地球上地幔的温和到狂野塑性
Mild-to-wild plasticity of Earth's upper mantle
AI总结：
该研究通过室温纳米压痕实验证明上地幔主要矿物橄榄石存在间歇性位错雪崩式塑性变形，并预测地幔深处流动以狂野波动为主，为深源地震等瞬态失稳机制提供新约束。
摘要：
长期以来，人们一直认为地球的上地幔流动是以缓慢且近乎连续的蠕变方式发生的。这种行为在经典的高温变形实验中可以观察到，并且是地球动力学模型的基本组成部分。然而，最新一代高分辨率实验能够感知位错运动速率的时间异质性，这些实验揭示出从金属到冰的各种材料都表现出一系列被称为“温和到狂野塑性”的行为。目前仍不清楚橄榄石——地球的上地幔中最丰富的矿物——是否总是表现出温和的连续流动，还是可以在塑性应变速率上表现出间歇性的狂野波动。在这里，我们证明橄榄石表现出可测量的狂野性，即使在其行为被预测为相对温和的条件下也是如此。在室温下进行的纳米压痕实验中，连续的塑性流动被间歇性的位移爆发所打断，这些爆发的位移幅值呈对数正态分布，表明存在相关位错运动的雪崩，这些雪崩约占总塑性应变的8 ± 6%。值得注意的是，温和到狂野塑性的框架预测，狂野性应随地球深度的增加而增强，软流圈上地幔的流动几乎完全由晶粒尺度上的变形狂野波动所实现。地质材料中间歇性塑性的认识为位错介导流动的微观物理模型提供了新的约束，并提出了关于在原本韧性状态下的瞬态不稳定性机制的问题，例如深源地震和慢滑移事件。
英文摘要：
The flow of Earth's upper mantle has long been considered to occur by slow and near-continuous creep. Such behaviour is observed in classical high-temperature deformation experiments and is a fundamental component of geodynamic models. However, the latest generation of high-resolution experiments, capable of sensing temporal heterogeneities in rates of dislocation motion, have revealed that materials ranging from metals to ice exhibit a spectrum of behaviours termed mild-to-wild plasticity. It remains unknown whether olivine, the most abundant mineral in Earth's upper mantle, always exhibits mild continuous flow or can exhibit intermittent wild fluctuations in plastic strain rate. Here, we demonstrate that olivine exhibits measurable wildness, even under conditions at which its behaviour is predicted to be relatively mild. During nanoindentation experiments conducted at room temperature, continuous plastic flow is punctuated by intermittent bursts of displacement with log-normally distrubuted magnitudes, indicating avalanches of correlated dislocation motion that account for approximately 8 +/- 6% of the plastic strain. Remarkably, the framework of mild-to-wild plasticity predicts that wildness should increase with depth in the Earth, with flow of the asthenospheric upper mantle occurring almost entirely by wild fluctuations of deformation at the grain scale. The recognition of intermittent plasticity in geological materials provides new constraints for microphysical models of dislocation-mediated flow and raises questions about the mehcanisms of transient instabilities in otherwise ductile regimes, such as deep earthquakes and slow-slip events.
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