Large quantities of magmatic rocks are developed on the southern margin of Gangdise belt. Previous studies mainly focused on the eastern part of this magmatic rock belt, which completed the theory of the tectonic framework and lithospheric structure as well as the evolution of the southern margin of the Gangdise belt. The Amuxiong complex is in the middle part of the magmatic rock belt on the southern margin of the Gangdise belt. The authors described zircon U-Pb geochronology, zircon Hf isotope and whole-rock geochemical analyses of hornblende gabbro and biotite monzonitic granite of the Amuxiong complex, discussed the emplacement order of these two types of magma, and clarified the genesis of magma and the hypogene geological process of the magma source area. The zircon U-Pb dating results of the biotite monzonitic granite and the hornblende gabbro are both at 49 Ma, suggesting magmatism of the Eocene period. The biotite monzonitic granite is I-type calc-alkaline granite, characterized by enrichment of the large ion lithophile elements (LILE), and depletion of the high field strength elements (HFSE), with the small positive εHf(t) value of -0.2~+2.6 and the Hf isotopic crustal model age t_DM^C of 1 136~393 Ma, suggesting that this hornblende gabbro belongs to typical gabbro. The rare earth element patterns show a gentle right wing, with very slight negative Eu anomalies, whereas the trace element pattern shows the enrichment of LILE and depletion HFSE, with the high positive εHf(t) value of +5.1~+16.8 and the young t_DM^C age of 798~46 Ma. The analytical results suggest that the hornblende gabbro was derived from the depleted mantle that had undergone lamellar fluid replacement, and that, after some differentiation, the magma of monzonite was derived from partial melting of juvenile lower crust and a small amount of old continental crust. There have been some disputes about the origin of the ancient materials in this area. Based on the analysis of previous results and the characteristics of magmatic rocks in this study, the authors hold that the contribution of the ancient materials came from the old Central Lhasa subterrane. By comparing the magmatism of the Gangdise magmatic belt in the same period, it is concluded that the main inducing mechanism of the magmatism of the Amuxiong complex might have been plate break off.