Craton-margin lithosphere drives rare earth element ore-forming carbonatite magmatism

The majority of light rare earth element (LREE) resources are derived from carbonatite-associated deposits at cratonic margins. However, the origin of ore-forming carbonatite magmas remains unclear. Here, we conducted high pressure-temperature experiments to investigate LREE behavior during carbonate-rich sediment recycling. Results show that, during subduction, the calcic carbonates progressively concentrate LREE, becoming the principal LREE carriers and, upon melting at higher pressures, generate LREE-rich melts. As the melts ascend through cratonic lithospheric mantle, precipitation of extremely LREE-poor magnesite induces further enrichment, producing melts with LREE concentrations up to 156 times those of sedimentary carbonates. These melts are comparable to natural ore-forming carbonatites, highlighting that craton-margin lithosphere drives LREE ore-forming carbonatite magmatism. Our global compilation shows that LREE concentrations in carbonatites positively correlate with the associated deposit tonnage, suggesting that ore-forming carbonatites fundamentally control the deposit reserve magnitude. These findings provide a unified framework for the formation and global distribution of carbonatite-hosted deposits at cratonic margins.