Pervasive fluid-rock interaction in subducted oceanic crust revealed by oxygen isotope zoning in garnet

Abstract Dehydration reactions in the subducting slab liberate fluids causing major changes rock density, volume and permeability. Although it is well known that can migrate interact with surrounding rocks, fluid pathways remain challenging to track consequences of fluid-rock interaction processes are often overlooked. In this study, we investigate pervasive a sequence schists mafic felses exposed Theodul Glacier Unit (TGU), Western Alps. This unit embedded within metaophiolites Zermatt-Saas Zone reached eclogite-facies conditions during Alpine convergence. Chemical mapping situ oxygen isotope analyses garnet from reveal sharp chemical zoning between xenomorphic core euhedral rim, associated drop ~ 8‰ ? 18 O. Thermodynamic O models show large amount low H 2 required change reactive bulk composition cannot be produced by dehydration fels TGU only, requires contribution serpentinites. The calculated time-integrated flux across rocks 1.1 × 10 5 cm 3 /cm , which above open-system behaviour threshold argues for flow at kilometre-scale under high-pressure conditions. transient variations caused lawsonite breakdown identified as possible trigger influx. schist permeability (~ –20 m ) comparable determined experimentally blueschist