Details

Autor(en) / Beteiligte

• Lai, Xiaojing
• Zhu, Feng
• Gao, Jing
• Greenberg, Eran
• Prakapenka, Vitali B.
• Meng, Yue
• Chen, Bin

Titel

Melting of the Fe‐C‐H System and Earth's Deep Carbon‐Hydrogen Cycle

Ist Teil von

• Geophysical research letters, 2022-07, Vol.49 (13), p.n/a

Ort / Verlag

Washington: John Wiley & Sons, Inc

Erscheinungsjahr

2022

Quelle

Wiley-Blackwell Full Collection

Beschreibungen/Notizen

• The occurrences and cycling of slab‐originated carbon and hydrogen are considered to be controlled by their reactions with metallic iron from mantle disproportionation and slab serpentinization, to form Fe alloys containing carbon and hydrogen. Here we show experimental results on the phase relations and melting of the Fe‐C‐H system using laser‐heated diamond anvil cell and X‐ray diffraction techniques up to 72 GPa. The incorporation of hydrogen was found to lower the eutectic melting temperatures of Fe‐C alloy by ∼50–178 K at 20–70 GPa, facilitating the formation of metallic liquids in the deep mantle and thus enhancing the mobility and deep cycling of subducted carbon and hydrogen. Hydrogen also substitutes with carbon in Fe‐C metal to form hydride and diamond at relatively high‐temperature conditions (e.g., 42.6 GPa, >1885 K and 71.8 GPa, >1798 K). The hydrogen‐carbon‐enriched metallic liquids provide the necessary fluid environment for superdeep diamond growth. Plain Language Summary Deep carbon and hydrogen cycles (cycles between the surface and deep Earth) have significant influence on the physical and chemical evolution of our habitable planet, which affects the long‐term climate and ecosystem evolution. Subduction of oceanic floor carries carbon‐ and hydrogen‐rich species such as carbonates, hydrous minerals, and organic compounds into the deep Earth, where these species may react with the metallic iron there and form Fe‐C‐H alloy. In this study, we reproduced the extreme high‐pressure and high‐temperature conditions of the deep Earth using a technique called laser‐heated diamond anvil cell. Combined with high‐energy X‐ray diffraction, we studied the phase relation and melting behavior of the Fe‐C‐H system simultaneously at high pressure and high temperature. We find that the melting temperatures of the Fe‐C‐H system is lower than the temperatures of the mantle at depth, indicating Fe‐C‐H alloy may be molten along mantle geotherm. Therefore, the mobility of carbon and hydrogen in the deep mantle is enhanced, facilitating the cycling of deep carbon and hydrogen. Further, the substitution of carbon by hydrogen in carbon‐rich alloys may account for the formation of diamonds of deep origin, and the Fe‐C‐H melts can provide the fluid environment to grow large diamonds in deep Earth. Key Points Phase relations and eutectic melting temperatures of Fe‐C‐H alloys were determined up to 72 GPa Hydrogen depresses the melting temperatures of the Fe‐C system by ∼50–178 K at 20–70 GPa Hydrogen incorporation into the Fe‐C‐H system leads to the exsolution of diamonds at high temperatures