Hostname: page-component-78c5997874-ndw9j Total loading time: 0 Render date: 2024-11-13T00:55:55.694Z Has data issue: false hasContentIssue false
  • English
  • Français

Electron microscope and microprobe analysis of chlorite–mica stacks in the Wenlock turbidites, mid Wales, U.K.

Published online by Cambridge University Press:  01 May 2009

Andrew J. Dimberline
Andrew J. Dimberline
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

Chlorite–mica stacks in the Wenlock turbidites have been studied using backscattered electron microscopy and electron microprobe analysis, combined with thin-section work and bulk rock chemical analysis. The stacks occur in fine sandstones and silt–mud turbidites and range in length from < 30 μm to 1.5 mm. They consist of interlayered packets of Fe-rich chlorite and mica.

Combined textural and chemical data suggest that many of the stacks represent altered detrital biotite micas. A four-stage alteration sequence is proposed:

(1) Subaerial alteration of biotite, in the source area, to interlayered biotite–hydrobiotite/vermiculite.

(2) Post-depositional collapse of vermiculite to form a mica phase under conditions of high K+/H+ in the sediment pore waters.

(3) Decrease in K+/H+ ratio, possibly due to H+ build up in the fermentation zone, causing alteration of biotite layers to chlorite.

(4) Kinking of the stacks and pressure solution of chlorite early in the development of cleavage.

Type
Articles
Information
Geological Magazine , Volume 123 , Issue 3 , May 1986 , pp. 299 - 306
Copyright
Copyright © Cambridge University Press 1986

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Attlewell, P. B. & Taylor, R. K.. 1969. A microtextural interpretation of a Welsh slate. International Journal of Rock Mechanics and Mining Sciences 6, 423–38.CrossRefGoogle Scholar
Bassett, W. A. 1959. The origin of the vermiculite deposit at Libby, Montana. The American Mineralogist 44, 282–99.Google Scholar
Bayliss, R. 1975. Nomenclature of the trioctahedral chlorites. Canadian Mineralogist 13, 178–80.Google Scholar
Beach, A. 1979. Pressure solution as a metamorphic process in deformed terrigenous sedimentary rocks. Lithos 12, 51–8.CrossRefGoogle Scholar
Beutner, E. C. 1978. Slaty cleavage and related strain in Martinsburg Slate, Delaware Water Gap, New Jersey. American Journal of Science 278, 1–23.CrossRefGoogle Scholar
Bjorlykke, K. 1971. Petrology of Ordovician sediments in Wales. Norsk Geologisk Tidsskrift 51, 123–39.Google Scholar
Bouma, A. H. 1962. Sedimentology of Some Flysch Deposits. Amsterdam: Elsevier, 168 pp.Google Scholar
Brenchley, P. J. 1969. Origin of matrix in Ordovician greywackes, Berwyn Hills, North Wales. Journal of Sedimentary Petrology 39, 1297–301.CrossRefGoogle Scholar
Brindley, G. W. & Brown, G. (eds.). 1980. Crystal Structures of Clay Minerals and their X-ray Identification. London: The Mineralogical Society, 495 pp.CrossRefGoogle Scholar
Craig, J., Fitches, W. R. & Maltman, A. J. 1982. Chlorite-mica stacks in low-strain rocks from central Wales. Geological Magazine 119, 243–56.CrossRefGoogle Scholar
Cummins, W. A. 1957. The Denbigh Grits: Wenlock Greywackes in Wales. Geological Magazine 94, 433–51.CrossRefGoogle Scholar
Davies, W. & Cave, R. 1976. Folding and cleavage determined during sedimentation. Sedimentary Geology 15, 89–133.CrossRefGoogle Scholar
Deer, W. A., Howie, R. A. & Zussman, J. 1966. An Introduction to the Rock Forming Minerals. London: Longman, 528 pp.Google Scholar
Doyle, L. J., Carder, K. L. & Steward, R. G. 1983. The hydraulic equivalence of mica. Journal of Sedimentary Petrology 53, 643–8.Google Scholar
Englund, J.-O. & Jorgensen, P. 1973. A chemical classification system for argillaceous sediments and factors affecting their composition. Geologiska Foreningerts i Stockholm Forhandlinger 95, 87–97.CrossRefGoogle Scholar
Evans, L. J. & Adams, W. A. 1975. Chlorite and illite in some Lower Palaeozoic mudstones of mid Wales. Clay Minerals 10, 387–97.CrossRefGoogle Scholar
Foster, M. D. 1962. Interpretation of the composition and a classification of the chlorites. US Geological Survey Professional Paper 414-A, 33 pp.Google Scholar
Frey, M. 1970. The step from diagenesis to metamorphism in pelitic rocks during Alpine orogenesis. Sedimentology 15, 261–79.CrossRefGoogle Scholar
Frey, M. 1974. Alpine metamorphism of pelitic and marly rocks of the central Alps. Schweizerische Mineralogische und Petrographische Mittelungen 54, 489–506.Google Scholar
Frey, M. 1978. Progressive low-grade metamorphism of a black shale formation, central Swiss Alps, with special reference to pyrophyllite and margarite bearing assemblages. Journal of Petrology 19, 95–135.CrossRefGoogle Scholar
Hall, M. S. & Lloyd, G. E. 1981. The SEM examination of geological samples with a semiconductor backscattered electron detector. American Mineralogist 66, 362–8.Google Scholar
Hayes, J. B. 1970. Polytypism of chlorite in sedimentary rocks. Clays and Clay Minerals 18, 285–306.CrossRefGoogle Scholar
Hoo Lee, Jung, Peacor, D. R., Lewis, D. D. & Wintsch, R. P. 1984. Chloriterillite/muscovite interlayered and interstratifiedcrystals: A TEM/STEM study. Contributions to Mineralogy and Petrology 88, 372–85.CrossRefGoogle Scholar
Kisch, H. J. 1983. Mineralogy and petrology of burial diagenesis (burial metamorphism) and incipient metamorphism in clastic rocks. In Diagenesis in Sediments and Sedimentary Rocks (eds. Larsen, G. & Chilingar, B. V.), pp. 289–495. Amsterdam: Elsevier.Google Scholar
Komar, P. D., Baba, Jumpei & Cui, Bingquan. 1984. Grain-size analyses of mica within sediments and the hydraulic equivalence of mica and quartz. Journal of Sedimentary Petrology 54, 1379–91.Google Scholar
Kranck, K. 1984. Grain size characteristics of turbidites. In Fine-grained Sediments: Deep-Water Processes and Facies (eds. Stow, D. A. V. & Piper, D. J. W.), pp. 83–92. Geological Society Special Publications: Blackwell Scientific Publications.Google Scholar
Krinsley, D. H., Pye, K. & Kearsley, A. T. 1983. Applications of backscattered electron microscopy in shale petrology. Geological Magazine 120, 109–14.CrossRefGoogle Scholar
Maltman, A. J. 1981. Primary bedding-parallel fabrics in structural geology. Journal of the Geological Society of London 138, 475–83.CrossRefGoogle Scholar
Perrin, R. M. 1971. The Clay Mineralogy of British Sediments. London: The Mineralogical Society, 247 pp.Google Scholar
Pye, K. & Krinsley, D. H. 1983. Mudrocks examined by backscattered electron microscopy. Nature 301, 412–13.CrossRefGoogle Scholar
Pye, K. & Krinsley, D. H. 1984. Petrographic examination of sedimentary rocks in the SEM using backscattered electron detectors. Journal of Sedimentary Petrology 54, 877–88.Google Scholar
Sawhney, B. L. 1967. Interstratification in vermiculite. Proceedings of the 15th Conference, Pittsburgh, Pennsylvania. The Clay Minerals Society, pp. 75–84.Google Scholar
Scott, A. D. & Smith, S. J. 1966. Susceptibility of interlayer potassium in micas to exchange with sodium. Clays and Clay Minerals 14, 69–81.CrossRefGoogle Scholar
Stewart, W. S. 1983. Palaeobotany and the Evolution of Plants. Cambridge, England: Cambridge Univerity Press, 405 pp.Google Scholar
Stoch, L. & Sikora, W. 1976. Transformations of micas in the process of kaolinization of granites and gneisses. Clays and Clay Minerals 24, 156–62.CrossRefGoogle Scholar
Stow, D. A. V. & Shanmugam, B. 1980. Sequence of structures in fine-grained turbidites: comparison of recent deepsea and ancient flysch sediments. Sedimentary Geology 25, 23–42.CrossRefGoogle Scholar
van der Pluum, B. A. & Kaars-Supesteun, C. H. 1984. Chlorite-mica aggregates: morphology, orientation, development and bearing on cleavage formation in very-low-grade rocks. Journal of Structural Geology 6, 399–407.CrossRefGoogle Scholar
Voll, G. 1960. New work on petrofabrics. Liverpool and Manchester Geological Journal 2, 503–97.CrossRefGoogle Scholar
Weber, K. 1981. Kinematic and metamorphic aspects of cleavage formation in very low grade metamorphic slates. Tectonophysics 78, 291–306.CrossRefGoogle Scholar
White, S. H., Huggett, J. M. & Shaw, H. F. 1985. Electron-optical studies of phyllosilicate intergrowths in sedimentary and metamorphic rocks. Mineralogical Magazine 49, 413–23.CrossRefGoogle Scholar
White, S. H. & Knipe, R. J. 1978. Microstructure and cleavage development in selected slates. Contributions to Mineralogy and Petrology 66, 165–74.CrossRefGoogle Scholar
Wilson, M. J. 1970. A study of weathering in a soil derived from a biotite-hornblende rock. Clay Minerals 8, 291–303.CrossRefGoogle Scholar
Woodland, B. G. 1982. Gradational development of dominant slaty cleavage, its origin and relation to chlorite porphyroblasts in the Martinsburg Formation, eastern Pennsylvania. Tectonophysics 82, 89–124.CrossRefGoogle Scholar
Woodland, B. G. 1985. Relationship of concretions and chlorite-muscovite porphyroblasts to the development of domainal cleavage in low-grade metamorphic deformed rocks from north-central Wales, Great Britain. Journal of Structural Geology 7, 205–15.CrossRefGoogle Scholar