Serpentinisation, fluid flow, hydrogen and methane production at magma-poor margins: an example from the West Iberia margin

点击翻译按钮获取中文摘要

A key challenge in Earth system science today is to quantify the fluxes of elements that are exchanged between crust, ocean and atmosphere as a result of tectonics. First steps towards this effort have focused on estimating element fluxes during hydrothermal circulation at mid-ocean ridges. These studies, however, have ignored the thermodynamics and kinetics of water-rock reactions, which greatly affect those fluxes. In addition, element fluxes during extension at continental margins remain practically unexplored. Continental margins are often found on both sides of present oceans, hence occupy an area of the sea-floor that is similar to or larger than that of mid-ocean ridges.This project focuses on estimating the amount of serpentinization-derived H2 and CH4 fluxes produced during hydrothermal circulation within actively extending lithosphere at magma-poor margins. The importance of these margins in the global cycle of H2 and CH4 resides not only on the amount they produce, but also on the fact that they host serpentinite-based hydrothermal systems of lower temperature ( < 200°C) than those at mid-ocean ridges, where chemosynthetic communities can thrive. This project gathers expertise in three modelling components, tectonic deformation during extension, hydrothermal circulation and thermodynamics of water-rock reactions, which will be coupled to evaluate H2 and CH4 fluxes. Our results will be benchmarked against one of the best, if not the best, set of observations currently available at a continental margin: a 3D multichannel and wide-angle seismic survey and three iODP expeditions at the magma-poor West Iberia margin. Hydrothermal circulation at this margin occurred during extension ~112 M yrs ago, hence its pattern is poorly constrained. To circumvent this problem we intend to give a range of H2 and CH4 fluxes that are compatible with plausible hydrothermal flow patterns and the data. These estimates will be extrapolated to other less well-known magma-poor margins in order to assess their importance in the global production of H2 and CH4, and evaluate their potential for hosting sub-seafloor chemosynthetic life and, in the future, its consequences for the global carbon cycle. This a challenging project that will produce know-how in key areas of Earth sciences in order to quantify elements fluxes between crust and ocean and enhance our understanding of the Earth system feedbacks.