Size effects resolve discrepancies in 40 years of work on low-temperature plasticity in olivine.
Size effects resolve discrepancies in 40 years of work on low-temperature plasticity in olivine.
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DOI：
10.1126/sciadv.1701338
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发表时间：
2017-09
期刊：
影响因子：
13.6
通讯作者：
Wilkinson AJ
中科院分区：
文献类型：
--
作者：
Kumamoto KM;Thom CA;Wallis D;Hansen LN;Armstrong DEJ;Warren JM;Goldsby DL;Wilkinson AJ
地幔矿物橄榄石在低温塑性变形时，其强度受其晶粒大小的控制。岩石圈地幔中橄榄石在低温和高应力下的强度对许多地球动力学过程，包括岩石圈挠曲和板块边界的形成，都有着重要的控制作用。不幸的是，实验室得出的岩石圈条件下橄榄石的强度值是高度可变的，并显着不同意从地球物理观测推断。我们通过纳米压痕表明，橄榄石的强度取决于变形的长度尺度，较小体积的材料表现出较大的屈服应力的实验。这种“尺寸效应”解决了以前使用其他技术测量橄榄石强度的差异。它也证实了最近的流动法橄榄石，提出了一个更弱的岩石圈地幔比以前估计，从而使实验测量到更接近地球物理学的限制。进一步的影响包括增加的困难，激活塑性冷，细粒剪切带和断层表面粗糙度的演变，由于纳米到微米尺寸的凹凸体的尺寸依赖性变形的影响。
When deforming by low-temperature plasticity, the strength of the mantle mineral olivine is controlled by its grain size. The strength of olivine at low temperatures and high stresses in Earth’s lithospheric mantle exerts a critical control on many geodynamic processes, including lithospheric flexure and the formation of plate boundaries. Unfortunately, laboratory-derived values of the strength of olivine at lithospheric conditions are highly variable and significantly disagree with those inferred from geophysical observations. We demonstrate via nanoindentation that the strength of olivine depends on the length scale of deformation, with experiments on smaller volumes of material exhibiting larger yield stresses. This “size effect” resolves discrepancies among previous measurements of olivine strength using other techniques. It also corroborates the most recent flow law for olivine, which proposes a much weaker lithospheric mantle than previously estimated, thus bringing experimental measurements into closer alignment with geophysical constraints. Further implications include an increased difficulty of activating plasticity in cold, fine-grained shear zones and an impact on the evolution of fault surface roughness due to the size-dependent deformation of nanometer- to micrometer-sized asperities.
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