The fate of Venusian chlorine

Venus and Earth are alike in size and composition and share similarly productive histories of volatile degassing. Yet while chlorine (Cl) is concentrated in Earth’s surface reservoirs, it is nearly absent from the atmosphere of Venus. The fate of Venusian Cl offers insights into the evolution of magmatism and history of volcanic degassing on Venus and similar telluric planets. Here we explore the potential for sodalite (Na ₈ Al ₆ Si ₆ O ₂₄ Cl ₂ ), crystallised from erupted volcanics, to act as a long-term Cl-sink in planetary crust. By estimating alkaline melt production on Venus and the partitioning of Cl between sodalite and Venusian silicate melts, we constrain Cl sequestration into sodalite-stable alkaline volcanics. We find that phonolites containing up to 7 mol% sodalite can be produced through 91–98% fractionation of low-degree partial melts originating from the Venusian upper mantle. Overall, just ~750 m of alkaline volcanic resurfacing has the capacity to sequester an Earth-like Cl budget within sodalite-bearing lithologies.