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.