The end of the atmospheric xenon Archean’s evolution: a study of the Great Oxygenation Event period

Several geochemical tracers (S, C, O, Xe) underwent irreversible global changes during the Precambrian, and in particular during the Great Oxygenation Event (GOE), between the Archean and Proterozoïc eons [1]. Xenon is of particular interest as it presents a secular isotopic evolution during the Archean that ceased around the time of the GOE. In this regard Xe is somewhat analogous to mass-independent fractionation sulfur (MIF-S) in that it can be used to categorically identify Archean atmospheric components [2]. Xe isotopes in the modern atmosphere are strongly mass-dependent fractionated (MDF-Xe), with a depletion of the light isotopes relative to the heavy ones. There was a continuous Xe isotope evolution from primitive Xe to modern Xe that ceased between 2.6 and 1.8 Ga [2] and this evolution has been attributed to coupled H⁺-Xe⁺ escape to space [3].

The purpose of this project is to document the Xe composition of the paleo-atmosphere trapped in well-dated hydrothermal quartz fluid inclusions with ages covering the Archean-Proterozoic transition to better constraint its link with the GOE.

We have measured an isotopically fractionated Xe composition of 2.0 ± 1.8 ‰ relative to modern atmosphere at 2441 ± 1.6 Ma, in quartz vein from the Seidorechka sedimentary formation (Imandra-Varzuga Greenstone belt, Russia). A slightly younger sample from the Polisarka sedimentary formation (Imandra-Varzuga Greenstone belt, Russia) of 2434 ± 6.6 Ma does not record such fractionation and is indistinguishable from the modern atmospheric composition. A temporal link between the disappearance of the Xe isotopes fractionation and the MIF-S signature at the Archean-Proterozoic transition is clearly established for the Kola Craton. The mass-dependent evolution of Xe isotopes is the witness of a cumulative atmospheric process that may have played an important role in the oxidation of the Earth's surface [3], independently of biogenic O₂ production that started long before the permanent rise of O₂ in the atmosphere [4].

 

[1] Catling & Zahnle, 2020, Sciences Advances 6, eaax1420. [2] Avice et al., 2018, Geochimica et Cosmochimica Acta 232, 82-100 [3] Zahnle et al., 2019, Geochimica et Cosmochimica Acta 244, 56-85. [4] Lyons et al., 2014, Nature 506, 307-315.