Xenocrystic zircons challenge an intraoceanic arc origin of the Eoarchean Isua supracrustal belt, SW Greenland

The onset of plate tectonics on Earth remains controversial, with the ~3.8–3.7 Ga Isua supracrustal belt in SW Greenland often cited as evidence for Eoarchean subduction and intraoceanic arc magmatism. This model mainly relies on the reported absence of relatively old xenocrystic zircons in Isua rocks. We present new zircon U-Pb geochronology revealing ~3.97–3.75 Ga ages from supposedly ≤3.72 Ga Isua lithologies. These ages are associated with different zircon morphologies and textures, including inherited cores or individual grains with sector zoning and magmatic oscillatory zoning. Trace element signatures (enriched Pb, Th, U, and LREE) of relevant rocks indicate assimilation of more evolved crust. These findings suggest that Isua supracrustal rocks were emplaced onto an older, evolved, potentially polymetamorphosed crustal foundation, effectively ruling out juvenile intraoceanic arc origins.