Abstract Analyses of three oriented rock samples collected in the footwall of a major normal fault in Central Italy provide insights into textural properties of a lithified carbonate fault core. Data from lithified fault rocks are very rare and we document here the grain size distribution in a fault core at an unprecedented scale range, which complements already existing observations obtained from sieve, sedimentation and/or laser diffraction methods in loose deposits. X-ray powder diffraction analysis shows that the samples, which are located at a mutual distance of few tens of meters, are exclusively made of calcite. Mesoscopic samples and polished thin sections oriented normal to the fault plane have been analysed with high resolution scanner (HRS), transmission optical microscopy (TOM) and scanning electron microscopy in back-scattered mode (BS-SEM). Textural features of tectonised calcite crystals have been quantified using image analysis on digitalised photographs at magnifications from 1:1 to 9000:1, documenting size dimensions of grains from cm to sub-μm. The obtained D values have average values of 1.65 in 2D, overlapping with those independently obtained by box-counting methods in the core of the same fault by previous authors. Textures of calcite clasts in tectonised and lithified rocks can be appropriately quantified by the analytical protocols proposed here. This work represents the first multi-scale image analysis, from sub- μm to cm sizes, of the core portion of a normal fault that cut into carbonate rocks. Our study provides a template for similar investigations to be carried on other faults that will help to better understand the relations between fault textures and deformation processes.

中文翻译：

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使用多尺度图像分析的碳酸盐岩岩化断层核的粒度和粒度分布：以 San Benedetto-Gioia dei Marsi 断层（意大利中部）为例

摘要 对在意大利中部一条主要正断层下盘收集的三个定向岩石样本进行分析，可以深入了解岩化碳酸盐断层核的结构特性。来自岩化断层岩的数据非常罕见，我们在此记录了断层核中的粒度分布在前所未有的规模范围内，这补充了通过筛分、沉积和/或激光衍射方法在松散沉积物中获得的现有观察结果。X射线粉末衍射分析表明，相距几十米的样品完全由方解石制成。已使用高分辨率扫描仪 (HRS) 分析了垂直于断层面的细观样品和抛光薄片，背散射模式的透射光学显微镜 (TOM) 和扫描电子显微镜 (BS-SEM)。构造化方解石晶体的纹理特征已通过对放大倍数为 1:1 至 9000:1 的数码照片进行图像分析进行量化，记录了从厘米到亚微米的晶粒尺寸。获得的 D 值在 2D 中的平均值为 1.65，与之前作者在同一断层核心中通过框计数方法独立获得的值重叠。构造化和岩化岩石中方解石碎屑的质地可以通过此处提出的分析方案适当量化。这项工作代表了切割成碳酸盐岩的正断层核心部分的第一次多尺度图像分析，从亚微米到厘米大小。