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• Acoustic and electrical measurements were performed on ilmenite-rutile aggregates. • Experiments were conducted at the pressure and temperature conditions of the lunar mantle. • Fe-Ti oxides increase the electrical conductivity and the seismic velocities of the lunar mantle. • Field datasets are reproduced with overturned ilmenite-bearing cumulates containing 20% melt. The overturn of titanium-rich mantle cumulates has been invoked to explain the structure and dynamics of the Moon. These dense cumulates are stable at the core-mantle boundary (CMB) and could explain field observations inferred from geophysical studies. We report acoustic and electrical experiments on natural ilmenite-rutile aggregates up to 4.5 GPa and 1920 K. Seismic velocities show a weak pressure and temperature dependence, with Vs ∼4.2 (+/-0.2) km/s and Vp ∼ 8.0 (+/-0.2) km/s at the CMB conditions. Conductivity increases by a factor of 104 from 373 to 1920 K and is >103 S/m above 1573 K. Seismic and electrical models for the lunar mantle based on our results, considering mixtures of Fe-Ti oxides and olivine, indicate that field velocity and conductivity estimates are reproduced satisfactorily with 3–16 vol.% Fe-Ti oxides and 20 vol.% melt. Interactions between a Ti-rich, melt-bearing layer and the adjacent core likely affect the cooling and magnetic history of the Moon. [ABSTRACT FROM AUTHOR]

Subduction of oceanic lithosphere transports surface H 2 O into the mantle. Recent studies show that dense SiO 2 in the form of stishovite, an abundant mineral in subducted oceanic crust at depths greater than ∼270 km, has the potential to host and transport a considerable amount of H 2 O into the lower mantle, but the H 2 O storage capacity of SiO 2 phases at high pressure and temperature remains uncertain. We investigate the hydration of stishovite and its higher-pressure polymorphs, β -stishovite and seifertite, with in situ X-ray diffraction experiments at high pressures and temperatures. The H 2 O contents in SiO 2 phases are quantified based on observed increases in unit cell volume relative to the anhydrous SiO 2 system. Density functional theory (DFT) computations permit calibration of water content as a function of volume change based on interstitial substitution of H 2 O. Regression of our experimental data indicates an H 2 O storage capacity in stishovite of ∼3.5 wt% in the transition zone and shallow lower mantle, decreasing to about 0.8 wt% at the base of the mantle. We find that SiO 2 -bearing subducted oceanic crust can accommodate all the H 2 O in slab lithosphere that survives sub-arc dehydration. Hydration of silica phases in subducted oceanic crust and their unparalleled capacity to host significant amounts of H 2 O even at high mantle temperatures provides a unique mechanism for transport and storage of water in the deepest mantle. • Quantification of the H 2 O storage capacity in hydrous silica in the deep mantle. • Parameterization of the H 2 O storage capacity in hydrous silica as a function of P-T. • Interstitial substitution of H 2 O dominates incorporation water of hydrous silica. • Hydrous silica plays an important role in transporting water to the deep Earth. [ABSTRACT FROM AUTHOR]