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 δ^56/54Fe spanning over nearly 5‰ 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.

与蒸发和冷凝相关的分馏效应对太阳系当前的元素和同位素组成产生了重大影响。尽管由于撞击加热而在陨石中观察到中等挥发性元素的同位素分馏，但对超高速撞击过程中发生的过程的确切性质仍知之甚少。通过研究微陨石中的 Fe，我们在这里表明，撞击事件不仅会导致熔化、熔体排出和蒸发，还涉及一系列复杂的过程，包括冷凝、同位素不同储层之间不同程度的混合以及大气再入过程中的烧蚀蒸发. 超高速撞击不仅可以产生同位素重的喷射物，还可以产生同位素轻的喷射物，δ ^56/54Fe 跨越近 5‰，对于更易挥发的元素可能会有更大的变化。这里展示的地球撞击喷出物的机制改变了我们对撞击处理对行星地壳同位素演化影响的理解。