2:45 PM - 3:00 PM
[SIT20-05] The elastic behaviour of Fe-bearing calcium-ferrite (CF) type phase to lower mantle pressure
Keywords:Calcium-ferrite type phase, CF, Elasticity, Lower Mantle, Aluminous Phases, Brillouin Scattering
The calcium-ferrite-type phase (CF) is the dominant Al-bearing phase in MORB compositions throughout most of the Earth's lower mantle. It comprises up to 20 Volume% of basaltic compositions at lower mantle conditions. As a major phase, it has a significant impact on mineral physical models of the Earth's lower mantle. To date, however, the elastic properties of this phase have been determined only for simple compositions, which are not representative of those which can be encountered in MORB, impacting mineral physical models.
Here, we present the single-crystal elastic properties, and seismic velocities of a Fe-bearing CF-type phase, with a composition relevant to MORB. We also conducted independent density determinations, as obtained through Brillouin scattering and X-ray diffraction measurements. Experiments were conducted at eight different pressures up to 26 GPa at room temperature.
We determined an equation of state, based on the Brillouin scattering experiments, in which KT0 = 188.4(7) GPa with KT0' = 4.61(8) and GR,0 =126.4(9) GPa with GR,0' = 2.1(1). We further find that our axial compressibility data is in excellent agreement with the compressibility observed by X-ray diffraction. In this, the c-axis is the stiffest. The a- and b-axes are of comparable compressibility, though the b-axis was found to be slightly more compressible. Both, the elastic moduli and seismic velocities, are lower than reported in previous computational and experimental studies on simpler systems. This suggests that the presence of Fe affects the acoustic wave velocities of this phase significantly and therefore needs to be taken into account in mineral physical models, describing the fate of subducting slabs in the lower mantle.
We observe the onset of the proposed spin transition in octahedrally coordinated Fe3+ in calcium-ferrite type phase around 25 GPa. While we do not observe a softening of the bulk modulus, we do find that the bulk modulus is significantly lower than anticipated based on extrapolation from the lower pressure measurements.
Here, we present the single-crystal elastic properties, and seismic velocities of a Fe-bearing CF-type phase, with a composition relevant to MORB. We also conducted independent density determinations, as obtained through Brillouin scattering and X-ray diffraction measurements. Experiments were conducted at eight different pressures up to 26 GPa at room temperature.
We determined an equation of state, based on the Brillouin scattering experiments, in which KT0 = 188.4(7) GPa with KT0' = 4.61(8) and GR,0 =126.4(9) GPa with GR,0' = 2.1(1). We further find that our axial compressibility data is in excellent agreement with the compressibility observed by X-ray diffraction. In this, the c-axis is the stiffest. The a- and b-axes are of comparable compressibility, though the b-axis was found to be slightly more compressible. Both, the elastic moduli and seismic velocities, are lower than reported in previous computational and experimental studies on simpler systems. This suggests that the presence of Fe affects the acoustic wave velocities of this phase significantly and therefore needs to be taken into account in mineral physical models, describing the fate of subducting slabs in the lower mantle.
We observe the onset of the proposed spin transition in octahedrally coordinated Fe3+ in calcium-ferrite type phase around 25 GPa. While we do not observe a softening of the bulk modulus, we do find that the bulk modulus is significantly lower than anticipated based on extrapolation from the lower pressure measurements.