Geochronology, petrogenesis and geodynamic implications of the Early–Middle Jurassic granites of the southern Zhangguangcai Range (NE China)

Early–Middle Jurassic granitoids are widely exposed in the southern Zhangguangcai Range (NE China), but their petrogenesis and tectonic significance remain debated. This study presents zircon U–Pb geochronology, whole-rock geochemistry, zircon trace element data, and Sr–Nd–Pb–Hf isotopic constraints on representative alkali-feldspar granites and syenogranites sampled in the Dongxi, Jilin, Wula, and Erlong Mountain areas. Zircon U–Pb ages indicate emplacement from 192 Ma (Dongxi) to 174 Ma (Erlong Mountain), defining a coherent magmatic episode during Early–Middle Jurassic. The granitoids exhibit typical A-type (A2) affinities, characterized by high SiO₂ and alkali contents, enrichment in LILE and HFSE, negative Eu anomalies, high Fe₂O₃T/MgO ratios, and positive εHf(t) (6.0–11.5) and εNd(t) (0.3–3.73) values. These features suggest derivation from dominantly juvenile mantle-derived magmas through extensive fractional crystallization of mafic-to-intermediate melts, with limited crustal assimilation. The coexistence of coeval A-type and I-type granitoids implies a genetically linked magmatic system controlled by variable differentiation. Geochemical characteristics, magma generation depths (~22–34 km), and structural relationships indicate formation in a back-arc extensional setting related to subduction of the Mudanjiang oceanic lithosphere and indirectly to westward subduction of the Palaeo-Pacific plate.