MICRO RAMAN SPECTROSCOPY OF FLUID INCLUSIONS IN CHERTS: EXTENDING LIFE DETECTION STRATEGIES TO GEOCHRONOLOGY

Ancient terrestrial hydrothermal deposits such as cherts have yielded invaluable information regarding early life on Earth. Similar, although microcrystalline silica-rich lithologies have been identified in several regions on Mars, and these deposits could likely contain signatures useful in constraining paleo-environmental conditions as well as in the detection of a primitive martian biosphere. Carbon-rich phases that reflect the original conditions and source of the vein-forming fluids can become trapped within fluid inclusions in quartz grains upon crystallization retaining their original isotopic signature over time. Heavy noble gases (Ar, Kr, and Xe) and their isotopic imprints can also accompany these carbonaceous phases. In this study we improve upon previous work utilizing Raman microscopy as a tool to measure CO₂ densities and isotopic composition by characterizing the composition of fluid inclusions in thin sections of cherts from the 1.88 Ga Gunflint Formation. Areas of megaquartz contained fluid inclusions of 1-2 mm in size with mixtures of CO₂, CH₄, and CO₃. Estimations of CO2 density and therefore depth of entrainment are consistent with metamorphic grades of the host rock. The goal is to correlate the Raman measurements of carbon-rich fluids with heavy noble gas isotope measurements using laser desorption mass spectrometry. Establishing the provenance of siliceous deposits using these stable species will help constrain the true origins of otherwise ambiguous biosignatures within the same deposits. By utilizing stable geochemical signatures, we can pinpoint the exact origins of host materials and correlate our findings with detailed characterizations of the more bio-relevant components. Our research will also develop the tools to establish a geochronometer that can be applied to life detection.