CERIUM LEAD AND LEAD-ISOTOPE RATIOS IN ARC MAGMAS AND THE ENRICHMENT OF LEAD IN THE CONTINENTS

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