Subduction is one of the most important manifestations of plate tectonics on Earth and is the primary vector for mass transfer from Earth’s surface to its interior. The subduction of sediments and hydrated oceanic lithosphere is a critical step in the whole Earth cycle of elements, leading to secular variations in the chemistry of the mantle and exosphere. The slab is not a closed system: Metamorphic reactions with depth, such as those involving dehydration and melting, result in an open system redistribution of fluid- and melt-mobile elements from the slab. Partitioning of mobile from immobile elements in the slab dictates which elements recycled back to surface reservoirs through volcanic arcs and those which are subducted into the lower mantle. This session focuses on the mechanisms, timing, and consequences of the metamorphic and igneous processes that drive mass-transfer between the slab, mantle wedge, and arc. We invite contributions from petrology, geochemistry, and isotope geology that are aimed at deciphering micro to macro scale processes in the slab and arc to reconstruct geochemical cycles at convergent margins.