Serpentinization-mediated H2-generation and its genesis link to supra-subduction zone ophiolites

Natural hydrogen, a pivotal alternative energy source for achieving net-zero carbon emissions, has attracted considerable global interest. It is generated by multiple geological processes, of which the serpentinization of Fe(II)-rich rocks is a well-established primary source of natural hydrogen. Large ophiolite complexes associated with supra-subduction zone (SSZ) processes represent major geological reservoirs of Fe(II) on Earth. In this review, we systematically examine the spatiotemporal distribution, hydrogen-generating lithology and mineral assemblages, and geochemical characteristics of hydrogen-generating rock units in SSZ-type ophiolites with high natural hydrogen contents distributed around the Neo-Tethys realm. The results identify three key geological features associated with natural hydrogen accumulation in SSZ-type ophiolites: (1) the dominant hydrogen-generating lithology assemblage consists of harzburgite, dunite and lherzolite; (2) the upper ophiolite lavas unit is characterized by extreme enrichment in albite, depletion in K-feldspar, exhibiting the immobile element patterns of normal mid-ocean ridge basalt (N-MORB) with high Th/Nb ratios, deriving from a depleted mantle source; (3) the lower mantle peridotites unit exhibits a CIPW normative mineral composition marked by a W-shaped distribution of forsterite, fayalite, enstatite, and ferrosilite. The upper rock units of the ophiolite complexes, sealed by deep-sea sediments, pillow lavas, and dolerite/gabbroic dykes, are considered the most favorable structural position for natural hydrogen accumulation. The geological framework established in this review represents a significant advancement in the precise identification of SSZ-type ophiolite complexes, expands the potential frontiers for natural hydrogen exploration, and provides a scientific foundation for the scalable and economic recovery of natural hydrogen resources.