Biogenic Carbon in Magmatic Minerals and Implications for the Preservation and Obliteration of Hadean Isotopic Biosignatures

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The preservation of geologic materials from the early period when Earth became a habitable planet is precarious. Only rare examples of detrital zircon crystals have escaped obliteration since the Hadean eon. These crystals also host a rich inclusion assembly which attests to their formation conditions. The presence of light carbon isotopic compositions of graphite inclusions in Hadean zircon has been interpreted to indicate an early emergence of terrestrial life. We aim to follow up on this discovery by investigating graphite inclusions in minerals from post-Hadean granites by (1) devising criteria which can aid in identifying post entrapment disturbance of inclusions, and (2) constraining how graphite in igneous rocks relates to biogenic carbonaceous materials, and how these materials contribute to magmatic carbon budgets. The proposed research will, for the first time, use correlated micro-analytical imaging and high spatial resolution mass-spectrometry techniques to resolve the origins of graphite in magmatic rocks, especially as inclusions. Insights gained from two S-type granite locations in northeastern North America and Central Europe will improve the interpretation of Hadean graphite inclusions in zircon. The methodologies we plan to develop will be implemented in a collaborative search for additional carbonaceous inclusions from the Hadean by an international research consortium, which currently has succeeded in identifying the largest number of Hadean zircon crystals worldwide.