Sanukitoid stable isotopes reveal complex crust-mantle dynamics in the early Earth

The Archean to Paleoproterozoic Earth underwent significant changes in surface, crust and mantle systems, yet interactions between these reservoirs remain poorly constrained. Sanukitoids are generated by mantle–crust interaction, and thus provide a record of early Earth recycling processes. Here we combine Barium (Ba) and Magnesium (Mg) stable isotopes with radiogenic isotopes and elemental data from 3.4-2.1 Ga sanukitoids to trace crust-mantle interaction across this critical interval. Archean sanukitoids display highly variable Ba and Mg isotopic compositions, suggesting contributions from altered ocean crust, hydrothermal barite and/or sediment. In contrast, Paleoproterozoic sanukitoids show uniformly lighter isotopic signatures, closely resembling Phanerozoic arc magmas influenced by pelagic sediments. Importantly, Ba isotope fractionation before the Great Oxidation Event indicates local sulfate production and oxidized conditions in sanukitoid sources. These results reveal variable recycling of locally-oxidized ocean crust since the Paleoarchean, and confirm sanukitoids as a key archive of early Earth crust-mantle dynamics.