LAUSR

Abstract Subduction zones are important in materials’ cycling between Earth’s surface and mantle. We report lithium (Li) contents and isotopic compositions (δ7Li) of ultrahigh-pressure (UHP) marbles of the Dabie-Sulu orogen, with the aim of elucidating the geochemical behavior of Li isotopes during deep subduction of surficial carbonates and exploring the application of Li isotopes in tracing subduction and material-cycling. Pure UHP marbles (with δ7Li values up to 21.5‰) show significantly heavier isotopic compositions than those of the mantle (2.0‰–5.7‰; average 3.7‰), while impure marbles containing some silicates have δ7Li values as low as 1.3‰. Weathering, fluid infiltration, and isotopic fractionation have negligible effects on the Li isotopic compositions of UHP marbles. Exhumed UHP marbles might be good samples to study those residual carbonates entering into the deep mantle. When subducted carbonates transport heavy Li isotopic signatures to mantle depths, they may result in local Li isotopic heterogeneity. As Li is a trace element and UHP marbles have significantly different δ7Li signatures to the mantle, Li isotopic geochemistry might be useful in tracing deep carbon cycling.