The Suanjingzi adakitic granites consist of three intrusive rocks, namely, medium- to coarse- grained gneissic biotite granodiorite, medium- to coarse- grained biotite granodiorite and medium- to fine- grained biotite monzonite granite, which were the products of three magmatic intrusive activities of the same magmatic melting event. Zircon LA- ICP- MS U- Pb dating result shows that the Suanjingzi adakitic granites emplaced in the Early Carboniferous between 350. 0Ma and 351. 7Ma (the Middle Hercynian Period). Geochemically, the pluton is characterized by high content of SiO 2 (67. 81%～70. 93%) and Al 2O 3 (14. 94%～16. 07%), middle content of K 2O+Na 2O (6. 01%～6. 74%), lower ratios of K 2O/Na 2O (0. 37～0. 69), and low content of Ti, Ca, Fe, and MgO (0. 99%～1. 61%), with the ratios of (K 2O+Na 2O)/Al 2O 3 varying between 0. 37 and 0. 45, and the ratios of A/CNK between 0. 95 and 1. 03. All these features indicate that the pluton belongs to peraluminous- weakly metaluminous calc- alkaline granites. In respect of trace elements, the rocks have a high content of Sr (409×10 -6 ～548×10 -6 ), and the low contents of Y (8. 1×10 -6 ～17. 7×10 -6 ) and Yb (0. 83×10 -6 ～1. 73×10 -6 ), and enriched in LILE (K, Rb, Ba) and HFSE (Th), but depleted in Ta, Nb and Ti. The chondrite- normalised REE distribution pattern of the Suanjingzi pluton displays a right dipping shape, distinct fractionation between LREE and HREE, enrichment of LREE and depletion of HREE, and unobvious Eu anomalies (δEu=0. 64～1. 13), suggesting characteristic of the typical adakites. The geochronological and geochemical features of the Suanjingzi pluton indicate: ①The Suanjingzi granitic pluton belongs to peraluminous- weakly metaluminous and unfractionated I- type granites with the typical adakite characteristics; ②magmas were probably derived from partial melting of the lower crust basaltic rocks with the mantle wedge metasomatized by subducted slab- released fluids/melts, and contaminated by the volcanic arc components during magma uprising; ③the pluton was probably formed in an active continental margin volcanic arc setting in the Middle Hercynian Period, and it can be deduced that the subduction- collision effect between the Tarim Plate and the Kazakhstan Plate continued to the Early Carboniferous in the Beishan Mountains.