Elastic properties of ferrous bearing MgSiO3 and their relevance to ULVZs
Elastic properties of ferrous bearing MgSiO3 and their relevance to ULVZs
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DOI：
10.1093/gji/ggv045
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发表时间：
2015-04
影响因子：
2.8
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
我们利用初始分子动力学计算了MgSiO3、FeSiO3和(Fe0.5Mg0.5)SiO3钙钛矿在最低地幔条件(136GPa, 2000–4000K)下的弹性常数。在 0°K 时，FeSiO3 钙钛矿的 Vp 和 Vs 分别比 MgSiO3 低 12% 和 18%，这与之前的工作一致。然而，对于高自旋（而不是低自旋）态，速度差随着温度的增加而增加，并且在 4000K 时，端元 FeSiO3 的 Vp 和 Vs 分别比 MgSiO3 低 19% 和 34%。我们发现，对于所有相关的铁浓度，(dlnVs/dlnVp)T,Pof FexMg1-xO3 仍低于 2，并且低于大多数超低速区域 (ULVZ) 中看到的 3 值。此外，除了在 ULVZ 中观察到的最大密度增加和最小剪切波降低之外，我们无法通过增加钙钛矿中的二价铁含量来同时匹配 ULVZ 所观察到的密度增加和剪切波速度降低。假设目前对 ULVZ 特性的地震估计是准确的，我们的结果表明，仅靠二价铁富集并不能解释 ULVZ。
We usedab initiomolecular dynamics to calculate the elastic constants of MgSiO3, FeSiO3and (Fe0.5Mg0.5)SiO3perovskite under lower-most mantle conditions (136 GPa, 2000–4000 K). At 0 K,VpandVsfor FeSiO3perovskite are 12 and 18 per cent lower, respectively than those for MgSiO3, in agreement with previous work. The difference in velocity, however, increases with temperature for high spin (but not low spin) states and at 4000 K,VpandVsfor the end-member FeSiO3are, respectively, 19 and 34 per cent lower than those of MgSiO3. We find that (dlnVs/dlnVp)T,Pof FexMg1-xO3remains below 2 for all relevant iron concentrations and lower than the value of 3 seen in most ultralow velocity zones (ULVZ). Moreover, we are unable to match simultaneously the observed density increase and shear wave velocity reduction shown by ULVZs by increasing the ferrous iron content in perovskite except for the largest density increases and the smallest shear wave decreases observed in ULVZs. Assuming that current seismic estimates of ULVZ properties are accurate, our results suggest that ferrous iron enrichment alone cannot explain ULVZs.