The presence of weak phyllosilicates in mature carbonate fault zones has been invoked to explain weak faults. However, the relation between frictional strength, fault stability, mineralogical composition, and fabric of fault gouge, composed of strong and weak minerals, is poorly constrained. We used a biaxial apparatus to systematically shear different mixtures of shale (68% clay, 23% quartz and 4% plagioclase) and calcite, as powdered gouge, at room temperature, under constant normal stresses of 30, 50, 100 MPa and under room-dry and pore fluid-saturated conditions, i.e. CaCO₃-equilibrated water. We performed 30 friction experiments during which velocity-stepping and slide-hold-slide tests were employed to assess frictional stability and to measure frictional healing, respectively. Our frictional data indicate that the mineralogical composition of fault gouges significantly affects frictional strength, stability, and healing as well as the presence of CaCO₃-equilibrated water. Under room-dry condition, the increasing shale content determines a reduction in frictional strength, from μ = 0.71 to μ = 0.43, a lowering of the healing rates and a transition from velocity-weakening to velocity-strengthening behavior. Under wet condition, with increasing shale content we observe a more significant reduction in frictional strength (μ = 0.65–0.37), a near-zero healing and a velocity strengthening behavior. Microstructural investigations evidence a transition from localized deformation promoted by grain size reduction, in calcite-rich samples, to a more distributed deformation with frictional sliding along clay-enriched shear planes in samples with shale content greater than 50%. For faults cutting across sedimentary sequences composed of carbonates and clay-rich sediments, our results suggest that clay concentration and its ability to form foliated and interconnected networks promotes important heterogeneities in fault strength and slip behavior.

在成熟的碳酸盐岩断层带中存在弱的层状硅酸盐已被用来解释弱断层。但是，由强矿物和弱矿物组成的断层泥的摩擦强度，断层稳定性，矿物组成和断层构造之间的关系受约束较弱。我们使用双轴仪器在室温，恒定的常应力30、50、100 MPa和室温下，系统性地剪切了粉状凿岩的页岩（68％粘土，23％石英和4％斜长石）和方解石的不同混合物-干燥和孔隙流体饱和的条件，即CaCO ₃平衡水。我们进行了30项摩擦实验，在这些实验中，分别采用速度步进和滑动-保持-滑动测试来评估摩擦稳定性和测量摩擦愈合。我们的摩擦数据表明，断层泥的矿物学组成会显着影响摩擦强度，稳定性和愈合以及CaCO ₃的存在。平衡水。在室内干燥条件下，页岩含量的增加决定了摩擦强度的降低，从μ= 0.71降低至μ= 0.43，愈合速度降低，并且从速度减弱状态转变为速度增强状态。在潮湿条件下，随着页岩含量的增加，我们观察到摩擦强度显着降低（μ= 0.65–0.37），接近零愈合和速度增强行为。微观结构研究表明，在页岩含量大于50％的样品中，从方解石富集的样品中，由于晶粒尺寸减小而引起的局部变形过渡到了沿富含粘土的剪切平面的摩擦滑动而发生的分布更广泛的变形。对于跨越碳酸盐岩和富含粘土的沉积物组成的沉积层序的断层，