## 5 Discussion
### Phase D\({}_{3}\) Deformation: Timing and Dynamical Context  
The D\({}_{3}\)-phase deformation is predominantly characterized by NW-directed shearing of the hanging wall within ductile shear zones, which truncated both D\({}_{1}\)- and D\({}_{2}\)-phase structures. Previous studies [36; 37; 38] interpret the Woka ductile shear zone as a northward oblique-slip shear zone that developed during the Early Miocene (21-24 Ma). This deformation was likely triggered by N-S-oriented extensional stress within the Lhasa terrane, resulting from the ongoing India-Asia continental collision during this period. Furthermore, [PERSON] et al. (2020) [39] reported that high-temperature deformation within the Yeba Group mylonites in the Woka shear zone is dominated by grain boundary migration (GBM) and subgrain rotation (SGR), while low-temperature deformation is characterized by bulging recrystallization (BLG). The late-stage low-temperature deformation features overprint the earlier high-temperature deformation structures. The two stages of the temperature environment studied in this article are the products of different tofacies of the same stage of a ductile deformation event, and it is also a product of a progressive deformation process. This provides microstructural and kinematic evidence for the tectonic regime transition from the Oligocene to Miocene in the Lhasa terrane, consistent with the crustal rheological layering observed in this region [39]. The central segment of the Gangdese orogenic belt underwent a phase of rapid exhumation during the Early Miocene (\(\sim\)23 Ma), an event that closely coincides with thetemporal framework of coeval shear zone activity. Emerging constraints from integrated studies [40; 41; 42] reveal the multistage Cenozoic exhumation of the central Gangdese orogen: an initial pulse at \(\sim\)45 Ma (Middle Eocene), followed by two discrete rapid exhumation episodes at \(\sim\)23 Ma and \(\sim\)10 Ma. Notably, high-precision geochronological constraints from the Woka ductile shear zone (22.38 \(\pm\) 0.31 Ma [39]) demonstrate that its tectonic activity was precisely synchronized with the second exhumation pulse. Since the Miocene, in the Gangdese magmatic belt, the tectonic superposition of north-south post-collision extension and east-west extensional collapse has occurred owing to lateral variations in the crust-thickened gradient in the Lhasa terrane. The activity of the Gangdese thrust-reverse fault system (GCT) triggered extensive sedimentation in the overlapping zone between the Lhasa terrane and the Indian plate. This process induced flexural bending and deformation along the southern margin of the Gangdese basement, accelerated crustal uplift, and led to the development of a shear zone in the rear of the basement [39; 43]. Therefore, we interpret the D\({}_{3}\)-phase tectonic deformation as the result of the transition from compressional to lateral extensional regimes in the Lhasa terrane, driven by the combined effects of GCT activity and the uplift of the Gangdese basement (Figure 7c). In summary, the tectonic evolution of the Yeba Volcanic Arc can be summarized as follows: during the Late Cretaceous (\(\sim\)90-79 Ma), the flat-slab subduction of the Neo-Tethys Ocean generated a compressional back-arc tectonic regime. Under this N-S-directed compressional stress, the Cretaceous Gangdese back-arc basin underwent E-W-trending brittle-ductile shearing, leading to the formation of transpressional ductile shear zones within the Yeba Group. The D\({}_{1}\)-phase ductile deformation event is constrained to have occurred at \(\sim\)79 Ma (Figure 7a). During the Late Cretaceous (\(\sim\)79-70 Ma), under a nearly N-S-oriented compressional stress regime, the entire back-arc basin system in the Southern Gangdese--including the Yeba Group and its overlying strata--was extruded upward in response to the subduction of the Neo-Tethyan oceanic lithosphere.