Abstract
We report elastic wave velocity (Vp: P-Waves velocity, and Vs: S-wave velocities) measurements of iron-enriched pyrolite aggregates by a combination of ultrasonic interferometry, synchrotron radiation techniques and multi-anvil apparatus experiments. We carried out eight synchrotrons in situ experiments on two different bulk pyrolite compositions with Fe/(Fe + Mg) ratio (Fe#) of 0.17 and 0.27, over a range of pressures from 3 to 16 GPa and temperatures up to 1000 °C. These data are complemented by seven laboratory ex situ experiments between 5 and 16 GPa and temperatures varying from 900 °C to 1300 °C, using the same starting compositions. Based on these results and previous data on pyrolite composition, we modeled the effect of iron on seismic profiles along several possible Martian areotherms.If, as reported in previous works, the Martian mantle had a very high Fe#, for instance Fe# = 0.27, it would be composed of four layers separated by three seismic discontinuities. They would be located at depths of ∼620 km (ΔVp of +8.25 %; ΔVs of +6.72 %), ∼880 km (ΔVp of +2.35 %; ΔVs of 0.03 %) and ∼ 1130 km (ΔVp of −17.88 %; ΔVs of −13.05 %). However, since there is no major discontinuity inferred by InSight's seismic data at depths shallower than 1000 km, we conclude that the Martian mantle presents a Fe# significantly lower than 0.20. For the Fe#0.17 composition, our experiments show a single discontinuity (ΔVp of +5.62 %; ΔVs of +10.44 %) induced by the transition from olivine to wadsleyite at ∼980 km depth, which is compatible with the seismic data.