Kinetic and equilibrium controls of the diagenetic illitization of smectite
X-ray diffraction, chemical, petrographic and SEM analyses of mudrock samples from borehole Borchard A-2, drilled in Plio-Pleistocene Colorado River delta mudrocks of the Imperial Valley, southern California, show a continuous mineralogical sequence from 20 to 100 percent illite layers in mixed-layer illite/smectite (M-L I/S) over the temperature range 70/sup 0/ to 210/sup 0/C. K-spar progressively decreases, but does not disappear, over the same interval. Diagenetic chlorite appears at 190/sup 0/C and kaolinite is lost at 210/sup 0/C. Ordering of the M-L I/S changes from R=0 to R=1 at 145/sup 0/C and from R=1 to Rgreater than or equal to 3 at 175/sup 0/C. There are no systematic chemical variations in the bulk fraction with depth and temperature. The <0.1 um fraction shows increases in K/sub 2/O, Al/sub 2/O/sub 3/, and decreases in SiO/sub 2/ and Fe/sub 2/O/sub 3/ with depth and temperature, variations which are compatible with progressive low-grade metamorphic illitization of smectite. Comparison of temperatures and mineral assemblages in this Plio-Pleistocene Borchard A-2 with similar low-grade metamorphic sequences of earlier Tertiary and Mesozoic ages indicate that the illitization reaction is kinetically controlled up to 175/sup 0/C and the development of Rgreater than or equal to 3 ordering, but is equilibrium controlled beyond that point.
- Research Organization:
- Univ. of Montana, Missoula (USA)
- OSTI ID:
- 6070161
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SMECTITE
DIAGENESIS
PETROGRAPHY
REACTION KINETICS
TEMPERATURE EFFECTS
CALIFORNIA
CHLORITE MINERALS
DRILL CORES
EQUILIBRIUM
FELDSPARS
GEOCHEMISTRY
ILLITE
MINERALOGY
PLEISTOCENE EPOCH
PLIOCENE EPOCH
SCANNING ELECTRON MICROSCOPY
X-RAY DIFFRACTION
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CENOZOIC ERA
CHEMISTRY
CLAYS
COHERENT SCATTERING
DIFFRACTION
ELECTRON MICROSCOPY
FEDERAL REGION IX
GEOLOGIC AGES
KINETICS
MICROSCOPY
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
QUATERNARY PERIOD
SCATTERING
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TERTIARY PERIOD
USA
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)
580400 - Geochemistry- (-1989)