Mass transfers during fluid-rock interactions at divergent and convergent plate boundaries

Abstract

Fluids and reactions between fluids and rock evoke significant mass and energy transfers in the marine realm. Phyllosilicate-rich shear zone rocks from a detachment fault zone (Mid-Atlantic Ridge) formed by hydrothermal alteration of hybrid ultramafica mafic rocks. Extensional strain and deformation focus in these weak lithologies and initiate a feedback loop between hydration and strain localization, which likely play a key role in detachment faults worldwide. Carbonates, precipitated from CO2-rich, oxidizing fluids, have formed in veins in metavolcanic and -sedimentary clasts at depths <20 km within the subduction channel (Mariana subduction system). Their existence proofs of C mobilization from the slab at shallow portions of subduction zones. Serpentinites from the basal plane of the mantle wedge (Mariana subduction zone) contain high contents of fluid-mobile elements (Li, B, Sr, Rb, Cs, Ba) that were mobilized during dehydration of the slab. Element concentrations vary with slab-depths and the sources of the serpentinization fluids, and provide a continuous record of slab dehydration reactions.