Collisional magmatism records many information of material cycling between crust and mantle during subduction and collision and it is of great importance to reveal their source nature and crustmantle interaction for understanding tectonic evolution of the orogenic belt. Mafic microgranular enclaves (MMEs) are widely distributed in Nanshankou biotitemonzogranite of the East Tianshan. Geochemically, the host biotitemonzogranites show intermediaacidic, metaluminous, alkaline and potassiumrich signatures, whereas the MMEs are relatively poor in silicon and potassium. The host biotitemonzogranite are enriched in Rb, K, Th, U and depleted in Sr, P, Nb, Ti and display moderately Zr, Hf peaks in the primitive mantle normalized trace element spidergram, and moderately to strongly Eu depletions (046~057) in the chondritite normalized REE distribution patterns. The MMEs share similar trace and rare earth elements characteristics to those of the host rocks, but are relatively enriched in Sr, P and more depleted in Zr, Hf, and display weakly to moderately Eu depletions (080~093). Zircon LaICPMS UPb dating gave ages of 2982 ± 20 Ma and 2940 ± 27 Ma for MMEs and biotitemonzogranite, respectively, indicating the Early Permian emplacement. The dioritic enclaves and their host granites have positive εHf(t) values (731~1198 for MMEs, 694~1214 for host granites) and relatively low n(176Hf)/n(177Hf) with fairly similar model ages (450~656Ma). It is suggested that the MMEs and host granites were derived from the same parental magma that resulted from partial melting of the NeoproterozoicEarly Paleozoic depleted mantle sourced juvenile crust which was triggered by the heat of asthenosphere upwelling after the postcollisional slab breakoff.