What coupled cerium and neodymium isotopes tell us about the deep source of oceanic carbonatites

- We present the first Ce isotope compositions measured in carbonatite samples.
- We model REE contents & Ce isotope ratios of mantle reservoirs (D″ boundary layer).
- We discuss the origin of the carbon of the oceanic carbonatite source.

We present the first Ce isotope compositions together with Nd and Pb isotope ratios measured for whole rocks and mineral separates (apatite, titanite) from oceanic carbonatites and associated silicate samples from the Cape Verde and Canary archipelagos (Atlantic Ocean). We compare them with measurements performed on carbonatites from Tamazert (Morocco) for which a common source has been suggested. We couple the La/Ce and Sm/Nd systems in order to model the rare-earth-element concentrations and the Ce-Nd isotope compositions of marine carbonates and mantle and/or mantle-derived reservoirs, notably the D″ boundary layer. We discuss the two contrasting models that have been previously presented for the origin of the carbon of the oceanic carbonatite source: recycled marine carbonates via subduction vs. primordial carbon. Our measurements favour the recycling of marine carbonates in the source of oceanic carbonatites. We use Pb isotope ratios together with experimental petrology constraints to discuss the age and depth of carbonate recycling in the mantle.