It was long assumed that subduction zone metamorphism acts as a barrier to recycling of volatiles into the Earth’s mantle. In particular, the inability of noble gases to form chemical bonds lead to a long standing assumption that noble gases are ‘unsubductable’ and the difficulty of measuring pristine mantle noble gas signatures, meant that this view went unchallenged until very recently. There is now a growing recognition that subduction of heavy noble gases (Ar, Kr and Xe) is highly significant, but most workers still consider He and Ne to be ‘unsubductable’.
This talk presents new evidence from combined studies of noble gases and halogens in lithologies from the seafloor and subduction zones; and of halogens and H2O in magmatic glasses from arcs, back arcs, MORB and oceanic islands. We identify serpentinised lithosphere as the dominant reservoir enabling subduction of seawater-derived volatile components into the deep mantle beyond magmatic arcs. In addition, we show that subduction of atmospheric neon (as well as Ar, Kr and Xe) has been sufficiently important that it changes the way that mantle neon isotope signatures should be interpreted. This has profound implications for how noble gases contribute to our understanding of Earth’s formation.