Petrogenesis and tectonic evolution characteristics of Late Triassic Wufengshan pluton in the Xiuyan area, Liaodong Peninsula: Petrogeochemistry, zircon U−Pb age and Hf isotopic evidences

Objective The Xiuyan area in the Liaodong Peninsula is situated in the northeastern segment of the Jiao-Liao-Ji Belt, which is part of the eastern margin of the North China Craton. This study aims to identify the rock types, characterize their petrogeochemical features, determine the diagenetic age, and elucidate the regional geological structural background related to the formation of the Wufengshan pluton in the study area.

Methods We conducted petrological analysis, zircon LA-ICP-MS U-Pb dating, and whole-rock and zircon Hf isotope geochemical studies on the Wufengshan pluton. Comparative analyses were also carried out with the previously documented Late Triassic Shuanglinggou and Huanghuagou plutons in the same region.

Results The Wufengshan pluton is composed of porphyritic amphibole biotite monzogranite, with a LA-ICP-MS U-Pb age of 228.0 ± 1.26 Ma. It is characterized by high SiO₂ and alkali contents, a K₂O/Na₂O ratio close to 1 (ranging from 0.97 to 1.00, averaging 0.99), and an A/CNK value less than 1.1. The rock shows significant fractionation between light and heavy rare earth elements (LREE and HREE), with weak to moderate negative Eu anomalies. Overall, it belongs to the aluminous-high potassium calc-alkaline series of I-type granite. Geochemically, it is enriched in large ion lithophile elements (LILE) and LREE, while depleted in high field strength elements (HFSE), indicating a crustal source. Additionally, the pluton exhibits high Sr, low Y and Yb contents, and low Nb and Ta concentrations, showing geochemical affinities typical of North China-type adakitic rocks. These features suggest that the magma may have originated from partial melting of thickened lower crust induced by mantle-derived magmas. A higher Nb/Ta ratio further indicates the involvement of mantle-derived materials, suggesting some degree of magma mixing. Hf isotope data show εHf(t) values ranging from –13.69 to –26.22, with TDM1 values between 1411.77 Ma and 1893.57 Ma, and TDM2 values between 2130.38 Ma and 2913.22 Ma—both older than the pluton’s formation age. These results imply that the primary magma of the Wufengshan pluton was mainly derived from the melting of reworked ancient crustal materials. These findings are consistent with those of the Late Triassic Shuanglinggou and Huanghuagou plutons, suggesting a similar tectonic setting.

Conclusions The Wufengshan pluton represents a North China-type adakitic granite formed during a collisional tectonic event. The magma likely originated from partial melting of the thickened lower crust and may have been mixed with mantle-derived mafic magma. It is inferred that magma generation was triggered by the retreating subduction of the North China Craton beneath the Yangtze Block during deep continental collision, which may have contributed to the subsequent fragmentation of the lithospheric plates.