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<p>Molecular hydrogen (H<sub>2</sub>) and methane (CH<sub>4</sub>) are among the most crucial volatiles in the Earth system, serving as key energy carriers for both geological and biological processes. Extensive studies have constrained the formation mechanisms, redox conditions, and global fluxes of abiotic H<sub>2</sub> and CH<sub>4</sub> at divergent plate boundaries, particularly at mid-ocean ridges where fluid-rock reactions such as serpentinization are well characterized. In contrast, subduction zones, the representative convergent boundaries, act as efficient “factories” for the abiotic formation of H<sub>2</sub> and CH<sub>4</sub>, yet the underlying processes and fluxes remain far less constrained. Within the subducting slab, the decomposition of organic matter and a series of high-pressure water-rock interactions can produce both biogenic and abiogenic H<sub>2</sub> and CH<sub>4</sub> under varying redox conditions. This review integrates recent advances and highlights four depth-dependent mechanisms that govern the formation of abiotic H<sub>2</sub> and CH<sub>4</sub> in subduction settings: shallow, low-pressure serpentinization during slab initiation, intermediate forearc serpentinization at elevated pressures, deep metamorphic fluid re-equilibration, and ultra-deep mantle metasomatism under ultra-high-pressure conditions. A comparison of potential gas fluxes between divergent and convergent boundaries suggests that subduction zones may represent a previously underestimated source of abiotic H<sub>2</sub> and CH<sub>4</sub>. The upward migration and release of these gases could significantly influence hydrocarbon seepage, deep biosphere activity, and the redox evolution of Earth’s volatile cycles, underscoring the need for integrated experimental, thermodynamic, and isotopic investigations to quantify these processes better.</p>

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Oceanic subduction zones: Factory of abiogenic hydrogen and methane

  • 期刊论文

  • 发表日期：

    2026年6月24日

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  • Yuhang Lu,
  • Jiaxin Zhang,
  • Wenbo Xu,
  • Guibin Zhang,
  • Lifei Zhang,
  • Renbiao Tao

摘要

Molecular hydrogen (H2) and methane (CH4) are among the most crucial volatiles in the Earth system, serving as key energy carriers for both geological and biological processes. Extensive studies have constrained the formation mechanisms, redox conditions, and global fluxes of abiotic H2 and CH4 at divergent plate boundaries, particularly at mid-ocean ridges where fluid-rock reactions such as serpentinization are well characterized. In contrast, subduction zones, the representative convergent boundaries, act as efficient “factories” for the abiotic formation of H2 and CH4, yet the underlying processes and fluxes remain far less constrained. Within the subducting slab, the decomposition of organic matter and a series of high-pressure water-rock interactions can produce both biogenic and abiogenic H2 and CH4 under varying redox conditions. This review integrates recent advances and highlights four depth-dependent mechanisms that govern the formation of abiotic H2 and CH4 in subduction settings: shallow, low-pressure serpentinization during slab initiation, intermediate forearc serpentinization at elevated pressures, deep metamorphic fluid re-equilibration, and ultra-deep mantle metasomatism under ultra-high-pressure conditions. A comparison of potential gas fluxes between divergent and convergent boundaries suggests that subduction zones may represent a previously underestimated source of abiotic H2 and CH4. The upward migration and release of these gases could significantly influence hydrocarbon seepage, deep biosphere activity, and the redox evolution of Earth’s volatile cycles, underscoring the need for integrated experimental, thermodynamic, and isotopic investigations to quantify these processes better.