Abstract Triaxial high temperature (900 °C) deformation experiments were conducted at constant strain rate in a Paterson-type deformation apparatus on cylinders of Carrara marble with two right or left stepping, non-overlapping weak inclusions of Solnhofen limestone, oriented at 45° to the cylinders’ longitudinal axes. Applying different values of confinement (30, 50, 100 and 300 MPa) we induced various amounts of brittle deformation in the marble matrix and investigated the effect of brittle precursors on the initiation and development of heterogeneity-induced high temperature shear zones. Viscosity contrast between the matrix and the inclusions induces local stress concentration at the tips of these latter. The initial arrangement of the inclusions results in either an overpressured (contractional) or underpressured (extensional) domain in the step-over region of the sample. At low confinement (30 and 50 MPa) abundant brittle deformation is observed, but the spatial distribution of microfractures is dependent on the kinematics of the step-over region: microcracks occur either along the shearing plane between inclusions (in extensional bridge samples), or broadly distributed outside the step-over region (contractional bridge samples). Accordingly, ductile deformation localizes along the inclusions plane in the extensional bridge samples as opposed to distributing over large areas of the matrix in the contractional bridge samples. If microcracking is suppressed (high confinement), strain is accommodated by viscous creep and strain progressively de-localizes in extensional bridge samples. Our experiments demonstrate that brittle precursors enhance the degree of localization in the ductile deformation regime, but only if the interaction of pre-existing heterogeneities induces an extensional mean stress regime in between.

中文翻译：

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实验变形碳酸盐岩脆韧转变应变局域材料异质性几何排列的控制

摘要 在帕特森型变形装置中以恒定应变速率对卡拉拉大理石圆柱体进行了三轴高温 (900 °C) 变形实验，该圆柱体具有两个左右阶梯，Solnhofen 石灰岩的非重叠弱包裹体，取向为 45°至气缸的纵轴。应用不同的限制值（30、50、100 和 300 MPa），我们在大理石基质中引起了不同程度的脆性变形，并研究了脆性前体对非均质性引起的高温剪切带的产生和发展的影响。基体和夹杂物之间的粘度差异导致后者尖端的局部应力集中。夹杂物的初始排列导致样品跨区中的超压（收缩）或欠压（伸展）域。在低限制（30 和 50 MPa）下，观察到大量脆性变形，但微裂纹的空间分布取决于跨区的运动学：微裂纹沿夹杂物之间的剪切面出现（在拉伸桥样品中），或广泛分布在跨步区域之外（收缩桥样本）。因此，延性变形沿拉伸桥样品中的夹杂物平面局部化，而不是分布在收缩桥样品中的大面积基体上。如果微裂纹被抑制（高度限制），应变通过粘性蠕变来适应，并且应变在拉伸桥样品中逐渐离域。我们的实验表明，脆性前体增强了延性变形区域中的局部化程度，但前提是预先存在的非均质性的相互作用会在两者之间产生拉伸平均应力状态。