六甲山系横尾地域における化学風化速度について

Abstract

To estimate chemical weathering rate of granitic rocks, natural waters in a very smallbasin in the Rokko mountains have been collected weekly over a six-year period (1980-1985). The XRD indicates that kaolinite is the main product of plagioclase alteration inthe weathered granitic rocks. The water compositions are plotted in the field of stabilityof kaolinite in a phase diagram for the system Na-SiO2-Al2O3-H2O. This fits the XRDevidence that the main product phase is kaolinite, and it indicates that solution/kaoliniteequilibrium may play a role in controlling the water compositions. The amount of kaoliniteproduced by CO2-bearing water reacting with granitic rocks is estimated as 35.1 g/m2/year, and the total amount of weathering rocks is estimated as 55.3 g/m2/year.