Potassium isotopic evidence for sedimentary input to the mantle source of Lesser Antilles lavas

Arc magmas derived from mantle melting often have trace element and isotopic signatures that indicate crustal contributions. The origin extent of contributions are critical constraints for quantifying crust-mantle recycling at subduction zones; however, it is difficult to distinguish between inputs the downgoing oceanic slabs over-riding arc crust. Here we present a novel study using stable potassium (K) isotopes fingerprint long-debated in lavas Martinique Island, Lesser Antilles arc. We find δ41K varies −0.66 0.01‰ correlates with chemical parameters radiogenic isotope ratios. These correlations cannot be produced by assimilation crust during magma ascent. Rather, they reflect sources been modified input subducted sediments. Most display strong negative correlation compositions, typical values −0.37‰ much lower −0.66‰, suggesting addition <1% 5% sediments their sources. Notable divergence this occurs three samples variably high (−0.28 0.01‰), which likely caused isotopically heavy K-bearing fluids slab dehydration. Our indicates substantial fraction large ion lithophile elements, including K thus nascent crust, inherited crust; useful tracers cycling process.