Interrogating leaching procedures of meteorites for triple oxygen isotope analyses

Triple oxygen isotope analyses of meteorites are a fundamental tool for classifying meteorites and investigating early solar system processes. However, its utility can be significantly compromised by terrestrial oxygen contamination during weathering processes on Earth's surface. Aiming to restore the original bulk oxygen isotope composition of meteorites through the removal of terrestrial weathering products, leaching procedures with hydrochloric acid (HCl) or ethanolamine thioglycollate (EATG) are often employed, but their effects remain poorly understood. Therefore, here we obtained high-precision triple oxygen isotope data for a comprehensive set of meteorites to systematically evaluate the efficacy and consequences of these leaching methods as a function of meteorite group, weathering grade, petrologic type, and find/fall location and status. Our data for untreated and leached bulk meteorite powders show that leaching can cause shifts of several permil in ¹⁸O/¹⁶O and ¹⁷O/¹⁶O in aqueously altered and pristine chondrites, and lower magnitude shifts in thermally metamorphosed chondrites and achondrites. Though some shifts can be explained by removal of terrestrial weathering products, many suggest the inadvertent removal of indigenous phases. As such, this study highlights the benefits and disadvantages of leaching methods for meteorites, which can be best assessed by analyses of both untreated and HCl/EATG-leached aliquots.