关键词: 猫儿界花岗斑岩, 锆石U-Pb定年, 地球化学特征, 新元古代, 苗儿山—越城岭

Abstract: Based on detailed studies on zircon U-Pb geochronology, whole-rock geochemical and Nd isotope compositions of the Mao’erjie granite porphyry in the northwestern Miao’ershan-Yuechengling area, the emplacement age, genetic type and source of the granite porphyry are discussed. LA-ICP-MS U-Pb dating of the zircons from three granite porphyry samples yielded weighted mean 206Pb/238U ages of 824.3±4.5 Ma, 825.4±4.1 Ma, and 826.8±4.8 Ma, respectively, indicating that the Mao’erjie granite porphyry was emplaced in the Neoproterozoic. It is peraluminous with high silica contents and is enriched in large ion lithophile elements (LILE) such as Cs, Rb, U and K, and high field-strength elements (HFSE) such as Th and Hf, but is relatively depleted in Ba, Sr and Ti. Its chondrite-normalized REE pattern is right-inclined and has obvious Eu negative anomaly (δEu=0.37-0.43). The εNd (t) values of the granite porphyry are from -6.3 to -8.7, and the TDM2 (Nd) values are from 2.00 to 2.20 Ga, indicating that the granite porphyry was formed by partial melting of old crust-derived basement material. Ten inherited zircon grains with U-Pb ages of 852-861 Ma were found in the three dated granite porphyry samples and yield a weighted average age of 856.3±7.4 Ma, implying the existence of ~856 Ma magmatic activity in the Miao’ershan-Yuechengling district. It can be speculated that ~856 Ma magmatic rocks was involved during the formation of the Mao’erjie granite porphyry.

Key words: Mao’erjie granite porphyry, zircon U-Pb dating, geochemical characteristics, Neoproterozoic, Miao’ershan-Yuechengling