关键词: 岩石地球化学, 成岩年龄, 绿泥石温度计, 新盟山, 英安玢岩

Abstract: Based on detailed geological investigation, this paper investigated the whole-rock element geochemistry, zircon U-Pb dating and chlorite mineral chemistry of Xinmegnshan dacite porphyry in Changning City, Hunan Province. With reference to previous research, we discussed petrochemical characteristics, magmatic age, magma sources, as well as relationship with mineralization in Shuikoushan orefield. LA-ICP-MS zircon U-Pb isotopic analyses showed that Xinmegnshan dacite porphyry erupted during the Late Jurassic, with a weighted mean 206Pb/238U age of 152.9±1.2 Ma (MSWD=0.27, 2σ, N=17). Xinmegnshan dacite porphyry was rich in Light Rare Earth Elements (LREEs) and Rb, Th, U, La, Pb, Nd, Zr, Hf, while depleted in Heavy Rare Earth Elements (HREEs) and Nb, Ta, Ba, Sr, P, showing crust-derived affinities, and might be contaminated by mantle material. Chlorite was mainly clinochlore with alteration temperature of 280℃ , which was similar to that of the Cu-Mo mineralization in this orefield. During Late Jurassic, the tectonic extension and thinning of the continental lithosphere in the study area induced partial melting of the crust, and produced granitic magma, which might mix with a small amount of mantle material. The magma then invaded along deep faults and formed Xinmegnshan dacite porphyry. At the late stage of magma crystallization, as Cu-Mo precipitation, the hydrothermal fluid replaced the dacite porphyry continuously and resulted in widespread chloritization.

Key words: petrochemistry, diagenetic age, chlorite thermometer, Xinmegnshan, dacite porphyry