The world’s oceans contain up to 5.5 times less water by mass than is believed to exist in the Earth’s interior (i.e. Earth’s mantle and core). Yet the presence of volatiles such as H2O, CO2, C, CH4 (i.e. H-C-O) in the Earth’s interior are often overlooked despite critical for life on Earth.The chief means of replenishment of the Earth’s interior with volatiles over geological time is via subduction (i.e. the transport of crustal material into the Earth’s deep interior by large-scale tectonic processes) but constraints are very poor as natural samples from the deep Earth’s interior subduction zones are inaccessible. High pressure experimental investigations however can overcome that problem by simulating deep Earth’s mantle conditions and processes.The research proposed here will experimentally determine the maximum storage capacity, solubility and behaviour of volatile components (CHO) in nominally anhydrous minerals (NAMs; minerals which do not contain essential structural H2O) during subduction of carbonated, hydrated oceanic crustal material into the mantle’s transition zone (410-660 km depth) and lower mantle, by applying a novel experimental approach. This new experimental approach will for the first time enable determination of maximum H2O contents of NAMs in equilibrium with the full phase assemblage in volatile-bearing subducted oceanic crust. This was not achieved in numerous previous studies which concentrated on simple, monomineralic systems.This fundamental research will allow constraints to be placed on the fluxes of H2O but also CO2 recycled into the mantle at subduction zones, a critical step in the Earth’s overall volatile budget. It will also allow assessment of the influence of such volatiles on many mantle processes including partial melting, metasomatism, litholigical density and seismic velocity variations and others, as volatiles exert a major control on the way mantle lithologies behave chemically and physically.