Olivine crystals align during diffusion creep of Earth's upper mantle
Olivine crystals align during diffusion creep of Earth's upper mantle
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DOI：
10.1038/nature12570
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发表时间：
2013-10-17
期刊：
影响因子：
64.8
通讯作者：
Hiraga, Takehiko
中科院分区：
文献类型：
--
作者：
Miyazaki, Tomonori;Sueyoshi, Kenta;Hiraga, Takehiko
位错蠕变过程中产生的橄榄石晶体学择优取向（CPO）被认为是地球上地幔弹性各向异性的主要原因，并常被用来确定地幔流动的方向。然而，一个基本的问题仍然是，是否橄榄石晶体的排列是唯一产生的位错蠕变。在这里，我们报告的发展CPO在无铁橄榄石（即镁橄榄石）在扩散蠕变过程中，CPO的强度和图案取决于温度和熔体的存在下，控制晶界上的晶面的外观。在这些晶体学控制的边界上的晶界滑动由扩散调节，有助于晶粒旋转，从而导致CPO。我们表明，强径向各向异性预计在温度对应的深度，在那里开始融化的深度，强各向异性和低地震速度检测。相反，弱的各向异性预计在对应的深度几乎各向同性地幔的温度。我们建议扩散蠕变地幔流的主要手段。
The crystallographic preferred orientation (CPO) of olivine produced during dislocation creep is considered to be the primary cause of elastic anisotropy in Earth's upper mantle and is often used to determine the direction of mantle flow. A fundamental question remains, however, as to whether the alignment of olivine crystals is uniquely produced by dislocation creep. Here we report the development of CPO in iron-free olivine (that is, forsterite) during diffusion creep; the intensity and pattern of CPO depend on temperature and the presence of melt, which control the appearance of crystallographic planes on grain boundaries. Grain boundary sliding on these crystallography-controlled boundaries accommodated by diffusion contributes to grain rotation, resulting in a CPO. We show that strong radial anisotropy is anticipated at temperatures corresponding to depths where melting initiates to depths where strongly anisotropic and low seismic velocities are detected. Conversely, weak anisotropy is anticipated at temperatures corresponding to depths where almost isotropic mantle is found. We propose diffusion creep to be the primary means of mantle flow.