Abstract. Calcite and dolomite are the two most common minerals in carbonate-bearing faults and shear zones. Motivated by field examples from exhumed seismogenic faults in the Italian Central Apennines, we investigated the frictional and microstructural evolution of gouge mixtures consisting of 50 wt % calcite and 50 wt % dolomite using a rotary-shear apparatus. The gouges were sheared at a range of slip rates (30 µm s⁻¹–1 m s⁻¹), displacements (0.05–0.4 m), and normal loads (17.5–26 MPa), under both room humidity and water-dampened conditions. The frictional behaviour and microstructural evolution of the gouges were strongly influenced by the presence of water. At room humidity, slip strengthening behaviour was observed up to slip rates of 0.01 m s⁻¹, which was associated with gouge dilation and the development of a 500–900 µm wide slip zone cut by Y-, R-, and R1-shear bands. Above a slip rate of 0.1 m s⁻¹, dynamic weakening accompanied the development of a localised <100 µm thick principal slip zone preserving microstructural evidence for calcite recrystallization and dolomite decarbonation, while the bulk gouges developed a well-defined foliation consisting of organized domains of heavily fractured calcite and dolomite. In water-dampened conditions, evidence of gouge fluidization within a fine-grained principal slip zone was observed at a wide range of slip-rates from 30 µm s⁻¹ to 0.1 m s⁻¹, suggesting that caution is needed when relating fluidization textures to seismic slip in natural fault zones. Dynamic weakening in water-dampened conditions was observed at 1 m s⁻¹, where the principal slip zone was characterised by patches of recrystallized calcite. However, local fragmentation and reworking of recrystallized calcite suggests a cyclic process involving formation and destruction of a heterogeneous slip zone. Our microstructural data show that development of a well-defined gouge foliation at these experimental conditions is limited to high-velocity (>0.1 m s⁻¹) and room humidity, supporting the notion that some foliated gouges and cataclasites may form during seismic slip in natural carbonate-bearing faults.

中文翻译：

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干方解石和湿方解石-白云石切屑的摩擦性能和微观结构演变

摘要。方解石和白云石是含碳酸盐岩断层和剪切带中最常见的两种矿物。根据意大利中部亚平宁山脉中发掘出的地震断层的现场实例，我们使用旋转剪切设备研究了由50％（重量）方解石和50％（重量）方解石组成的断层混合物的摩擦和微观结构演变。在室内湿度和潮湿环境下，这些凿子在一定的滑移率（30 µm s ^-1 –1 ms ^-1），位移（0.05–0.4 m）和法向载荷（17.5–26 MPa）范围内被剪切。。切屑的摩擦行为和微观结构演变受到水的存在的强烈影响。在室内湿度下，观察到滑移强化行为，直至滑移率达0.01 m s ^-1，这与凿孔扩张和Y-，R-和R1剪切带切开的500-900 µm宽滑动带有关。超过0.1 m s ^-1的滑移速率时，动力减弱伴随着局部＜100 µm厚度的主滑移带的发展，保留了方解石重结晶和白云岩脱碳的微观结构证据，而大体积的切屑形成了清晰的叶状结构，包括方解石和白云石严重破裂。在潮湿的条件下，在从30 µm s ^-1到0.1 m s ^-1的宽滑移率范围内，都可以观察到细粒主滑移区域内的泥屑流化现象。，建议在将流化纹理与自然断层带的地震滑动联系起来时需要谨慎。在1 m s ^-1处观察到在潮湿环境中的动态减弱，其中主要的滑移带以重结晶方解石块为特征。但是，再结晶方解石的局部破碎和返工表明存在一个循环过程，涉及非均质滑带的形成和破坏。我们的微观结构数据表明，在这些实验条件下，定义明确的凿孔的发育仅限于高速（> 0.1 m s ^-1）和室内湿度，这支持了在自然滑移过程中可能会形成某些凿孔和分解的裂孔的观点。含碳酸盐岩的断层。