The petrology, whole rock geochemistry and geochronology of the late Early- Jurassic Beichanggang (BCG) granodiorite and its dark microgranular enclaves in the Songnen- Zhangguangcai Range were reported in this paper. Abundant mafic magmatic enclaves (MMEs) are contained in the BCG granodiorite. The MMEs are characterized by typical magma structure and long prisms of apatite. The plagioclase crystal in the MMEs shows obviously compositional and structural imbalance. Both the host rock and MMEs are metaluminous, high- K calc- alkaline series or high- K calc- alkaline series to calc- alkaline series rocks. They have similar rare earth element patters and primitive mantle- normalized trace element variation patterns. Both of them show positive εNd(t) and zircon εHf(t) values. In the Harker diagram, a good linear relationship is showed in the host rock, MMEs and the earlier mafic rocks in this area. The above characteristics indicate that the MMEs are products of magma mixing and derived from partial melting of asthenospheric mantle which have been metasomatized by the slab- derived fluids or melts. While the host rock were derived from the partial melting of the Meso- neoproterozoic mafic lower crust, combined with minor part of depleted mantle materials. The host rocks and the MMEs yield consistent zircon U- Pb ages (173±2. 0 Ma and 173±1. 5 Ma, respectively), which is interpreted as the magma mixing age. Tectonically, Zhangguangcai Range represents an incipient continental back- arc tectonic setting which resulted from the palaeo- Pacific slab subducting W- NW beneath East Asia in Early Jurassic (~185 Ma). The occurrence of Beichanggang granodiorite and MMEs suggests continuous mantel derived magmatism and an extensional environment in the late Early- Jurassic (~173 Ma). Subsequently, mantle magmatic underplating resulted in partial melting of the lower crust and formation of the studied granodiorite, which indicates a lateral crustal growth event.