Seismic Wave Velocities in Earth's Mantle from Mineral Elasticity

Buchen, Johannes

doi:10.1002/9781119528609.ch3

Cited by 6 publications

(9 citation statements)

References 330 publications

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“…This strategy has the advantage that only one set of V 0 , K T0 , and K' T0 needs to be determined for the high-spin state, the low-spin state, and the mixed-spin region, while the electronic contribution to the spincrossover equation is calculated separately. Buchen (2021) further showed that a good fit to the experimentally measured P-V data can be obtained even when most of these parameters, such as Δ 0 , b, 2 and the fit to the experimental data points is shown in Figure 3a. The EOS curve interpolates well the data points in both the high-spin state region and across the spin crossover, while the population density of the high-spin and low-spin electronic states, shown in the inset of Figure 3a, confirms that the transition is broad and takes place over a pressure interval of more than 30 GPa, as was previously observed by Chang et al (2013).…”

Section: Spin Crossover In Fe-bearing Al-phase Dmentioning

confidence: 85%

“…The number of data points collected after the onset of the spin crossover (i.e., above 38 GPa) is limited and does not allow to refine separate EOS parameters for the Fe-bearing Al-phase D sample in the high-and low-spin states. However, a fit of all data points (i.e., before and across the spin crossover) can be obtained using a new semi-empirical formalism that has been recently proposed by Buchen (2021). In this formalism, the contribution of the spin crossover to the elastic energy (and thus to pressure) is obtained from the volume dependency of crystal-field parameters such as the crystal-field splitting Δ and the Racah parameters B and C: where the zero in the subscript denotes parameters at room pressure.…”

Section: Spin Crossover In Fe-bearing Al-phase Dmentioning

confidence: 99%

“…In this formalism, the contribution of the spin crossover to the elastic energy (and thus to pressure) is obtained from the volume dependency of crystal-field parameters such as the crystal-field splitting Δ and the Racah parameters B and C: where the zero in the subscript denotes parameters at room pressure. The total Helmholtz free energy (F) at a given volume is then calculated by summing the elastic energy obtained from the finite strain equation (i.e., BM3 EOS in this case), the energies associated with the three most populated electronic states (i.e., 6 A 1 , 2 T 2 , and 4 T 1 for Fe 3+ ) according to the equations proposed by Tanabe and Sugano (1954), and a term accounting for configurational entropy (Buchen 2021). Finally, pressure is calculated by differentiating the total Helmholtz free energy relative to volume as P = -(∂F/∂V) T .…”

Section: Spin Crossover In Fe-bearing Al-phase Dmentioning

confidence: 99%

“…and c, are fixed to values determined by previous studies for octahedrally coordinated Fe 2+ and Fe 3+ cations in other compounds, while only B 0 and δ are refined. Following the examples provided byBuchen (2021), we assumed C/B to be constant and equal to 4.73, which implies c = b, with b = -2 (as Fe 3+ in CF-type aluminous phase, Buchen 2021) and Δ 0 = 14750 cm -1 (as Fe 3+ in corundum,Lehmann and Harder 1970;Krebs and Maisch 1971), while B 0 and δ were refined. The resulting fit parameters are reported in Table…”

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confidence: 99%

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Structure and compressibility of Fe-bearing Al-phase D

Criniti,

Ishii,

Kurnosov

et al. 2023

American Mineralogist

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Due to its large thermal stability, Al-phase D, the (Al,Fe 3+ ) 2 SiO 6 H 2 member of the dense hydrous magnesium silicate (DHMS) phase D, may survive along hot subduction geotherms or even at ambient mantle temperatures in the Earth's transition zone and lower mantle, playing therefore a major role as water reservoir and carrier in the Earth's interior. We have investigated the crystal structure and highpressure behavior of Fe-bearing Al-phase D with a composition of Al 1.53(2) Fe 0.22(1) Si 0.86(1) O 6 H 3.33( 9) by means of single-crystal X-ray diffraction. While the structure of pure Al-phase D (Al 2 SiO 6 H 2 ) has space group P6 3 /mcm and consists of equally populated and half-occupied (Al,Si)O 6 octahedra, Feincorporation in Al-phase D seems to induce partial ordering of the cations over the octahedral sites, resulting in a change of the space group symmetry from P6 3 /mcm to P6 3 22 and in well-resolved diffuse scattering streaks observed in X-ray images. The evolution of the unit-cell volume of Fe-bearing Alphase D between room pressure and 38 GPa, determined by means of synchrotron X-ray diffraction in a diamond anvil cell, is well described by a 3 rd -order Birch-Murnaghan equation of state having isothermal bulk modulus K T0 = 166.3(15) GPa and first pressure derivative K' T0 = 4.46(12). Above 38 GPa, a change in the compression behavior is observed, likely related to the high-to-low spin crossover of octahedrally coordinated Fe 3+ . The evolution of the unit-cell volume across the spin crossover was modelled using a recently proposed formalism based on crystal-field theory, which shows that the spin crossover region extends from about 30 to 65 GPa. Given the absence of abrupt changes in the compression mechanism of Fe-bearing Al-phase D before the spin crossover, we show that the strength of H-bonds and likely their symmetrization do not greatly affect the elastic properties of phase D solid solutions, independently of their compositions.

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Section: Spin Crossover In Fe-bearing Al-phase Dmentioning

confidence: 85%

Section: Spin Crossover In Fe-bearing Al-phase Dmentioning

confidence: 99%

Section: Spin Crossover In Fe-bearing Al-phase Dmentioning

confidence: 99%

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confidence: 99%

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Structure and compressibility of Fe-bearing Al-phase D

Criniti,

Ishii,

Kurnosov

et al. 2023

American Mineralogist

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“…Success has been achieved in constraining chemistries that match observed seismic velocities over a broad region of depth. With increasing degrees of sophistication, thermodynamic models examining effects of compositions in the form of either mechanical mixtures or solid solutions have succeeded in matching average elastic velocities, their gradients with depth, and mineral phase changes in the transition zone (e.g., Buchen, 2021; Cammarano et al., 2005; Chust et al., 2017; Stixrude & Lithgow‐Bertelloni, 2011; Wang et al., 2018; Xu et al., 2008).…”

Section: Introductionmentioning

confidence: 99%

Mantle Phase Changes Detected From Stochastic Tomography

et al. 2023

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Introduction Observed and Predicted Phase ChangesThe best-known solid phase changes in Earth's silicate mantle are commonly detected from the reflection and conversion of body waves interacting with sharp, near discontinuous, changes in velocity and density occurring at or near 410 and 660 km depth (e.g., Niu et al., 2005;Shearer, 1991). These phase changes also produce multi-pathed body waveforms between 15° and 35° great circle range (e.g., Burdick & Helmberger, 1978;Chu et al., 2012). The steepness of the inferred P and S velocity gradients between 410 and 660 km in reference Earth models, however, cannot be explained by plausible silicate mantle chemistry without the existence of at least one more phase change between 410 and 660 km (Anderson, 1989). When the tools of mineral physics are applied to a constrained composition of the Earth's mantle, up to two additional phase changes are predicted to occur between the 410 and 660 km. Several other phase changes are also predicted above and below this zone, each having a unique behavior in their Clapeyron slope and the widths in depth over which each occurs (Figure 1). The widths of more than half of these are on the order of 15-60 km (e.g., Stixrude & Lithgow-Bertelloni, 2007, 2011, some expressed primarily by changes in velocity gradient, making them difficult to detect from reflected and converted body waves having similar or shorter wavelengths. As demonstrated in Figure 1, the parameterization Abstract Stochastic tomography, made possible by dense deployments of seismic sensors, is used to identify phase changes in Earth's mantle that occur over depth intervals. This technique inverts spatial coherences of amplitudes and travel times of body waves to determine the depth and dependence of the spatial spectrum of seismic velocity. This spectrum is interpreted using the predicted thermodynamic stability of mineral composition and phase as a function of temperature and pressure, in which the metamorphic temperature derivative of seismic velocities is used as a proxy for the effects of heterogeneity induced in a region undergoing a phase change. Peaks in the temperature derivative of seismic velocity closely match those found from applying stochastic tomography to elements of Earthscope and Flex arrays. Within ±12 km, peaks in the fluctuation of P velocity at 425, 500, and 600 km depth beneath the western US agree with those predicted by a mechanical mixture of harzburgite and basalt, 180 K cooler than a 1600 K adiabat in the mantle transition zone. A broad peak at 250 km depth may be associated with chemical heterogeneity induced by dehydration of subducted oceanic sediments, and a peak at 775 km depth with a phase change in subducted basalt. Non-detection of predicted phase changes less than 10 km in width is consistent with the resolution possible with the seismic arrays used in the inversion, including the sharp endothermic phase change near 660 km. These interpretations are consistent with the known history of plate subduction beneath North America.

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Toward Imaging Flow at the Base of the Mantle with Seismic, Mineral Physics, and Geodynamic Constraints

Nowacki

Cottaar

2021

Mantle Convection and Surface Expressions

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Seismic Wave Velocities in Earth's Mantle from Mineral Elasticity

Cited by 6 publications

References 330 publications

Structure and compressibility of Fe-bearing Al-phase D

Structure and compressibility of Fe-bearing Al-phase D

Mantle Phase Changes Detected From Stochastic Tomography

Toward Imaging Flow at the Base of the Mantle with Seismic, Mineral Physics, and Geodynamic Constraints

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