Isotopic evolution of planetary crusts by hypervelocity impacts evidenced by Fe in microtektites

Fractionation effects related to evaporation and condensation had a major impact on the current elemental and isotopic composition of the Solar System. Although isotopic fractionation of moderately volatile elements has been observed in tektites due to impact heating, the exact nature of the processes taking place during hypervelocity impacts remains poorly understood. By studying Fe in microtektites, here we show that impact events do not simply lead to melting, melt expulsion and evaporation, but involve a convoluted sequence of processes including condensation, variable degrees of mixing between isotopically distinct reservoirs and ablative evaporation during atmospheric re-entry. Hypervelocity impacts can as such not only generate isotopically heavy, but also isotopically light ejecta, with delta Fe-56/54 spanning over nearly 5 parts per thousand and likely even larger variations for more volatile elements. The mechanisms demonstrated here for terrestrial impact ejecta modify our understanding of the effects of impact processing on the isotopic evolution of planetary crusts. Fe isotopic composition of the distal ejecta of a terrestrial impact crater records both evaporation and condensation, refining the nature of the isotopic fractionation taking place during hypervelocity impacts in the Solar System.

Automated summary

Fractionation effects related to evaporation and condensation have a significant impact on the elemental and isotopic composition of the Solar System. Hypervelocity impacts not only lead to melting and evaporation, but also involve processes such as condensation, mixing between isotopically distinct reservoirs, and ablative evaporation during atmospheric re-entry, generating ejecta with varied isotopic compositions.