The role of common components in the mantle of volcanic rocks erupted in the northern, central, and southern parts of the Sayan-Mongolian low-velocity domain is determined for identification of the sub-lithospheric convective isotopic homogenization of a material in mantle sources in the past 90 Ma. It is inferred that the sources of volcanism in the Baikal rift system were due to divergent reactivating of the convective mantle within a geodynamic province of the disintegrated supercontinent Rodinia, whereas those in Southern Goby were originated through convergent clearing of the Sayan-Mongolian low-velocity domain from stagnated paleoslab fragments in the geodynamic province of the closed Phanerozoic paleooceans (Solonker and Ural-Mongolian). Sources of recent volcanism in the transitional Hangay region, which corresponded to the closed Mongolian-Okhotsk Gulf of Paleo-Pacific, formed under conditions of spatially combined convergent and divergent processes but reveal predominating features of the disintegrated Rodinia mantle.