Abstract
Clay minerals in shales from cores at Site 808, Nankai Trough, have been studied using X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), and analytical electron microscopy (AEM) to compare the rates and mechanisms of illitization with those of coeval bentonites, which were described previously. Authigenic K-rich smectite having a high Fe content (∼7 wt. %) was observed to form directly as an alteration product of volcanic glass at a depth of ∼500 meters below seafloor (mbsf) with no intermediate precursor. Smectite is then largely replaced by Reichweite, R, (R = 1) illite-smectite (I-S) and minor illite and chlorite over depths from ∼550 to ∼700 mbsf. No further mineralogical changes occur to the maximum depth cored, ∼1300 m. Most smectite and I-S in shales are derived from alteration of glass, rather than being detrital, as is usually assumed. Discrete layer sequences of smectite, I-S, or illite coexist, indicating discontinuities of the transformation from smectite to (R = 1) I-S to illite. Authigenic Fe-rich chlorite forms concomitantly with I-S and illite, with the source of Fe from reactant smectite.
Smectite forms from glass with an intermediate precursor in coeval bentonites at approximately the same depth as in shales, but the smectite remains largely unchanged, with the exception of exchange of interlayer cations (K → Na → Ca) in response to formation of zeolites, to the bottom of the core. Differences in rates of illitization reflect the metastability of the clays. Temperature, structure-state, and composition of reactant smectite are ruled out as determining factors that increase reaction rates here, whereas differences in water/rock ratio (porosity/permeability), Si and K activities, and organic acid content are likely candidates.
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Abercrombie, H.J., Hutcheon, I.E., Bloch, J.D., and deCaritat, P. (1994) Silica activity and the smectite-illite reaction. Geology, 22, 539–542.
Ahn, J.H. and Peacor, D.R. (1985) Transmission electron microscopic study of diagenetic chlorite in Gulf Coast argillaceous sediments. Clays and Clay Minerals, 33, 228–236.
Ahn, J.H. and Peacor, D.R. (1988) Transmission and analytical electron microscopy study of the smectite-to illite transition. Clays and Clay Minerals, 34, 165–179.
Ahn, J.H., Peacor, D.R., and Coombs, D.S. (1988) Formation mechanisms of illite, chlorite and mixed-layer illite-chlorite in Triassic volcanogenic sediments from the Southland Syncline, New Zealand. Contributions to Mineralogy and Petrology, 99, 82–89.
Aja, S.U., Rosenberg, P.E., and Kittrick, J.A. (1991) Illite equilibria in solution: I. Phase relationships in the system K2O-Al2O3-SiO2-H2O between 25 and 250 °C. Geochimica et Cosmochimica Acta, 55, 1353—1364.
Altaner, S.P. and Grim, R.E. (1990) Mineralogy, chemistry, and diagenesis of the tuffs in the Sucker Creek Formation (Miocene), eastern Oregon. Clays and Clay Minerals, 38, 561–572.
Altaner, S.P. and Ylagan, R.E (1997) Comparison of structural models of mixed-layer illite/smectite and reaction mechanisms of smectite illitization. Clays and Clay Minerals, 45, 517–533.
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.
Dong, H., Peacor, D.R., and Freed, R.L. (1997) Phase relations among smectite, R1 illite-smectite, and illite. American Mineralogist, 82, 379–391.
Dong, H., Hall, C.M., Peacor, D.R., Masuda, H., and Halliday, A.M. (1998) 40Ar/39Ar dating of smectite formation in bentonites from Nankai Trough, Japan. Clay Mineral Society Meeting Program and Abstracts, 34th Annual Meeting, 76.
Drits, V., Srodon, J., and Eberl, D.D. (1997) XRD measurement of mean crystallite thickness of illite and illite/smectite: Reappraisal of the Kubier index and the Scherrer equation. Clays and Clay Minerals, 45, 461–475.
Eggleton, R.A. (1987) Non-crystalline Fe-Si-Al-oxyhydr-oxides. Clays and Clay Minerals, 35, 29–37.
Eslinger, E. and Glasmann, J.R. (1993) Geofhermometry and geochronology using clay minerals—an introduction. Clays and Clay Minerals, 41, 117–118.
Essene, E.J. and Peacor, D.R. (1995) Clay mineral thermometry—A critical perspective. Clays and Clay Minerals, 43, 540–553.
Freed, R.L. and Peacor, D.R. (1989) Geopressured shale and sealing effect of the smectite to illite transition. American Association of Petroleum Geologists Bulletin, 73, 1223–1232.
Guthrie, G. and Reynolds, R.C., Jr. (1998) A coherent TEM-and XRD-description of mixed-layer illite/smectite: Computer simulations. Canadian Mineralogist, 36, 1421–1434.
Hover, V.C. and Peacor, D.R. (1999) Direct evidence for potassium uptake in smectite during early diagenesis of marine sediments and MORB: Balancing the global potassium budget. Clay Mineral Society Meeting Program and Abstracts, 36th Annual Meeting, Purdue University, West Lafayette, 50.
Hower, J., Eslinger, E.V., Hower, M.E., and Perry, E.A. (1976) Mechanism of burial metamorphism of argillaceous sediment: 1. Mineralogical and chemical evidence. Geological Society of American Bulletin, 87, 725–737.
Huang, W.L., Longo, J.M., and Pevear, D.R. (1993) An experimentally derived kinetic model for smectite-illite conversion and its use as a geothermometer. Clays and Clay Minerals, 41, 162–177.
Kim, J.-W., Peacor, D.R., Tessier, D., and Elsass, F.A. (1995) Technique for maintaining texture and permanent expansion of smectite interlayers for TEM observations. Clays and Clay Minerals, 43, 51–57.
Li, G., Peacor, D.R., and Coombs, D.S. (1997) Transformation of smectite to illite in bentonite and associated sediments from Kaka Point, New Zealand: Contrast in rate and mechanism. Clays and Clay Minerals, 45, 54–67.
Li, G., Peacor, D.R., and Essene, E.J. (1998) The formation of sulfides during alteration of biotite to chlorite-corrensite. Clays and Clay Minerals, 46, 649–657.
Lindgreen, H., Jacobsen, H., and Jacobsen, H.J. (1991) Dia-genetic structural transformations in North Sea Jurassic illite/smectite. Clays and Clay Minerals, 39, 54–69.
Masuda, H., Tanaka, H., Gamo, T., Soh, W., and Taira, A. (1993) Major element chemistry and alteration mineralogy of volcanic ash, Site 808 in the Nankai Trough. I. Proceedings of Ocean Drilling Program Scientific Results 131B, I. Hill, A. Taira, and J.V. Firth, eds., Ocean Drilling Program, College Station, Texas, 175–183.
Masuda, H., O’Neil, J.R., Jiang, W-.T, and Peacor, D.R. (1996) Relation between interlayer composition of authi-genic smectite, mineral assemblages, I/S formation rate and fluid composition in silicic ash of the Nankai Trough. Clays and Clay Minerals, 44, 443–459.
Merriman, R.J., Roberts, B., Peacor, D.R., and Hirons S.R. (1995) Strain-related differences in the crystal growth of white mica and chlorite: A TEM and XRD study of the development of metapelitic microfabrics in the Southern Uplands thrust terrane, Scotland. Journal of Metamorphic Geology, 13, 559–576.
Moore, D.M. and Reynolds, R.C., Jr. (1997). X-ray Diffraction and the Identification and Analysis of Clay Minerals, 2nd edition. Oxford University Press, New York, 332 pp.
Nadeau, P.H. (1998) Evolution, current situation, and geological implications of the “fundamental particle” concept. Canadian Mineralogist, 36, 1409–1414.
Peacor, D.R. (1998) Implications of TEM data for the concept of fundamental particles. Canadian Mineralogist, 36, 1397–1408.
Reynolds, R.C., Jr. (1992) X-ray diffraction studies of illite/ smectite from rocks, <1 μm randomly oriented powders, and <1 μm oriented powder aggregates: The absence of laboratory-induced artifacts. Clays and Clay Minerals, 40, 387–396.
Shipboard Scientific Party (1991) Site 808. In I. Hill, A. Taira, and J.V. Firth, eds.. Proceedings of Ocean Drilling Program, Initial Reports, 131, Ocean Drilling Program, College Station, Texas, 71–269.
Small, J.S. (1993) Experimental determination of the rates of precipitation of authigenic illite and kaolinite in the presence of aqueous oxalate and comparison to the K/Ar ages of authigenic illite in reservoir sandstones. Clays and Clay Minerals, 41, 191–208.
Tazaki, K., Fyfe, W.S., and Van Der Gaast, S.J. (1989) Growth of clay minerals in natural and synthetic glasses. Clays and Clay Minerals, 37, 348–354.
Underwood, M., Pickering, K., Gieskes, J.M., Kastner, M., and Orr, R. (1993) Sedimentary facies evolution of the Nankai forearc and its implications for the growth of the Shimanto accretionary prism. I. Proceedings of the Ocean Drilling Program, Scientific Results, 131B, I. Hill, A. Taira, and J.V. Firth, eds., Ocean Drilling Program, College Station, Texas, 343–363.
Velde, B. and Vasseur, G. (1992) Estimation of the diagenetic smectite to illite transformation in time-temperature space. American Mineralogist, 77, 967–976.
Whitney, G. (1990) Role of water in the smectite-to-illite reaction. Clays and Clay Minerals, 38, 343–350.
Yau Y.-C., Peacor, D.R., and McDowell, S.D. (1987) Smec-tite-illite reactions in Saltan Sea shales: A transition and analytical electron microscope study. Journal of Sedimentary Petrology, 57, 335–342.
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Masuda, H., Peacor, D.R. & Dong, H. Transmission Electron Microscopy Study of Conversion of Smectite to Illite in Mudstones of the Nankai Trough: Contrast with Coeval Bentonites. Clays Clay Miner. 49, 109–118 (2001). https://doi.org/10.1346/CCMN.2001.0490201
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DOI: https://doi.org/10.1346/CCMN.2001.0490201