The Thermal Transformation of Smectite to Illite
Mixed-layered illite/smectite minerals composed of 80% illite layers have been identified from different argillaceous rocks that have been subjected to estimated peak temperatures that ranged from 250°C to 70°C, for durations of approximately 10 yr to 300 my. These observations strongly suggest that the reaction progress or extent is controlled by kinetic factors rather than by equilibrium factors. A sixth-order kinetic expression (first-order with respect to the pore-fluid activity ratio K/Na, and fifth-order with respect to the mole fraction of smectite) was successfully applied to the progressive illitization of smectite in the contact metamorphic zone adjacent to an 8.5-m-thick basalt dike that penetrates the upper Pierre Shale near Walsenberg, Colorado. The kinetic expression, together with its preexponential constant and activation energy (33 kcal/mol), provides a fair to good transformation model for a young geothermal sequence, and for burial diagenetic profiles that range in stratigraphic age from approximately a few million to 300 Ma.
The sixth-order model is an empirical device that explains the field evidence, but probably has little or no fundamental physical-chemical significance. The correct kinetic law is likely to be a chain of low-order reactions, each of which has kinetic constants that differ from the others.
KeywordsClay Zircon Hydrocarbon Sandstone Shale
Unable to display preview. Download preview PDF.
- Boles, J.R., and.Franks, S.G. 1979. Clay diagenesis in Wilcox sandstones of southwest Texas: Implications of smectite diagenesis on sandstone cementation. Journal of Sedimentary Petrology 49:55–70.Google Scholar
- Bruce, C.H. 1984 Smectite dehydration—its relation to structural development and hydrocarbon accumulation in northern Gulf of Mexico Basin. American Association of Petroleum Geologists Bulletin 68:673–683.Google Scholar
- Burst, J.F., Jr. 1969. Diagenesis of Gulf Coast clayey sediments and its possible relation to petroleum migration. American Association of Petroleum Geologists Bulletin 53:73–93.Google Scholar
- Hoffman, J., and Hower, J. 1979. Clay mineral assemblages as low grade metamorphic geothermometers: Application to the thrust faulted disturbed belt of Montana, U.S.A. In: Scholle, P.A., and Schluger, P.R. (eds.): Aspects of Diagenesis. Society of Economic Paleontologists and Mineralogists Special Publication 26, pp. 55–79.Google Scholar
- Jennings, S., and Thompson, G.R. 1986. Diagenesis of Plio-Pleistocene sediments of the Colorado River delta, southern California. Journal of Sedimentary Petrology 56:89–98.Google Scholar
- Johnsson, M.J. 1984. The thermal and burial history of south-central New York: Evidence from vitrinite reflectance, clay mineral diagenesis, and fission track dating of apatite and zircon. M.A. thesis, Dartmouth College, Hanover, NH, 155 pp.Google Scholar
- Kramer, M.S. 1981 Contact metamorphism of the Mancos Shale associated with the intrusion at Cerrillos, New Mexico. M.A. thesis, Dartmouth College, Hanover, NH, 102 pp.Google Scholar
- Lippmann, F. 1982. The thermodynamic status of clay minerals. In: van Olphen, H., and Veniale, F. (eds.): International Clay Conference 1981. Amsterdam, Elsevier Scientific Publishing Co., pp. 475–485.Google Scholar
- Lynch, L., and Reynolds, R.C., 1984. The stoichiometry of the illite-smectite reaction (abst.). Twenty-First Annual Meeting of the Clay Minerals Society, Baton Rouge, LA, p. 84.Google Scholar
- Perry, E.A., and Hower, J. 1972. Late-stage dehydration in deeply buried peletic sediments. American Association of Petroleum Geologists Bulletin 56:2013–2021.Google Scholar
- Pytte, A.M. 1982. The kinetics of the smectite to illite reaction in contact metamorphic shales. M.A. thesis, Dartmouth College, Hanover, NH, 78 pp.Google Scholar
- Reynolds, R.C., 1980. Interstratified clay minerals. In: Brindley, G.W., and Brown, G., (eds.): Crystal Structures of the Clay Minerals and Their X-Ray Identification. London, Mineralogical Society, 495 pp.Google Scholar
- Reynolds, R.C., 1981. Mixed-layered illite-smectite in a contact metamorphic environment (abst.). Eighteenth Annual Meeting of the Clay Minerals Society, University of Illinois at Urbana-Champaign, Urbana, IL, p. 5.Google Scholar
- Robie, R.A., Hemingway, B.S., and Fisher, J.R. 1978. Thermodynamic properties of minerals and related substances at 298.15 K and 1 bar (105 Pascals) pressure and at higher temperatures. U.S. Geological Survey Bulletin 1452, 456 pp.Google Scholar
- Środoń, J., and Eberl, D.D. 1984. Illite. In: Bailey, S.W. (ed.): Micas: Reviews in Mineralogy: Vol. 13. Reno, NV, Mineralogical Society of America, 584 pp.Google Scholar
- Tyler, L.D., Cuderman, J.F., Kruhansl, J.L., and Lappin, A.R. 1978. Near-surface heater experiments in argillaceous rocks. In: Seminar on In Situ Heating Experiments in Geologic Formations, Ludvika, Stripa, Sweden. Brussels, Belgium, Organization of Economic Cooperation and Development, pp. 31–43.Google Scholar