Iridium and other trace-metal enrichments from Hawaiian volcanoes

Particles and gases were sampled at Mauna Loa volcano during and after its eruption in March and April 1984, and at Kilauea volcano in 1983, 1984, and 1985. The samples were analyzed by INAA for more than 40 elements. Iridium was found at Kilauea and Mauna Loa in samples collected during as well as after fountaining activity. Osmium was only found in the Mauna Loa samples. Enrichment factors for Ir in the volcanic fumes range from 10 (super 4) to 10 (super 5) relative to the Hawaiian rock standard BHV01. Iridium fluxes at Mauna Loa and Kilauea ranged from 80 to 3,000 and 10 to 320 g/d, respectively. The amount of Ir released from the magma into the fumes was 1 to 12 percent. Calculations assuming Deccan volcanism as the source for Ir at the K/T boundary layer show that the concentration of Ir left in the basalts may be too low to account for all of the K/T Ir. It would require a very high fraction (> 80 percent) of the Ir to be purged from the basalt to account for all of it, which cannot be supported by the Hawaiian data. The implications of Ir from Hawaiian volcanoes for the K/T Ir anomaly are not conclusive but seem to weaken the volcanic explanation and strengthen the impact position. Since Ir has been found only in fumes from Hawaiian volcanoes, further investigations at other volcanoes, such as Piton de la Fournaise on Reunion Island, are needed to evaluate the importance of volcanoes as sources for the Ir found at the K/T boundary.