Elasticity of MgO to 130 GPa: Implications for lower mantle mineralogy

Motohiko Murakami, Yasuo Ohishi, Naohisa Hirao, Kei Hirose

Research output: Contribution to journalArticlepeer-review

44 Citations (Scopus)

Abstract

The aggregate shear wave velocities of MgO (periclase) have been determined throughout Earth's lower mantle pressure regime approaching 130 GPa using Brillouin spectroscopy in conjunction with synchrotron X-ray diffraction technique in a diamond anvil cell apparatus. We found that the extrapolations of the high-pressure shear wave velocities and shear moduli to ambient pressure are highly consistent with earlier studies. However, the measurements over a wide pressure range revealed that the pressure derivative of the shear modulus (dG/dP = G0′) of MgO is 1.92(2), which is distinctly lower than that of previous lower-pressure experiments. Compared with the previous results on (Mg,Fe)O ferropericlase, there is no clear correlation between iron content and G0′. We calculate that the shear wave velocity profile of lower mantle along the adiabatic geotherm applied by the lower G0′ value of periclase can remarkably well reproduce the global seismological 1-D velocity profile model with uniform composition model. The best-fitting result indicates the possibility of a lower mantle mineralogy with ~ 92 vol.% silicate perovskite phase, implying that the bulk composition of lower mantle is likely not to be pyrolitic but more chondritic. The present acoustic measurements performed over the large pressure range have thus led us to a better understanding of compositional model of the Earth's lower mantle.

Original languageEnglish
Pages (from-to)123-129
Number of pages7
JournalEarth and Planetary Science Letters
Volume277
Issue number1-2
DOIs
Publication statusPublished - 2009 Jan 15

Keywords

  • Brillouin spectroscopy
  • MgO
  • elastic properties
  • lower mantle
  • mineralogy
  • sound velocity

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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