Elastic properties of ferropericlase at lower mantle conditions and its relevance to ULVZs
Elastic properties of ferropericlase at lower mantle conditions and its relevance to ULVZs
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DOI：
10.1016/j.epsl.2015.02.023
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发表时间：
2015-05
影响因子：
5.3
通讯作者：
J. Muir;J. Brodholt
中科院分区：
文献类型：
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作者：
J. Muir;J. Brodholt
利用密度泛函理论（DFT）研究了Fe x Mg 1−x O在最低地幔温度和压力条件下的弹性。铁的加入降低了MgO的剪切模量，但根据铁的自旋状态对体积模量有不同的影响。铁在Fe x Mg 1−x O中的自旋态不仅与温度和压力有关，还与铁的浓度有关。在136 GPa时，低浓度（< 25%）的Fe几乎完全处于低自旋状态，而在非常高浓度（> 75%）时，它几乎完全处于高自旋状态。正如预期的那样，铁取代会大大降低地震速度。然而，铁的影响在高温下比在低温下更大，这意味着很难推断低温实验结果。我们不能同时与富铁方长石的密度和地震速度相匹配。这反映在（dln V s/dln V p） T， p中，在ULVZs中通常观察到约为3，但在富铁方长石中不超过约1.5。铁方石矿和铁钙钛矿的混合物可以使V s降低高达45%，这使得ULVZ V p， V s和密度的范围相匹配。我们还发现（dln V s/dln V p） T， p增加到最多3，但这个值强烈依赖于混合几何的边界。因此，我们得出结论，ulvz的性质可以很容易地用一个富含铁的单相下地幔来解释。
The elasticity of Fe x Mg 1− x O was examined under lowermost mantle temperature and pressure conditions using density functional theory (DFT). The addition of iron decreases the shear modulus of MgO but has varying effects on the bulk modulus depending on the spin state of the iron. The spin state of iron in Fe x Mg 1− x O is dependent on pressure and temperature but also on the concentration of iron. At 136 GPa, Fe in low concentrations (< 25%) is nearly entirely low spin, while at very high concentrations (> 75%) it is nearly entirely in the high spin state. There is, as expected, a large decrease in seismic velocities with iron substitution. However, the effect of Fe is greater at high-temperatures than at low-temperatures, meaning it is difficult to extrapolate low-temperature experimental results. We cannot simultaneously match the density and seismic velocities of ULVZs with Fe-enriched ferropericlase. This is reflected in (dln V s/dln V p) T, P, which in ULVZs is generally observed to be about 3, but does not exceed about 1.5 for Fe-enriched periclase. A mixture of ferropericlase and ferrous perovskite can cause V s decreases of up to 45%, which allows the range of ULVZ V p, V s and densities to be matched. We also find that (dln V s/dln V p) T, P increases up to as much as 3 but this value is strongly dependent on the bounds of the mixing geometry. We conclude, therefore, that the properties of ULVZs can be readily explained by a lower mantle with a single phase that is heavily enriched in Fe.