Intensive fragmentation is a pervasive process during rock avalanche propagation, with a series of typical shearing characteristics being generated, indicating the occurrence of differential shear-induced comminution of clasts. However, much less is known about how shearing evolves within a rock avalanche over long runout. In the Iymek rock avalanche (IRA), pervasive shear zones characterized by multistoried, multiscale, and multistyle shear structures are well developed along the travel path of the IRA, providing an invaluable opportunity to decipher the evolution of shear-induced fragmentation occurred in rock avalanches. In these shear zones, a series of indicative structures, including preserved stratigraphic sequences, jigsaw structures, Riedel shear arrays, sigmoidal shear planes, asymmetrical folds, bookshelf and boudin-like structures, and anastomosing shear networks, are identified. These structures indicate that a laminar-like flow regime characterized by low disturbance but intensive shearing should dominate the emplacement of the IRA, contributing to the formation of these pervasive shear structures and material facies. As indicated by the progressive evolution of these pervasive shear structures, three facies are determined from the transition zone to the accumulation zone, i.e., low-fragmented facies, ductile-dominated facies and brittle-dominated facies. The low-fragmented facies is mainly distributed in the transition zone, similar to a semisolid phase rather than the solid phase of the bedrock in the source area. Conversely, the brittle-dominated facies features a high fragmentation degree and is predominant in the accumulation zone, which mainly consists of a semifluid to fluid phase. This indicates that the rock avalanche mass should evolve from a solid phase to a fully fluid phase during propagation, which involves clast fracturing and comminuting, frictional sliding and rotation. Therefore, we propose that the rock avalanche is a classical cataclastic flow driven by progressive and differential shearing comminution during its laminar-like propagation instead of a granular flow. These results provide a significant basis for interpreting similar structures in other rock avalanche deposits and yield new insights for understanding the emplacement mechanisms of rock avalanches.

中文翻译：

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独特的剪切带表明，巨大的伊梅克岩石雪崩中普遍存在层流碎裂流

强烈破碎是岩石雪崩传播过程中普遍存在的过程，会产生一系列典型的剪切特征，表明发生了差异剪切引起的碎屑破碎。然而，人们对长跳动下岩石雪崩中剪切如何演变知之甚少。在伊梅克岩崩（IRA）中，沿着 IRA 的行进路径，普遍发育了以多层、多尺度和多样式剪切结构为特征的剪切带，为破译岩石雪崩中剪切引起的破碎演化提供了宝贵的机会。在这些剪切带中，识别出了一系列指示性结构，包括保存的地层序列、拼图结构、里德尔剪切阵列、S形剪切面、不对称褶皱、书架和布丹状结构以及吻合剪切网络。这些结构表明，以低扰动但强烈剪切为特征的层流流态应主导 IRA 的位置，有助于形成这些普遍的剪切结构和物质相。这些普遍存在的剪切构造的递进演化表明，从过渡带到聚集带，确定了低破碎相、韧性主导相和脆性主导相3种相。低碎裂相主要分布在过渡带，类似于源区基岩的半固态而不是固态。相反，脆性为主的相破碎程度高，在聚集带中占主导地位，主要由半流体到流体相组成。这表明岩石崩体在传播过程中应从固相演化为全流体相，其中涉及碎屑的破裂和粉碎、摩擦滑动和旋转。因此，我们认为岩石崩塌是一种经典的碎裂流，在其层流传播过程中由渐进和差异剪切粉碎驱动，而不是粒状流。这些结果为解释其他岩石雪崩沉积物中的类似结构提供了重要基础，并为理解岩石雪崩的侵位机制提供了新的见解。