Seismic wave speeds in Earth's lower mantle are governed by the elastic properties of the minerals ferropericlase and silicate perovskite. Therefore, knowing the velocity of sound though these minerals at high pressures and temperatures is essential to understanding properties of the lower mantle.
However, experimental studies of ferropericlase have been restricted to pressures below about 20 gigapascals, which is insufficient to model the change in the electron spin configuration of iron known to occur within the lower mantle pressures.
Past studies, using x-ray diffraction to produce the needed high pressures, showed increases in bulk modulus and bulk sound velocity for ferropericlase as pressure increased.
In this study, Lin et al. used the nuclear resonance inelastic x-ray scattering technique to measure compressional and shear wave velocities and the shear modulus of ferropericlase at pressures above and below the threshold for iron electron spin pairing changes.
The authors noted a dramatic jump in sound velocities across this transition as pressure increased. They suggest that models of seismic wave speed in the lower mantle be revised to reflect this result.
Title: Sound velocities of ferropericlase in the Earth's lower mantle
Authors: Jung-Fu Lin and Choong-Shik Yoo: Lawrence Livermore National Laboratory, Livermore, California, U.S.A.; Steven D. Jacobsen: Geophysical Laboratory, Carnegie Institute of Washington, Washington D.C., U.S.A.; Department of Geological Sciences, Northwestern University, Evanston, Illinois, U.S.A.; Wolfgang Sturhahn and Jiyong Zhao: Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, U.S.A.; Jennifer M. Jackson: Geophysical Laboratory, Carnegie Institute of Washington, Washington D.C., U.S.A.; now at Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, U.S.A.
Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL028099, 2006
The above story is based on materials provided by American Geophysical Union. Note: Materials may be edited for content and length.
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