黔西地区峨眉山玄武岩(东岩区)铂族元素地球化学特征

利用同位素稀释 等离子体质谱(ICP MS)方法测定了黔西水城、威宁等地的东岩区峨眉山玄武岩的铂族元素含量。结果表明,相对于原始地幔,东岩区峨眉山玄武岩的铂族元素发生了较强的分异作用,Os、Ir、Ru、Rh亏损,Pd、Pt则发生富集,相对配分模式为Pd Pt富集型;经球粒陨石及原始地幔标准化的铂族元素配分模式为向左陡倾斜型,具有陡的正斜率,Pd/Ir显著高于原始地幔、球粒陨石、原始上地幔等,而与地幔低度熔融形成的N MORB、大陆拉斑玄武岩等接近,表明峨眉山玄武岩的物质来源为上地幔熔融程度偏低的玄武岩浆。

GEOCHEMICAL CHARACTERISTICS OF THE PLATINUM-GROUP ELEMENTS IN EMEISHAN BASALTS, WESTERN GUIZHOU

The contents of the platinum group elements (PGE) in the Emeishan basalts in western Guizhou were determined using isotope dilution- ICP-MS. Obvious PGE differentiation of the Emeishan basalts in the eastern rock province is different from that of the primitive mantle. Os, Ir, Ru and Rh were depleted and Pd and Pt were enriched. The PGE distribution patterns are of the "Pd-Pt"-enrichment type. The chondrite- and mantle- normalized patterns are of the left, sharply inclined type with a big positive slope. The values of Pd/Ir are larger than those of the primitive mantle, chondrites and upper primitive mantle, but are close to those of N-MORB and continental tholeiites, which were formed by slow mantle melting, suggesting that the Emeishan basalts stemmed from basalt magma formed by slow melting of the upper mantle.