The recycling of elements through convergent plate boundaries strongly influences the chemical differentiation of Earth. It is widely accepted that hydrous fluid sourced from dehydrating subducting crust promotes melting in the mantle wedge and the formation of arc magmas. We investigate the liberation of volatiles and trace elements in subduction zones by combining studies on eclogite facies rocks with experimental studies. We have shown that trace elements are mainly hosted in minor and accessory phases.
From experimentally determined phase stabilities we can infer that the most significant trace element contribution to subduction zone liquids stems from fluid present melting of subducted sediments and altered oceanic crust. With innovative experimental techniques such as diamond traps and synthetic fluid inclusions, we are able to show that low temperature fluids (T<600°C) are not able to transport significant amounts of trace elements. Temperatures of around 800°C are required to produce observed trace element signatures of arc lavas. This is significant because such temperatures are considerably higher (up to 200°C!) than what numerical models predict.