Serpentinization-sourced natural hydrogen is among the most well-studied generative systems worldwide. Its understanding has greatly benefited from observations of active systems at slow-spreading mid-ocean ridges, such as those located in the Atlantic. As oceans close to form mountain belts through tectonic cycles - a process known as the Wilson cycle - these hydrogen-producing rock formations can be preserved and found within mountain belts, specifically in ophiolites—a term that encompasses rocks originating from ancient oceanic seafloors.
Over the past three decades, research has revealed that there are different ophiolites e going along with mantle rocks with distinct origins, compositions, geological histories and therefore hydrogen-generating potentials. This diversity is particularly striking in the Western Pyrenees, which has emerged as a hotspot for natural hydrogen exploration. In this area, mantle rocks of subcontinental origin were exhumed beneath sedimentary basins - such as the Mauléon basin - during a failed attempt to form an ocean ~100 My ago. Notably, the subsequent formation of the Pyrenees had a minimal impact on the pre-orogenic geology, preserving a high-potential mantle kitchen—a fault-controlled system connected to an upstream meteoric water recharge and a downstream hydrogen discharge area.
