Lead is anomalously enriched in the Earth’s continental crust, and in the magmas that give rise to new continental crust at convergent margins. A detailed study of volcanic rocks from the Aleutian island arc shows that this enrichment is a continuing process, and results from the efficient non-magmatic transfer of mantle-derived lead into the source of convergent-margin magmas. This process, acting through time, can also account for the pervasive depletion of lead in the oceanic mantle.