High-Pressure Brillouin Measurements on Magnesiowüstite, (Mg_0.94Fe_0.06)O

Jennifer M. Jackson^1*, Stanislav V. Sinogeikin¹, Jay D. Bass¹, Steven D. Jacobsen², Hans J. Reichmann³, and Stephen J. Mackwell⁴

¹Department of Geology, University of Illinois, Urbana, IL, U.S.A.
²Bayerisches Geoinstitut, Universität Bayreuth, Germany
³GeoForschungsZentrum Potsdam, Germany
⁴Lunar and Planetary Institute, Houston, TX, U.S.A

*jmjackso@uiuc.edu

The determination of accurate compositional models of Earth’s interior from observed seismological data requires knowledge of the elastic properties of candidate phases under conditions approaching those of Earth’s interior. Magnesiowüstite, (Mg,Fe)O, is expected to coexist with silicate perovskite in Earth’s lower mantle (660 – 2900 km depth). The effect of iron on the single-crystal elasticity of MgO at high-pressures is still poorly constrained. In this contribution, we present the single-crystal elastic properties of magnesiowüstite, (Mg_0.94Fe_0.06)O, measured by Brillouin scattering on a sample compressed to 13.3(4) GPa with a diamond anvil cell. Our measurements also allow us to assess the effect of iron on the pressure derivatives of the sound velocities and elastic moduli of MgO. Results indicate that 6% Fe in MgO does not significantly affect the pressure derivatives of the aggregate elastic properties of magnesiowüstite. At room-pressure, the elastic anisotropy of (Mg_0.94Fe_0.06)O is ~10% greater than that of MgO, in excellent agreement with results obtained using gigahertz ultrasonic interferometry on the same sample [1]. At the highest pressure obtained in this experiment, the elastic anisotropy of (Mg_0.94Fe_0.06)O is close that of MgO.

[1] Jacobsen, S.D., Reichmann, H.-J., Spetzler, H.A., Mackwell, S.J., Smyth, J.R., Angel, R.A., and McCammon, C.A., J. Geophys. Res., 107, 2001JB000490 (2002).