Potassium isotope evidence for sediment recycling into the orogenic lithospheric mantle

Post-collisional highly potassic magmatism in large orogenic belts has been taken as evidence for recycling of continent-derived K-rich sediments within the orogenic lithospheric mantle. Potassium isotopes may provide important insights into the origins of K in these magmas, since subducting sediments exhibit much more variable K isotopic compositions relative to the mantle. Here we report high precision K isotope data for 41 representative potassic and ultra-potassic volcanic rocks from the whole Alpine-Himalayan orogenic belt. delta K-41(NIST) (SRM3141a) of these samples vary from -1.55 parts per thousand to -0.32 parts per thousand, comparable to the range of global subducting sediments but significantly exceeding the range of pristine mantle defined by oceanic basalts (-0.42 +/- 0.08 parts per thousand). Monte Carlo simulation suggests this large K isotopic range can be reproduced by recycling of up to 5 % isotopically heterogeneous sediments into the depleted mantle. Our results highlight K isotopes as a potential tracer of recycled sediments in the mantle.