Geochronology,Geochemical Characteristics and Tectonic Implications of Early Cretaceous Zhouguan High-Mg Diorite Rock Mass in the Jiaodong Peninsula
The Jiaodong region represents the most significant gold ore cluster in China,with the temporal and spatial distribution of gold deposits being closely associated with Late Mesozoic granites.The emplacement timing of the Early Cretaceous Weideshan granite aligns with the epoch of large-scale gold mineralization,marking it as a crucial geological body for ore formation.The Zhouguan rock mass,a constituent of the Weideshan granite,exhibits a strong spatial and temporal correlation with gold mineralization.Based on comprehensive studies encompassing systematic petrology,zircon U-Pb isotope dating,and whole rock major and trace element geochemistry,the Zhouguan rock mass was emplaced during the late Early Cretaceous period,specifically between(119.4±1.1)Ma and(118±1)Ma.This emplacement coincided temporally with gold mineralization events.The rock mass is characterized by low silicon(Si),high magnesium(Mg),and rich sodium(Na)content,along with relatively elevated concentrations of chromium(Cr),nickel(Ni),cobalt(Co),and scandium(Sc),as well as a high Sr/Y ratio and significantly depleted zirconium(Zr)content.These rocks are classified within the high-potassium calc-alkaline series and are identified as high-Mg diorite.The magma is derived from the partial melting of the enriched lithospheric mantle and incorporates some crustal materials.The emplacement of magma in the Zhouguan rock mass and Weideshan granite induced significant uplift of the shallow crust,leading to the formation of a series of extensional structures.These structures facilitated the migration of ore-forming fluids and created favorable conditions for fluid enrichment and orebody formation.