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, 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.