蠕滑断裂带岩石组成和构造特征分析:以龙门山灌县-安县断裂带为例

断裂蠕滑可以连续释放部分构造应力，但仍可能造成重大的地质灾害，甚至具有发生大地震的可能性。断层岩是断裂作用中的直接产物，其物质组成和内部构造可为揭示断裂带滑移机制提供关键信息。2008年M_w 7.9汶川地震中破裂的龙门山灌县-安县断裂带具有蠕滑性质，是探究大陆内部蠕滑断裂滑移机制的最佳案例。本文以龙门山灌县-安县断裂带地表探槽和深部钻孔的断层岩为研究对象，通过碎屑统计、X射线粉末衍射矿物分析、光学显微镜和扫描电镜观测，结果显示该断裂带断层泥碎屑含量和颗粒大小均小于断层角砾岩，其粘土矿物含量高达50%以上，且断层岩中普遍发育粘土-碎屑组构以及拖尾构造、似S-C组构等多种压溶构造。综合分析发现压溶作用、低摩擦系数物质以及颗粒滑移对灌县-安县断裂带的蠕滑变形都发挥着重要作用，并且三者相辅相成，因此认为灌县-安县断裂带的蠕滑过程主要是压溶作用和摩擦-颗粒滑移机制共同作用，该认识可更好地了解地震周期并为区域防震减灾提供科学依据。

Rock composition and structural characteristics of creep-slip fault zone: A case of the Guanxian-Anxian fault zone in the Longmen Shan, China

The fault creep can continuously release part of the tectonic stress, but it may still cause major geological disasters and even large earthquakes. Fault rock is the direct product of faulting. Its material compositions and internal structures can provide the key information to reveal the slip mechanism of the fault zone. The Guanxian-Anxian fault zone of the Longmen Shan ruptured during the 2008 M_w 7.9 Wenchuan earthquake, which has the creep-slip behavior, is the best case to explore the creep-slip mechanism within continents. This study focuses on fault rocks of the Guanxian-Anxian fault zone in the surface trench and deep borehole by clastic statistics, X-ray powder diffraction mineral analysis, and observations of optical microscope and scanning electron microscope. The results show that the calst content and particle sizes of the fault gouge are smaller than those of the fault breccia, and the clay mineral content of the fault gouge even is more than 50%. Additionally, the fault rocks commonly develop many kinds of pressure solution structures such as fabric of clay-clast aggregates, trailing structure and analogous S-C fabric. Based on comprehensive analysis, we reveal that the materials with low friction, grain slipping, and pressure solution play important roles on creeping deformation of the Guanxian-Anxian fault zone, and the three factors complement each other. Therefore, it is believed that the creep process of the Guanxian-Anxian fault zone is mainly caused by the pressure dissolution and the friction-grain slipping mechanism together. This understanding can better understand the earthquake cycle and provide a scientific basis for regional earthquake prevention and mitigation.