¹Xi Deng, ¹Jinting Kang, ²Pei-Yi Li, ²Yun Jiang, ¹Haolan Tang, ³Yang Xiao, ^1,4Fang Huang
Geochimica et Cosmochimica Acta (in Press) Link to Article [10.1016/j.gca.2026.07.022]
¹State Key Laboratory of Lithospheric and Environmental Coevolution, University of Science and Technology of China, Hefei 230026, China
²Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China
³Sichuan Chuangyuan Weipu Analytical Technology Co., Ltd, Chengdu 610300, China
⁴Deep Space Exploration Laboratory, Hefei 230026, China
Copyright Elsevier

Rubidium (Rb) is a moderately volatile element (MVE), and its isotopic system has been widely applied to constrain evaporation and condensation processes during solar nebular evolution and planetary accretion. Tektites, natural glasses formed by the rapid melting and quenching of terrestrial crustal materials during hypervelocity impacts of extraterrestrial bodies, serve as critical geological archives for quantifying impact-driven volatile loss, particularly for MVE. Here, we report high-precision Rb isotopic data for tektites from the Australasian, North American, Central European, and Ivory Coast strewn fields, obtained via both micro-drilling (in-situ) and bulk dissolution analyses. In-situ edge–center–edge profile analyses of three australasites reveal negligible Rb concentration variations (<10%) and remarkable isotopic homogeneity, with δ87Rb ranging from –0.16 ± 0.01‰ to –0.09 ± 0.03‰ (2SD). The absence of resolvable elemental or isotopic zoning across these profiles rules out diffusion-limited evaporation as the dominant control on Rb behavior during tektite formation. Bulk δ87Rb for all analyzed tektites range from –0.22 ± 0.05‰ to –0.12 ± 0.03‰, yielding a weighted mean of –0.16 ± 0.06‰ (2SD, n = 14). This uniformity indicates no resolvable Rb isotopic fractionation and is consistent with the composition of the upper continental crust (δ87Rb = –0.14 ± 0.01‰). To further evaluate the volatility behavior of MVE under Earth-surface conditions, we perform thermodynamic modeling at ambient atmospheric pressure and oxidizing conditions. The model predicts a volatility sequence of Zn ≫ Rb ≥ K, consistent with the well-documented large Zn isotopic fractionations in tektites and the absence of measurable isotopic shifts in Rb and K. Collectively, these results may imply that Rb isotope fractionation is effectively suppressed during impact-induced evaporation under the oxidized, near-surface conditions of Earth.