Sound Velocities of FeO‐Bearing Ringwoodite and Majorite: Implication for Martian Mantle Seismic Profiles

Abstract Compressional and shear wave velocities ( Vp , Vs ) of candidate Martian deep‐mantle minerals, FeO‐rich ringwoodite ((Mg 0.66 Fe 0.34 ) 2 SiO 4 ) and majorite (Mg 0.75 Fe 0.10 Al 0.26 Ca 0.07 Si 0.84 O 3 ), were measured up to 25 GPa and 700 K using Brillouin light scattering coupled with externally‐heated diamond anvil cells. Thermoelastic modeling of our results and literature data along a representative areotherm showed that Vp and Vs of FeO‐bearing ringwoodite are approximately 7.5% and 11.0% higher than that of the majorite. Our results reveal that velocity profiles of these Martian deep‐mantle minerals are more sensitive to variations in the ringwoodite/majorite (Mg/Si) ratio than to thermal and FeO chemical perturbations. Our best‐fit velocity model to a recent seismic model by Samuel et al. (2023, https://doi.org/10.1038/s41586‐023‐06601‐8 ) indicates the Martian mantle contains approximately 67 vol.% ringwoodite and 33 vol.% majorite, suggesting a ringwoodite‐rich aggregate in the Martian lowermost solid mantle. The ringwoodite‐majorite mantle likely co‐evolved with the FeO and other incompatible elements in the molten silicate layer above the Martian core‐mantle boundary.