The Elastic Anisotropy Change Near the 410‐km Discontinuity: Predictions From Single‐Crystal Elasticity Measurements of Olivine and Wadsleyite
The Elastic Anisotropy Change Near the 410‐km Discontinuity: Predictions From Single‐Crystal Elasticity Measurements of Olivine and Wadsleyite
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DOI：
10.1002/2017jb015339
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发表时间：
2018-04
期刊：
影响因子：
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通讯作者：
Jin S. Zhang;J. Bass;B. Schmandt
中科院分区：
文献类型：
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作者：
Jin S. Zhang;J. Bass;B. Schmandt
我们提出了一个基于所有可用的单晶速度测量的具有~9-10 mol% Fe的橄榄石的单晶弹性模型。一组考虑热弹性效应的有限应变状态方程用于拟合各种压力-温度条件下的单个弹性模量。同样的分析被应用于重新分析实验确定的含水和无水含Fe的wadsleyite的单晶弹性模量。基于所获得的单个弹性模量的热弹性参数，然后我们计算了橄榄石和华兹华斯的各种弹性各向异性指数，并将其外推到地球地幔中预期的压力-温度条件。结果表明，弹性各向异性在地球的上过渡带（410-520公里深度）可能低于地震检测极限，如果它主要来自于晶格的优势取向的wadsleyite晶体。另一方面，橄榄石的弹性各向异性在410 km深度仍然相对较高（~19-25%）。因此，如果地幔流场在410 km深度附近诱导橄榄石和华德士来石的晶格择优取向，则预计410 km不连续面上的弹性各向异性会降低。
We present a model of the single‐crystal elasticity of olivine with ~9–10 mol% Fe based on all available single‐crystal velocity measurements. A set of finite strain equations of state that account for thermoelastic effects is used for fitting the individual elastic moduli at various pressure‐temperature conditions. The same analysis is applied to reanalyze the experimentally determined single‐crystal elastic moduli of hydrous and anhydrous Fe‐bearing wadsleyite. Based on the obtained thermoelastic parameters of individual elastic moduli, we then calculated various elastic anisotropy indices of olivine and wadsleyite and extrapolated them to the pressure‐temperature conditions expected in the Earth's mantle. The results suggest that the elastic anisotropy in the Earth's upper transition zone (410–520 km depth) is likely below the seismic detection limit if it originates primarily from the lattice preferred orientation of wadsleyite crystals. On the other hand, the elastic anisotropy of olivine is still relatively high (~19–25%) at 410 km depth. Thus, if a mantle flow field induces lattice preferred orientation of olivine and wadsleyite near 410 km depth, a reduction of elastic anisotropy is expected across the 410‐km discontinuity.