EA4.

Results for the ¹⁷O/¹⁶O and ¹⁸O/¹⁶O measurements for 5 separate analyses of a ¹⁰⁴Ru enriched spike solution. These isotope ratios were obtained by measuring ¹⁰⁴Ru¹⁶O₂¹⁷O and ¹⁰⁴Ru¹⁶O₂¹⁸O. These data have been corrected for oxide interferences using an assumed oxygen isotope composition [32]. The ¹⁷O/¹⁶O vs. ¹⁸O/¹⁶O slopes for each measurement varies from run to run, and moreover, are not in agreement with the slope of the terrestrial fractionation line (0.095). No interferences were identified on either ¹⁰⁴Ru¹⁶O₂¹⁷O or ¹⁰⁴Ru¹⁶O₂¹⁸O. Thus, the change in slope from run to run and the offset from the terrestrial fractionation line likely indicates a non-mass-dependent fractionation of ¹⁷O/¹⁶O relative to ¹⁸O/¹⁶O, as discussed in text.