The timing and duration of magmatism within the Gongpoquan arc in the Beishan Orogenic Collage (BOC) has been determined via zircon U–Pb age, zircon Hf, and whole-rock Sr–Nd isotopic compositions of Gongpoquan arc granitoids. Zircon U–Pb ages indicate that the Gongpoquan adakitic granitoids were emplaced at ca. 450 Ma, marking the earliest episode of adakitic granitoid magmatism in the Gongpoquan arc, north of the Yueyashan-Xichangjing (YX) ophiolite mélange. The geochemistry and isotopic characteristics of the adakitic granitoids indicate derivation from partial melting of the subducted YX oceanic slab, followed by mixing with older continental crust during magma ascent. The Late Ordovician adakitic granitoids may record initial subduction of the YX ocean. Quartz diorite samples yield zircon U–Pb ages of ca. 441 and 442 Ma, and show fertile Nd and Hf isotopic compositions, suggesting derivation from partial melting of ancient mafic lower crust. Additionally, monzogranite samples yield zircon U–Pb ages of ca. 446 Ma, and exhibit a range of epsilon Hf values up to 12.1 epsilon units, indicating that they are derived from partial melting of ancient mid-crust with involvement of depleted mantle-derived magma during subduction. Early Devonian monzogranite samples (zircon U–Pb: ca. 416 Ma) show A-type granite affinities, were derived from an evolved source and subjected to intense fractional crystallization in a post-collisional setting. We suggest that the initial northward subduction of the YX ocean occurred around 450 Ma and followed by the main oceanic subduction during the Late Ordovician to Late Silurian. The identification of A-type monzogranites in the Early Devonian indicates the post-collision, which represents the end of the evolution of the Gongpoquan arc.
