Séminaire Alban Cheviet

Impact of magma-sediment-fluid interactions on the sulphur cycle in sedimentary basins: example of the Guaymas Basin

Sedimentary basins are an important reservoir of volatile elements such as C, S, H, Cl and F on Earth, at the interface between surface reservoirs (oceans, biosphere and atmosphere) and deep reservoirs (lithosphere). Diagenetic and biological processes control the precipitation of dissolved sulphur in pore water into framboidal pyrite. This sulphur cycle can be disrupted by the emplacement of magmatic intrusions in the sediments. The metamorphic aureoles around the intrusions can produce large amounts of fluids that can migrate to the seafloor or be stored in the metamorphic aureoles. Fluids can also migrate into the magma and contaminate it. Assimilation of sediment into the magma can also enrich it with volatile elements. In this study we investigate the effect of magma-sediment interactions on the sulphur cycle in sedimentary basins. The study is based on samples from the IODP 385 expedition in the Guaymas Basin, where a shallow cone-shaped sill is emplaced in soft sediments with hydrothermal vents above the sill which are still active on the seafloor. Rocks with a peperitic texture, rich in sulphides, were collected to study these magma-sediment interaction processes. A detailed petrological study combined with LA-ICPMS and SIMS analyses was carried out to understand the mechanisms of sulphide formation and the different sources of metals and sulphur.