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| Titel |
High-pressure single-crystal elasticity measurements of Al-Fe-bridgmanite |
| VerfasserIn |
Alexander Kurnosov, Hauke Marquardt, Dan Frost, Tiziana Boffa-Ballaran, luca Ziberna |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250147187
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| Publikation (Nr.) |
 EGU/EGU2017-11310.pdf |
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| Zusammenfassung |
| The chemical composition of Earth’s lower mantle can be constrained by combining
seismological observations with mineral physics elasticity measurements. However, the
lack of laboratory data for Earth’s most abundant mineral (Mg,Fe,Al)(Al,Fe,Si)O3
bridgmanite has hampered any conclusive result. Here, we report single-crystal elasticity
measurements on Al-Fe-bearing bridgmanite (Mg0.9Fe0.1Si0.9Al0.1)O3 to pressures above
40 GPa. The experimetns were conducted using in-situ high-pressure Brillouin
spectroscopy and x-ray diffraction combined with advanced sample preparation that allows
for the simultaneous loading of two single-crystals with different crystallographic
orientations. Our measurements show that the elastic behavior of Fe-Al-bearing
bridgmanite is markedly different from the behavior of the MgSiO3 endmember reported
previously.
Values and uncertainties of K0, K0′, G0 and G0′ as well as the elastic constants Cij and
absolute pressure values for all experimental points were derived using a global fit of all our
experimental data, combining the usually employed Christoffel equation that relates elastic
constants and density to direction-dependent acoustic wave velocities with the finite strain
formalism.
We employ our data to model seismic wave velocities in the top portion of the lower
mantle, assuming a pyrolitic mantle composition and accounting for depth-dependent
changes in iron partitioning between bridgmanite and ferropericlase. We find excellent
agreement between our mineral physics predictions and the seismic Preliminary Reference
Earth Model down to at least 1200 km depth, indicating chemical homogeneity of the upper
and shallow lower mantle. A high Fe3+/Fe2+ ratio of about 2 in shallow lower mantle
bridgmanite is required to match seismic data, implying the presence of metallic iron in an
isochemical mantle. Our calculated velocities are in increasingly poor agreement with those
of the lower mantle at depths >1200 km, possibly indicating a decrease in the ferric iron
content of the lower mantle that has potential implications for geochemistry and geophysics. |
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