抄録
The dissolution experiment of anorthite was carried out under different partial pressures of CO2 (PCO2) to understand the role of weathering of Ca and Mg silicates in the removal of CO2 from the atmosphere in the Precambrian. A newly-developed apparatus can control PCO2 in a mineral-water reaction vessel and vary PCO2 and temperatures from 10−3.5 (the present atmospheric level, PAL) to 5.0 atm and from 40 to 150°C, respectively. The experiments were carried out at 150°C and pH 4.56, varying PCO2 from 10−3.5 to 1.2 atm. The dissolution rate of anorthite under high PCO2 (=1.2 atm) is faster than that under PAL by about 4 times. Calcium and Si dissolve congruently from anorthite under PAL, whereas a Ca/Si ratio in solution is lower under high PCO2. Our results suggest that the weathering rates and processes in the Archean are different from the present ones, and that the amount of Ca flux into the Archean ocean is less than that predicted assuming congruent dissolution of anorthite.
