攀枝花二叠纪火山岩发育有玄武岩和粗面岩的基性和碱性两个端元,区域上明显缺失中间过渡类型.玄武岩SiO2含量处于45.65％～49.32％范围内,粗面岩SiO2含量介于64.39％～69.17％之间,构成经典的"双峰式"火山岩特征组合.两者均具有富Na、贫K、轻稀土富集、轻重稀土明显分馏的特征.特征微量元素Nb/Ta、Th/Ta、Th/U比值变化相对较小,玄武岩分别为15.16、2.70和4.13,粗面岩分别为15.40、2.55和4.12,显示两者具有相似的地球化学属性.微量元素特征显示,除了Ti和Y等少数高场强元素不协调以外,玄武岩与粗面岩绝大多数微量元素变化规律相似,且Rb、Ce、Y、Nb、Hf、Ta等元素与洋岛玄武岩(OIB)特征一致,说明它们具有地幔柱构造系统下的岩浆属性,岩浆源于石榴石二辉橄榄岩岩石圈地幔的部分熔融.结合前人资料,攀枝花二叠纪双峰式火山岩的厘定,不仅暗示了岩浆形成于拉张的裂谷构造环境,也为西南地区二叠纪峨眉山大火成岩地幔柱成因提供支撑.%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.
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