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<p>Molecular H<sub>2</sub> released from Earth’s deep interior to the surface represents a promising natural clean energy source. However, the mechanisms governing H formation in the deep mantle remain inadequately understood. This study performed high-temperature and high-pressure experiments, coupled with <i>in-situ</i> X-ray diffraction (XRD) techniques, to simulate the interaction between subducted H<sub>2</sub>O and mantle Fe<sup>0</sup> in the presence of mantle minerals under conditions representative of subducting slabs in the deep upper mantle. The research results show that, with increasing pressure and temperature, H<sub>2</sub>O reacts with Fe<sup>0</sup> and silicates to form (Fe,Mg)O-silicate minerals (e.g., enstatite, olivine, and their high-pressure polymorphs) as well as iron hydride, FeH<sub><i>x</i></sub> (0⩽r⩽1) in the deep mantle. Upon isothermal decompression at high temperatures, FeH<sub><i>x</i></sub> decomposes back to Fe<sup>0</sup>, simultaneously releasing significant amounts of H<sub>2</sub>. Based on these experimental observations and plate tectonics, it is proposed that FeH<sub><i>x</i></sub> serves as a critical intermediate in the conversion of subducted H<sub>2</sub>O to H<sub>2</sub> in Earth’s deep mantle. The decomposition of FeH<sub><i>x</i></sub> in ascending mantle rocks offers a plausible explanation for the widespread occurrence of H<sub>2</sub>±CH<sub>4</sub> and Fe<sup>0</sup> in diamond inclusions and mantle xenoliths. The H<sub>2</sub> released from FeH<sub><i>x</i></sub> may migrate upward through deep faults or through magmatic degassing, potentially contributing to natural H<sub>2</sub> seepages or reservoirs within Earth’s subsurface.</p>

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Iron hydride (FeHx) as a crucial intermediate in transformation of subducted H2O to abiotic H2 in Earth’s deep mantle

  • 期刊论文

  • 发表日期：

    2025年4月18日

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  • Jintao Zhu,
  • Renbiao Tao,
  • Takayuki Ishii,
  • Daijo Ikuta,
  • Wenbo Xu,
  • Lifei Zhang,
  • Yutong Su,
  • Runchao Liu,
  • Zhijun Jin

摘要

Molecular H2 released from Earth’s deep interior to the surface represents a promising natural clean energy source. However, the mechanisms governing H formation in the deep mantle remain inadequately understood. This study performed high-temperature and high-pressure experiments, coupled with in-situ X-ray diffraction (XRD) techniques, to simulate the interaction between subducted H2O and mantle Fe0 in the presence of mantle minerals under conditions representative of subducting slabs in the deep upper mantle. The research results show that, with increasing pressure and temperature, H2O reacts with Fe0 and silicates to form (Fe,Mg)O-silicate minerals (e.g., enstatite, olivine, and their high-pressure polymorphs) as well as iron hydride, FeHx (0⩽r⩽1) in the deep mantle. Upon isothermal decompression at high temperatures, FeHx decomposes back to Fe0, simultaneously releasing significant amounts of H2. Based on these experimental observations and plate tectonics, it is proposed that FeHx serves as a critical intermediate in the conversion of subducted H2O to H2 in Earth’s deep mantle. The decomposition of FeHx in ascending mantle rocks offers a plausible explanation for the widespread occurrence of H2±CH4 and Fe0 in diamond inclusions and mantle xenoliths. The H2 released from FeHx may migrate upward through deep faults or through magmatic degassing, potentially contributing to natural H2 seepages or reservoirs within Earth’s subsurface.