Elastic Shear Anisotropy of Ferropericlase in Earth's Lower Mantle
Hauke Marquardt,1*
Sergio Speziale,1
Hans J. Reichmann,1
Daniel J. Frost,2
Frank R. Schilling,1
Edward J. Garnero3
Seismic shear anisotropy in the lowermost mantle most likely
results from elastic shear anisotropy and lattice preferred
orientation of its constituent minerals, including perovskite,
post-perovskite, and ferropericlase. Measurements of the elastic
shear anisotropy of single-crystal (Mg
0.9Fe
0.1)O up to 69 gigapascals
(GPa) show that it increased considerably across the pressure-induced
spin transition of iron between 40 and 60 GPa. Increasing iron
content further enhances the anisotropy. This leads to at least
50% stronger elastic shear anisotropy of (Mg,Fe)O in the lowermost
mantle compared to MgO, which is typically used in geodynamic
modeling. Our results imply that ferropericlase is the dominant
cause of seismic shear anisotropy in the lower mantle.
2 Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Germany.
3 School of Earth and Space Exploration, Arizona State University, Box 871404, Tempe, AZ 85287, USA.
Karlsruhe Institute of Technology, IBF, 76131 Karlsruhe, Germany.
* To whom correspondence should be addressed. E-mail: hama{at}gfz-potsdam.de
