## 3 Results
### Microstructures of Pseudotachylyte
#### 3.1.3 Multi-Stage Pseudotachylyte Veins in Granite Gneiss  
The host rock of this type of pseudotachylyte is fractured granite gneiss, which is similar to the host rock of the straight vein-type pseudotachylyte. (1) In sample AF21-4-2, three stages of pseudotachylyte veins can be observed (Figure 10A). The boundary between each vein and the host rock is clearly visible, and the veins have a banded morphology, with distinct cutting relationships between them. The first-stage pseudotachylyte vein is about 0.2 cm wide, developed within a shear zone, with an irregular shape and injection characteristics. The vein is black, with a high matrix content and fewer elastic clasts, and it is cut by a wider fracture zone greater than 1 cm. The second-stage pseudotachylyte vein is lighter in color, black-gray, and clearly cuts through the first-stage vein at a large angle. This vein contains a higher proportion of clastic clasts, with the clasts being plagioclase and quartz. The plagioclase clasts are angular or sub-angular, while the quartz clasts are sub-angular or sub-rounded (Figure 10C). The matrix shows de-glassified growth of cryptocrystalline mineral aggregates under scanning electron microscopy (Figure 10D,E), parallel to the fracture zone. Figure 10: Microstructures of multi-period pseudotachylytes in AF21-4-2. (**A**) AF21-4-2 under PPL, (1)–(3) are three stages of pseudotachylyte veins. (**B,C**) AF21-4-2 under XPL. (**D,E**) SEM of AF21-4-2. The third-stage pseudotachylyte vein is nearly parallel to the second-stage vein but locally cuts through it (Figure 10A, blue). The boundary between the two stages is straight and clear. The third-stage vein has a higher matrix content (Figure 10B), is black in color macroscopically, and contains clastic clastics of plagioclase and quartz. However, no de-glassified growth of cryptocrystalline minerals is observed in the matrix. The microstructure and composition of the third-stage vein are similar to those of the straight vein-type pseudotachylte. It is evident that the exposed fault rocks have undergone multiple coseismic slip events throughout geological history. Due to the limited distribution and retention of information in the first two stages of pseudotachylyte veins, this study focuses on the last stage of fresh pseudotachylyte, which is more widely exposed in outcrops. Table 2 summarizes the key characteristics of the various types of pseudotachylyte discussed above. Fabric of Quartz in Granite Gneiss and Mylonite Around Pseudotachylyte Under Electron Backscatter Diffraction (EBSD)  
Under different temperature conditions, the intracrystalline slip system of quartz varies, leading to different crystal preferred orientations (CPOs) [41; 42; 43]. When the temperature increases or the strain rate decreases, the main slip systems of quartz are basal slip, rhombic slip, and prismatic slip [44; 45]. Previous studies have shown that during the plastic deformation of quartz under non-coaxial shear strain, at low temperatures (250-350 \({}^{\circ}\)C), deformation primarily occurs through basal <a> dislocation slip creep; at medium-low temperatures (350-450 \({}^{\circ}\)C), it primarily occurs through rhombic <a> dislocation slip creep; at medium temperatures (450-600 \({}^{\circ}\)C), it mainly occurs through prismatic <a> dislocation slip creep; and at high temperatures (600-700 \({}^{\circ}\)C), it mainly occurs through prismatic <c> dislocation slip creep [44; 45; 46; 47; 48]. Among these, low-temperature fabrics can overlap with early high-temperature fabrics, and the evolution from high to low temperature in ductile shear zones can form composite fabric models [49]. Due to the limited number of slip systems in quartz, the slip systems can be analyzed simply from the c-axis pole figure. By examining the distribution of the extreme densities in the pole figure, the slip