[S-IT22] Interaction and Coevolution of the Core and Mantle in the Earth and Planets

[SIT22-28] High-P,T Easticity of Fe-Si and Fe-S Alloys

*Taku Tsuchiya¹ (1.Geodynamics Research Center, Ehime University)

Keywords:Ab initio computation, High-P,T elasticity of iron alloys, Inner core

Earth’s inner core (329~364 GPa and 5000~6000 K) is thought to be composed of solid Fe-Ni alloy with some unknown light elements (e.g., Mao et al., 1998; Kuwayama et al., 2008; Sha & Cohen, 2010). Thermoelasticity of iron alloys is therefore a key to interpreting seismological information of the inner core: density, seismic wave velocities, and their anisotropy. So far, several studies reported that pure hcp iron has a shear modulus distinctly larger than that of the inner core and a small P-wave anisotropy (e.g., Mao et al., 1998; Vocadlo et al., 2009). This large V_P/V_S ratio of the inner core is one of the remaining inexplicable features of the deep Earth, and it suggests the presence of mechanisms to lower the S-wave velocity in the inner core, such as a low-velocity component (Prescher et al., 2015), pre-melting effect (Martorell et al., 2013), anelasticity, and so on.

In this study, we perform ab initio molecular dynamics simulations of several alloy compositions including potential light element candidates of Si and S. Computations are conducted at the inner core P,T conditions. The obtained velocities, density and aggregate anisotropies are compared against seismological constraints and we discuss if these alloys are suitable to the inner core constituents or not.

Research supported by KAKENHI .JPN15H05834.