College of Earth Sciences & Technology, Southwest Petroleum University, Chengdu 610500, China

Panzhihua Permian volcanic rocks consist of basal and alkaline ends of basalt and trachyte, and the intermediate transitional types are absent. SiO₂ content in the basalt ranges from 45.65% to 49.32%, while SiO₂ content in the trachyte ranges from 64.39% to 69.17%, which constitute the classic “bimodal” volcanic assemblages. Both basalt and trachyte are enriched in Na and light rare earth elements, but depleted in K, with obvious light and heavy rare earth fractionation. In addition, the variation in typical trace elements ratios of Nb/Ta, Th/Ta, and Th/U is relatively small, the ratios in the basalt are 15.16, 2.70 and 4.13, and that in the trachyte are 15.40, 2.55 and 4.12, respectively, indicating that they have similar geochemical properties. Trace element characteristics show that, except minor high field elements like Ti and Y that are not consistent, changes of most trace elements in the basalt and trachyte are similar, and characteristics of Rb, Ce, Y, Nb, Hf and Ta is consistent with that of Ocean Island basalt (OIB), which indicate that the Panzhihua volcanic rocks are with magma property from mantle column structure system, and magma stemmed from partial melting of garnet lherzolite lithosphere mantle. Combined with the previous studies, the determination of the Permian bimodal volcanic rocks in Panzhihua not only implies that the magma was formed in the extensional rift tectonic environment, but also supports that the origin of the Permian Emeishan igneous province in southwest China is related to mantle plume.