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AGU: Geophysical Research Letters

 

Keywords

  • postperovskite
  • equation of state
  • D

Index Terms

  • Mineral Physics: Equations of state
  • Seismology: Mantle
  • Mineralogy and Petrology: Mantle processes
  • Mineral Physics: X-ray, neutron, and electron spectroscopy and diffraction

Abstract

Equation of state of NaMgF3 postperovskite: Implication for the seismic velocity changes in the D″ region

Justin Hustoft

Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

Krystle Catalli

Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

Sang-Heon Shim

Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

Atsushi Kubo

Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois, USA

Vitali B. Prakapenka

Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois, USA

Martin Kunz

Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, USA

Recent first-principles calculations have proposed that bulk sound speed (V Φ) decreases at the perovskite (Pv) → postperovskite (PPv) transition. Yet some measurements suggest an increase in V Φ at the PPv transition in (Mg,Fe)SiO3 and NaMgF3. Our new measurements on NaMgF3 up to 50 GPa under quasi-hydrostatic stress conditions reveal that the V Φ of PPv remains lower than that of Pv near the PPv transition, consistent with a first-principles study on NaMgF3. Combined with similar observations in (Mg,Fe)SiO3, MgGeO3, and CaIrO3, our result on NaMgF3 suggests that the V Φ decrease is a robust trend in the PPv transition and is controlled more by crystal structure than by chemical composition. Our finding also strengthens the proposal that the elastic properties of PPv can explain the small P-wave increase across the D″ discontinuity and the anticorrelation between the V Φ and S-wave velocity anomalies in the D″ region.

Received 21 March 2008; accepted 30 April 2008; published 31 May 2008.

Citation: Hustoft, J., K. Catalli, S.-H. Shim, A. Kubo, V. B. Prakapenka, and M. Kunz (2008), Equation of state of NaMgF3 postperovskite: Implication for the seismic velocity changes in the D″ region, Geophys. Res. Lett., 35, L10309, doi:10.1029/2008GL034042.

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