Petrogenesis of the Early Cretaceous Tietonggou Diorite and Its Geological Implications

Abstract

The Tietonggou pluton is mainly composed of gabbroic diorite and diorite. The petrology, zircon U-Pb age, and geochemistry of the Tietonggou diorite have been studied to determine its petrogenesis and metallogenic significance. The diorite samples have 56–58 wt% SiO2 and 11–14 wt% Al2O3 and are peraluminous and sodic (Na2O/K2O = 1.29–2.07). All the samples are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs; e.g., Rb, Ba, and Sr) but depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs; e.g., Zr, Nb, and Ta), suggesting subduction-related affinities. The rocks have narrow ranges of (206Pb/204Pb)t (18.5–19.0), (207Pb/204Pb)t (15.71–15.75), and (208Pb/204Pb)t (38.4–39.0) ratios, respectively. Zircons from the Tietonggou diorite yielded a weighted average U-Pb age of 132.86 ± 0.92 Ma (MSWD = 0.48), whilst those from the nearby Laowa diorite yielded 129.72 ± 0.61 Ma (MSWD = 1.05). This suggests that the rocks represent Early Cretaceous plutons, coeval with the peak lithospheric thinning in eastern North China Craton (NCC). The magma likely originated from partial melting of the enriched lithospheric mantle and was contaminated by ancient lower NCC crustal materials. Our study clarifies the tectonic background of the Tietonggou pluton and provides support for the study of the genesis of Fe–skarn deposits in western Shandong.