Equation of state and sound wave velocities of fayalite at high pressures and temperatures: implications for the seismic properties of the martian mantle

Abstract

Abstract. The elastic properties of a pure, synthetic fayalite aggregate were studied by coupled synchrotron X-ray diffraction and ultrasonic interferometry in a DIA-type multi-anvil press. Measurements at pressures up to about 7 GPa and temperatures up to 873 K yielded an adiabatic bulk modulus, KS0=127.2±0.3 GPa with (∂KS/∂P)T0=6.5±0.1, and a shear modulus, G0=53.3±0.4 GPa with (∂G/∂P)T0=1.25±0.05. When fixing (∂KS/∂P)T0=5.3 (after (∂KT/∂P)T0 from Nestola et al., 2011), KS0 increases to about 130 GPa. These estimates of (KS0,(∂KS/∂P)T0) follow a general linear trend, K=f(dK/dP), for fayalite. We define limited ranges for both bulk and shear moduli from previous studies, and we discuss how these variations affect seismic velocities and the determination of a mineralogical model in the context of the Mars InSight SEIS (Seismic Experiment for Interior Structure) experiment.

Structure and thermal expansion of end-member olivines I: Crystal and magnetic structure, thermal expansion, and spontaneous magnetostriction of synthetic fayalite, Fe2SiO4, determined by high-resolution neutron powder diffraction

“…The resulting value, = 12.8(2), is, however, higher than those published from high-pressure studies, which range between 4.1 and 5.3 (e.g. Graham et al , 1988; Béjina et al , 2019, 2021; Speziale et al , 2004; Zhang, 1998). This is an indication of the limitations of the model of equation 6 that are reflected in the fitted parameters.…”

“…If we apply this value of γ we obtain K 0 = 143(4) GPa which is a little larger than published values for K 0 , obtained directly from high-pressure studies, which lie between 128 and 136 GPa (e.g. Graham et al, 1988;Béjina et al, 2019Béjina et al, , 2021Speziale et al, 2004;Zhang, 1998;Zhang et al, 2017). The first derivative of the incompressibility with respect to pressure can also be estimated from the coefficient b.…”

“…Olivines with compositions between forsterite (Mg 2 SiO 4 ) and fayalite (Fe 2 SiO 4 ) are among the most studied minerals due to their abundance and importance in a spectrum of geological and cosmic environments, their physical properties determining, amongst other things, the formation and thermal evolution of planetary bodies. For example, as pointed out recently by Béjina et al (2021), determination of the thermoelastic properties of iron-rich olivine is likely to be crucial in understanding the Martian interior. Since the original determination of their crystal structures by Bragg and Brown (1926), there have been numerous investigations of the temperature dependence of the volume of the (Mg,Fe) 2 SiO 4 olivines.…”

“…For example, as pointed out recently by Béjina et al . (2021), determination of the thermoelastic properties of iron-rich olivine is likely to be crucial in understanding the Martian interior. Since the original determination of their crystal structures by Bragg and Brown (1926), there have been numerous investigations of the temperature dependence of the volume of the (Mg,Fe) 2 SiO 4 olivines.…”