Petrogenesis of the Shangzhuang pluton in northwestern Jiaodong: Evidence from petrography, geochemistry, geochronology, and Sr-Nd isotopic compositions

The extensive gold mineralization in the Northwest Jiaodong metallogenic concentration area is genetically related with Mesozoic magmatism, particularly with the Early Cretaceous magmatic activity. This study presents an integrated analysis of the Early Cretaceous Shangzhuang pluton, involving petrography, whole-rock geochemistry, zircon U-Pb dating by LA-MC-ICP-MS, and Sr-Nd isotopic investigations. Results show that the rare earth element (REE) patterns of Shangzhuang pluton are similar to those of adakitic rocks, indicating its typical adakitic affinity. Sr-Nd isotopic analyses yield ⁸⁷Sr/⁸⁶Sr value of 0.711932, ¹⁴³Nd/¹⁴⁴Nd of 0.511654, initial (⁸⁷Sr/⁸⁶Sr)i of 0.511577, εNd(t) of -13.57, and a two-stage depleted mantle model age(T_DM2) of 2 960 Ma. Zircon U-Pb dating constrains the emplacement age of the pluton to 128.7±0.29 Ma. Based on these data, it is proposed that during the early Early Cretaceous, the subduction and followed retracement of Pacific Plate induced upwelling of mantle-derived magmas, which provided a sustained heat source, triggering dehydration and partial melting of mafic lower crustal rocks to generate acidic-intermediate magmas. These magmas then mixed with contemporaneous acidic melts produced by partial melting of the Precambrian basement under similar thermal conditions. The hybrid magma then ascended along extensional strike-slip faults and underwent assimilation and contamination by upper crustal Linglong-type granites during its ascent. Ultimately, it was emplaced at favorable structural settings to form Shangzhuang pluton.