## 3 Structural Deformation Characteristics
### \(D_{3}\) Deformation  
The phase 3 (D\({}_{3}\)) deformation is primarily developed in the south-central Woka area and is manifested by the ductile deformation of granitic mylonites, granitic protromylonites, mylonitized andesites, and dacites. These lithologies collectively define an E-W-trending ductile shear zone, approximately 145 km long and \(\sim\)2 km wide. The regionally developed S\({}_{3}\) shear foliation exhibits a dominant orientation of 347\({}^{\circ}\angle\)/75\({}^{\circ}\). Additionally, mineral stretching lineations exhibit a preferred plunge orientation of 291\({}^{\circ}\angle\)/262\({}^{\circ}\). Feldspar rotated porphyoclasts, predominantly \(\sigma\)-type at the outcrop scale (Figure 5a), are aligned parallel to the S\({}_{3}\) foliation. Composed mainly of plagioclase and potassic feldspar, these porphyroclasts exhibit fine-grained groundmass tails that extend along the C-plane. S-C fabrics are well developed within the mylonite zones (Figure 5b), where feldspar and quartz aggregates rotate during shearing to define the S-planes, while the C-planes are defined by aligned dark minerals such as biotite. The mineral stretching lineations are primarily composed of feldspar, quartz, biotite, and amphibole (Figure 5d). Felsic veins are well developed in the mylonitized zones, forming kinematic indicators such as boulange structures (Figure 5c), asymmetric folds (Figure 5e), and asymmetric felsic bands (Figure 5f). These outcrop-scale ductile deformation indicators suggest a top-to-the-NW shear sense, characterized by the northwest-directed movement of the hanging wall.  
Figure 5: Characteristics of the D\({}_{3}\)-phase stretching in the Yéba rock group. (**a**) \(\sigma\)-type rotated porphyoclasts; (**b**) mylonitic S-C fabric; (**c**) “curved-neck bottle” structure; (**d**) mineral stretching lineation; (**e**) asymmetric folds; (**f**) asymmetric felsic bands—microscopic indicators of ductile shear; (**g**) \(\delta\)-type and \(\sigma\)-type rotated porphyroclasts; (**h**) \(\sigma\)-type rotated porphyroclasts; (**i**) asymmetric pressure shadows; (**j**) schematic diagram showing the structural characteristics of D\({}_{3}\)-phase deformation and its relationship with the D\({}_{1}\) and D\({}_{2}\) phases; Q = quartz; PI = plagioclase.  
At the microscopic scale, the rotated porphyoclasts in the mylonite zones are predominantly composed of feldspar and quartz, accounting for 35-45% of the rock volume. The groundmass is dominated by fine-grained felsic minerals and dark minerals (e.g., mica and amphibole), constituting 50-55%. In the protomylonite zones, feldspar is the dominant porphyroclastic phase (50-75%), with the groundmass composed mainly of dark minerals. Within the mylomitized zones, the abundance of porphyroclasts increases to 85-95%, primarily derived from fine-grained feldspar, quartz, and chert. The groundmass in these zones is composed predominantly of mica and fine-grained felsic minerals.  
Under shearing, quartz, mica, and feldspar exhibit deformation characterized by the formation of kinematic indicators, including quartz ribbons and rotated porphyroclasts. At the microscopic scale, the rotated porphyroclasts are classified into \(\delta\)-type and \(\sigma\)-type (Figure 5h), predominantly composed of K-feldspar, plagioclase, and quartz. Fine-grained minerals develop tails that wrap around the porphyroclasts. Asymmetric pressure shadows (Figure 5i) are characterized by fibrous quartz tails surrounding feldspar porphyroclasts. The long axes of the feldspar porphyroclasts align parallel to the S-foliation, while their tails extend along the C-foliation.  
The microstructural analysis aligns with macrostructural observations, indicating that the kinematic signature of the ductile shear zone is characterized by a top-to-the-NW shear sense (Figure 5j). The D\({}_{3}\)-phase ductile deformation developed within the Yeba Group in the southern study area overprints and truncates the earlier D\({}_{1}\) and D\({}_{2}\) deformations.