SHRIMPUPb zircon dating on the Mengku plagiogranite pluton in the Mengku iron deposit district in Xinjiang shows that it was formed at 400±6 Ma (MSDW=1.3).This age is similar to that of biotite granite at the north part of the No. 1 orebody (SHRIMPUPb dating is 404±8 Ma), indicating that they were formed at the beginning of the Early Devonian. These plutons intrude into the Kangbutiebao Formation, showing that Kangbutiebao Formation could have been much earlier than 404 Ma. The Mengku iron deposit is related to magmatic hydrothermal activity, and the ages of the plutons shows that iron mineralization formed in slightly later than 404~400 Ma. Geochemically, the Mengku plagiogranite is enriched in silica, Na, Th, La, Ce, Nd and LREE, is depleted in K with negative anomaly in Nb, Ta, Sr, P, Ti and moderate Eu negative anomaly (δEu=0.38~0.50). The Na2O/ K2O ratios are 6.36 to 13.3, indicating lowK series, and samples fall in the tholeiitic field in the SiO2K2O diagram. The A/CNK ratios range from 1.03 to 1.09, indicating that the pluton is weakly peraluminous. The 87Sr/86Sr initial ratios range from 0.70438 to 0.70986. The εNd(t) values of 1.04 to 2.17 indicate that the sources of the plagiogranite was mainly derived from mantlederived components, with limited assimilation of old crustal material. In combination with previous studies, we concluded that the Mengku pluton was formed in a continental arc and under an active extensional continental margin setting.