Geocheminar fall-2019

Differentiated planetary bodies exhibit small but discernible elevations in heavy/light stable isotope ratios among rock forming elements. Preferential evaporation of light isotopes from melt exposed to space is a possible mechanism. A theoretical framework has been developed for evaluating the isotopic effects of evaporation as a function of size of the body and the nature of any enveloping gas. We are testing this framework in the laboratory by laser heating aerodynamically levitated samples in gases of controlled compositions. Our data bear on the effects of variable saturation on evaporative isotope fractionation, providing tests of the theoretical predictions. Results show the 56Fe/54Fe the vapor/melt isotope fractionation factors defined by the experimental products are closer to unity than evaporation to vacuum and define Fe gas saturation values of ~0.7, corresponding to effective total pressures of 0.1 to 0.2 bar in the boundary layer of the flowing gas. Results like these constrain models for evaporative fractionation under ranges in relevant conditions.