Thermoelastic Properties of Ringwoodite [Fe_x,Mg_(1-x)]_2SiO_4: Its Relationship to the 520 km Seismic Discontinuity

TL;DR

This study uses advanced computational methods to calculate the elastic properties of ringwoodite, linking its behavior to the seismic discontinuity at 520 km depth in Earth's mantle.

Contribution

It combines DFT, QHA, and VDoS models to accurately predict elastic moduli of ringwoodite, providing new reference data for seismic discontinuity analysis.

Findings

Good agreement with experimental elastic moduli at various conditions

Identifies contrast in properties during beta-to-gamma transformation

Provides reference values for interpreting seismic data

Abstract

We combine density functional theory (DFT) within the local density approximation (LDA), the quasiharmonic approximation (QHA), and a model vibrational density of states (VDoS) to calculate elastic moduli and sound velocities of gamma-[Fe_x,Mg_(1-x)]_2SiO_4 (ringwoodite), the most abundant mineral of the lower Earth's transition zone (TZ). Comparison with experimental values at room-temperature and high pressure or ambient-pressure and high temperature shows good agreement with our first-principles findings. Then, we investigate the contrasts associated with the beta-to-gamma-[Fe_x,Mg_(1-x)]_2SiO_4 transformation at pressures and temperatures relevant to the TZ. This information offers clearly defined reference values to advance the understanding of the nature of the 520 km seismic discontinuity.