Thermoelastic Properties of Iron‐Rich Ringwoodite and the Deep Mantle Aerotherm of Mars

Abstract The Martian mantle is considered to have a higher Fe/Mg ratio than the Earth's mantle. Ringwoodite, γ‐(Mg,Fe) 2 SiO 4 , is likely the dominant polymorph of olivine in the core‐mantle boundary (CMB) region of Mars. We synthesized anhydrous iron‐rich ringwoodite with molar Mg/(Mg + Fe) = 0.44 and determined its thermal equation of state up to 35 GPa and 750 K by synchrotron X‐ray diffraction. Using a third order Birch‐Murnaghan equation of state, we obtain K T 0 = 182 (3) GPa, K′ = 4.6 (2), and α 0 = 3.18 (6) × 10 −5 K −1 . Using these results and an updated mineralogical model with an iron‐rich composition of Mg/(Mg + Fe) = 0.75 for the Martian mantle, we estimate ∼1900 K for the temperature of the D1000 seismic discontinuity inside Mars. The resulting adiabat predicts a warm aerotherm, which could explain the presence of partial melt at the CMB of Mars recently detected with seismic data from the 2019 InSight mission.