HR: 1330h
AN: H42F-1138    [PDF]
TI: Fundamental Experiments Of Fluid-Rock Reaction Due To A Mechanochemical Process: Implication For Seismic Fault Zones
AU: * Saruwatari, K
EM: kazuko@solid.eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, Graduate school of Science, University of Tokyo, Hongo 7 - 3 - 1, Bunkyo-ku, Toyko, 113-0033 Japan
AU: Kameda, J
EM: kameda@solid.eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, Graduate school of Science, University of Tokyo, Hongo 7 - 3 - 1, Bunkyo-ku, Toyko, 113-0033 Japan
AU: Tanaka, H
EM: tanaka@solid.eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, Graduate school of Science, University of Tokyo, Hongo 7 - 3 - 1, Bunkyo-ku, Toyko, 113-0033 Japan
AB: Fracture zones within active fault zones are known to be passages of fluids. The fluid penetration in the fracture zone leads into fluid-rock interaction that changes the physical and chemical properties of the fault zone materials, possibly affecting the dynamic behavior of the fault itself. The evidences of the interactions between fluids and destructed rocks are obtained as anomalous concentrations of gases and chemical elements along active faults (e.g., Wakita et al., 1980; Tanaka et al., 2001). One of the characteristic products is hydrogen gas that has been detected relative to fault activities since Wakita et al. (1980) found hydrogen anomalies along an active fault. The generation of hydrogen gas is due to the radical reaction between water molecule and active Si radicals on the new surface of crushed quartz grains (Kita et al., 1982; Kameda et al., in press). Another characteristic product in the fault zone is submicron size of low strength materials such as amorphous and clays which seem to be formed by fluid-mineral reactions like dissolution-precipitation and alteration reactions (e.g., Tanaka et al., 2001). In order to understand the fluid-rock reactions during the pulverization of rocks, we performed batch-style crushing experiments of single crystals of quartz, alkali feldspar and biotite and granites with pure water (pH7) under argon-filled conditions using a glove box at the ambient temperature and pressure. We measured pH of the solutions and hydrogen gas concentrations using a glass electrode and gas chromatograph, respectively. BET (Brunauer, Emmett and Teller) method was adopted for precise measurements of net surface areas of the samples, in order to estimate the destructed atomic bonds. Furthermore, cations and anions in the water are also measured by PerkinElmer atomic absorption spectrometry and Toso ion chromatograph. pH values decrease for the experiments of quartz single crystal with increasing crushing times, while the other single crystal and granite experiments show the pH increases. Hydrogen gas and BET surface area linearly increase with increasing the experimental duration time for all the crushing experiments. In the case of quartz, both amounts of hydrogen gas and hydrogen ions increase proportionally with increasing the newly formed surface area. The amounts of the hydrogen gas are consistent with the amounts of Si radicals estimated from electron spin resonance measurements by Hochestrasser and Antonini (1972). This indicates that the hydrogen gas was generated by consuming the most of Si radicals on the newly formed surface. The hydrogen ions, whose amounts are 5 times larger than those of the hydrogen gas, can be explained by the dissociation of silanols that are produced on the new quartz surface by hydrolysis (Saruwatari et al., submitted). For the other minerals and granite, the hydrogen gas is also generated by the Si radicals as same as quartz, whereas the amounts of hydrogen ions decrease with increases of Na+ and K+. The amounts of the alkali metal ions are more than those expected from the static dissolution and the increase of surface area. The discrepancy may be originated from the pulverization process. At the presentation, we will discuss the effect of the newly formed surface on the fluid-mineral reactions. Hochstrasser and Antonini, 1972, Surface Sci 32, 644-664. Kita et al., 1982, JGR 87, 10789-10795. Kameda et al., In Press, Bull. Chem. Saruwatari et al., submitted, Phys. Chem. Min. Tanaka et al., 2001, JGR 106, 8789-8810. Wakita et al., 1980, Science 210, 188-190.
DE: 4825 Geochemistry
DE: 4854 Physicochemical properties
DE: 8010 Fractures and faults
DE: 8045 Role of fluids
SC: Hydrology [H]
MN: 2003 Fall Meeting