Detachment faults that exhume mantle peridotites to the seafloor play a major role in the accommodation of plate divergence at slow‐spreading ridges. Using 99 samples of partially serpentinized peridotites dredged from a nearly amagmatic segment of the eastern part of the Southwest Indian Ridge, we characterize the deformation processes active in the root zone of detachment fault systems. The deformation is heterogeneous even at the sample scale and combines both brittle and crystal‐plastic mechanisms. Strain localization is initially controlled by strength contrasts at the grain scale between olivine and orthopyroxene and between variably oriented olivine crystals. Orthopyroxene deformation is primarily brittle (microfractures), but kink bands and dynamic recrystallization are locally observed. In contrast, olivine deforms primarily by dislocation creep with dynamic recrystallization under high deviatoric stresses (80–270 MPa). Olivine grains poorly oriented to deform by dislocation glide display kink bands and localized microfractures. Dynamic recrystallization controlled by strain and stress concentrations produce anastomosing zones of grain size reduction (GSR). GSR zones contain limited late to post‐kinematic amphibole, suggesting the presence of small volumes of hydrous fluids. Plagioclase, when present, is post‐kinematic. This heterogeneous high‐stress deformation is observed, with variable intensity, in every sample investigated, suggesting that it was pervasively distributed in the root region of axial detachments. Abyssal peridotite samples from more magmatically robust slow mid‐ocean ridges do not show this pervasive high stress deformation microstructure, implying magma, when present, tends to localize most of the strain at the root of axial detachment systems.

中文翻译：

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融化饥饿的中洋海岭分离断裂根部的应变局部化：西南印度洋海岭深渊橄榄岩的微观结构研究

将地幔橄榄岩驱散到海底的分离断层在缓缓扩张的山脊板块发散的调节中起着重要作用。使用从西南印第安海岭东部近乎岩浆部分挖出的99个部分蛇纹化橄榄岩样品，我们描述了在活动断裂根系中活跃的形变过程。即使在样品规模上，变形也是不均匀的，并且结合了脆性和结晶塑性机制。应变局部化最初是由橄榄石与邻苯二茂之间以及取向不同的橄榄石晶体之间的强度对比来控制的。邻二甲苯的变形主要是脆性的（微断裂），但局部观察到扭结带和动态再结晶。相比之下，橄榄石变形主要是由于在高偏应力（80-270 MPa）下位错蠕变和动态再结晶引起的。橄榄石晶粒因位错滑动而难以变形，显示出扭结带和局部微裂纹。由应变和应力集中控制的动态再结晶产生晶粒尺寸减小（GSR）的吻合区。GSR区域的晚期至运动后的闪石的数量有限，这表明存在少量的含水液体。斜长石存在时，是运动学后的。在每个调查的样品中均观察到这种非均质的高应力变形，强度不同，这表明它普遍分布在轴向脱离的根部区域。