Clast–cortex aggregates (CCAs) have been commonly reported in experimental and natural fault gouges. Here we discuss the formation process of CCAs and its mechanical implications, based on experimentally simulated fault gouges. We conducted low- to high-velocity rotary shear experiments on Ca-bentonite gouges at a normal stress of 1 MPa, slip rates of 0.01–1.31 m s⁻¹, and ambient temperature and humidity conditions. The CCAs consist of a central clast (mostly quartz fragments with subordinate clay aggregates) and a concentric rim of nano-clay particles (i.e., cortex). The CCAs range in size from 1 to 100 μm and developed adjacent to a foliated high-strain layer at all slip rates. The microstructures suggest that the CCA-rich layer was mainly deformed by granular flow, whereas the foliated high-strain layer was deformed by cataclastic flow. The increase in average size of the CCAs with displacement and the formation of their concentric rims suggest that the CCAs grew like a rolling snowball. The estimated strain rates obtained from the concentric layers of the CCAs and strain markers indicate the existence of a range of shear strain rates that favors granular flow and the formation and growth of CCAs.

碎屑-皮层聚集体 (CCA) 在实验和自然断层凿岩中经常被报道。在这里，我们基于实验模拟的断层泥讨论了 CCA 的形成过程及其机械影响。^{我们在 1 MPa 的正应力、0.01-1.31 m s -1}的滑移率下对 Ca-膨润土凿进行了低速到高速旋转剪切实验，以及环境温度和湿度条件。CCA 由一个中心碎屑（主要是石英碎片和从属粘土聚集体）和一个同心的纳米粘土颗粒边缘（即皮质）组成。CCA 的尺寸范围从 1 到 100 μm，并且在所有滑移率下都与叶状高应变层相邻。微观结构表明富含CCA的层主要由颗粒流动变形，而叶状高应变层则由碎裂流动变形。CCA 的平均尺寸随位移的增加及其同心轮缘的形成表明 CCA 像滚雪球一样增长。从 CCA 的同心层和应变标记获得的估计应变率表明存在一系列有利于颗粒流动和 CCA 形成和生长的剪切应变率。