Abstract C′ shear bands are ubiquitous structures in shear zones but their development is poorly understood. Previous research has determined they mostly occur in rocks with a high mechanical strength contrast. Using numerical models of viscoplastic deformation, we studied the effect of the proportion of weak phase and the phase strength contrast on C′ shear band development during simple shearing to a finite strain of 18. We found that C′ shear bands form in models with ≥5% weak phase when there is a moderate or high phase strength contrast, and they occur in all models with weak phase proportions ≥15%. Contrary to previous research, we find that C′ shear bands form when layers of weak phase parallel to the shear zone boundary rotate forwards. This occurs due to mechanical instabilities that are a result of heterogeneous distributions of stress and strain rate. C′ shear bands form on planes of low strain rate and stress, and not in sites of maximum strain rate as has previously been suggested. C′ shear bands are ephemeral and they either rotate backwards to the C plane once they are inactive or rotate into the field of shortening and thicken to form X- and triangle-shaped structures.

中文翻译：

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C'剪切带的短暂发展：一种数值模拟方法

摘要 C'剪切带是剪切带中普遍存在的结构，但对其发展知之甚少。先前的研究已经确定它们主要出现在具有高机械强度对比的岩石中。使用粘塑性变形的数值模型，我们研究了在简单剪切到 18 的有限应变期间，弱相的比例和相强度对比对 C' 剪切带发展的影响。我们发现 C' 剪切带在模型中形成 ≥ 5% 弱相当有中等或高相强度对比时，它们出现在所有弱相比例≥15% 的模型中。与之前的研究相反，我们发现当平行于剪切带边界的弱相层向前旋转时，会形成 C' 剪切带。这是由于应力和应变率的不均匀分布导致的机械不稳定性而发生的。C' 剪切带在低应变率和应力的平面上形成，而不是在先前建议的最大应变率的位置上形成。C' 剪切带是短暂的，一旦它们不活动，它们要么向后旋转到 C 平面，要么旋转到缩短和增厚的区域以形成 X 形和三角形结构。