Fluid Release from a Dehydrating Serpentinite by Reactive Porosity Waves

Dehydration of oceanic lithosphere during subduction is a key process in the Earth's deep volatile cycle. Field observations and studies of obducted meta-serpentinites that underwent dehydration at depth often show an interconnected, channelized vein network that formed during dehydration and served as pathway for fluid release from the dehydrating rock. Previous studies show that chemical heterogeneities in the bulk-rock composition lead to channelization of fluid flow from the onset of the dehydration process and how subsequent reactive fluid flow in the porous network causes further dehydration and channelization. On larger scales, fluid release from the rock is governed by mechanical processes such as porosity waves. While the micro- and meso-scale have been studied so far, this large-scale fluid release mechanism has not yet been explored for dehydrating serpentinite.

Here, we present a model for reactive porosity waves that investigates the large-scale fluid release from a dehydrating serpentinite. The model combines viscous rheology with the transport of dissolved silica in the fluid which has been shown to be a key metasomatic agent in the dehydration process. As input for our model, we use a multi-scale dataset of fully hydrated serpentinite from an ophiolite taken as representative for serpentinized oceanic lithosphere entering a subduction zone. We use the data to explore the formation of the vein network during dehydration and the behavior during large-scale fluid escape by reactive porosity waves.