We propose a structural evolutionary model for deformation band (DB) development via microcrack propagation and coalescence process in a normal fault zone affecting arkosic sandstones. Based on structural analysis and reconstruction of the paleostress, we infer that a sub-horizontal minimum principal stress (σ₃) in the NNW-SSE direction controlled the multiscalar evolution of microcracks and DBs. Two main sets of coalesced microcracks and DBs are recognized: (1) NE-SW and (2) E-W, in which the coalescence pattern of microcracks is also observed among the DBs at meso-scale. Our results suggest that the DBs develop during three deformation stages: (1) pore collapse followed by initial grain breakage and the formation of NE-SW tensile microcracks favoured by cleavage planes in feldspars. These microcracks coalesce through linking NW-SE shear microcracks to form intermediary microplanes. An intense microcracking crush the grains, enhancing the cataclastic process. The further coalescence of these intermediary microplanes with other intermediary microplanes and/or microcracks might generate through-going microplanes inside the band, causing the formation of E-W DBs; (2) the E-W structures coalesce through NE-SW hard-linking DBs, which corresponds to the DBs clusters, generating NE-SW intermediary planes at meso-scale; (3) the NE-SW intermediary planes coalesce through an E-W hard-linking structure, which results in the DB fault zone.

我们提出了一个结构演化模型，用于在影响暗砂质砂岩的正常断层带中通过微裂纹传播和合并过程发展形变带（DB）。基于结构分析和古应力的重建，我们推断子水平最小主应力（σ ₃）在NNW-SSE方向上控制了微裂纹和DB的多标量演化。可以识别出两个主要的合并的微裂纹和DB：（1）NE-SW和（2）EW，其中在中等规模的DB之间也观察到了微裂纹的合并模式。我们的研究结果表明，DBs在三个变形阶段发展：（1）孔隙崩塌，随后出现初始颗粒破裂，长石中劈裂面有利于NE-SW拉伸微裂纹的形成。这些微裂纹通过连接NW-SE剪切微裂纹以形成中间微平面而合并。强烈的微裂纹压碎了谷物，增强了碎裂过程。这些中间微平面与其他中间微平面和/或微裂纹的进一步融合可能会在频带内产生贯穿的微平面，导致EW DB的形成；（2）EW结构通过对应于DB集群的NE-SW硬链接DB合并，生成中尺度的NE-SW中间平面；（3）NE-SW中间平面通过EW硬链接结构合并，从而导致DB断层带。