MOR-type and SSZ-type ophiolites occur along the Dachadaban profile in North Qilian Mountains (NQM) of northwest China, which have recorded magmatic activities in different tectonic environments. Geochemical data show that the gabbro in the southern part of the profile has a pattern similar to N_MORB pattern, characterized by low SiO2 (48.04%～51.20%) and MgO (7.29%～10.81%), Mg index varying from 0.52 to 0.69, high TiO2 (1.27%～1.47%) and Al2O3 (12.66%～14.50%), and high (REE content ranging from 37.18×10-6 to 62.09×10-6, about 10 times higher than that of chondrite. The REE pattern indicates a flat distribution or slight LREE depletion relative to HREE, with （La/Yb）N ratios ranging from 0.66 to 0.80, and weak negative Eu anomalies (δEu from 0.83 to 0.91). The gabbro has similar Ti/V ratio to N-MORB, but is enriched with Rb, Ba, Th and U. Geochemical characteristics similar to N-MORB imply that the gabbro is of oceanic crust origin. Zircons separated from a gabbro sample are fine_grained (50～100 μm) and mostly have long prismatic shape. CL images show that zircons contain an oscillatory zone with Th/U ratio ranging from 0.72 to 1.18, suggesting a magmatic origin. All zircons are concordant and have an age of 505±8 Ma by SHRIMPU-Pb dating, representing the formation time of gabbro. This gabbro is coeval with the Aoyougou (504 Ma) and Dongcaohe gabbro (497 Ma) in NQM, suggesting a common oceanic spreading and formation of oceanic crust at the end of Cambrian in the North Qilian Mountain. By contrast, pillow lavas from the northern part of the profile are characterized by high SiO2 (52.33%～55.62%) and MgO (10.43%～14.17%), Mg index varying from 0.72 to 0.78, low TiO2 (0.29%～0.44%) and Al2O3 (10.10%～13.34%), and low ΣREE content (9.93×10-6～19.04×10-6), 10 times lower than ΣREE content of chondrite. The REE pattern displays LREE depletion with (La/Yb）N ratios ranging from 0.45 to 0.69. Most pillow lava samples have negative Eu anomalies (δEu ranging from 0.58 to 1.08), with distinct negative-Nb, Ta anomalies and a Ti/V ratio similar to that of arc tholeiite. The overall geochemical characteristics resemble those of boninite, which originated from an island arc related to the northward subduction of oceanic crust. Pillow lavas were formed slightly later (483 Ma), consistent with the field relationship of pillow lavas overlying gabbro. These data indicate that there is about 20 Ma time difference from the formation of oceanic crust to the production of island arc. This study provides important constraints for the evolution of ocean basin in the NQM.