Stress-induced amorphization triggers deformation in the lithospheric mantle
Stress-induced amorphization triggers deformation in the lithospheric mantle
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DOI：
10.1038/s41586-021-03238-3
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发表时间：
2021-03
期刊：
影响因子：
64.8
通讯作者：
Vahid Samae;P. Cordier;S. Demouchy;C. Bollinger;J. Gasc;S. Koizumi;A. Mussi;D. Schryvers;H. Idrissi
中科院分区：
文献类型：
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作者：
Vahid Samae;P. Cordier;S. Demouchy;C. Bollinger;J. Gasc;S. Koizumi;A. Mussi;D. Schryvers;H. Idrissi
富橄榄石岩石的力学性质是决定岩石圈与软流圈之间力学耦合的关键。在晶体材料中，晶体缺陷的运动是塑性流动的基础。然而，由于富含橄榄石的岩石的主要组成部分没有足够的滑动系统，需要额外的变形机制来满足应变条件。实验研究表明，橄榄石中存在一种非牛顿的、对晶粒尺寸敏感的机制，包括晶界滑动。然而，很少有微观结构的调查已进行晶界滑动，并没有达成共识，是否一个单一的或多个物理机制在发挥作用。最重要的是，没有理论框架，将晶界力学多晶塑性模型。在这里，我们确定了一种机制，在富含橄榄石的岩石晶界变形。我们发现，在镁橄榄石，非晶化发生在应力下的晶界和富含橄榄石的岩石的韧性的发病是由于在这些非晶层的晶界流动性的激活。这一机制可能在地球深处触发塑性过程，在那里遇到高应力条件（例如，在脆塑性转变）。我们提出的机制是特别相关的岩石圈软流圈边界，橄榄石达到玻璃化转变温度，引发其粘度下降，从而促进晶界滑动。
The mechanical properties of olivine-rich rocks are key to determining the mechanical coupling between Earth’s lithosphere and asthenosphere. In crystalline materials, the motion of crystal defects is fundamental to plastic flow, , –. However, because the main constituent of olivine-rich rocks does not have enough slip systems, additional deformation mechanisms are needed to satisfy strain conditions. Experimental studies have suggested a non-Newtonian, grain-size-sensitive mechanism in olivine involving grain-boundary sliding,. However, very few microstructural investigations have been conducted on grain-boundary sliding, and there is no consensus on whether a single or multiple physical mechanisms are at play. Most importantly, there are no theoretical frameworks for incorporating the mechanics of grain boundaries in polycrystalline plasticity models. Here we identify a mechanism for deformation at grain boundaries in olivine-rich rocks. We show that, in forsterite, amorphization takes place at grain boundaries under stress and that the onset of ductility of olivine-rich rocks is due to the activation of grain-boundary mobility in these amorphous layers. This mechanism could trigger plastic processes in the deep Earth, where high-stress conditions are encountered (for example, at the brittle–plastic transition). Our proposed mechanism is especially relevant at the lithosphere–asthenosphere boundary, where olivine reaches the glass transition temperature, triggering a decrease in its viscosity and thus promoting grain-boundary sliding.