The Re-Os isotopic system serves as an important tracer of recycled crust in Earth's deep mantle because of the large Re/Os ratios and time-integrated enrichment of radiogenic Os in Earth's crust. However, the Re distribution in Earth's known reservoirs is mass imbalanced, and the behavior of Re during subduction remains little understood. We performed laboratory experiments to determine the partition coefficients of Re between pyrrhotite and silicate melt (graphic) at 950–1080°C, 1–3 GPa, and oxygen fugacities (in log units relative to the fayalite-magnetite-quartz [FMQ] buffer) of FMQ–1.3 to FMQ +2. The obtained graphic values are 200–25,000, which increase with decreasing oxygen fugacity and the total iron content (FeOtot) of silicate melt but decrease with increasing temperature or decreasing pressure. Applying graphic to constrain the behavior of Re during slab melting demonstrates that slab melts contribute minimal Re to the sub-arc mantle, with most Re dissolved in sulfides subducted into Earth's deep mantle. Deep storage of recycled oceanic basalts and sediments can explain the mass imbalance of Re in Earth's primitive mantle, depleted mantle, and crust.

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