Mars exploration is focused on seeking evidence of habitable environments and microbial life. Terrestrial glassy basalts may be the closest Mars‐surface weathering analog and observations increasingly indicate their potential to preserve biogeochemical records. The textures, major and trace element geochemistry, and N concentrations and isotopic compositions of subaerial, subglacial and continental lacustrine hyaloclastites from Antarctica, Iceland, and Oregon, respectively, were studied using micro‐imaging and chemical methods, including gas‐source mass spectrometry. Alteration by meteoric‐sourced waters occurred in circum‐neutral, increasingly alkaline low‐temperature conditions of ∼60°C–100°C (Iceland) and ∼60°C–170°C (Antarctica). Incompatible large ion lithophile element (LILE) enrichments compared to mid‐ocean ridge basalt (MORB) are consistent with more advanced alteration in Antarctic breccias consisting of heulandite‐clinoptilolite, calcite, erionite, quartz, and fluorapophyllite. Granular and tubular alteration textures and radial apatite represent possible microbial traces. Most samples contain more N than fresh MORB or ocean island basalt reflecting enrichment beyond concentrations attributable to igneous processes. Antarctic samples contain 52–1,143 ppm N and have δ15Νairvalues of −20.8‰ to −7.1‰. Iceland‐Oregon basalts contain 1.6–172 ppm N with δ15Ν of −6.7‰ to +7.3‰. Correlations between alteration extents, N concentrations, and concentrations of K2O, other LILEs, and Li and B, reflect the siting of secondary N likely as NH4+replacing K+and potentially as N2in phyllosilicates and zeolites. Although much of the N enrichment and isotope fractionation presented here is not definitively biogenic, given several unknown factors, we suggest that a combination of textures, major and trace element alteration and N and other isotope geochemical compositions could constitute a compelling biosignature in samples from Mars' surface/near‐surface.
Craters of the Moon National Monument and Preserve (CotM) is a strong terrestrial analog for lava tube formations on Mars. The commonality of its basalt composition to Martian lava tubes makes it especially useful for probing how interactions between water, rock, and life have developed over time, and what traces of these microbial communities may be detectable by current flight‐capable instrumentation. Our investigations found that secondary mineral deposits within these caves contain a range of underlying compositions that support diverse and active microbial communities. Examining the taxonomy, activity, and metabolic potential of these communities revealed largely heterotrophic life strategies supported by contributions from chemolithoautotrophs that facilitate key elemental cycles. Finally, traces of these microbial communities were detectable by flight‐capable pyrolysis and wet chemistry gas chromatography‐mass spectrometry methods comparable to those employed by the Sample Analysis at Mars (SAM) instrument aboard the Curiosity rover and the Mars Organic Molecule Analyzer (MOMA) on the upcoming Rosalind Franklin rover. Using a suite of methods for chemical derivatization of organic compounds is beneficial for resolving the greatest variety of biosignatures. Tetramethylammonium hydroxide (TMAH), for example, allowed for optimal resolution of long chain fatty acids. Taken together, these results have implications for the direction of mass spectrometry as a tool for biosignature detection on Mars, as well as informing the selection of sampling sites that could potentially host biosignatures.more » « less
- NSF-PAR ID:
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Planets
- Medium: X
- Sponsoring Org:
- National Science Foundation
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