Equation Of State And Sound Wave Velocities Of Fayalite At High Pressures And Temperatures: Implications For The Seismic Properties Of The Martian Mantle

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 873K yielded an adiabatic bulk modulus, K-S0 = 127.2 +/- 0.3 GPa with (partial derivative K-S/partial derivative P)(T0) = 6.5 +/- 0.1, and a shear modulus, G(0) = 53.3 +/- 0.4 GPa with (partial derivative K-S/partial derivative P)(T0) = 1.25 +/- 0.05. When fixing (partial derivative K-S/partial derivative P)(T0) = 5.3 (after (partial derivative K-S/partial derivative P)(T0) from Nestola et al., 2011), K-S0 increases to about 130 GPa. These estimates of (K-S0, (partial derivative K-S/partial derivative 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.