Study of mineral inclusions in diamonds indicates their origin from different depth levels, up to the lower mantle. However, most diamonds, which have been transported to the surface by kimberlite magma, originate from the continental lithosphere. Precipitation of lithospheric diamonds is connected with initial stages of carbonatite metasomatism of relatively reduced depleted peridotite of cratonic roots. Multiply metasomatic episodes and their different degree of reactions are recorded in the composition of garnet from peridotite xenoliths. Pronounced interaction of metasomatic carbonatite melt with peridotite causes disappearance of diamonds and changes modal mineralogy of initial rocks. Partial melting of such metasomatized material with the degree of melting below 1% leads to the formation of kimberlite-carbonatite magmatic assemblages. The rare example of mantle modification is related to reactions with reduced CHO-fluid containing H2O and presumably methane and other hydrocarbons, which have been identified in some diamonds worldwide. The review of experimental data on melting of the carbonated systems shows that the most realistic metasomatic agent (liquid phase) for material transport in the mantle would be H2O-poor carbonatitic melt. Based on high-pressure experiments it was argued that carbonates from subducting slabs undergo significant melting at the transition zone depths. In turn, this melting must segregate and form the carbonatite diapirs, which can rise through the mantle by the dissolution-precipitation mechanism. These diapirs can easily oxidize presumably reduced mantle column at about 550-200 km depths and create oxidized channels. Indeed, ascent of such diapirs and redox reactions with the mantle at the front create important mechanism for the formation of ultradeep diamonds at the rear. At the level of the lithosphere-asthenosphere boundary such diapirs form a source for the formation of kimberlite and related magmas. It is argued that the primary kimberlite melt composition can be in many cases close to carbonatite with the SiO2 content below 10-15%.