HR: 09:30h
AN: T21A-07 [PDF]
TI: High-Pressure Brillouin Measurements on Single-Crystal Ferropericlase, (Mg0.94Fe0.06)O: Implications
for Earth's Lower Mantle
AU: * Jackson, J M
EM: jmjackso@uiuc.edu
AF: University of Illinois, Department of Geology,
1301 W. Green St., Urbana, IL 61801 United States
AU: Bass, J D
EM: jaybass@uiuc.edu
AF: University of Illinois, Department of Geology,
1301 W. Green St., Urbana, IL 61801 United States
AU: Sinogeikin, S V
EM: sinogeik@uiuc.edu
AF: University of Illinois, Department of Geology,
1301 W. Green St., Urbana, IL 61801 United States
AU: Jacobsen, S D
EM: Steven.Jacobsen@uni-bayreuth.de
AF: Universitat Bayreuth, Bayerisches Geoinstitut, Bayreuth, 95440
Germany
AU: Reichmann, H -
EM: hanni@gfz-potsdam.de
AF: GeoForschungsZentrum, Telegrafenberg, Potsdam, 14473
Germany
AU: Mackwell, S J
EM: Mackwell@lpi.usra.edu
AF: Center for Advanced Space Studies, Lunar and Planetary Institute, Houston, TX 77058 United States
AB:
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. Ferropericlase, (Mg,Fe)O,
is expected to coexist with silicate perovskite in Earth's lower mantle (660 C 2900 km depth), and will therefore have a
major influence on all properties in this region of the Earth. However, 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 ferropericlase, (Mg$_{0.94}$Fe$_{0.06}$)O [hereafter referred to as Fe6], measured by Brillouin scattering on a sample
compressed to 13.3(4) GPa with a diamond anvil cell. Within the uncertainties, we find that at room-pressure the bulk
modulus of Fe6 is unchanged from MgO, but that the shear modulus of Fe6 is about 7% less than that of MgO. Furthermore, the
elastic anisotropy of Fe6 is about 10% greater than that of MgO at room-pressure, in excellent agreement with results
obtained using gigahertz ultrasonic interferometry on the same sample [1]. 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 mol%
Fe in MgO does not significantly affect the pressure derivatives of the aggregate elastic properties of ferropericlase
compared to MgO. At the highest pressure obtained in this experiment, the elastic anisotropy of Fe6 is close to that of MgO.
In light of these new high-pressure measurements on Fe6 and other recent measurements on Al-bearing MgSiO$_{3}$ perovskite
[2], implications for the mineralogy of Earth's lower mantle will be discussed.
{\it References:}
[1] S.D. Jacobsen {\it et al.} (2002) J. Geophys. Res., 107, 2001JB000490
[2] J.M. Jackson {\it et al.} (2003) Geophys. Res. Abstr., 5, EGS-AGU-EUG Joint Assembly, France, EAE03-A-12122.
DE: 1025 Composition of the mantle
DE: 3900 MINERAL PHYSICS
DE: 3909 Elasticity and anelasticity
DE: 3924 High-pressure behavior
DE: 3934 Optical, infrared, and Raman spectroscopy
SC: Tectonophysics [T]
MN: 2003 Fall Meeting