ROLE OF WATER IN THE SMECTITE-TO-ILLITE REACTION

A series of hydrothermal experiments was performed to determine the effect of fluid abundance on the reaction of smectite to illite. Experiments were conducted on K-saturated montmorillonite in a closed system at 250° to 400°C using run times of 1, 7, 14, 30, and 60 days at 100 MPa (1 kbar) pressure. In fluid-deficient systems, the rate and extent of illitization was significantly inhibited. The effect became less pronounced at higher temperatures. In addition, the low-fluid experiments produced fewer crystalline byproducts than did the fluid-rich runs, and the I/S was more difficult to disperse and orient in the fluid-deficient samples, suggesting enhanced cementation at grain contacts or the production of particle morphologies that did not lend themselves to orientation. -from Author