6/26（月）17:00-18:00にOnlineで第７回岩石ー流体セミナーを行いました。参加者は１５名です。講演者はYongsheng Huangさんで、マントル炭酸塩化の水熱反応実験を行い、NaClとCO2の濃度が炭酸塩化に与える影響と、アウターライズでの炭酸塩化の量について議論しました。
Important role of mantle serpentinite carbonation of bending faults in deep carbon cycle
Yongsheng Huang
State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
Serpentinite carbonation contributes to the deep carbon (C) cycle. Recently, geophysical and numerical studies implied a potentially larger C storage in slab mantles. However, a quantitative determination of carbon uptake at outer rise regions is lacking. Here, we experimentally constrain the carbonation reaction in serpentinite–H2O–CO2–NaCl systems with various salinity (XNaCl) and CO2 concentrations (XCO2) at 140–180 MPa and 300–500 °C, corresponding to bending fault conditions. The porous reaction zone (~50% porosity) promotes the carbonation reaction through continuous supply of CO2-bearing fluids to the chemical reaction front. We find that NaCl can effectively decrease the reaction rate of serpentinite carbonation, especially at low salinities < 5 wt.%. This is most likely attributed to that the presence of NaCl reduces the water activity, CO2 activity, and diffusivity, and increases the magnesite solubility. We fit an empirical equation (temperature, pressure, XCO2, XNaCl) for reaction rate based on our results, which makes us able to calculate C uptake in slab mantles contributed by serpentinite carbonation at outer rise regions with realistic temperature, pressure, CO2 concentration, and salinity.