10:45 AM - 12:15 PM
[SCG45-P18] Volume expansion through carbonation of mantle rocks with H2O–CO2 fluids at 0.18GPa and 200–400°C: Implication for deep tremors
Keywords:serpentinite, carbonation, dehydration reaction, deep tremors
Johannes (1969, Am J Sci) reported experiments in the MgO-SiO2-CO2-H2O system. Here we report a new series of experiments in the MgO-CaO-SiO2-H2O-CO2 system using Internally-heated gas vessel at AIST, Japan and hydrothermal apparatus at Shizuoka University, Japan. Carbonation reactions in a temperature range of 200-400 degree C are compared with the phase diagrams experimentally reported by Johannes (1969, Am J Sci) and through thermodynamic calculation using Perple_X software (Connolly, 2005, Earth Planet Sci Lett). We suggest a possible relation between carbonation reactions and deep tremors and slow-slip events in forearc regions.
Oxalic acid dihydrate (OAD), which decomposes into carbon dioxide and water at high temperature and high pressure, is added to mixed powders, sealed in a metal capsule, and reacted in hydrothermal experiments. The starting materials are one mixture of olivine : diopside : OAD = 1 : 1 : 2 and the other of a mixture of antigorite : diopside : OAD = 1 : 1 : 2. Olivine has a composition of 0.9 Mg/(Mg+Fe), whereas diopside and antigorite have almost Mg-end compositions. The amounts of carbon dioxide and water are estimated by weighting procedures and examined with Raman microscopy and Field Emission Scanning Electron Microscope with Energy Dispersive System.
Carbonation and serpentinization of olivine and carbonation and deserpentinization of serpentine increase their solid volumes. In addition, carbonation of serpentine causes dehydration reaction. Such water release and volume expansion may increase pore-water pressure. Slow earthquakes occur under temperature conditions similar to the present experimentation at around 1.5GPa and 500 degree C (Ikuta et al., 2023 submitted to J Geophys Res). The effects of pressure on the reactions remain to be known experimentally and should be calculated thermodynamically using Perple_X.
Oxalic acid dihydrate (OAD), which decomposes into carbon dioxide and water at high temperature and high pressure, is added to mixed powders, sealed in a metal capsule, and reacted in hydrothermal experiments. The starting materials are one mixture of olivine : diopside : OAD = 1 : 1 : 2 and the other of a mixture of antigorite : diopside : OAD = 1 : 1 : 2. Olivine has a composition of 0.9 Mg/(Mg+Fe), whereas diopside and antigorite have almost Mg-end compositions. The amounts of carbon dioxide and water are estimated by weighting procedures and examined with Raman microscopy and Field Emission Scanning Electron Microscope with Energy Dispersive System.
Carbonation and serpentinization of olivine and carbonation and deserpentinization of serpentine increase their solid volumes. In addition, carbonation of serpentine causes dehydration reaction. Such water release and volume expansion may increase pore-water pressure. Slow earthquakes occur under temperature conditions similar to the present experimentation at around 1.5GPa and 500 degree C (Ikuta et al., 2023 submitted to J Geophys Res). The effects of pressure on the reactions remain to be known experimentally and should be calculated thermodynamically using Perple_X.