Abstract: 　　
　　The Eastern Himalayan Syntaxis and its southeastern region serve as a critical channel for the eastward extrusion or/and expansion of Tibetan Plateau material, where the deformation/rheology mechanisms and seismic anisotropy of the lithosphere provide key insights into plateau uplift and lateral growth. This study investigates lower-crustal garnet pyroxenites (27–44 km depth) and lithospheric mantle spinel lherzolites (50–78 km depth) from the Ailao Shan-Red River shear zone and adjacent regions, integrating petrographic analysis, microstructural observations, crystallographic preferred orientations (CPOs) measurements, metamorphic-deformation thermobarometry, and whole-rock seismic velocity modeling to constrain the lithospheric seismic anisotropy and its tectonic implications. Our key findings include: (1) Microstructural analysis reveals that garnet in lower-crustal pyroxenites behaves as a rigid phase with rotational deformation, while clinopyroxene accommodates strain via dislocation creep. In the lithospheric mantle, olivine exhibits both A-type (high-temperature, low-pressure simple shear) and AG-type (melt-present) CPOs, with orthopyroxene and clinopyroxene also deforming predominantly by dislocation creep, indicating polyphase plastic deformation and static recrystallization. (2) Seismic velocities show distinct layering: garnet pyroxenites exhibit Vp = 8.01–8.07 km/s and Vs = 4.54–4.57 km/s with weak anisotropy (AVp = 0.6–1.4%, AVs = 0.7–1.1%), whereas spinel lherzolites display higher velocities (Vp = 8.03–8.08 km/s, Vs = 4.60–4.61 km/s) and stronger anisotropy (AVp = 3.8–8.0%, AVs = 3.0–6.6%). (3) Velocity controls differ between lithologies: garnet content dominates bulk seismic velocity in pyroxenites, while anisotropy correlates with clinopyroxene content; in lherzolites, seismic properties are primarily controlled by olivine, with orthopyroxene and clinopyroxene exerting a diluting effect, and deformation intensity significantly influences anisotropy. (4) From the mid-crust to the lithospheric mantle, a vertical velocity model reveals stepwise increases: mica schist (Vp = 6.12–6.46 km/s) → granodiorite (Vp = 6.69–6.78 km/s) → amphibolite (Vp = 6.30–6.69 km/s) → garnet pyroxenite (Vp = 8.01–8.07 km/s) → spinel lherzolite (Vp = 8.03–8.08 km/s), with the amphibolite layer (Vs = 3.59–4.01 km/s) acting as a key interface for crust-mantle velocity transitions. Integrated with previous published geophysical data, we propose a tectonic model wherein: (1) mid-lower crustal amphibolites and partial melts are the primary sources of crustal anisotropy; (2) mantle anisotropy reflects southeastward lithospheric extrusion driven by asthenospheric upwelling, with clear crust-mantle decoupling.
　　The Eastern Himalayan Syntaxis and its southeastern region serve as a critical channel for the eastward extrusion or/and expansion of Tibetan Plateau material, where the deformation/rheology mechanisms and seismic anisotropy of the lithosphere provide key insights into plateau uplift and lateral growth. This study investigates lower-crustal garnet pyroxenites (27–44 km depth) and lithospheric mantle spinel lherzolites (50–78 km depth) from the Ailao Shan-Red River shear zone and adjacent regions, integrating petrographic analysis, microstructural observations, crystallographic preferred orientations (CPOs) measurements, metamorphic-deformation thermobarometry, and whole-rock seismic velocity modeling to constrain the lithospheric seismic anisotropy and its tectonic implications. Our key findings include: (1) Microstructural analysis reveals that garnet in lower-crustal pyroxenites behaves as a rigid phase with rotational deformation, while clinopyroxene accommodates strain via dislocation creep. In the lithospheric mantle, olivine exhibits both A-type (high-temperature, low-pressure simple shear) and AG-type (melt-present) CPOs, with orthopyroxene and clinopyroxene also deforming predominantly by dislocation creep, indicating polyphase plastic deformation and static recrystallization. (2) Seismic velocities show distinct layering: garnet pyroxenites exhibit Vp = 8.01–8.07 km/s and Vs = 4.54–4.57 km/s with weak anisotropy (AVp = 0.6–1.4%, AVs = 0.7–1.1%), whereas spinel lherzolites display higher velocities (Vp = 8.03–8.08 km/s, Vs = 4.60–4.61 km/s) and stronger anisotropy (AVp = 3.8–8.0%, AVs = 3.0–6.6%). (3) Velocity controls differ between lithologies: garnet content dominates bulk seismic velocity in pyroxenites, while anisotropy correlates with clinopyroxene content; in lherzolites, seismic properties are primarily controlled by olivine, with orthopyroxene and clinopyroxene exerting a diluting effect, and deformation intensity significantly influences anisotropy. (4) From the mid-crust to the lithospheric mantle, a vertical velocity model reveals stepwise increases: mica schist (Vp = 6.12–6.46 km/s) → granodiorite (Vp = 6.69–6.78 km/s) → amphibolite (Vp = 6.30–6.69 km/s) → garnet pyroxenite (Vp = 8.01–8.07 km/s) → spinel lherzolite (Vp = 8.03–8.08 km/s), with the amphibolite layer (Vs = 3.59–4.01 km/s) acting as a key interface for crust-mantle velocity transitions. Integrated with previous published geophysical data, we propose a tectonic model wherein: (1) mid-lower crustal amphibolites and partial melts are the primary sources of crustal anisotropy; (2) mantle anisotropy reflects southeastward lithospheric extrusion driven by asthenospheric upwelling, with clear crust-mantle decoupling.