Laser-ablation microprobe (LAM)-ICPMS unravels the highly siderophile element geochemistry of the oceanic mantle

The highly siderophile element (HSE) contents of base-metal sulphides have been determined by laser-ablation microprobe (LAM)-ICPMS in abyssal peridotites from the Mid-Atlantic and South West Indian ridges. (Pd/Ir)N (0.007¯505, N: CI-chondrite-normalised), (Pt/Ir)N (0.001¯0.77) and (Rh/Ir)N (0.159¯273) vary significantly between both grains and samples, irrespective of indicators of melt removal, but in line with bulk-rock platinum-group element (PGE) ratios and sulphide modal abundances. Positive deviations of PGE abundance ratios in whole-rock analyses are due to late-precipitated Cu¯Ni-rich magmatic sulphides from incompletely extracted partial melts. These results contradict explanations of the HSE systematics of the oceanic mantle as reflecting global scale processes such as core¯mantle exchange.