P‐V‐T equation of state of MgSiO₃ perovskite based on the MgO pressure scale: A comprehensive reference for mineralogy of the lower mantle

Abstract

In situ P‐V‐T measurements of MgSiO3 perovskite were carried out up to 110 GPa and 2500 K, using a sintered‐diamond multianvil apparatus and a laser‐heated diamond anvil cell together with synchrotron radiation. The P‐V‐T data sets obtained by multianvil experiments (28–63 GPa and 300–1500 K) and diamond anvil cell experiments (52–108 GPa and 300, 1500–2430 K) are consistent with each other. The equation of state of MgSiO3 perovskite was subsequently represented by a Mie‐Grüneisen‐Debye model, using the equation of state of MgO as reference for pressure determination. In this study, we provide mutually consistent and precise P‐V‐T equations of state of MgSiO3 perovskite and MgO applicable to the bottom of the Earth's lower mantle. These P‐V‐T equations of state and derivative thermodynamic and elastic properties are essential for mineralogy of the lower mantle as a comprehensive reference.

Icosahedral AlCuFe quasicrystal at high pressure and temperature and its implications for the stability of icosahedrite

“…A Ge solid-state detector was used for collecting diffraction patterns in energy dispersive mode. The Bragg angle was set using a horizontal goniometer41. Energy and diffraction angles were calibrated before the measurements using known energy values of characteristic X-rays of several metal standards (Cu, Mo, Ag, Ta, Pt, Au and Pb) and known lattice parameters of gold.…”

Computational support for a pyrolitic lower mantle containing ferric iron

“…However, physical properties of LM minerals determined from high-pressure (P) and high-temperature (T ) experiments have some uncertainties due to technical difficulties, which give substantial discrepancies on this issue. Several different models have been proposed [2][3][4][5][6][8][9][10][11][12][13][14][15] depending on the research approaches used. Generally, experiments based on the multianvil apparatus propose a pyrolitic LM (refs 2,8,9).…”

“…However, experimental measurements of the elasticity of these minerals at realistic lower-mantle pressures and temperatures remain impractical. As a result, di erent compositional models for the Earth's lower mantle have been proposed [2][3][4] . Theoretical simulations, which depend on empirical evaluations of the e ects of Fe incorporation into these minerals, support a pyrolitic lower mantle that contains a significant amount of ferropericlase 5,6 , much like the Earth's upper mantle.…”

“…In the pyrolite model, a Mg/Si ratio of ∼1.3 is proposed, yielding a notable amount of (Mg,Fe)O ferropericlase (Fp), a solid solution of MgO and FeO together with Fe-and Al-bearing MgSiO 3 bridgmanite (MgBr). A particular composition with the olivine-like Mg/Si ratio as high as 2.0 was however suggested by the equations of state (EoS) measurements using multianvil apparatus with sintered diamonds 3 . An alternative view that the LM is MgBr dominant, corresponding to the perovskitic or chondritic model (Mg/Si ∼ 1.0), is proposed based on diamond-anvil cell experiments 4,10,11 .…”

“…Comparison of the aggregate elasticity of potential minerals with observations is the usual way to estimate the LM composition, and the preliminary reference Earth model 17 (PREM) is often used as a reference [2][3][4][5][6]14 . Nevertheless, the elasticity of LM minerals is sensitive to the incorporation of dilute substitutional solutes 18 , such as Fe and Al.…”