H2 formation in subduction zone

Dihydrogen (H₂) is a promising decarbonized energy source, but traditional artificial production methods emit CO₂ and/or consume a lot of energy. However, there are natural sources of H₂ on Earth originating from diverse geochemical processes. A recent study above the Nazca plate subduction in the Andes, detected variations in the H₂ emanation function on the slab dip angle. This H₂ release is likely the result of peridotite hydration in the mantle wedge, notably through serpentinization. The water required for peridotite hydration is sourced from dehydration of the subducting plate as it sinks into the Earth's mantle.

This study aims to understand the influence of slab dip angle on H₂ production in the mantle wedge using the pTatin2D code. Fluid circulation were implemented based on two principles:

• The hydration and dehydration capacity of rocks under varying pressure and temperature conditions is predicted using tables from the thermodynamic software PerpleX.
• The velocity of free water is equivalent to that of surrounding rocks, with a vertical component related to percolation.

Numerical simulations show that in the case of flat subduction, the mantle hydration zone, where H₂ is produced, is wide and extending up to 500 km from the trench. On the other hand, in the case of a steep subduction, the zone is narrower, and is located between the trench and the volcanic arc. Magma formation competes with H₂ generation for the use of water released from the subducting plate. During the transition from steep to flat subduction, the mantle hydration zone undergoes widening while the volcanic zone migrates significantly away from the trench. This transition may also trigger oceanic crust melting, resulting in a shift in magma composition before the volcanism intensity diminishes and then disappears.