Plate tectonics plays a crucial role in the evolution of Earth’s continents and oceans. However, the impact of oceanic subduction and continental collision on the continental lithospheric mantle within collisional orogenic belts is still a matter of debate. To address this issue, we performed a thorough analysis of mafic rocks in the Nixiong area within the central Lhasa Terrane, southern Tibet. The mafic rocks are composed of diabases and basalts formed during syn-collisional period (~50 Ma). The diabases have low SiO₂ and moderate MgO contents, and are enriched in large ion lithophile elements and depleted in high field strength elements. They show high ⁸⁷Sr/⁸⁶Sr_i (0.711451–0.712084) and low ε_Nd(t) (−7.9 to −6.44), as well as enriched Hf-Pb isotope compositions (ε_Hf(t) = -7.58 to −6.59; ²⁰⁶Pb/²⁰⁴Pb_i = 18.59–18.71; ²⁰⁷Pb/²⁰⁴Pb_i = 15.71–15.72; ²⁰⁸Pb/²⁰⁴Pb_i = 39.33–39.53). Geochemical modelling suggests that the diabases were formed through the partial melting of peridotite at high temperatures and shallow depths, with significant addition of subduction-related components to the primary melts. The diabases probably originated from a metasomatized lithospheric mantle due to subduction of Neo-Tethyan slab. The basalts display similar SiO₂ but lower MgO contents compare with the diabases. They are also characterized by extremely high ⁸⁷Sr/⁸⁶Sr_i (0.713332–0.713448), low ε_Nd(t) (−10.32 to −9.96), and significantly enriched Hf-Pb isotope compositions (ε_Hf(t) = -12.30 to −12.05; ²⁰⁶Pb/²⁰⁴Pb_i = 18.81–18.85; ²⁰⁷Pb/²⁰⁴Pb_i = 15.74–15.75; ²⁰⁸Pb/²⁰⁴Pb_i = 39.81–39.88), corresponding to an extremely enriched lithospheric mantle. Integrated with the previous studies, the Nixiong mafic rocks exhibit the most enriched isotopic compositions among the arc- or syn-collision-related mafic rocks in southern Tibet. These extremely isotopically enriched components were most likely derived from the ancient continental lithospheric mantle beneath the central Lhasa Terrane. Our results provided unambiguous evidence that the pre-existing ancient continental lithospheric mantle could persist locally during the prolonged oceanic subduction and subsequent continental collision.