Effects of hydrogen and iron on the silicon diffusivity of wadsleyite

Akira Shimojuku, Tomoaki Kubo, Eiji Ohtani, Tomoki Nakamura, Ryuji Okazaki

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

We determined the temperature dependence of Si diffusion rates in polycrystalline Mg2SiO4 wadsleyite under nominally dry conditions (20-60wt.ppmH2O), at a pressure of 18GPa and temperatures between 1450 and 1600°C. Diffusion experiments were conducted using an isotopic tracer diffusion method. Diffusion profiles were obtained by a depth-profiling mode using a secondary ion mass spectrometer. Diffusion coefficients were calculated from the obtained diffusion profiles by numerical simulation after correcting for the convolution effect using surface roughness. Since all the obtained diffusion profiles were composed of volume and grain-boundary diffusion regimes, we determined the volume and grain-boundary diffusion coefficients simultaneously. Si diffusion rates in Mg2SiO4 wadsleyite with 20-60wt.ppmH2O were about half an order of magnitude slower than those with 14-507wt.ppmH2O reported by Shimojuku et al. [Shimojuku, A., Kubo, T., Ohtani, E., Yurimoto, H., 2004. Si self-diffusion in wadsleyite: implications for rheology of the mantle transition zone and subducting plates. Geophys. Res. Lett. 31, doi:10.1029/2004GL020002] with correcting the convolution effect in both data. The Si diffusivity in Mg2SiO4 wadsleyite was comparable for the volume diffusion and the grain-boundary diffusion in (Mg0.9Fe0.1)2SiO4 wadsleyite with similar water contents reported by Shimojuku et al. [Shimojuku, A., Kubo, T., Ohtani, E., Nakamura, T., Okazaki, R., Dohmen, R., Chakraborty, S., 2009. Si and O diffusion in (Mg,Fe)2SiO4 wadsleyite and ringwoodite and its implications for the rheology of the mantle transition zone. Earth Planet. Sci. Lett. 284, 103-112]. Analysis of point defect chemistry based on the positive dependence between Si diffusion rates and water content implies that Si diffusion in Mg2SiO4 wadsleyite under hydrous conditions occurs by a vacancy diffusion mechanism. Enhancement of the Si diffusivity through hydrogen incorporation possibly leads to water weakening in wadsleyite, because Si is the slowest diffusing species.

Original languageEnglish
Pages (from-to)175-182
Number of pages8
JournalPhysics of the Earth and Planetary Interiors
Volume183
Issue number1-2
DOIs
Publication statusPublished - Nov 1 2010

Fingerprint

wadsleyite
diffusivity
silicon
hydrogen
iron
grain boundary
grain boundaries
effect
rheology
convolution integrals
mass spectrometers
moisture content
Earth mantle
diffusion coefficient
transition zone
profiles
surface roughness effects
water content
ringwoodite
mantle

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Geophysics
  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science

Cite this

Effects of hydrogen and iron on the silicon diffusivity of wadsleyite. / Shimojuku, Akira; Kubo, Tomoaki; Ohtani, Eiji; Nakamura, Tomoki; Okazaki, Ryuji.

In: Physics of the Earth and Planetary Interiors, Vol. 183, No. 1-2, 01.11.2010, p. 175-182.

Research output: Contribution to journalArticle

Shimojuku, Akira ; Kubo, Tomoaki ; Ohtani, Eiji ; Nakamura, Tomoki ; Okazaki, Ryuji. / Effects of hydrogen and iron on the silicon diffusivity of wadsleyite. In: Physics of the Earth and Planetary Interiors. 2010 ; Vol. 183, No. 1-2. pp. 175-182.
@article{7204d7748dd5421e97eb1ed3981dc6c4,
title = "Effects of hydrogen and iron on the silicon diffusivity of wadsleyite",
abstract = "We determined the temperature dependence of Si diffusion rates in polycrystalline Mg2SiO4 wadsleyite under nominally dry conditions (20-60wt.ppmH2O), at a pressure of 18GPa and temperatures between 1450 and 1600°C. Diffusion experiments were conducted using an isotopic tracer diffusion method. Diffusion profiles were obtained by a depth-profiling mode using a secondary ion mass spectrometer. Diffusion coefficients were calculated from the obtained diffusion profiles by numerical simulation after correcting for the convolution effect using surface roughness. Since all the obtained diffusion profiles were composed of volume and grain-boundary diffusion regimes, we determined the volume and grain-boundary diffusion coefficients simultaneously. Si diffusion rates in Mg2SiO4 wadsleyite with 20-60wt.ppmH2O were about half an order of magnitude slower than those with 14-507wt.ppmH2O reported by Shimojuku et al. [Shimojuku, A., Kubo, T., Ohtani, E., Yurimoto, H., 2004. Si self-diffusion in wadsleyite: implications for rheology of the mantle transition zone and subducting plates. Geophys. Res. Lett. 31, doi:10.1029/2004GL020002] with correcting the convolution effect in both data. The Si diffusivity in Mg2SiO4 wadsleyite was comparable for the volume diffusion and the grain-boundary diffusion in (Mg0.9Fe0.1)2SiO4 wadsleyite with similar water contents reported by Shimojuku et al. [Shimojuku, A., Kubo, T., Ohtani, E., Nakamura, T., Okazaki, R., Dohmen, R., Chakraborty, S., 2009. Si and O diffusion in (Mg,Fe)2SiO4 wadsleyite and ringwoodite and its implications for the rheology of the mantle transition zone. Earth Planet. Sci. Lett. 284, 103-112]. Analysis of point defect chemistry based on the positive dependence between Si diffusion rates and water content implies that Si diffusion in Mg2SiO4 wadsleyite under hydrous conditions occurs by a vacancy diffusion mechanism. Enhancement of the Si diffusivity through hydrogen incorporation possibly leads to water weakening in wadsleyite, because Si is the slowest diffusing species.",
author = "Akira Shimojuku and Tomoaki Kubo and Eiji Ohtani and Tomoki Nakamura and Ryuji Okazaki",
year = "2010",
month = "11",
day = "1",
doi = "10.1016/j.pepi.2010.09.011",
language = "English",
volume = "183",
pages = "175--182",
journal = "Physics of the Earth and Planetary Interiors",
issn = "0031-9201",
publisher = "Elsevier",
number = "1-2",

}

TY - JOUR

T1 - Effects of hydrogen and iron on the silicon diffusivity of wadsleyite

AU - Shimojuku, Akira

AU - Kubo, Tomoaki

AU - Ohtani, Eiji

AU - Nakamura, Tomoki

AU - Okazaki, Ryuji

PY - 2010/11/1

Y1 - 2010/11/1

N2 - We determined the temperature dependence of Si diffusion rates in polycrystalline Mg2SiO4 wadsleyite under nominally dry conditions (20-60wt.ppmH2O), at a pressure of 18GPa and temperatures between 1450 and 1600°C. Diffusion experiments were conducted using an isotopic tracer diffusion method. Diffusion profiles were obtained by a depth-profiling mode using a secondary ion mass spectrometer. Diffusion coefficients were calculated from the obtained diffusion profiles by numerical simulation after correcting for the convolution effect using surface roughness. Since all the obtained diffusion profiles were composed of volume and grain-boundary diffusion regimes, we determined the volume and grain-boundary diffusion coefficients simultaneously. Si diffusion rates in Mg2SiO4 wadsleyite with 20-60wt.ppmH2O were about half an order of magnitude slower than those with 14-507wt.ppmH2O reported by Shimojuku et al. [Shimojuku, A., Kubo, T., Ohtani, E., Yurimoto, H., 2004. Si self-diffusion in wadsleyite: implications for rheology of the mantle transition zone and subducting plates. Geophys. Res. Lett. 31, doi:10.1029/2004GL020002] with correcting the convolution effect in both data. The Si diffusivity in Mg2SiO4 wadsleyite was comparable for the volume diffusion and the grain-boundary diffusion in (Mg0.9Fe0.1)2SiO4 wadsleyite with similar water contents reported by Shimojuku et al. [Shimojuku, A., Kubo, T., Ohtani, E., Nakamura, T., Okazaki, R., Dohmen, R., Chakraborty, S., 2009. Si and O diffusion in (Mg,Fe)2SiO4 wadsleyite and ringwoodite and its implications for the rheology of the mantle transition zone. Earth Planet. Sci. Lett. 284, 103-112]. Analysis of point defect chemistry based on the positive dependence between Si diffusion rates and water content implies that Si diffusion in Mg2SiO4 wadsleyite under hydrous conditions occurs by a vacancy diffusion mechanism. Enhancement of the Si diffusivity through hydrogen incorporation possibly leads to water weakening in wadsleyite, because Si is the slowest diffusing species.

AB - We determined the temperature dependence of Si diffusion rates in polycrystalline Mg2SiO4 wadsleyite under nominally dry conditions (20-60wt.ppmH2O), at a pressure of 18GPa and temperatures between 1450 and 1600°C. Diffusion experiments were conducted using an isotopic tracer diffusion method. Diffusion profiles were obtained by a depth-profiling mode using a secondary ion mass spectrometer. Diffusion coefficients were calculated from the obtained diffusion profiles by numerical simulation after correcting for the convolution effect using surface roughness. Since all the obtained diffusion profiles were composed of volume and grain-boundary diffusion regimes, we determined the volume and grain-boundary diffusion coefficients simultaneously. Si diffusion rates in Mg2SiO4 wadsleyite with 20-60wt.ppmH2O were about half an order of magnitude slower than those with 14-507wt.ppmH2O reported by Shimojuku et al. [Shimojuku, A., Kubo, T., Ohtani, E., Yurimoto, H., 2004. Si self-diffusion in wadsleyite: implications for rheology of the mantle transition zone and subducting plates. Geophys. Res. Lett. 31, doi:10.1029/2004GL020002] with correcting the convolution effect in both data. The Si diffusivity in Mg2SiO4 wadsleyite was comparable for the volume diffusion and the grain-boundary diffusion in (Mg0.9Fe0.1)2SiO4 wadsleyite with similar water contents reported by Shimojuku et al. [Shimojuku, A., Kubo, T., Ohtani, E., Nakamura, T., Okazaki, R., Dohmen, R., Chakraborty, S., 2009. Si and O diffusion in (Mg,Fe)2SiO4 wadsleyite and ringwoodite and its implications for the rheology of the mantle transition zone. Earth Planet. Sci. Lett. 284, 103-112]. Analysis of point defect chemistry based on the positive dependence between Si diffusion rates and water content implies that Si diffusion in Mg2SiO4 wadsleyite under hydrous conditions occurs by a vacancy diffusion mechanism. Enhancement of the Si diffusivity through hydrogen incorporation possibly leads to water weakening in wadsleyite, because Si is the slowest diffusing species.

UR - http://www.scopus.com/inward/record.url?scp=78649451966&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=78649451966&partnerID=8YFLogxK

U2 - 10.1016/j.pepi.2010.09.011

DO - 10.1016/j.pepi.2010.09.011

M3 - Article

AN - SCOPUS:78649451966

VL - 183

SP - 175

EP - 182

JO - Physics of the Earth and Planetary Interiors

JF - Physics of the Earth and Planetary Interiors

SN - 0031-9201

IS - 1-2

ER -