Silica activity and the smectite-illite reaction
Abstract
Early silicate diagenesis is characterized by the precipitation of minerals with high silica activity, such as opaline silica, smectite, and clinoptilolite, and by pore-water silica activities exceeding quartz saturation. With burial, this early, high-silica activity diagenesic facies is succeeded by a low-silica activity facies distinguished by quartz precipitation and progressive development of illite as the nonexpandable component of mixed-layer clays. We suggest that the smectite-illite reaction occurs as a consequence of the reduction of silica activity at the onset of quartz precipitation. Data from oceanic and sedimentary basins confirm that the smectite-illite reaction does not control aqueous silica activities. Where the smectite-illite reaction occurs at higher temperatures, aqueous silica activities likewise reach quartz saturation at higher temperatures.
- Publication:
-
Geology
- Pub Date:
- June 1994
- DOI:
- 10.1130/0091-7613(1994)022<0539:SAATSI>2.3.CO;2
- Bibcode:
- 1994Geo....22..539A