High-Pressure Elasticity of (Al,Fe)-bearing Bridgmanite: Implications to Lower-Mantle Geophysics and Geochemistry
Abstract
Our knowledge of the geophysics, geochemistry, and geodynamics of the Earth's lower mantle critically relies on the chemical and physical properties, such as density (ρ), compressional, and shear wave velocities (VP, VS), of candidate minerals at relevant pressure-temperature (P-T) conditions. For instance, comparison between mineral physics on VP, VS, and ρ of candidate minerals and 1D seismic profiles1 has been extensively used to constrain the mineralogical model in the region2,3. Furthermore, the observed seismic anisotropy in the lower mantle was generally attributed to the deformation of candidate minerals under mantle convections4. However, the geophysics and geochemistry of the lower mantle are still poorly understood due to the limited experimental studies on the elasticity of bridgmanite, the most abundant mineral in the lower mantle2,3. Additionally, studies indicated that chemical perturbations, such as Fe and/or Al enrichment in bridgmanite, will greatly affect its elasticity at high pressure5. Here, we have used combined Brillouin light scattering and impulsive stimulated light scattering techniques, developed in our group, to reliably measure both VS and VP of bridgmanite in diamond anvil cells. We will present our recent investigations on the elasticity of lower-mantle bridgmanite including polycrystalline and single crystals with different Fe and Al contents at high pressure5,6. Together with the thermoelastic modeling of P, T and chemical (Fe and/or Al) effects on the velocity and density profile of bridgmanite, our results could provide multiple and internally-consistent constraints to the composition and temperature of the lower mantle. Furthermore, combining the determined high-pressure single-crystal elasticity of bridgmanite with literature reports on the lattice preferred orientations at relevant P, T and stress conditions4, we will report a geophysical model that could help better understand the seismically-observed shear wave radial anisotropy at the topmost lower mantle.
1. Dziewonski, A. et al. Phys Earth Planet In 25, 297 (1981) 2. Kurnosov, A. et al. Nature 543, 543 (2017). 3. Murakami, M. et al. Nature 485, 90 (2012) 4. Tsujino, N. et al. Nature 539, 81 (2016) 5. Fu, S. et al. Earth Planet Sc Lett 518, 116 (2019). 6. Fu, S. et al. Geophys Res Lett 45, 4725 (2018).- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR31B0073F
- Keywords:
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- 3909 Elasticity and anelasticity;
- MINERAL PHYSICS;
- 3924 High-pressure behavior;
- MINERAL PHYSICS;
- 5139 Transport properties;
- PHYSICAL PROPERTIES OF ROCKS;
- 8124 Earth's interior: composition and state;
- TECTONOPHYSICS