Earth’s geodynamic evolution constrained by (182)W in Archean seawater

Radiogenic isotope systems are important geochemical tools to unravel geodynamic processes on Earth. Applied to ancient marine chemical sediments such as banded iron formations, the short-lived (182)Hf-(182)W isotope system can serve as key instrument to decipher Earth’s geodynamic evolution. Here we show high-precision (182)W isotope data of the 2.7 Ga old banded iron formation from the Temagami Greenstone Belt, NE Canada, that reveal distinct (182)W differences in alternating Si-rich (7.9 ppm enrichment) and Fe-rich (5.3 ppm enrichment) bands reflecting variable flux of W from continental and hydrothermal mantle sources into ambient seawater, respectively. Greater (182)W excesses in Si-rich layers relative to associated shales (5.9 ppm enrichment), representing regional upper continental crust composition, suggest that the Si-rich bands record the global rather than the local seawater (182)W signature. The distinct intra-band differences highlight the potential of (182)W isotope signatures in banded iron formations to simultaneously track the evolution of crust and upper mantle through deep time.