A Neoarchean (ca. 2500 Ma) age for jaspilite-carbonate BIF hosting purported micro-fossils from the Eoarchean (≥3750 Ma) Nuvvuagittuq supracrustal belt (Québec, Canada)

In the exploration of the origin and evolution of early life on Earth, age determinations of fossil occurrences are of critical importance. Purported microbial fossils preserved in chert and jasper are commonly assigned indirect dates due to a lack of suitable minerals for geochronology in the fossil-bearing horizons. Such indirect dating methods commonly result in age estimates that predate the hosted putative fossil structures, especially when considering possible formation of these structures in post-depositional hydrothermal/metamorphic events. Herein, we report a Neoarchean (ca. 2.5 Ga) U-Pb ID-TIMS zircon and apatite age for jaspilite and carbonate-bearing iron formation that hosts putative ferruginous “microbial fossil structures” in the Eoarchean Nuvvuagittuq supracrustal belt (NSB) in northern Québec (Canada). In situ oxygen isotope and REE compositions suggest apatite and calcite separated from jaspilite are hydrothermal in origin. Collectively, our results suggest that some of these ferruginous “microbial fossil structures” could be primary biogenic structures produced in an Eoarchean hydrothermal environment that survived subsequent late Archean metamorphism and deformation. In contrast, some are possibly abiogenic structures formed via Liesegang-type processes during late Archean hydrothermal activity. A broader assessment of the ages of putative biostructures in Eoarchean and Paleoarchean rocks, wherein incorrect age assignment remains a persistent problem, is therefore warranted.