Behavior of Volatile Metals in Basaltic Systems: Insights from Kilauea Iki and Loihi Volcanoes, Hawaii

The magmatic behavior of trace metals is an important tool in understanding a number of geologic processes including core-mantle interactions in plumes, volcanic degassing, ore deposit formation, and volcanic-environmental interactions. The behaviors of more volatile metals, however, are poorly understood compared to that of highly volatile elements (H, C, Cl, S) and more refractory lithophile trace elements. In particular it remains unclear how and when high temperature magmatic processes might fractionate these elements. One limitation is the lack of techniques capable of measuring concentrations of volatile metals in small sample volumes. We present results here for LA-ICP-MS analysis of trace elements with a range of geochemical affinities (lithophile, chalcophile, and siderophile) as well as volatility (Tl, Pb, In, Sn, Zn, Bi, Rb, B, Sb, Ag, Cu, Cr, Co, V, Ba, Sr, Ce, Mo, Sc, U, Y, Zr, and W) in well-characterized samples from Loihi and Kilauea Volcanoes, Hawaii. Accurate microanalysis of volatile trace metals is complicated by micro-heterogeneity and/or generally low concentrations in many commonly used standard glasses. Here we report suitability of USGS GSE-1G glass as a calibration standard for LA-ICP-MS. Using a 193 nm ArF Excimer laser we are able to achieve accuracies <10% for most trace metals when present in concentrations >10 ppm. Moreover, accuracies were significantly improved over those obtained using NIST-610 as a calibration standard. Analyses were made of glass, olivine, and olivine-hosted melt inclusions from the 1959 eruption of Kilauea Iki. Electron microprobe analysis shows strong olivine-control on compositional trends at Kilauea Iki. Melt inclusions show more complex variability including evidence for diffusive Fe-loss, considerable S degassing, and variable melt Na, K, Si, Ca, and P. Incompatible and refractory elements (e.g., Ce-Ba) are tightly correlated in both glass and melt inclusions. Trace metals, including those with high volatility, also generally appear to behave incompatibly and appear unaffected by shallow degassing. Analyses on a range of submarine glasses and olivine-hosted melt inclusions from the 1996 eruption of Loihi Seamount, where studies of submarine particulates suggest high temperature transfer of some volatile metals into submarine hydrothermal systems, show no evidence for degassing of sulfur. Analysis of melt inclusion and glass trace metal concentrations provides a means to investigate the processes of high temperature volatile metal loss prior to eruption.