摘要: δ-(Al,Fe)OOH is considered to be one of the most important hydrous phases on Earth, remaining stable under the extreme conditions throughout the mantle. The behavior of δ-(Al,Fe)OOH at high pressure is essential to understanding the deep water cycle. δ-(Al_0.956Fe_0.044)OOH crystals synthesized at 21 GPa and 1473 K were investigated by high-pressure Brillouin light scattering spectroscopy and synchrotron X-ray diffraction up to 135.4 GPa in diamond anvil cells. The incorporation of 5 mol% FeOOH increases the unit-cell volume of δ-AlOOH by ~1% and decreases the shear-wave velocity (V_S) by ~5% at 20-135 GPa. In particular, the compressional (V_P) and shear (V_S) wave velocities of δ-(Al_0.956Fe_0.044)OOH are 7%-16% and 10%-24% greater than all the major minerals in the mantle transition zone including wadsleyite, ringwoodite, and majorite. The distinctly high sound velocities of δ-(Al_0.956Fe_0.044)OOH at 20-25 GPa may contribute to the seismic anomalies observed at ~560-680 km depths in the cold and stagnant slab beneath Izu-Bonin and/or Korea. Furthermore, the V_S of δ-(Al_0.956Fe_0.044)OOH is about 10% and 4%-12% lower than iron-bearing bridgmanite Mg_0.96Fe_0.05Si_0.99O₃ and ferropericlase (Mg_0.92Fe_0.08)O, respectively, under the lowermost mantle conditions, which might partially contribute to the large low-shear-velocity provinces and ultralow velocity zones at the bottom of the lower mantle.