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This study focuses on the geology, geochemistry, zircon U‐Pb geochronology and tectonic settings of the three types of seamount basalts from the Xingshuwa subduction accretionary complex in the Xar Moron area, eastern margin of the Central Asian Orogenic Belt (CAOB). The seamount remnants are composed of carbonate ‘cap’ sediments, large volumes of pillow and massive basalts, carbonate breccia slope facies and radiolarian cherts. Group 1 basalts are characterized by high contents of P2O5 and TiO2 with alkaline affinity and LREE enrichment, indicating that they are derived from intraplate magma. Group 2 basalts display N‐MORB LREE depletion patterns, indicating that they were formed at a mid‐ocean ridge. Group 3 basalts have shown distinct Nb depletion and high Th/Yb ratios, indicating that they were generated in an island arc tectonic setting. The zircon U‐Pb age of Group 1 basalt sample XWT18‐131 is 576.4 ± 9.4 Ma, suggesting that the oceanic island seamount was the product of intraplate magmatism related to a mantle plume or ‘hot spot’ in the late Neoproterozoic. The zircon U‐Pb age of Group 2 basalt sample XWT18‐132 is 483 ± 22 Ma, indicating that the Paleo‐Asian Ocean (PAO) was continuously expanding in the Early Ordovician. The zircon U‐Pb age of Group 3 basalt sample XWT18‐101 is 240.5 ± 8.2 Ma, suggesting that this area underwent the evolutionary path of ocean‐continent transition, developing towards continentalization during the Middle Triassic. Thus, we believe that there was both mantle plume‐related intraplate magmatism and intraoceanic subduction during the evolution of the PAO, the CAOB possibly being an evolutionary model of an intraoceanic subduction and mantle plume magmatism complex.

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We report herein on new zircon U–Pb ages, the major and trace elements of whole-rock, and the Sr–Nd–Hf isotope composition for adakitic intrusives collected from the West Ujimqin district in the Southeast region of the Central Asian Orogenic Belt (CAOB). These data provide important constraints on the petrogenetic evolution and geodynamic setting of late Permian magmatism in the Southeast CAOB. The U–Pb dating of zircon shows that the ages of Seerbeng pluton and Nuhetingshala pluton in West Ujimqin are 255.3 ± 0.71 and 254.4 ± 1.2 Ma, respectively, which signifies that these are products of magmatic activity in the late Permian. The adakitic intrusives are characterized by high levels of Sr (Sr ≥ 741 ppm), low Y, low Yb, high Sr:Y ratios, and strongly fractionated rare earth elements (10.3 < LaN/YbN < 22.5), which is similar to the features of the adakite. The magmatic zircons exhibit positive Hf values (+8.1 to +13.3), and young two-stage model ages vary from 430 to 760 Ma. The high εNd(t) and low (87Sr:86Sr)i indicate that the adakitic granite derived from the partial melting of subducted oceanic slab. The high level of Mg# [100 × Mg/(Mg + Fe) in atomic number] and abundant Cr–Ni indicate that magmatic melts interacted with olivine rocks in the mantle. Considering these results and the regional rock assemblies, we conclude that the Paleo-Asian Ocean had not yet completely closed in the late Permian, and northward subduction continued, with the subducted slab possibly breaking off.