Determination of mercury isotope compositions in chondritic meteorites

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Mercury (Hg) is more volatile than the other highly volatile metals (e.g. Cd, Tl or Pb), but less volatile than ices like water. So far, only two Hg isotope data for the rather primitive Murchison and Allende chondrites (Lauretta et al., 2001) and very few accurate Hg abundance data are published for chondrites. Within the moderate precision possible at the time, no significant Hg stable isotope fractionation was observed for the two chondrites relative to the terrestrial standard. More recent Hg isotope studies, that focused on natural terrestrial and experimental samples, showed that many processes including volatilization and equilibrium partitioning between vapor and liquid Hg are associated with mass-dependent (MDF) and mass-independent (MIF) isotope fractionations. Furthermore, Cd and Zn stable isotope fractionations are frequently observed in chondritic meteorites. The very high volatility of Hg, the presence of MDF and MIF for Hg in terrestrial and experimental samples and the presence of MDF for other volatile metals all suggest that Hg isotopes provide a promising tracer for processes affecting volatile elements and ices in the early solar system. Thus, Hg isotope cosmochemistry may contribute to the understanding of primary volatile element depletion, secondary redistribution of volatile elements, e.g. on parent bodies, and the source of volatiles in the terrestrial planets. Furthermore, we will apply acid leaching and partial thermal Hg release to at least the Murchison CM2 chondrite to infer whether measurable nucleosynthetic Hg anomalies survived processing in the early solar system.The demand for a comprehensive, highly precise and accurate study of Hg isotopes in chondrites requires the setup of very sophisticated analytical methods. Preliminary work for Hg separation from rock powders using a direct mercury analyzer and first results for Hg isotope analysis by cold vapor MC-ICP-MS are reported within this proposal.