Lead (Pb) fluxes and Pb isotopic compositions from Masaya Volcano, Nicaragua

摘要

We report Pb concentrations and isotopic compositions measured in plume aerosol and Pele's hair (lava) samples collected from Masaya volcano, Nicaragua, to provide the first data pertaining to Pb emissions from the Central American volcanic arc. Lead isotopic compositions, determined by Thermal Ionisation Mass Spectrometry, in the Pele's hair samples were found to be ~(206)Pb/~(207)Pb ～ 1.196, ~(208)Pb/~(207)Pb ～ 2.46 and ~(206)Pb/~(204)Pb ～ 18.6. Mean Pb fluxes from Masaya were calculated to be 1.0 ton Pb yr~(-1) with a mean plume Pb/S_((gas)) ratio of 1.3 x 10~(-5). Also, it was found that the majority of Pb emitted was present in the fine aerosol (<2.5 μm diameter) fraction but that the percentage of Pb in the fine aerosol fraction decreased from 96% in the dry daytime plume to 61% in the condensed night-time plume. The contribution from the filter blank was usually a substantial fraction of the total amount of Pb measured, requiring the data to be corrected for blank contributions using Pb isotopic systematics.