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.