Zircon trace element evidence for early hydrothermal activity on Mars

Abstract

Finding direct evidence for hydrous fluids on early Mars is of interest for understanding the origin of water on rocky planets, surface processes, and conditions essential for habitability, but it is challenging to obtain from martian meteorites. Micro- to nanoscale microscopy of a unique impact-shocked zircon from the regolith breccia meteorite NWA7034 reveals textural and chemical indicators of hydrothermal conditions on Mars during crystallization 4.45 billion years ago. Element distribution maps show sharp alternating zoning defined by marked enrichments of non-formula elements, such as Fe, Al, and Na, and ubiquitous nanoscale magnetite inclusions. The zoning and inclusions are similar to those reported in terrestrial zircon crystallizing in the presence of aqueous fluid and are here interpreted as primary features recording zircon growth from exsolved hydrous fluids at ~4.45 billion years. The unique record of crustal processes preserved in this grain survived early impact bombardment and provides previously unidentified petrological evidence for a wet pre-Noachian martian crust.