Syn-kinematic mineral reactions play an important role for the mechanical properties of polymineralic rocks. Mineral reactions (i.e., nucleation of new phases) may lead to grain size reduction, producing fine-grained polymineralic mixtures, which have a strongly reduced viscosity because of the activation of grain-size-sensitive deformation processes. In order to study the effect of deformation–reaction feedback(s) on sample strength, we performed rock deformation experiments on “wet” assemblages of mafic compositions in a Griggs-type solid-medium deformation apparatus. Shear strain was applied at constant strain rate (10⁻⁵ s⁻¹) and constant confining pressure (1 GPa) with temperatures ranging from 800 to 900 ^∘C. At low shear strain, the assemblages that react faster are significantly weaker than the ones that react more slowly, demonstrating that reaction progress has a first-order control on rock strength. With increasing strain, we document two contrasting microstructural scenarios: (1) the development of a single throughgoing high-strain zone of well-mixed, fine-grained aggregates, associated with a significant weakening after peak stress, and (2) the development of partially connected, nearly monomineralic shear bands without major weakening. The lack of weakening is caused by the absence of interconnected well-mixed aggregates of fine-grained reaction products. The nature of the reaction products, and hence the intensity of the mechanical weakening, is controlled by the microstructures of the reaction products to a large extent, e.g., the amount of amphibole and the phase distribution of reaction products. The samples with the largest amount of amphibole exhibit a larger grain size and show less weakening. In addition to their implications for the deformation of natural shear zones, our findings demonstrate that the feedback between deformation and mineral reactions can lead to large differences in mechanical strength, even at relatively small initial differences in mineral composition.

中文翻译：

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变形和相变的铁素体组合体的微观结构与阻力之间的关系

运动学上的矿物反应对于多矿物岩石的力学性能起着重要作用。矿物反应（即，新相的成核）可能会导致晶粒尺寸减小，产生细颗粒的多矿物混合物，由于激活了对晶粒尺寸敏感的变形过程，其粘度大大降低。为了研究变形反应反馈对样品强度的影响，我们在Griggs型固体介质变形仪中对镁铁质成分的“湿”组合进行了岩石变形实验。以恒定的应变速率（10 ^-5  s ^-1）和恒定的围压（1 GPa）施加剪切应变，温度范围为800至 ^900∘C.在低剪切应变下，反应较快的组件比反应较慢的组件弱得多，这表明反应进程对岩石强度具有一级控制。随着应变的增加，我们记录了两种相反的微观结构情况：（1）均匀混合的细粒骨料的单一贯穿高应变区的发展，与峰值应力后的明显减弱有关；（2）应力的发展。部分连接的几乎单矿物的剪切带，而没有明显减弱。缺乏弱化是由于没有相互连接的细颗粒反应产物的充分混合的聚集体。反应产物的性质以及因此机械弱化的强度在很大程度上由反应产物的微观结构控制，例如，闪石的量和反应产物的相分布。具有最大量闪石的样品表现出较大的晶粒尺寸，并且显示较少的弱化。除了对天然剪切带变形的影响外，我们的发现还表明，变形和矿物反应之间的反馈可能导致机械强度的巨大差异，即使矿物成分的初始差异较小。