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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Shear waves in the diamond-anvil cell reveal pressure-induced instability in (Mg,Fe)O
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Shear waves in the diamond-anvil cell reveal pressure-induced instability in (Mg,Fe)O

机译：金刚石-砧室中的剪切波揭示了（Mg，Fe）O中压力引起的不稳定性

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The emerging picture of Earth's deep interior from seismic tomography indicates more complexity than previously thought. The presence of lateral anisotropy and heterogeneity in Earth's mantle highlights the need for fully anisotropic elasticity data from mineral physics. A breakthrough in high-frequency (gigahertz) ultrasound has resulted in transmission of pure-mode elastic shear waves into a high-pressure diamond-anvil cell using a P-to-S elastic-wave conversion. The full elastic tensor (c(ij)) of high-pressure minerals or metals can be measured at extreme conditions without optical constraints. Here we report the effects of pressure and composition on shear-wave velocities in the major lower-mantle oxide, magnesiowustite-(Mg,Fe)O. Magnesiowustite containing more than approximate to50% iron exhibits pressure-induced c(44) shear-mode softening, indicating an instability in the rocksalt structure. The oxide closer to expected lower-mantle compositions (approximate to20% iron) shows increasing shear velocities more similar to MgO, indicating that it also should have a wide pressure-stability field. A complete sign reversal in the c44 pressure derivative points to a change in the topology of the (Mg,Fe)O phase diagram at approximate to50-60% iron. The relative stability of Mg-rich (Mg,Fe)O and the strong compositional dependence of shear-wave velocities (and partial derivativec(44)/partial derivativeP) in (Mg,Fe)O implies that seismic heterogeneity in Earth's lower mantle may result from compositional variations rather than phase changes in (Mg,Fe)O.
机译：地震层析成像对地球深处内部的新显示表明比以前想象的要复杂。地球地幔中存在横向各向异性和非均质性，这凸显了对来自矿物物理学的完全各向异性弹性数据的需求。高频（千兆赫）超声技术的突破导致使用P到S弹性波转换将纯模态弹性剪切波传输到高压金刚石-砧座中。高压矿物或金属的全弹性张量（c（ij））可以在没有光学约束的极端条件下进行测量。在这里，我们报告了压力和成分对主要下地幔氧化物菱镁矿-（Mg，Fe）O的剪切波速度的影响。含铁量超过约50％的镁铝镁橄榄石表现出压力诱导的c（44）剪切模式软化，表明岩盐结构不稳定。接近预期的下地幔成分的氧化物（铁含量约为20％）显示出与MgO相似的增加的剪切速度，表明它也应具有较宽的压力稳定性场。 c44压力导数的完全符号反转表明（Mg，Fe）O相图的拓扑在铁含量接近50-60％时发生了变化。 （Mg，Fe）O中富含Mg的（Mg，Fe）O的相对稳定性和剪切波速度（和偏导数c（44）/偏导数P）的强成分依赖性意味着地球下地幔的地震异质性可能由（Mg，Fe）O的成分变化而不是相变引起。

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