## 3 Results
### Microstructures of Pseudotachylyte
#### 3.1.2 Distributed Fine Vein-Type Pseudotachylyte Along the Foliation of Mylonite  
This type of pseudotachylyte appears in mylonite, with discontinuous fine veins of pseudotachylyte distributed along the foliation.  
(1) In sample AF19-44C, the banded pseudotachylyte fine veins are distributed along the foliation of the granite mylonite, with clear but discontinuous boundaries. The veins are intermittent or taper off, and their shape is not straight but rather curved (Figure 8A). Two types of quartz grains are observed in the surrounding mylonite: one type is larger, with deformed edges bending to form bulging structures, and under crossed polarized light, sheared deformation bands are visible (Figure 8B); the other type consists of quartz aggregates with smaller grain size, showing allotriomorphic or subhedral shapes, and are arranged in bands between larger mineral grains. These quartz grains exhibit undulatory extinction (Figure 8B-D). The fine-grained quartz aggregates form banded structures along the foliation, exhibiting distinct plastic flow features (Figure 8D-G). The pseudotachylyte veins and the quartz bands alternate in a directional arrangement and exhibit plastic deformation characteristics (Figure 8A,E-G), indicating that the pseudotachylyte and fine quartz aggregates underwent plastic deformation together.  
Figure 8: Microstructures of pseudotachylyte distributed along the foliation in AF19-44C. (**A**) AF19-44C under PPL. (**B–D**) AF19-44C under XPL. (**E–G**) SEM of AF19-44C.  
(2) Sample AF19-43G also contains fine veins of pseudotachylyte with plastic deformation. The host rock in this sample shows a porphyritic structure under polarized light, with plagioclase phenocrysts exhibiting \(\sigma\)-shaped or eye-shaped textures (Figure 9A-C). Under scanning electron microscopy, crushed structures are visible inside the phenocrysts, with fractures filled by quartz veins. The tailing ends of the phenocrysts show elongated fine-grained quartz and biotite aggregates, which surround the plagioclase grains (Figure 9D,E), indicating that the plagioclase has undergone hydrolysis to form quartz. The fine-grained aggregates of plagioclase, quartz, and biotite form a banded structure, with quartz subgrains developing, and the edges of the grains show bulging and subgrain rotation recrystallization (Figure 9B,C), indicating medium-temperature dislocation creep in quartz.  
Along the foliation, fine pseudotachylyte veins exhibit a directional distribution, with discontinuous boundaries, interruptions, or tapering. The deformation features of the pseudotachylyte veins are consistent with those of the quartz bands, and the veins deform  
Figure 9: Microstructures of pseudotachylyte that underwent plastic deformation in AF19-43G. (**A**) AF19-43G under PPL. (**B**,**C**) AF19-43G under XPL. (**D**,**E**) SEM of AF19-43G.  
plastically around the eye-shaped plagioclase phenocrystals (Figure 9A-C). These features suggest that after the formation of pseudotachylyte, it and the fine quartz aggregates underwent plastic deformation together. Under scanning electron microscopy, granular magnetite inclusions were observed within the pseudotachylyte (Figure 9D,E).