DOI: 10.1016/j.epsl.2020.116672
论文题名: Fe–Mg interdiffusion in wadsleyite and implications for water content of the transition zone
作者: Zhang B. ; Zhao C. ; Yoshino T.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2021
卷: 554 语种: 英语
中文关键词: electrical conductivity
; Fe–Mg interdiffusion
; mantle transition zone
; wadsleyite
; water
英文关键词: Aggregates
; Diffusion in solids
; Electromagnetic induction
; Magnesium compounds
; Silicon
; Silicon compounds
; Chemical heterogeneities
; Diffusion profiles
; Electrical conductivity
; Electron microprobes
; Interdiffusion rate
; Mantle transition zone
; Multi-anvil apparatus
; Solid-state diffusion
; Iron compounds
; electrical conductivity
; heterogeneity
; ringwoodite
; transition zone
; wadsleyite
; water chemistry
; water content
; water quality
英文摘要: Fe–Mg interdiffusion rates in polycrystalline wadsleyite aggregates have been determined as a function of water content (up to ∼0.345 wt.% H2O) at 16 GPa and 1373–1773 K in a Kawai-type multi-anvil apparatus. Pre-synthesized water-poor and -rich polycrystalline wadsleyite were used as starting materials. Diffusion profiles were obtained across the interface between Fe-free and -bearing diffusion couples, namely, Mg2SiO4 and (Mg0.9Fe0.1)2SiO4 aggregates by electron microprobe. Fe–Mg interdiffusivities by experiments yield DFe−Mg(m2/s)=D0XFenCH2Orexp[−(E+αXFe+βCH2O)/RT], where D0 = 1.33−0.23+0.20× 10−11 m2/s, n = 0.19 ± 0.04, r = 0.29 ± 0.12, E = 92 ± 2 kJ/mol, α = −45 ± 12, and β = −134 ± 2. Our results indicate that water significantly enhances the rates of Fe–Mg interdiffusion in wadsleyite (a factor of 2.4 for fixed temperature and Fe concentration) compared to that in ringwoodite. Although under hydrous condition the transition zone shows the maximum Fe–Mg mixing efficiency as revealed by diffusivity-depth profile in the mantle, homogenization of existing chemical heterogeneity is still very limited at geological time scale only through solid-state diffusion. Combined with the Nernst–Einstein relation, the results suggest that the contribution of water to the electrical conductivity of wadsleyite or ringwoodite may be overestimated from Fe–Mg interdiffusion data at high water content. Further calculation demonstrates that ∼0.1–0.5 wt.% H2O is sufficient to account for the high conductivity values in the upper part (410–520 km) of the mantle transition zone as observed by electromagnetic induction studies. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165744
Appears in Collections: 气候变化与战略
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作者单位: Key Laboratory of Geoscience Big Data and Deep Resource of Zhejiang Province, School of Earth Sciences, Zhejiang University, Hangzhou, 310027, China; Institute for Planetary Materials, Okayama University, Misasa, Tottori, 682-0193, Japan
Recommended Citation:
Zhang B.,Zhao C.,Yoshino T.. Fe–Mg interdiffusion in wadsleyite and implications for water content of the transition zone[J]. Earth and Planetary Science Letters,2021-01-01,554