Water budget in flat vs. steep subduction: implication for volcanism and potential for H 2 production

In this study, we model the processes of (de)hydration and melting within subduction zones using a thermo-mechanical modeling approach. Multiple 2D simulations are conducted to investigate how the subduction angle influences the water budget in oceanic-continental subduction, focusing mainly on the variation of slab dip angle along the strike of the Andes. It appears that in the case of flat subduction, the mantle hydration zone is large, extending up to 500 km from the trench. This extent depends on the length of flat slab segment which, in turn, depends on the velocity of the overriding plate. 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 hydration of the mantle wedge for the use of water expelled from the subducting plate. In the transition from a steep to a flat slab, the mantle hydration zone widens and the volcanic zone moves away from the trench. The oceanic crust may undergo melting, leading to a change in magma composition and the development of adakitic volcanism, before volcanism diminishes in intensity and then disappears. Our study provides geodynamic insights into observations related to volcanism in the Pampean flat slab in South America. Using the quantification of water involved in mantle wedge hydration as a proxy for H 2 production, we propose that flat subductions are the most promising areas for H 2 exploration. Additionally, deep H 2 production appears to be particularly sensitive to the amount of subducted sediments, regardless of whether subduction is flat or steep. Lower plate serpentinization does not affect deep H 2 production. Dans cette étude, nous modélisons les processus de (dé)hydratation et de fusion au sein des zones de subduction en utilisant une approche de modélisation thermo-mécanique. Plusieurs simulations 2D sont menées pour étudier comment le pendage du panneau plongeant influence le bilan hydrique lors de la subduction océan-continent, dans le but de reproduire les variations du pendage le long des Andes. Il apparait qu’en cas de subduction plate la zone d’hydratation du manteau est large et peut s’étendre jusqu’à 500 km de la fosse. L’étendue dépend de la longueur du segment de slab plat, qui est-elle-même influencée par la vitesse de la plaque chevauchante. En cas de slab penté, la zone est plus étroite, et elle est située entre la fosse et l’arc volcanique. La formation de magma entre en compétition avec l’hydratatio