Equation of State and Spin Crossover of (Al, Fe)‐Phase H
Equation of State and Spin Crossover of (Al, Fe)‐Phase H
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DOI：
10.1029/2022jb026291
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发表时间：
2023-03
期刊：
影响因子：
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通讯作者：
B. Strozewski;J. Buchen;W. Sturhahn;T. Ishii;I. Ohira;S. Chariton;B. Lavina;Jiyong Zhao;T. Toellner;J. Jackson
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文献类型：
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作者：
B. Strozewski;J. Buchen;W. Sturhahn;T. Ishii;I. Ohira;S. Chariton;B. Lavina;Jiyong Zhao;T. Toellner;J. Jackson
氢进入地球内部深处的运输可能会对下地幔动力学以及俯冲物质的地震特征产生影响。由于δ - AlOOH （δ相）、MgSiO2(OH)2 （H相）和ε - FeOOH在高温高压下的稳定性，它们的固溶体可以将大量的氢输送到地核-地幔边界深处。我们约束了(Al, Fe) -相H: Al0.84Fe3+ 0.07Mg0.02Si0.06OOH的状态方程，包括自旋交叉在Fe3+原子中的影响，使用粉末X射线衍射测量到125 GPa，由同步加速器Mössbauer光谱测量支持(Al, Fe) -相H和δ - (Al, Fe)OOH。与δ‐（Al, Fe）OOH （32-40 GPa）相比，（Al, Fe）相H中Fe3+自旋态的变化导致体声速显著降低，且发生在不同的压力范围（48-62 GPa）。轴向可压缩性的变化表明，在30gpa附近(Al, Fe) - H相中氢键的可压缩性降低，这可能与氢键对称有关。俯冲洋壳中（Al, Fe）相H的形成可能有助于地震波在中-下地幔（~ 1,100-1,550 km）的散射。1-4 wt.% （Al, Fe）相H的积累可以再现一些大、低地震速度省份的地震特征。我们的研究结果表明，（δ‐AlOOH）‐（MgSiO2(OH)2）‐（ε‐FeOOH）固溶体中相的电子结构变化对组成敏感，并且这些相在俯冲洋壳中的存在可以在整个下地幔中被地震探测到。
The transport of hydrogen into Earth's deep interior may have an impact on lower mantle dynamics as well as on the seismic signature of subducted material. Due to the stability of the hydrous phases δ‐AlOOH (delta phase), MgSiO2(OH)2 (phase H), and ε‐FeOOH at high temperatures and pressures, their solid solutions may transport significant amounts of hydrogen as deep as the core‐mantle boundary. We have constrained the equation of state, including the effects of a spin crossover in the Fe3+ atoms, of (Al, Fe)‐phase H: Al0.84Fe3+ 0.07Mg0.02Si0.06OOH, using powder X‐ray diffraction measurements to 125 GPa, supported by synchrotron Mössbauer spectroscopy measurements on (Al, Fe)‐phase H and δ‐(Al, Fe)OOH. The changes in spin state of Fe3+ in (Al, Fe)‐phase H results in a significant decrease in bulk sound velocity and occurs over a different pressure range (48–62 GPa) compared with δ‐(Al, Fe)OOH (32–40 GPa). Changes in axial compressibilities indicate a decrease in the compressibility of hydrogen bonds in (Al, Fe)‐phase H near 30 GPa, which may be associated with hydrogen bond symmetrization. The formation of (Al, Fe)‐phase H in subducted oceanic crust may contribute to scattering of seismic waves in the mid‐lower mantle (∼1,100–1,550 km). Accumulation of 1–4 wt.% (Al, Fe)‐phase H could reproduce some of the seismic signatures of large, low seismic‐velocity provinces. Our results suggest that changes in the electronic structure of phases in the (δ‐AlOOH)‐(MgSiO2(OH)2)‐(ε‐FeOOH) solid solution are sensitive to composition and that the presence of these phases in subducted oceanic crust could be seismically detectable throughout the lower mantle.