Seismic anisotropy, dominant slip systems and phase transitions in the lowermost mantle
Seismic anisotropy, dominant slip systems and phase transitions in the lowermost mantle
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DOI：
10.1093/gji/ggab278
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发表时间：
2021-07
影响因子：
2.8
通讯作者：
B. Chandler;Li-Wei Chen;Mingming Li;B. Romanowicz;H. Wenk
中科院分区：
文献类型：
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作者：
B. Chandler;Li-Wei Chen;Mingming Li;B. Romanowicz;H. Wenk
地幔底部存在地震各向异性已得到很好的证实，但对于下地幔矿物中的变形机制还没有达成共识。镁后钙钛矿(PPV)具有强烈的各向异性，但不同的研究对起作用的主要滑移系统存在分歧。在这里，我们的目标是通过实施来自原子模型和高压变形实验的最新结果，再加上一个真实的成分和一个三维地球动力学模型来进一步限制这一点，以比较由此产生的变形引起的各向异性与最低地幔的地震观测。我们解释了从桥锰矿(PV)到PPV的正向和反向相变。我们发现，无论是具有(001)或(010)滑移的PPV都可以解释较冷地区的地震观测到的各向异性，在这些地区，下井变为水平流动，但只有具有(001)滑移的模型与较热的大规模上升流的根部的地震观测相匹配。允许部分熔融不会改变这些结论，但它显著增加了各向异性的强度，并降低了上升流底部的剪切和压缩速度。
The presence of seismic anisotropy at the base of the Earth's mantle is well established, but there is no consensus on the deformation mechanisms in lower mantle minerals that could explain it. Strong anisotropy in magnesium post-perovskite (pPv) has been invoked, but different studies disagree on the dominant slip systems at play. Here, we aim to further constrain this by implementing the most recent results from atomistic models and high-pressure deformation experiments, coupled with a realistic composition and a 3-D geodynamic model, to compare the resulting deformation-induced anisotropy with seismic observations of the lowermost mantle. We account for forward and reverse phase transitions from bridgmanite (Pv) to pPv. We find that pPv with either dominant (001) or (010) slip can both explain the seismically observed anisotropy in colder regions where downwellings turn to horizontal flow, but only a model with dominant (001) slip matches seismic observations at the root of hotter large-scale upwellings. Allowing for partial melt does not change these conclusions, while it significantly increases the strength of anisotropy and reduces shear and compressional velocities at the base of upwellings.