Investigation of thallium fluxes from subaerial volcanism-Implications for the present and past mass balance of thallium in the oceans
A suite of 34 volcanic gas condensates and particulates from Kilauea (Hawaii), Mt. Etna and Vulcano (Italy), Mt. Merapi (Indonesia), White Island and Mt. Nguaruhoe (New Zealand) were analysed for both Tl isotope compositions and Tl/Pb ratios. When considered together with published Tl–Pb abundance data, the measurements provide globally representative best estimates of Tl/Pb = 0.46 ± 0.25 and ε 205 Tl = −1.7 ± 2.0 for the emissions of subaerial volcanism to the atmosphere and oceans (ε 205 Tl is the deviation of the 205 Tl/ 203 Tl isotope ratio from NIST SRM 997 isotope standard in parts per 10,000). Compared to igneous rocks of the crust and mantle, volcanic gases were found to have (i) Tl/Pb ratios that are typically about an order of magnitude higher, and (ii) significantly more variable Tl isotope compositions but a mean ε 205 Tl value that is indistinguishable from estimates for the Earth’s mantle and continental crust. The first observation can be explained by the more volatile nature of Tl compared to Pb during the production of volcanic gases, whilst the second reflects the contrasting and approximately balanced isotope fractionation effects that are generated by partial evaporation of Tl during magma degassing and partial Tl condensation as a result of the cooling and differentiation of volcanic gases.