Insights into the formation of Fe- and Mg-rich aqueous solutions on early Mars provided by the ALH 84001 carbonates
Abstract
The chemical and isotopic pattern of the zoned carbonate globules in the ALH 84001 meteorite reveals a unique aqueous environment on early Mars. If the evolution of the fluid composition was dictated primarily by carbonate precipitation, the zoning pattern of the carbonates can constrain the fluid to have had an Mg/Ca mole ratio > ~5.3 and a Fe/Ca mole ratio > ~1 prior to the formation of the carbonates. Chemical equilibrium modeling of water–rock interactions indicates that low temperatures and low pH favor the formation of an aqueous solution with elevated Mg and Fe concentrations. The modeling shows that a sufficiently Fe- and Mg-rich fluid could have formed through low-temperature (< 100 °C) subsurface aqueous alteration of an ALH 84001-type rock at pH 5–7. This range of pH corresponds to an elevated CO₂ fugacity (~ 0.1–1 bar). Formation of ALH 84001 carbonates could have been driven by degassing of CO₂ and corresponding pH increase in near-surface environments during an upwelling of subsurface CO₂-rich solutions. This scenario is consistent with the unaltered nature of the ALH 84001 rock and with chemical and isotopic composition of its carbonates.
Additional Information
Critical reviews and recommendations made by Nick Tosca and an anonymous reviewer improved this manuscript and are greatly appreciated. This material is based upon the work supported by grants from the National Aeronautics and Space Administration issued through the Mars Fundamental Research Program to Dr. Niles and Dr. Zolotov. We thank Mikhail Mironenko for sharing the GEOCHEQ code which was used for these calculations.Additional details
- Eprint ID
- 119719
- Resolver ID
- CaltechAUTHORS:20230307-649991000.14
- NASA
- Created
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2023-03-12Created from EPrint's datestamp field
- Updated
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2023-03-12Created from EPrint's last_modified field