Oxyhydroxides like δ-(Al,Fe)OOH may stabilize “water” in Mid-Ocean Ridge Basalt (MORB) subducted into the Earth's lower mantle. The single-crystal elasticity of δ-(Al,Fe)OOH has not been experimentally constrained, hampering an accurate evaluation of the seismic detectability of this high-pressure solid solution, and the presence of “water,” in the deep Earth. Here, we report the first experimental single-crystal elasticity results of δ-(Al_0.97Fe_0.03)OOH measured by X-ray diffraction and Brillouin spectroscopy. We use our results to compute seismic properties of hydrous and anhydrous MORB at pressures and temperatures expected in slabs at shallow lower mantle conditions. We show that hydrous MORB is less dense than anhydrous MORB, but has faster aggregate seismic velocities. This suggests that hydration in MORB has an effect on velocities opposite to that observed in other lithologies, and further indicates that hydration of MORB increases the seismic contrast to the background mantle.

中文翻译：

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浅层下地幔中δ-(Al,Fe)OOH单晶的高压弹性和含水MORB的地震探测能力

δ-(Al,Fe)OOH 等羟基氧化物可以稳定俯冲到地球下地幔中的大洋中脊玄武岩 (MORB) 中的“水”。δ-(Al,Fe)OOH 的单晶弹性在实验上没有受到限制，这阻碍了对这种高压固溶体的地震可探测性的准确评估，以及地球深处“水”的存在。在这里，我们报告了 δ-(Al _0.97 Fe _0.03)OOH 通过 X 射线衍射和布里渊光谱法测量。我们使用我们的结果来计算含水和无水 MORB 在浅层下地幔条件下预期的板坯压力和温度下的地震特性。我们表明含水 MORB 的密度低于无水 MORB，但具有更快的总地震速度。这表明 MORB 中的水合作用对速度的影响与在其他岩性中观察到的相反，并进一步表明 MORB 的水合作用增加了与背景地幔的地震对比度。