Large igneous province volcanism represents extensive mantle melting that has contributed to Earth’s chemical differentiation and lithospheric and climatic changes. Compositional heterogeneities in the mantle, such as accumulated recycled crust, may make key contributions to large igneous province activity. One class of rocks capable of producing distinctive mantle heterogeneities is the iron formations, uniquely dense Fe-rich sedimentary rocks formed in Earth’s early oceans. Although numerous iron formations were preserved on continents, with some becoming major Fe ore deposits, large amounts of iron formations may also have been recycled into the mantle, with uncertain consequences. Here we use statistical analysis of time series to show that from 3,200 to 1,000 Myr ago, most iron formation deposition ages are correlated with large igneous province activity 241 ± 15 Myr later, and that these events are coupled on long timescales. Linking observations from tectonics, geodynamics, mineral physics and seismology studies, we hypothesize that dense accumulations of subducted iron formations can form highly conductive Fe-rich zones in the lowermost mantle and facilitate the formation of thermal anomalies that produce mantle plume upwellings, and, ultimately, large igneous provinces. Although uncertainties remain regarding the precise nature of Archaean and Proterozoic convergent tectonics, facilitation of large igneous province activity by subducted iron formations would link Earth’s ocean chemistry to the pace of heat flow, crustal production and chemical differentiation.