Located on the southern margin of the Central Asian giant orogenic belt, the Beishan orogenic belt is one of the key areas for dissecting the accretionary tectonic process of the southern margin of the Central Asian orogenic belt. Researchers have a great controversy about the closing time of the Paleo-Asian Ocean and focus on whether the Devonian ancient Asian Ocean was still subducting or closed. In this study, the authors firstly identified a pluton with typical adakite characteristics in Heishantou area on the southern margin of the Beishan orogenic belt. The geochemical characteristics and zircon U-Pb chronology of the pluton were studied to discuss its genesis and geodynamic significance. The Heishantou pluton is dominated by granodiorite and partially consist of tonalite. The weighted average age of granodiorite LA-ICP-MS zircon U-Pb is 407.7±1.6 Ma. Geochemical data show that the Heishantou pluton belong to peraluminous, calc-alkaline series, with typical adakite characteristics:high silicon (SiO₂=60.85%~67.81%), high alumina (Al₂O₃=15.59%~16.98%), low magnesium (MgO=0.55%~1.53%,Mg^#=0.36~0.46), rich sodium and poor potassium (Na₂O=2.65%~3.54%,K₂O=1.09%~3.16%,Na₂O/K₂O=0.96~2.44), high Sr (Sr=253×10^-6~487×10^-6) low Y and Yb (Y=5.65×10^-6~16.70×10^-6,Yb=0.37×10^-6~0.96×10^-6) compositions, with high Sr/Y ratio (25.75~73.58). Their light rare earth elements (LREE) are enriched, with obvious light and heavy rare earth fractionation. The samples do not have obvious Eu anomaly (0.66~1.31, averaging 0.92). Moreover, trace element composition is characterized by enrichment of LILEs such as Rb, K, Th and U, and depletion of high field strength elements HSFEs such as Nb, Ta, Ti and P. Geochemical characteristics show that these adakites were formed by partial melting of the subducting oceanic crust, and the residual minerals of the crust sources might have been garnet and rutile. Based on this study and regional geological data, the authors hold that the Liuyuan Ocean (Paleo-Asian Ocean) was still in the subduction and collision stage during the Early Devonian and had the characteristics of "scissoring" closure from west to east. The upper limit of the closing time of the Paleozoic ocean basin is Early Carboniferous in the Beishan area.