoshino, Takashi
AU - Sakamoto, Naoya
AU - Yurimoto, Hisayoshi
N1 - Funding Information:
The authors are indebted to D. Yamazaki, A. Shimojuku, F. Xu and N. Tsujino for beneficial discussions and S. Yamashita for interpretation of Fourier-transform infrared spectra. The authors also thank two reviewers, Dr. W.L. Du Frane and S. Demouchy for their constructive comments which improved the manuscript. This work was supported by Grants-in-Aid for Scientific Research Grant Numbers JP15H05827 and 24244087 to TY from the Japan Society for the Promotion of Science . We thank Lucy Muir, PhD, from Edanz Group ( www.edanzediting.com/ac ) for editing a draft of this manuscript.
Publisher Copyright:
© 2017 Elsevier B.V.
PY - 2018/2/15
Y1 - 2018/2/15
N2 - Knowledge of the distribution of water in the Earth's mantle is key to understanding the mantle convection and geochemical evolution of the Earth. As wadsleyite and ringwoodite can incorporate large amounts of water in their crystal structures, proton conduction has been invoked to account for the widespread conductive anomalies observed in the mantle wedge, where descending slab stagnates at the transition zone. However, there is a lot of controversy on whether proton conduction by itself is able to explain such anomalies, because of large discrepancy in the extent of the water effect deduced from previous electrical conductivity measurements on hydrous polycrystalline wadsleyite and ringwoodite. Here we report the hydrogen self-diffusion coefficient obtained from H–D interdiffusion experiments in wadsleyite single-crystal couples. Our results demonstrate that the effect of water on the electrical conductivity of wadsleyite is limited and hydrous wadsleyite by itself is unable to explain conductive anomalies in the transition zone. In contrast, the expected hydrogen effective diffusion does not allow the wide propagation of water between the stagnant slab and surrounding mantle, probably leading to persistence of local water saturation and continuous release of supercritical fluids at the stagnant slab roof on geological time scales. This phenomenon provides an alternative explanation for both the high-conductivity and seismic-velocity anomalies observed in the mantle wedge at the transition-zone depth.
AB - Knowledge of the distribution of water in the Earth's mantle is key to understanding the mantle convection and geochemical evolution of the Earth. As wadsleyite and ringwoodite can incorporate large amounts of water in their crystal structures, proton conduction has been invoked to account for the widespread conductive anomalies observed in the mantle wedge, where descending slab stagnates at the transition zone. However, there is a lot of controversy on whether proton conduction by itself is able to explain such anomalies, because of large discrepancy in the extent of the water effect deduced from previous electrical conductivity measurements on hydrous polycrystalline wadsleyite and ringwoodite. Here we report the hydrogen self-diffusion coefficient obtained from H–D interdiffusion experiments in wadsleyite single-crystal couples. Our results demonstrate that the effect of water on the electrical conductivity of wadsleyite is limited and hydrous wadsleyite by itself is unable to explain conductive anomalies in the transition zone. In contrast, the expected hydrogen effective diffusion does not allow the wide propagation of water between the stagnant slab and surrounding mantle, probably leading to persistence of local water saturation and continuous release of supercritical fluids at the stagnant slab roof on geological time scales. This phenomenon provides an alternative explanation for both the high-conductivity and seismic-velocity anomalies observed in the mantle wedge at the transition-zone depth.
KW - H–D interdiffusion
KW - electrical conductivity
KW - mantle transition zone
KW - supercritical fluid
KW - wadsleyite
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U2 - 10.1016/j.epsl.2017.12.032
DO - 10.1016/j.epsl.2017.12.032
M3 - Article
AN - SCOPUS:85039734146
VL - 484
SP - 309
EP - 317
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
SN - 0012-821X
ER -