Lithospheric relamination and disruption of mantle carbon during supercontinent cycles

Carbon exchange between Earth’s surface and its deep interior surely occurs but evidence is scant and the processes are poorly understood. Although isotopes and mineral inclusions from eclogitic diamonds suggest deep recycling of crustal material, the fate of subducted carbon, specifically whether it can survive deep subduction to relaminate with the continental lithosphere and therefore be accessible to later cratonic magmatism, remains unclear. Here we demonstrate a coupled relationship between the C and Nd isotopes of mantle-derived carbonate-rich magmas, carbonatites and kimberlites, where both isotopes for both rock types consistently fluctuate between more or less mantle-derived carbon and magmatism. Time series analysis of these datasets further reveals statistically significant cycles of ~500 and ~250 million years, corresponding to supercontinent and Wilson cycles, respectively. Exploring a possible mechanism, we perform geodynamic modelling that demonstrates that carbonate sediment may subduct beyond sub-arc depth and ascend to the overlying cratonic lithosphere, providing a carbon source for kimberlite and carbonatite magmatism. The periodicity of kimberlites and carbonatites, revealed by their C and Nd isotopes, stems from, as supported by our modelling, the subduction of carbonate sediment and its relamination onto cratonic keels during supercontinent assembly, then its disruption and incorporation in kimberlite and carbonatite magmatism during supercontinent breakup.