High pressure-temperature phase relations of basaltic crust up to mid-mantle conditions

A substantial amount of subducted basaltic crusts may exist in the lower mantle. It features distinct chemical composition from peridotitic mantle and plays important roles dynamic evolution Earth's interior. However, mineral phases present crust is still poorly constrained. Here, we determined phase relations normal mid-ocean ridge basalt (MORB) up to 52 GPa at 2000 K by multi-anvil press. Throughout our experiments, assemblages consist five including bridgmanite, stishovite, calcium perovskite (davemaoite), ferrite new hexagonal aluminous phases. The density MORB calculated previously published thermoelastic data 2-3% higher than that average mantle, which consistent with literature. a host potassium but only occupies 1-2 vol.% due limited abundance MORB. This indicates doesn't affect elastic properties basalt. Electron energy-loss spectra recovered Al-rich bridgmanite show significant enrichment ferrous iron (75-85%) compared Al-poor (∼30%), against previous studies showing ferric ratio increases Al content. Ferric exhibits strong partitioning into (41-64%), whereas (14-28%) (5-27%) remain Fe2+-enriched. oxygen vacancy component MgAlO2.5 ∼11% 40 GPa, much (2-3%), possibly producing viscosity contrast mid-mantle would explain slab stagnation plume thinning between 660 km 1000 depth. presence iron-rich deep contribute seismic large low-shear-velocity provinces.