Multiple magma sources and incremental assembly of the late Mesozoic Yunmengshan batholith, North China Craton: Constraints from zircon Hf-O isotopes and apatite geochemistry

The Late Mesozoic Yunmengshan (YMS) batholith, exposed along the northern margin of the North China Craton, comprises the Shicheng diorite and the main granitoids, and provides important records of Late Jurassic–Early Cretaceous magmatism in the Yanshan Belt. We present in situ zircon U-Pb ages and Hf-O isotopes, together with apatite geochemistry, to constrain its magma sources and emplacement history. Zircon U-Pb dating identifies three magmatic episodes at ca. 156 Ma, ca. 143 Ma, and ca. 139–137 Ma for the Shicheng diorites, Yunmengshan medium-grained monzogranites, and fine-grained monzogranites, respectively, demonstrating incremental batholith assembly. The Shicheng diorite has zircon ε Hf (t) values of −17.8 to −13.4 and δ 18 O values of 5.7 ‰ to 6.9 ‰. Combined with its major and trace element compositions, it suggests derivation mainly from an enriched lithospheric mantle source with variable involvement of crustal materials. In contrast, the medium- and fine-grained monzogranites display similarly negative but variable zircon ε Hf (t) values (−21.3 to −14.7 and − 25.6 to −12.1, respectively) and relatively homogeneous zircon δ 18 O values (5.8 ‰ to 7.0 ‰). These isotopic characteristics indicate derivation mainly from isotopically heterogeneous Neoarchean to Paleoproterozoic mafic lower crust beneath the North China Craton. Apatite trace element compositions further reveal contrasting crystallization histories between the two granitoid facies. Apatite from the medium-grained monzogranites record stronger effects of progressive plagioclase crystallization prior to or during apatite growth and a greater influence of allanite fractionation, whereas these effects are weaker in apatite from the fine-grained monzogranites. The two granitoid facies are therefore interpreted as genetically related but distinct magma batches rather than products of continuous fractional crystallization from a single parental magma. The Yunmengshan batholith thus records multiple magma sources and incremental assembly, involving mantle-derived magmatism, crust-mantle interaction, and subsequent reworking of ancient lower crust during subduction-related lithospheric modification beneath the North China Craton.