LA-ICP-MS zircon U-Pb dating, geochemical features and geological implications of Xiaomeihe rock mass in Xiaoshan Mountain, western Henan Province

The Xiaomeihe rock mass lies in northern Xiaoshan Mountain. In this study, sample XMH01 of biotite quartz monzonite was analysed by LA-ICP-MS. 30 zircon spots were analyzed, and results of 23 spots are adjacent to 207Pb/235U-206Pb/238U in the concordia diagram, with U-Pb ages clustered in 2644~2695Ma, 2490~2546Ma, 2367Ma, 1844~1859Ma, 143.6Ma and 129.6~133.8Ma. The weighted average 206Pb/238U age of 9 zircon spots ranging from 129.6Ma to 133.8Ma is 131.5±0.9Ma, which is regarded as the formation age of the Xiaomeihe rock mass. The ages of total 23 U-Pb zircon spots of the Xiaomeihe rock mass formed a zircon age spectrum from late Archean to early Cretaceous, which recorded the corresponding regional magmatic theramal events. The Xiaomeihe rock mass is characterized by higher alkali and lower MgO. Compositional spots of the Xiaomeihe rock mass fall into the high-K calc-alkaline series. In chondrite-normalized REE patterns, the characteristics of LREE enrichment and HREE depletion without obvious Eu anomaly have been shown. The (La/Yb)N ratios are from 18.36 to 24.78. In the spider diagram, negative anomalies of Nb, Ta, P and Ti are displayed. Samples of the Xiaomeihe rock mass have higher Sr and lower Yb and Y, suggesting adakitic granite. The Xiaomeihe rock mass originated from partial melting of the thickened lower crust, and its residual phases of partial melting source included garnet and rutile. The Xiaomeihe rock mass was the product of lithosphere delamination in the early Cretaceous, and magma (fluid) mixing triggered by it formed the zircon U-Pb age spectrum. The formation of the Xiaomeihe rock mass was close to the Early Cretaceous extensive and intense mineralization and diagenetic epoch of Xiaoqinling-Xiaoshan Mountain-Xiong'er Mountain area, during which deep fluids were rapidly discharged in the process of lithosphere delamination. It is concluded that the Xiaomeihe rock mass possesses endogenetic metallogenic potential and hence should be considered as one of the prospecting targets in northern Xiaoshan Mountain area.