Effects of Fe-enrichment on the equation of state and stability of (Mg,Fe)SiO3 perovskite

Fe-rich natural orthopyroxenes with compositions of (Mg0.61Fe0.38Ca0.01)SiO3 (Fe#38) and (Mg0.25Fe0.74Ca0.01)SiO3 (Fe#74) were studied at pressures up to 155GPa and temperatures up to 3000K. Single-phase orthorhombic GdFeO3-type perovskite was synthesized by heating to ∼2000K at 63GPa for the Fe#38...

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Bibliographic Details
Published in:Earth and planetary science letters 2013-01, Vol.361 (C), p.249-257
Main Authors: Dorfman, Susannah M., Meng, Yue, Prakapenka, Vitali B., Duffy, Thomas S.
Format: Article
Language:English
Subjects:
[formula omitted] region
Bulk modulus
Compressing
Earth
Equations of state
Heating
Iron
lower mantle
perovskite
Perovskites
post-perovskite
Stability
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Summary:Fe-rich natural orthopyroxenes with compositions of (Mg0.61Fe0.38Ca0.01)SiO3 (Fe#38) and (Mg0.25Fe0.74Ca0.01)SiO3 (Fe#74) were studied at pressures up to 155GPa and temperatures up to 3000K. Single-phase orthorhombic GdFeO3-type perovskite was synthesized by heating to ∼2000K at 63GPa for the Fe#38 composition and at 72GPa for the Fe#74 composition. At lower pressures, heating both compositions resulted in a mixture of perovskite, SiO2 and (Mg,Fe)O. These measurements provide new constraints on the dependence of (Mg,Fe)SiO3 perovskite stability on pressure and composition. Upon further compression and heating at 89 and 99GPa, Fe#38 and Fe#74 perovskites transformed to two-phase mixtures of perovskite and post-perovskite, consistent with previous findings that increasing Fe content lowers the transition pressure. The volume of (Mg,Fe)SiO3 perovskites increases linearly with Fe-content. Volume data were fit to the Birch–Murnaghan equation of state. The bulk modulus at 80GPa is 550–560GPa for both Fe-rich perovskites, comparable to or slightly higher than the values measured for MgSiO3 perovskite at this pressure, indicating that the bulk modulus of perovskite is not strongly sensitive to Fe content. ► Single-phase orthorhombic (Mg,Fe)SiO3 perovskite synthesized with up to 74% FeSiO3. ► Dramatic increase in the solubility of Fe2+ in perovskite observed from 60 to 80GPa. ► Fe-incorporation in perovskite has no significant effect on compressibility. ► Fe-rich compositions have broad perovskite/post-perovskite stability regions in the deep mantle.
ISSN:0012-821X
1385-013X
DOI:10.1016/j.epsl.2012.10.033