Fig. 2

Hydrothermal experiments on metasomatic reactions. a Ol–Opx contact at 250 °C and P_sat (modified after Ogasawara et al. 2013). Left panel: photograph of the reaction zones at the Ol–Opx contacts after 1520 h. Right panel: ratio of the volume of serpentine to the total solid volume (V_srp/V_solid) versus distance from the tube top, along with the V_srp/V_solid ratio predicted by the reaction–diffusion model (red curves). b Ol–Qz contact at 300 °C and P_sat (modified after Oyanagi et al. 2020). Top: photograph of the reaction zones at the Ol–Qz contact after 3258 h. Bottom: Back-scattered electron (BSE) images of the products at 0 and 10 mm from the Ol–Qz contact. c Ol–Pl contact at 250 °C and P_sat (modified after Oyanagi et al. 2018). Top: photograph of the reaction zones at the Ol–Pl contact after 7980 h with the positions of Al and Ca, Si, and hydration fronts. The Si front is identified by the appearance of brucite and magnetite, and the Ca and Al front is identified by the chemical compositions of serpentine minerals. Bottom: BSE images of the products at the Ol–Pl contact (left) and of serpentine with Al zoning (right). d Temperature–X_CO2 diagram at 200 MPa showing the equilibrium phase relationship in the MgO–SiO₂–H₂O–CO₂ system for an MgO:SiO₂ ratio of 2:1 (modified after Johannes 1969). e BSE image and interpretation of a harzburgite–CO₂–H₂O experiment at 600 °C and 2.0 GPa after 192 h (modified after Sieber et al. 2022). f X-ray computed tomographic image of the product of a serpentinite–CO₂–H₂O experiment at 700 °C and 2.5 GPa after 96 h (modified after Sieber et al. 2020). Ol: olivine, Opx: orthopyroxene, Qz: quartz, Srp: serpentine, Brc: brucite, Pl: plagioclase, Mag: magnetite, Ca-Sap: Ca-saponite, Mgs: magnesite, Tlc: talc, Atg: antigorite, Cb: carbonate, Vac: vacancy