title: Dehydration of chlorite explains anomalously high electrical conductivity in the mantle wedges.
abstract: Mantle wedge regions in subduction zone settings show anomalously high electrical conductivity (~1 S/m) that has often been attributed to the presence of aqueous fluids released by slab dehydration. Laboratory-based measurements of the electrical conductivity of hydrous phases and aqueous fluids are significantly lower and cannot readily explain the geophysically observed anomalously high electrical conductivity. The released aqueous fluid also rehydrates the mantle wedge and stabilizes a suite of hydrous phases, including serpentine and chlorite. In this present study, we have measured the electrical conductivity of a natural chlorite at pressures and temperatures relevant for the subduction zone setting. In our experiment, we observe two distinct conductivity enhancements when chlorite is heated to temperatures beyond its thermodynamic stability field. The initial increase in electrical conductivity to ~3 × 10(-3) S/m can be attributed to chlorite dehydration and the release of aqueous fluids. This is followed by a unique, subsequent enhancement of electrical conductivity of up to 7 × 10(-1) S/m. This is related to the growth of an interconnected network of a highly conductive and chemically impure magnetite mineral phase. Thus, the dehydration of chlorite and associated processes are likely to be crucial in explaining the anomalously high electrical conductivity observed in mantle wedges. Chlorite dehydration in the mantle wedge provides an additional source of aqueous fluid above the slab and could also be responsible for the fixed depth (120 ± 40 km) of melting at the top of the subducting slab beneath the subduction-related volcanic arc front.
authors.affiliation: Laboratoire Magmas et Volcans, CNRS UMR 6524, Université Blaise Pascal, Institut de Recherche pour le Développement, 63178 Clermont-Ferrand, France.
authors.forename: Geeth
authors.initials: G
authors.lastname: Manthilake
authors.affiliation: Laboratoire Magmas et Volcans, CNRS UMR 6524, Université Blaise Pascal, Institut de Recherche pour le Développement, 63178 Clermont-Ferrand, France.
authors.forename: Nathalie
authors.identifier: 0000-0002-1859-1107
authors.initials: N
authors.lastname: Bolfan-Casanova
authors.affiliation: Laboratoire Magmas et Volcans, CNRS UMR 6524, Université Blaise Pascal, Institut de Recherche pour le Développement, 63178 Clermont-Ferrand, France.
authors.forename: Davide
authors.initials: D
authors.lastname: Novella
authors.affiliation: Earth, Ocean, and Atmospheric Sciences, Florida State University, Tallahassee, FL 32306, USA.
authors.forename: Mainak
authors.initials: M
authors.lastname: Mookherjee
authors.affiliation: Laboratoire Magmas et Volcans, CNRS UMR 6524, Université Blaise Pascal, Institut de Recherche pour le Développement, 63178 Clermont-Ferrand, France.
authors.forename: Denis
authors.identifier: 0000-0002-9921-4572
authors.initials: D
authors.lastname: Andrault
mesh_terms: D002712:Chlorides / Q000737:chemistry*; D003681:Dehydration; D004553:Electric Conductivity; D019015:Geologic Sediments; D008962:Models, Theoretical
chemical_list: D002712:Chlorides; C001599:chlorite
keywords: Electrical conductivity; aqueous fluid; chlorite; dehydration; high pressure; magnetite; subduction systems