Hannuoba basalts, which erupted in early Miocene of Neogene, are located on the northern margin of North China Block as a basaltic plateau and cover an area of about 1700km2.These basalts consist of intercalated alkaline basalt and subalkaline basalt with mantle xenoliths in basanite and alkaline dorgalite. The ages of basalts vary upward from 24.5 Ma to 13.6Ma.The distinct geological character is that the early alkaline basalt and the late subalkaline basalt are in rhythmicity, as has been recognized by many geologists. In general, SiO2increases gradually (42.91%→50.17%) from basanite, alkaline-olivine basalt, olivine tholeiite to quartz tholeiite, Mg#is usually 0.55~0.63 in basanite, 0.63~0.66 in alkaline-olivine basalt, and 0.59~0.66 in olivine tholeiite. Correspondingly, norma-tive nepheline decreases and hypersthene and quartz ncrease. The REE partition patterns vary with the rock types of the basalt, i.e., bulk REE concentration decreases from basanite to quartz tholeiite, LREE decreases and HREE increases slightly. Rare earth elements and other incompatible elements are ifferentiated extensively. On the whole, the incompatible elements istribution patterns resemble those of OIB. In La/Sm-La plot, the samples studied are projected as an inclined array from upper right to lower left, and accordingly the rock types change from basanite to quartz tholeiite. The concentration of compatible element Cr varies from low to high to medium and the concentration of Ni increases slightly from basanite to tholeiite, but the change is not so remarkable, and Co shows no notable changes. All of this suggests a partial melting process and the melting extent increases from basanite to quartz tholeiite. When the geological and geochemical characteristics are related to high temperature and high pressure melting experiments on peridotite, it can be concluded that the main magmatic process is the incremental partial melting. Gravitational instability caused by local thermal anomaly may induce the diapiric ascent of mantle material , leading to depressure partial melting. Phase change also occurs in Al_rich phase such as garnet. When the mantle diapir ascends to the spinel stability field, melting sequence of mineral phases is Cpx→Spn→Opx→Ol (Ito & Kennedy, 1976). Melting of Cpx which is the main Na_bearing phase in mantle peridotite will produce normative nepheline basanite magma. Further melting will cause Spn which contains the main part of Cr in peridotite and some other minerals like Opx to enter the melt, leading to decrease of SiO2and increase of Cr in melt and resulting in the composition of alkaline olivine basalt. With the increasing of melting, more Opx enters melt, thus the norm ne and Cr concentration decreases and norm hy increases, making the melt composition move towards olivine tholeiite. When the mantle diapir enters the plagioclase stability field, there occurs incongruent melting of Opx, i. e., En→Ol+SiO2. This will form quartz tholeiitic magma.The mantle plume theory is used to interpret the induction of diapir and the generation of Hannuoba basalts. Deep mantle hot plume supplied the heat needed for partial melting and some of incompatible elements_rich fluids to decrese the solidus temperature. This caused diapiric ascent of mantle material and consequently the pressure release. On the way up, diapirite would melt at different phase stability depths. The mantle plume might have occurred several times in the same place under the stationary plate (Van Keken, 1997) and caused rhythmic basalt eruptions. The mantle plume theory can also be used to explain the correlation with OIB type of incompatible element distribution pattern. Hence the petrogenetic model can be called multicyclic increment partial melting.