The lithium isotopic composition and geochemical implication of ultrahigh-pressure marbles from the Dabie-Sulu orogen, China

Subduction zones are important in materials’ cycling between Earth’s surface and mantle. As Li isotopic compositions of sedimentary carbonates (δ7Li = 5.2‰–31‰) differing markedly from those of the mantle (2.0‰–5.7‰), it is important to know if Li isotopic compositions of carbonates could be used to tracing deep carbon cycling. Here we report that meta-sedimentary carbonates could preserve their original heavy Li isotopic signatures (with δ7Li values up to 21.5‰) when subducted from surface to the mantle depths (the yellow arrow) and that the related carbonatitic or carbonate-rich silicate melts may retain various degrees of heavy Li isotopic signatures locally in the mantle (the yellow arrow). We infer that some mantle-derived magmas may have recorded the elevated δ7Li signatures induced by recycled carbonates (the yellow arrow) and thus Li isotopic geochemistry could be useful in tracing deep carbon cycling.