Thermal elasticity of (Fex,Mg1−x)2SiO4 olivine and wadsleyite
Identifieur interne : 000385 ( Main/Exploration ); précédent : 000384; suivant : 000386Thermal elasticity of (Fex,Mg1−x)2SiO4 olivine and wadsleyite
Auteurs : M. Nú Ez-Valdez [États-Unis] ; Z. Wu [République populaire de Chine] ; Y. G. Yu [États-Unis] ; R. M. Wentzcovitch [États-Unis]Source :
- Geophysical Research Letters [ 0094-8276 ] ; 2013-01-28.
Abstract
We present first‐principles results for elastic moduli (bulk, K, and shear, G) and acoustic velocities (compressional, VP, shear, VS, and bulk VΦ) of olivine (α) and wadsleyite (β) (Fex,Mg1 − x)2SiO4, at high pressure (P) and temperature (T) with varying iron content (0 ≤ x ≤ 0.125). Pressure and temperature derivatives of these properties are analyzed. We show that adding 12.5% of Fe in forsterite softens VP and VS by ∼3–6%, the same effect as raising temperature by ∼1000 K in dry olivine at 13.5 GPa—the same is true in wadsleyite. This study suggests that Fe is effective in producing seismic velocity heterogeneity at upper mantle and transition zone conditions and should be another key ingredient, in addition to temperature and water content variations, in interpreting seismic heterogeneities in the transition zone. The effect of Fe on density, elastic, and velocity contrasts across the α → β transition is also addressed at relevant conditions. We show that simultaneous changes of composition, temperature, and pressure do not affect significantly the relative density contrasts. We also find that compressional and shear impedance contrasts result primarily from velocity discontinuities rather than density discontinuity.
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DOI: 10.1002/grl.50131
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Nú Ez-Valdez</name><affiliation wicri:level="1"><country xml:lang="fr">États-Unis</country><wicri:regionArea>School of Physics and Astronomy, University of Minnesota, Minnesota, Minneapolis</wicri:regionArea><wicri:noRegion>Minneapolis</wicri:noRegion></affiliation></author><author><name sortKey="Wu, Z" sort="Wu, Z" uniqKey="Wu Z" first="Z." last="Wu">Z. Wu</name><affiliation wicri:level="3"><country xml:lang="fr">République populaire de Chine</country><wicri:regionArea>School of Earth and Space Sciences, University of Science and Technology of China, Anhui, Hefei</wicri:regionArea><placeName><settlement type="city">Hefei</settlement><region type="province">Anhui</region></placeName></affiliation></author><author><name sortKey="Yu, Y G" sort="Yu, Y G" uniqKey="Yu Y" first="Y. G." last="Yu">Y. G. Yu</name><affiliation wicri:level="1"><country xml:lang="fr">États-Unis</country><wicri:regionArea>Department of Chemical Engineering and Materials Science, University of Minnesota, Minnesota, Minneapolis</wicri:regionArea><wicri:noRegion>Minneapolis</wicri:noRegion></affiliation></author><author><name sortKey="Wentzcovitch, R M" sort="Wentzcovitch, R M" uniqKey="Wentzcovitch R" first="R. M." last="Wentzcovitch">R. M. Wentzcovitch</name><affiliation wicri:level="1"><country xml:lang="fr">États-Unis</country><wicri:regionArea>Department of Chemical Engineering and Materials Science, Minnesota Supercomputing Institute (MSI), University of Minnesota, Minnesota, Minneapolis</wicri:regionArea><wicri:noRegion>Minneapolis</wicri:noRegion></affiliation></author></analytic><monogr></monogr><series><title level="j">Geophysical Research Letters</title><title level="j" type="abbrev">Geophys. Res. Lett.</title><idno type="ISSN">0094-8276</idno><idno type="eISSN">1944-8007</idno><imprint><publisher>Blackwell Publishing Ltd</publisher><date type="published" when="2013-01-28">2013-01-28</date><biblScope unit="volume">40</biblScope><biblScope unit="issue">2</biblScope><biblScope unit="page" from="290">290</biblScope><biblScope unit="page" to="294">294</biblScope></imprint><idno type="ISSN">0094-8276</idno></series><idno type="istex">E668F77777E876D78DFD3A0EA2EB9797EB4E24AC</idno><idno type="DOI">10.1002/grl.50131</idno><idno type="ArticleID">GRL50131</idno></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0094-8276</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass><langUsage><language ident="en">en</language></langUsage></profileDesc></teiHeader><front><div type="abstract">We present first‐principles results for elastic moduli (bulk, K, and shear, G) and acoustic velocities (compressional, VP, shear, VS, and bulk VΦ) of olivine (α) and wadsleyite (β) (Fex,Mg1 − x)2SiO4, at high pressure (P) and temperature (T) with varying iron content (0 ≤ x ≤ 0.125). Pressure and temperature derivatives of these properties are analyzed. We show that adding 12.5% of Fe in forsterite softens VP and VS by ∼3–6%, the same effect as raising temperature by ∼1000 K in dry olivine at 13.5 GPa—the same is true in wadsleyite. This study suggests that Fe is effective in producing seismic velocity heterogeneity at upper mantle and transition zone conditions and should be another key ingredient, in addition to temperature and water content variations, in interpreting seismic heterogeneities in the transition zone. The effect of Fe on density, elastic, and velocity contrasts across the α → β transition is also addressed at relevant conditions. We show that simultaneous changes of composition, temperature, and pressure do not affect significantly the relative density contrasts. We also find that compressional and shear impedance contrasts result primarily from velocity discontinuities rather than density discontinuity.</div></front></TEI><affiliations><list><country><li>République populaire de Chine</li><li>États-Unis</li></country><region><li>Anhui</li></region><settlement><li>Hefei</li></settlement></list><tree><country name="États-Unis"><noRegion><name sortKey="Nu Ez Aldez, M" sort="Nu Ez Aldez, M" uniqKey="Nu Ez Aldez M" first="M." last="Nú Ez-Valdez">M. Nú Ez-Valdez</name></noRegion><name sortKey="Wentzcovitch, R M" sort="Wentzcovitch, R M" uniqKey="Wentzcovitch R" first="R. M." last="Wentzcovitch">R. M. Wentzcovitch</name><name sortKey="Yu, Y G" sort="Yu, Y G" uniqKey="Yu Y" first="Y. G." last="Yu">Y. G. Yu</name></country><country name="République populaire de Chine"><region name="Anhui"><name sortKey="Wu, Z" sort="Wu, Z" uniqKey="Wu Z" first="Z." last="Wu">Z. 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