EGU24-5003, updated on 08 Mar 2024
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Importance of mantle serpentinite carbonation in bending faults for the deep carbon cycle

Yongsheng Huang1,2, Satoshi Okumura3, Kazuhisa Matsumoto3, Naoko Takahashi4, Hong Tang5, Guoji Wu1,2,6, Tatsumi Tsujimor3,7, Michihiko Nakamura3, Atsushi Okamoto8, and Yuan Li1,2
Yongsheng Huang et al.
  • 1Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, State Key Laboratory of Isotope Geochemistry, Guangzhou, China (
  • 2CAS Center for Excellence in Deep Earth Science, Guangzhou 510640, China
  • 3Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
  • 4Geochemical Research Center, Graduate School of Science, The University of Tokyo, Tokyo, 113-0033, Japan
  • 5South China Sea Environmental Monitoring Center, SOA, Guangzhou 510300, China.
  • 6College of Earth and Planetary Sciences, University of the Chinese Academy of Sciences, Beijing 100049, China
  • 7Center for North Asian Studies, Tohoku University, Sendai, 980-8576, Japan
  • 8Graduate School of Environmental Studies, Tohoku University, Sendai, Japan

Serpentinite carbonation contributes to the deep carbon (C) cycle. Recently, geophysical and numerical studies have identified considerable hydrothermal alterations in deep bending faults beneath outer-rise regions, implying potentially significant C storage in the slab mantle. However, quantitative determination of C uptake in outer-rise regions is lacking. Here, we experimentally constrained the serpentinite carbonation in H2O–CO2–NaCl fluids under bending fault conditions to estimate C uptake in the slab mantle. We found that serpentinite carbonation produced talc and magnesite along the serpentinite surface. The porous reaction zones (49.2% porosity) promoted the progress of the carbonation reaction through a continuous supply of CO2-bearing fluids to the reaction front. Strikingly, NaCl effectively decreased the serpentinite carbonation efficiency, particularly at low salinities (< 5.0 wt%), which is likely attributed to the reduction in H2O and CO2 activities (aH2O and aCO2) and transport rate of reactants, the change in pH of fluids, and the enhancement of magnesite solubility. We fitted an empirical equation for the reaction rate of serpentinite carbonation in bending faults and found that this reaction could contribute to a flux of 25–100 Mt C/yr in subduction zones. Our results shed new light on the deep C cycle and the serpentinite carbonation in environments with high salinities.

How to cite: Huang, Y., Okumura, S., Matsumoto, K., Takahashi, N., Tang, H., Wu, G., Tsujimor, T., Nakamura, M., Okamoto, A., and Li, Y.: Importance of mantle serpentinite carbonation in bending faults for the deep carbon cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5003,, 2024.