The Upper Member of the Ordovician Majiagou Formation (referred to as the "M5" member) in the Ordos Basin is characterized by the presence of two layers of tuffs, which are commonly used as regional marker beds for stratigraphic correlation. Investigation of the zircon ages of these tuffs can help establish the chronostratigraphic framework of the Majiagou Formation and provide insights into its depositional period and tectonic background. Zircon SHRIMP U-Pb dating and Hf isotope analysis were conducted on tuffs from wells S148 and T56 in the M5 member of the basin. The obtained zircon ages of these two samples are 458.4±2.4 Ma and 460.9±2.9 Ma, respectively. Based on these results, the deposition of the Majiagou Formation is constrained to the Middle Ordovician Darriwilian to Upper Ordovician Sandbian stages. The measured n(176Hf)/n(177Hf) ratios of in-situ zircon Hf isotopes range from 0.282687 to 0.280820, and εHf(t) values vary from +6.67 to +11.32, with two-stage model ages ranging from 720 to 1024 Ma. Comparison of the zircon U-Pb ages and Hf isotope characteristics of the tuffs surrounding the basin suggests that the volcanic tuffs of the Majiagou Formation may have originated from the North Qinling and/or North Qilian orogenic belts in the southwestern part of the basin. Furthermore, it is inferred that prior to the emplacement of the tuffs, the North Qinling and/or North Qilian Ocean initiated a northward subduction and entered a stage of ocean-land transition, indicating the transformation of the western and southern margins of the basin into an active continental margin during the Late Middle Ordovician.