Sound Velocities of Al‐Bearing Phase D up to 22 GPa and 1300 K

Sound velocities of Al‐bearing phase D were investigated up to 22 GPa and 1300 K using in situ synchrotron X‐ray techniques combined with ultrasonic measurements in a multianvil apparatus. The isothermal bulk modulus of Al‐bearing phase D was found to be ~16.7% lower than that of Mg‐endmember, suggesting a strong effect of Al incorporation on the bulk modulus of phase D. Al‐bearing phase D has higher P ‐ ( V P ) and S ‐ ( V S ) wave velocities compared to other mantle transition zone minerals, up to 4.3% for V P and up to 9.6% for V S compared with hydrous iron‐bearing ringwoodite, which might engender reduction of velocity contrast between anhydrous mantle and hydrous slab components. The accumulation of hydrated slab components carrying Al‐phase D in the uppermost lower mantle can explain some local negative shear velocity perturbations (Δ V S ) up to −1.5%, although Δ V P (−0.5%) is expected to remain below the detection limit of seismological techniques.