Dating Fault Activity Based on Surface Texture of Quartz Grains from the Bailong River Fault

Abstract

AbstractMuch important information referring to fault motion (e.g., fault activities period, intensity, frequency, and even dynamic background) can be revealed by resolving fault gouge, which is the result of fault motion while extruding or grinding. The field investigation encompassed sample collecting from the Bailong River fault system of the western segment of the Qinling Orogenic Belt (QOB); 44 samples of fault gouges were collected for quartz micro‐morphology analysis. These samples were analyzed using field emission scanning electron microscopy. In addition, 14 samples were tested for thermo‐luminescence dating. The results showed that most of the surface textures of quartz grains are characterized by fish scale, moss‐like texture, and stalactite. However, a small amount of orange peel‐like fractures and worm‐hole‐like shaped surface texture were observed. Moreover, a few typical conchoids or subconchoidal fractures in quartz grains can be seen. This implies that the Bailong River Fault was active repeatedly during the Quaternary period, but the main motion period is the Pleistocene. The 14 thermo‐luminescence dating values showed two age groups: 343.29–184.06 ka and 92.18–13.87 ka. These study data reveal that fault movement started during the Pliocene, occurred frequently in the early‐middle period of the Pleistocene, and the peak frequency of the motion was reached in the early Pleistocene. The fault motions were stopped terminated in the early Holocene. The results are significant for the natural disaster risk evaluation in the western segment of the QOB.