1. Survey of Regional Geological & Mineral Resources of Jilin Province, Changchun 130022, China;
2. Geological Survey of Jilin Province, Changchun 130102, China

Aegirine trachytes were newly recognized in northern Dunhua-Mishan fault belt, between the Bahekou and Huangnihe towns, Jilin Province. Aegirine trachytes are characterized by enrichment in alkaline minerals represented by aegirine, conformably overlying the alkaline basalt of Chuanfishan Period. Whole-rock K-Ar isotopic dating reveals ages of 25.64±0.53 Ma, 27.36±0.45 Ma, 28.45±0.56 Ma, 28.55±0.43 Ma, 28.63±0.45 Ma and 28.65±0.61 Ma, which belong to Oligocene. The geochemical analysis shows average SiO₂ content of 59.05% for the aegirine trachytes, with high alkaline and enriched K₂O contents. They are depleted in LILEs(Sr, Ba, V, Cr)and enriched in HFSEs(Nb, Ta, Hf, Zr)and LREE, with high ∑REE abundances, right-inclined REE distribution patterns and obvious negative Eu anomalies.Integrating all the results, it is indicated that the aegirine trachytes were derived from strongly fractioned crystallization of alkaline basaltic magma, under an intensive extensional setting during Oligocene and the mantle-derived magma evolved from alkaline basalt to aegirine trachyte.