Influence of hydrogen on Fe-Mg interdiffusion in (Mg,Fe)O and implications for Earth's lower mantle

Sylvie Demouchy; Stephen J. Mackwell; David L. Kohlstedt

doi:10.1007/s00410-007-0193-9

Influence of hydrogen on Fe-Mg interdiffusion in (Mg,Fe)O and implications for Earth's lower mantle

Sylvie Demouchy, Stephen J. Mackwell, David L. Kohlstedt

Earth and Environmental Sciences-Twin Cities

Research output: Contribution to journal › Article › peer-review

31 Scopus citations

Abstract

Interdiffusion of Fe and Mg in (Mg,Fe)O has been investigated experimentally under hydrous conditions. Single crystals of MgO in contact with (Mg_0.73Fe_0.27)O were annealed hydrothermally at 300 MPa between 1,000 and 1,250°C and using a Ni-NiO buffer. After electron microprobe analyses, the dependence of the interdiffusivity on Fe concentration was determined using a Boltzmann-Matano analysis. For a water fugacity of ∼300 MPa, the Fe-Mg interdiffusion coefficient in Fe_xMg_1-xO with 0.01 ≤ x ≤ 0.25 can be described by D̃ = D̃_0x^B exp^-(Q+Cx)/RT with D̃₀ = (5 ± 1) × 10^-4 m² s^-1, Q = 270 ± 20 kJ mol^-1, B = 0.8 ± 0.1, and C = -80 ± 10 kJ mol^-1. For x = 0.1 and at 1,000°C, Fe-Mg interdiffusion is a factor of ∼4 faster under hydrous than under anhydrous conditions. This enhanced rate of interdiffusion is attributed to an increased concentration of metal vacancies resulting from the incorporation of hydrogen. Such water-induced enhancement of kinetics may have important implications for the rheological properties of the lower mantle.

Original language	English (US)
Pages (from-to)	279-289
Number of pages	11
Journal	Contributions to Mineralogy and Petrology
Volume	154
Issue number	3
DOIs	https://doi.org/10.1007/s00410-007-0193-9
State	Published - Sep 2007

Bibliographical note

Funding Information:
Acknowledgments SD thanks Christian Holzapfel for helpful advice at the early stage of the project, Mark Zimmerman for his generous assistance with running the Paterson apparatus, Nathalie Bolfan-Casanova for fervently and generously debating issues on point defects in (Mg,Fe)O, Catherine McCammon for Mössbauer analysis of the starting material, and Hans Keppler for access to his FTIR lab at the Bayerisches Geoinstitut. Electron microprobe analyses were carried out (with the help of Ellery Frahm) at the Electron Microprobe Laboratory, Department of Geology and Geophysics, University of Minnesota-Twin Cities. NSF supported the research through the grant NSF EAR-0337012 (to SJM) and NSF EAR-0439747 (to DLK). This paper is LPI publication #1326.

Keywords

Earth's mantle
Fe-Mg interdiffusion
Hydrogen
Periclase

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10.1007/s00410-007-0193-9

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title = "Influence of hydrogen on Fe-Mg interdiffusion in (Mg,Fe)O and implications for Earth's lower mantle",

abstract = "Interdiffusion of Fe and Mg in (Mg,Fe)O has been investigated experimentally under hydrous conditions. Single crystals of MgO in contact with (Mg0.73Fe0.27)O were annealed hydrothermally at 300 MPa between 1,000 and 1,250°C and using a Ni-NiO buffer. After electron microprobe analyses, the dependence of the interdiffusivity on Fe concentration was determined using a Boltzmann-Matano analysis. For a water fugacity of ∼300 MPa, the Fe-Mg interdiffusion coefficient in FexMg1-xO with 0.01 ≤ x ≤ 0.25 can be described by {\~D} = {\~D}0xB exp-(Q+Cx)/RT with {\~D}0 = (5 ± 1) × 10-4 m2 s-1, Q = 270 ± 20 kJ mol-1, B = 0.8 ± 0.1, and C = -80 ± 10 kJ mol-1. For x = 0.1 and at 1,000°C, Fe-Mg interdiffusion is a factor of ∼4 faster under hydrous than under anhydrous conditions. This enhanced rate of interdiffusion is attributed to an increased concentration of metal vacancies resulting from the incorporation of hydrogen. Such water-induced enhancement of kinetics may have important implications for the rheological properties of the lower mantle.",

keywords = "Earth's mantle, Fe-Mg interdiffusion, Hydrogen, Periclase",

author = "Sylvie Demouchy and Mackwell, {Stephen J.} and Kohlstedt, {David L.}",

note = "Funding Information: Acknowledgments SD thanks Christian Holzapfel for helpful advice at the early stage of the project, Mark Zimmerman for his generous assistance with running the Paterson apparatus, Nathalie Bolfan-Casanova for fervently and generously debating issues on point defects in (Mg,Fe)O, Catherine McCammon for M{\"o}ssbauer analysis of the starting material, and Hans Keppler for access to his FTIR lab at the Bayerisches Geoinstitut. Electron microprobe analyses were carried out (with the help of Ellery Frahm) at the Electron Microprobe Laboratory, Department of Geology and Geophysics, University of Minnesota-Twin Cities. NSF supported the research through the grant NSF EAR-0337012 (to SJM) and NSF EAR-0439747 (to DLK). This paper is LPI publication #1326.",

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T1 - Influence of hydrogen on Fe-Mg interdiffusion in (Mg,Fe)O and implications for Earth's lower mantle

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AU - Mackwell, Stephen J.

AU - Kohlstedt, David L.

N1 - Funding Information: Acknowledgments SD thanks Christian Holzapfel for helpful advice at the early stage of the project, Mark Zimmerman for his generous assistance with running the Paterson apparatus, Nathalie Bolfan-Casanova for fervently and generously debating issues on point defects in (Mg,Fe)O, Catherine McCammon for Mössbauer analysis of the starting material, and Hans Keppler for access to his FTIR lab at the Bayerisches Geoinstitut. Electron microprobe analyses were carried out (with the help of Ellery Frahm) at the Electron Microprobe Laboratory, Department of Geology and Geophysics, University of Minnesota-Twin Cities. NSF supported the research through the grant NSF EAR-0337012 (to SJM) and NSF EAR-0439747 (to DLK). This paper is LPI publication #1326.

PY - 2007/9

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N2 - Interdiffusion of Fe and Mg in (Mg,Fe)O has been investigated experimentally under hydrous conditions. Single crystals of MgO in contact with (Mg0.73Fe0.27)O were annealed hydrothermally at 300 MPa between 1,000 and 1,250°C and using a Ni-NiO buffer. After electron microprobe analyses, the dependence of the interdiffusivity on Fe concentration was determined using a Boltzmann-Matano analysis. For a water fugacity of ∼300 MPa, the Fe-Mg interdiffusion coefficient in FexMg1-xO with 0.01 ≤ x ≤ 0.25 can be described by D̃ = D̃0xB exp-(Q+Cx)/RT with D̃0 = (5 ± 1) × 10-4 m2 s-1, Q = 270 ± 20 kJ mol-1, B = 0.8 ± 0.1, and C = -80 ± 10 kJ mol-1. For x = 0.1 and at 1,000°C, Fe-Mg interdiffusion is a factor of ∼4 faster under hydrous than under anhydrous conditions. This enhanced rate of interdiffusion is attributed to an increased concentration of metal vacancies resulting from the incorporation of hydrogen. Such water-induced enhancement of kinetics may have important implications for the rheological properties of the lower mantle.

AB - Interdiffusion of Fe and Mg in (Mg,Fe)O has been investigated experimentally under hydrous conditions. Single crystals of MgO in contact with (Mg0.73Fe0.27)O were annealed hydrothermally at 300 MPa between 1,000 and 1,250°C and using a Ni-NiO buffer. After electron microprobe analyses, the dependence of the interdiffusivity on Fe concentration was determined using a Boltzmann-Matano analysis. For a water fugacity of ∼300 MPa, the Fe-Mg interdiffusion coefficient in FexMg1-xO with 0.01 ≤ x ≤ 0.25 can be described by D̃ = D̃0xB exp-(Q+Cx)/RT with D̃0 = (5 ± 1) × 10-4 m2 s-1, Q = 270 ± 20 kJ mol-1, B = 0.8 ± 0.1, and C = -80 ± 10 kJ mol-1. For x = 0.1 and at 1,000°C, Fe-Mg interdiffusion is a factor of ∼4 faster under hydrous than under anhydrous conditions. This enhanced rate of interdiffusion is attributed to an increased concentration of metal vacancies resulting from the incorporation of hydrogen. Such water-induced enhancement of kinetics may have important implications for the rheological properties of the lower mantle.

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KW - Fe-Mg interdiffusion

KW - Hydrogen

KW - Periclase

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Influence of hydrogen on Fe-Mg interdiffusion in (Mg,Fe)O and implications for Earth's lower mantle

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