The processes causing the vertical accretion of juvenile material from the mantle are thought to have impacted the subcontinental lithospheric mantle (SCLM) beneath the Central Asia Orogenic Belt (CAOB). Cenozoic alkali basalts occur throughout Central and East Asia encompassing southern Siberia, central and southern Mongolia, northeast China and the Russian Far East. Some basalts carry fragments of mantle rocks. These basalts provide direct evidence about the nature and composition of the deep lithosphere and contain a record of mantle processes. In this study, we summarize in situ Os model ages on sulfides in peridotitic xenoliths from off-cratonic settings (in the basalts from Tariat [1.5 Ma], Mongolia; Vitim [14 and 0.65 Ma], Khamar Daban Range [KDR; 17 Ma] and Sviyaginsky volcano [12 Ma], Russia) of the CAOB to examine SCLM formation. Mantle xenoliths collected from these volcanic fields are predominantly spinel lherzolites composed of olivines, orthopyroxenes, clinopyroxenes and spinels, with garnet- and spinel-garnet lherzolites only found in Vitim. Geothermal evidence suggests these lherzolites represent residual SCLM, some of which is quite refractoryand may be ancient. Most of their Os TMA from the least-disturbed sulfides (187Re/188Os<0.07), and TRD from higher Re/Os sulfides without later introduction/loss of Os, yield model ages ranging from 0.3 to 3.0 Ga, with peaks around 1.7–1.4, 1.2–0.9 and 0.7–0.5 Ga the CAOB region formed at least by the Proterozoic time, and that some domains are Archean. Younger sulfide Os ages (1.2–0.9 and 0.7–0.5 Ga) may mark the commencement of the Central Asia Orogeny since the Neoproterozoic and involvement of the mantle. These sulfide Os ages, recording formation of the SCLM and subsequent metasomatism by juvenile crustal-growth events, are consistent with the thermotectonic events recorded in the overlying crust of the ancient microcontinents, where the sampled volcanic fields are located. All geochemical characteristics of the Tariat, Vitim, Khamar Daban Range and Sviyaginsky peridotites reveal that ancient, refractory Archean–Proterozoic lithospheric mantle is embedded in the younger, fertile post-Archean lithospheric mantle beneath the CAOB. The ancient Archean–Proterozoic mantle domain has survived, but may have been subjected to metasomatic re-enrichment during Central Asia Orogeny since the Neoproterozoic and the Cenozoic extension with intraplate volcanism in this region. Comparing the lithospheric mantle domains from the above regions as revealed by Os model ages, with ancient microcontinents at least Mesoproterozoic in age and predating formation of the CAOB, significantly diminishes the volume of new juvenile crust generated during the orogeny. Although significant mantle involvement during evolution of the CAOB has been proposed, the extent of ancient continental material may be larger than previously estimated.