Abstract The Boda Claystone Formation is the most promising host rock for the disposal of high-level radioactive waste in Hungary. The formation has several properties obstructing the migration of radionuclides; however, structural heterogeneities may nonetheless act as migration pathways. Therefore, understanding the tectonic evolution of the formation is vital. Previous research has identified four different vein generations in the BAF–2 well. This study deals with the generation of veins that contain characteristic microstructures, such as curved wall rock inclusions in bands, trails and cone-in-cone arrangements. Based on optical, cathodoluminescence and electron microscopy, together with X-ray fluorescence and Raman microspectroscopy, these veins appear to have potentially formed during early diagenetic processes. Vein development was continuous and occurred along horizontal surfaces. The abovementioned structural elements were formed by growing crystals; however, primary crystal morphologies were presumably replaced during diagenetic and hydrothermal processes. A theoretical model is described, which could be responsible for the horizontal and continuous vein opening and simultaneous crystallisation in sediments with high (but easily degraded) effective porosity. According to this model, compaction, pressure solution, elevated pore fluid pressures, seepage forces and the force of crystallisation can all play important roles in the formation of these types of veins.

中文翻译：

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二叠系博达粘土岩组早期成岩位移脉的潜在形成机制

摘要 博达粘土岩组是匈牙利处理高放废物最有前景的主岩。该地层具有多种阻碍放射性核素迁移的特性；然而，结构异质性仍然可以作为迁移途径。因此，了解地层的构造演化至关重要。先前的研究已经在 BAF-2 井中确定了四种不同的脉代。本研究涉及包含特征微结构的脉的生成，例如带状、轨迹和锥中锥排列中的弯曲围岩包裹体。根据光学、阴极发光和电子显微镜，连同 X 射线荧光和拉曼显微光谱，这些矿脉似乎是在早期成岩过程中形成的。静脉发育是连续的，沿水平面发生。上述结构元件是通过生长晶体形成的；然而，原生晶体形态可能在成岩和热液过程中被取代。描述了一个理论模型，该模型可能负责在具有高（但容易降解）有效孔隙度的沉积物中水平和连续的静脉开放和同时结晶。根据该模型，压实、压力溶解、孔隙流体压力升高、渗流力和结晶力都可以在这些类型的脉的形成中发挥重要作用。据推测，原始晶体形态在成岩和热液过程中被取代。描述了一个理论模型，该模型可能负责在具有高（但容易降解）有效孔隙度的沉积物中水平和连续的静脉开放和同时结晶。根据该模型，压实、压力溶解、孔隙流体压力升高、渗流力和结晶力都可以在这些类型的脉的形成中发挥重要作用。据推测，原始晶体形态在成岩和热液过程中被取代。描述了一个理论模型，该模型可能负责在具有高（但容易降解）有效孔隙度的沉积物中水平和连续的静脉开放和同时结晶。根据该模型，压实、压力溶解、孔隙流体压力升高、渗流力和结晶力都可以在这些类型的脉的形成中发挥重要作用。