Zongwulong tectonic belt is an important tectonic unit on the northern margin of Qaidam Basin, but its tectonic properties remain controversial. In this study, a diorite intrusion was recognized in central Xuji area of the Zongwulong tectonic belt, and its petrography, geochemistry, zircon U-Pb chronology and Lu-Hf isotopes were studied. The intrusion time of the diorite is 258±1 Ma;light rare-earth elements are enriched while heavy rare-earth elements are depleted, with weak negative Eu anomaly; it is relatively enriched in large ionic lithophile elements such as Rb, K and Sr, but strongly depleted in high field strength elements such as P, Ti and Nb. The content of Cr and Ni are 38.0×10^-6~92.8×10^-6 and 6.7×10^-6~14.1×10^-6 respectively, Mg^# values are 50~56, Rb/Sr ratios are 0.32~0.34, Ti/Zr ratios are 23.26~32.30, Ti/Y ratios are 145.29~163.97, Nb/Ta ratios are 10.45~11.45, Th/La ratios are 0.39~0.51, Ba/La ratios are 15.04~16.60, ²⁰⁷Pb/²⁰⁴Pb_(i) ratios are 15.602~15.611, zircon εHf(t) values are -8.52~-3.00, and the two-stage Hf model ages are 1 563~1 478 Ma[εHf(t)=-4.37~-3.00] and 1 827~1 790 Ma[εHf(t)=-8.52~-7.98]. It can thus be concluded that the magma was derived from mixture of the crust and the mantle, where the ancient crustal material was dominant. Combined with regional geological studies, it is suggested that the marginal rifting in the central and western regions of the Zongwulong tectonic belt should be later than that in the east.