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- (VP) and S- (VS) wave velocities compared to other mantle transition zone minerals, up to 4.3% for VP and up to 9.6% for VS 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 (ΔVS) up to −1.5%, although ΔVP (−0.5%) is expected to remain below the detection limit of seismological techniques.
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)