Impact of magmatic activity and magma-sediment-fluid interactions on the transfer and sequestration of volatiles

Volcanic basins play a central role in the exchange of volatiles between the lithosphere, hydrosphere, atmosphere and biosphere. The intrusion of magmas into sedimentary basins induces complex interactions between magma, sediments and fluids, profoundly modifying the biogeochemical cycles of carbon and sulphur. These phenomena are known to have contributed to major climatic and biological crises throughout Earth's history, but the mechanisms by which volatiles are partially trapped are still poorly understood.
This thesis studies the magma-sediment-fluid interaction processes and their consequences for the mobilisation and sequestration of carbon and sulphur in the Guaymas Basin (Gulf of California), a young system where basaltic sills were emplaced in unconsolidated sediments rich in organic matter and pore water. Three levels of interaction have been identified:
(1) contact metamorphism, which causes dehydration and decarbonation of the sediments. (2) magmatic contamination, where hydration of the magma by metamorphic fluids and contamination by fluids from the sediments disrupt magma crystallisation (3) late hydrothermal circulation.
Taken together, these processes allow several hundred thousand tonnes of sulphur and large quantities of carbon to be stored locally. On a basin-wide scale, these interactions make the sills veritable volatile traps, modifying the global balance of greenhouse gases emitted during magmatic intrusions.
This study shows that, contrary to the classic paradigm of complete degassing into the atmosphere, a significant proportion of volatiles can be sequestered in magmatic and metamorphic rocks over the long term.