# Devolatilization of Subducting Slabs, Part II: Volatile Fluxes and Storage

## TL;DR

This study uses a reactive transport model to analyze how water and carbon are released and stored during subduction, highlighting the effects of fluid flow, lithological interfaces, and sediment removal on volatile fluxes.

## Contribution

It introduces a two-dimensional reactive transport model to quantify volatile fluxes and storage during subduction, considering fluid flow, lithology, and sediment removal effects.

## Key findings

- Up-slab fluid flow peaks at subarc depths.
- Hydrated slab mantle enhances decarbonation and carbonation.
- Sediment removal increases surface volatile fluxes.

## Abstract

Subduction is a crucial part of the long-term water and carbon cycling between Earth's exosphere and interior. However, there is broad disagreement over how much water and carbon is liberated from subducting slabs to the mantle wedge and transported to island-arc volcanoes. In the companion paper Part I, we parameterize the metamorphic reactions involving H$_2$O and CO$_2$ for representative subducting lithologies. On this basis, a two-dimensional reactive transport model is constructed in this Part II. We assess the various controlling factors of CO$_2$ and H$_2$O release from subducting slabs. Model results show that up-slab fluid flow directions produce a flux peak of CO$_2$ and H$_2$O at subarc depths. Moreover, infiltration of H$_2$O-rich fluids sourced from hydrated slab mantle enhances decarbonation or carbonation at lithological interfaces, increases slab surface fluxes, and redistributes CO$_2$ from basalt and gabbro layers to the overlying sedimentary layer. As a result, removal of the cap sediments (by diapirism or off-scraping) leads to elevated slab surface CO$_2$ and H$_2$O fluxes. The modelled subduction efficiency (the percentage of initially subducted volatiles retained until $\sim$200 km deep) of H$_2$O and CO$_2$ is increased by open-system effects due to fractionation within the interior of lithological layers.