Hostname: page-component-78c5997874-94fs2 Total loading time: 0 Render date: 2024-11-14T03:26:46.529Z Has data issue: false hasContentIssue false
  • English
  • Français

Micropores and micropermeable texture in alkali feldspars: geochemical and geophysical implications

Published online by Cambridge University Press:  05 July 2018

F. David L. Walker ,
Martin R. Lee  and
Ian Parsons
F. David L. Walker
Affiliation:
Department of Geology and Geophysics, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JW, Scotland
Martin R. Lee
Affiliation:
Department of Geology and Geophysics, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JW, Scotland
Ian Parsons
Affiliation:
Department of Geology and Geophysics, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JW, Scotland
Get access Rights & Permissions [Opens in a new window]

Abstract

Scanning Electron Microscopy and Transmission Electron Microscopy show that normal, slightly turbid alkali feldspars from many plutonic rocks contain high concentrations of micropores, from ∼1 µm to a few nm in length, typically 0.1 µm. There may be 109 pores mm−3 and porosities as high as 4.75 vol.% have been observed, although ∼1% is typical. Only ‘pristine’ feldspars, which are dark coloured when seen in the massive rock, such as in larvikite and some rapakivi granites, are almost devoid of pores. Weathering enlarges prexisting pores and exploits sub-regularly spaced edge dislocations which occur in semicoherent microperthites, but the underlying textures which lead to skeletal grains in soils are inherited from the high temperature protolith. Most pores are devoid of solid inclusions, but a variety of solid particles has been found. Although the presence of fluid in pores cannot usually be demonstrated directly, crushing experiments have shown that Ar and halogens reside in fluids. Some pores are ‘negative crystals’, often with re-entrants defined by the {110} Adularia habit, while others have curved surfaces often tapering to thin, cusp-shaped apices. The variable shape of pores accounts for the ability of some pores to retain fluid although the texture is elsewhere micropermeable, as shown by 18O exchange experiments.

Apart from rare, primary pores in pristine feldspar, pore development is accompanied by profound recrystallization of the surrounding microtexture, with partial loss of coherency in cryptoperthites. This leads to marked ‘deuteric coarsening’ forming patch and vein perthite, and replacement of ‘tweed’ orthoclase by twinned microcline. The Ab- and Or-rich phases in patch perthite are made up of discrete subgrains and the cuspate pores often develop at triple-junctions between them. Coarsened lamellar and vein perthites are composed of microporous subgrain textures. These ‘unzipping’ reactions result from fluid-feldspar interactions, at T <450°C in hypersolvus syenites and T < 350°C in a subsolvus granites, and are driven by elastic strain-energy in coherent cryptoperthites and in tweed textures. Further textural change may continue to surface temperatures. In salic igneous rocks there is a general connection between turbidity and the type of mafic mineral present; pristine alkali feldspars occur in salic igneous rocks with a preponderance of anhydrous mafic phases.

Because alkali feldspar is so abundant (and larger, 10 μm pores have previously been described in plagioclase), intracrystal porosity is a non-trivial feature of a large volume of the middle and upper crust. The importance of pores in the following fields is discussed: 39Ar/40Ar dating and ‘thermochronometry’; oxygen exchange; Rb and Sr diffusion; weathering; experimental low-temperature dissolution; development of secondary porosity and diagenetic albitization; leachable sources of metals; nuclear waste isolation; deformation; seismic anisotropy; electrical conductivity. Important questions concern the temperature range of the development of the textures and their stability during burial and transport into the deeper crust.

Keywords

feldsparalkalimicroporesmicropermeable texture
Type
Mineralogy
Information
Mineralogical Magazine , Volume 59 , Issue 396 , September 1995 , pp. 505 - 534
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1995

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

Aagaard, P., Egeberg, P.K., Saigal, G.C., Morad, S., and Bj0rlykke, K. (1990) Diagenetic albitization of detrital K-feldspars in Jurassic, Lower Cretaceous and Tertiary clastic reservoir rocks from offshore Norway, II. Formation water chemistry and kinetic considerations. J. Sediment. Petrol, 60, 575–81.CrossRefGoogle Scholar
Aberdam, D. (1965) Utilisation de la microscopie electronique pour l'etude des feldspaths. Observations sur des microperthites. Sci. de la Terre, 6, 76 pp.Google Scholar
Aldahad, A.A., and Morad, S. (1987) A SEM study of dissolution textures of detrital feldspars in Proterozoic sandstones, Sweden. Amer. J. Sci., 287, 460–514.Google Scholar
Atkinson, B.K. (1982) Subcritical crack propagation in rocks: theory, experimental results and applications. J. Struct. Geol, 4, 41–56.CrossRefGoogle Scholar
Berner, R.A., and Holdren, G.R. (1977) Mechanism of feldspar weathering: Some observational evidence. Geology, 5, 369–72.2.0.CO;2>CrossRefGoogle Scholar
Berner, R.A., and Holdren, G.R. (1979) Mechanism of feldspar weathering-II. Observations of feldspars from soils. Geochim. Cosmochim. Acta, 43, 1173–86.CrossRefGoogle Scholar
Bernotat-Wulf, H., Bertelmann, D. and Wondratschek, H. (1988) The annealing behaviour of Eifel sanidine (Volkesfeld) III. The influence of the sample surface and the sample size on the order-disorder transformation rate. N. Jb. Miner. Mh, 11, 503–15.Google Scholar
Bevan, J., and Savage, D. (1989) The effect of organic acids on the dissolution of K-feldspar under conditions relevant to burial diagenesis. Mineral. Mag., 53, 415–25.CrossRefGoogle Scholar
Blum, A.E. (1994) Feldspars in weathering. In Feldspars and their reactions. (Parsons, I., ed.), NATO ASI Series, C421, Kluwer Academic Publishers, Dordrecht, 595-630.Google Scholar
Boldryev, V.V. (1979) Control of the reactivity of solids. Ann. Rev. Mater. Sci., 9, 455-69CrossRefGoogle Scholar
Bradbury, M.H., and Green, A. (1986) Retardation of radionuclide transport by fracture flow in granite and argillaceous rocks. Commission of the European Communities, Nuclear Science and Technology, Final Report EUR 10619 EN. Google Scholar
Brown, W.L., and Willaime, C. (1974) An explanation of exsolution orientations and residual strain in cryptoperthites. In The feldspars (MacKenzie, W.S. and Zussman, J., eds.), Manchester University Press, 440-59.Google Scholar
Brown, W.L. and Parsons, I. (1984) The nature of potassium feldspar, exsolution microtextures and development of dislocations as a function of composition in perthitic alkali feldspars. Contrib. Mineral. Petrol, 86, 335–341.CrossRefGoogle Scholar
Brown, W.L. and Parsons I (1988) Zoned ternary feldspars in the Klokken intrusion: exsolution textures and mechanisms. Contrib. Mineral. Petrol, 98, 444–454.CrossRefGoogle Scholar
Brown, W.L. and Parsons, I. (1989) Alkali feldspars: ordering rates, phase transformations and behaviour diagrams for igneous rocks. Mineral. Mag., 54, 25–42.CrossRefGoogle Scholar
Brown, W.L. and Parsons, I. (1993) Storage and release of elastic strain energy: the driving force for low-temperature reactivity and alteration of alkali feldspar. In Defects and processes in the solid state: geoscience applications. The Mclaren volume (Boland, J. and Fitz Gerald, J.D., eds.), Elsevier Science Publishers BV, Amsterdam, 267-90.Google Scholar
Brown, W.L. and Parsons, I. (1994) Feldspars in igneous rocks. In Feldspars and their reactions (Parsons, I., ed.), NATO ASI Series, C421, Kluwer Academic Publishers, Dordrecht, 449-99.Google Scholar
Brown, W.L., Becker, S.M., and Parsons, I. (1983) Cryptoperthites and cooling rate in a layered syenite pluton: a chemical and TEM study. Contrib. Mineral Petrol, 82, 13–25.CrossRefGoogle Scholar
Burgess, R. and Parsons, I. (1994) Argon and halogen geochemistry of hydrothermal fluids in the Loch Ainort granite, Isle of Skye, Scotland. Contrib. Mineral. Petrol, 114, 345–55.CrossRefGoogle Scholar
Burgess, R., Kelley, S.P., Parsons, I., Walker, F.D.L. and Worden, R.H. (1992) 40Ar-39Ar analysis of perthite microtextures and fluid inclusions in alkali feldspars from the Klokken syenite, South Greenland. Earth Planet. Sci. Lett., 109, 147–67.CrossRefGoogle Scholar
Chapman, N.A. and McKinley, I.G. (1987) The Geological Disposal of Nuclear Waste. John Wiley and Sons, Chichester, 280 pp.Google Scholar
Conover, W.J. (1980) Practical non-parametric statistics. 2nd Edn., Wiley. 493 pp.Google Scholar
Crampin, S. and Lovell, J.H. (1991) A decade of shear-wave splitting in the Earth's crust: what does it mean? what use can we make of it? and what should we do next. Geophys. J. Int., 107, 387–407.CrossRefGoogle Scholar
Crampin, S. and Leary, P. (1993) Limits to crack density: the state of fractures in crustal rocks. 63rd Ann. Int. SEG Meeting, Washington, Expanded Abstracts, 758-61.CrossRefGoogle Scholar
Dengler, L. (1976) Microcracks in crystalline rocks. In Electron microscopy in mineralogy (Wenk, H.R., ed.), Springer, Berlin, Heidelberg, New York, 550-6.Google Scholar
Dodson, M.H. (1973) Closure temperature in cooling geochronological and petrological systems. Contrib. Mineral. Petrol, 40, 259–74.CrossRefGoogle Scholar
Eggleton, R.A. and Buseck, P.R. (1980) High resolution electron microscopy of feldspar weathering. Clays Clay Minerals, 28, 173–8.CrossRefGoogle Scholar
Farver, J.R. and Yund, R.A. (1990) The effect of hydrogen, oxygen, and water fugacity on oxygen diffusion in alkali feldspar. Geochim. Cosmochim. Ada, 54, 2953-64CrossRefGoogle Scholar
Ferry, J.M. (1985) Hydrothermal alteration of Tertiary igneous rocks from the Isle of Skye, northwest Scotland. II. Granites. Contrib. Mineral. Petrol, 91, 283–304.CrossRefGoogle Scholar
Fitz Gerald, J.D and Harrison, T.M. (1993) Argon diffusion domains in K-feldspar 1: microstructures in MH-10. Contrib. Mineral. Petrol, 113, 367–80.CrossRefGoogle Scholar
Folk, R.L. (1955) Note on the significance of ‘turbid’ feldspars. Amer. Mineral, 40, 356–7.Google Scholar
Foland, K.A. (1994) Argon diffusion in feldspars. In Feldspars and their reactions (Parsons, I., ed.), NATO ASI Series, C421, Kluwer Academic Publishers, Dordrecht, 415-47.Google Scholar
Foster, D.A., Harrison, T.M., Copeland, P. and Heizler, M.T. (1990) Effects of excess argon within large diffusion domains on K-feldspar age spectra. Geochim. Cosmochim. Ada, 54, 1699–708.CrossRefGoogle Scholar
Frost, B.R. and Bucher, K. (1994) Is water responsible for geophysical anomalies in the deep continental crust? A petrological perspective. Tectonophysics, 231, 293–309.CrossRefGoogle Scholar
Frost, B.R., Fyfe, W.S., Tazaki, K. and Chan, T. (1989) Grain-boundary graphite in rocks and implications for high electrical conductivity in the lower crust. Nature, 340, 134–6.CrossRefGoogle Scholar
Fung, P.C., Bird, G.W., Mclntyre, N.S., Sanipelli, G.G., Lopata, V.J. (1980) Aspects of feldspar dissolution. Nuclear Technology, 51: 188-96.CrossRefGoogle Scholar
Gandais, M., Guillemin, C. and Willaime, C. (1974) Study of boundaries in cryptoperthites. Eighth Int. Cong. Elec. Micros., Canberra, 508-9.Google Scholar
Giletti, B.J. (1985) The nature of oxygen transport within minerals in the presence of hydrothermal water and the role of diffusion. Chem. Geoi, 53, 197–206.CrossRefGoogle Scholar
Giletti, B.J. (1991) Rb and Sr diffusion in alkali feldspars, with implications for cooling histories of rocks. Geochim. Cosmochim. Ada, 55, 1331–43.CrossRefGoogle Scholar
Giletti, B.J. (1994) Isotopic equilibrium/disequilibrium and diffusion kinetics in feldspars. In Feldspars and their reactions (Parsons, I., ed.) NATO ASI Series, C421, Kluwer Academic Publishers, Dordrecht, 351-82.CrossRefGoogle Scholar
Gottlicher, J. and Kroll, H. (1990) Order/disorder transformation in KGaSi3O8. Third International Symposium of Experimental Mineralogy, Petrology and Geochemistry, Edinburgh. Terra Abstracts, 2, 77.Google Scholar
Graham, CM. and Elphick, S.C. (1994) Hydrogen in feldspars and related silicates. In Feldspars and their reactions (Parsons, I., ed.), NATO ASI Series, C421, Kluwer Academic Publishers, Dordrecht, 383-414.Google Scholar
Grisak, G.E. and Pickens, J.F. (1980) Solute transport through fractured media, I: the effect of matrix diffusion. Water. Resources Res., 16, 719–30.CrossRefGoogle Scholar
Guthrie, G.D. and Veblen, D.R. (1991) Turbid alkali feldspars from the Isle of Skye, northwest Scotland. Contrib. Mineral. Petrol, 108, 298–304.CrossRefGoogle Scholar
Harrison, T.M. (1990) Some observations on the interpretation of feldspar 40Ar/39Ar results. Chem. Geol. (Isotope Geoscience Section), 80, 219–29.CrossRefGoogle Scholar
Harrison, T.M., Heizler, M.T. and Lovera, O.M. (1993) In vacuo crushing experiments and K-feldspar thermochronometry. Earth Planet. Sci. Lett., 117, 169–80.CrossRefGoogle Scholar
Harrison, T.N., Parsons, I. and Brown, P.E. (1990) Mineralogical evolution of fayalite-bearing rapakivi granites from the Prins Christians Sund pluton, South Greenland. Mineral. Mag., 54, 57–66.CrossRefGoogle Scholar
Helgeson, H.C., Murphy, W.M. and Aagaard, P. (1984) Thermodynamic and kinetic constraints on reaction rates among minerals and aqueous solutions. II. Rate constants, effective surface area and the hydrolysis of feldspar. Geochim. Cosmochim. Ada, 48, 2405–32.CrossRefGoogle Scholar
Holdren, G.R. Jr. and Berner, R.A. (1979) Mechanism of feldspar weathering.-I. Experimental studies. Geochim. Cosmochim. Ada, 43, 1161–71.CrossRefGoogle Scholar
Holdren, G.R. Jr., Casey, W.H., Westrich, H.R., Carr, M. and Boslough, M. (1988) Bulk dislocation densities and dissolution rates in a calcic plagioclase. Chem. Geol., 70, 79.CrossRefGoogle Scholar
Hyndman, R.D. and Shearer, P.M. (1989) Water in the lower continental crust: modelling magnetotelluric and seismic reflection results. Geophys. J. Int., 98, 343–65.CrossRefGoogle Scholar
Hunter, R.F. (1987) Textural equilibrium in layered igneous rocks. In Origins of Igneous Layering (Parsons, I., ed.), NATO ASI Series, C196, D. Reidel, Dordrecht, 473–503.CrossRefGoogle Scholar
Jones, A.G. (1992) Electrical conductivity of the continental lower crust. In Continental Lower Crust (Fountain, D.M., Arculus, R.J. and Kay, R.W., eds.), Elsevier, 81-143.Google Scholar
Keller, W.D. (1978) Kaolinization of feldspar as displayed in scanning electron micrographs. Geology, 6, 184–8.2.0.CO;2>CrossRefGoogle Scholar
Lasaga, A.C. and Blum A.E. (1986) Surface chemistry, etch-pits and mineral water reactions. Geochim. Cosmochim. Ada, 50, 2363–79.CrossRefGoogle Scholar
Leary, P.C. (1991) Deep borehole evidence for fractal distribution of fractures in crystalline rock. Geophys. J. Int., 107, 615–27.CrossRefGoogle Scholar
Lee, M.R. and Parsons, I. (in press) Microtextural controls of weathering of perthitic alkali feldspars. Geochimica Cosmochimica Ada. Google Scholar
Lee, M.R., Waldron, K.A. and Parsons, I. (1995) Exsolution and alteration microtextures in alkali feldspar phenocrysts from the Shap granite. Mineral. Mag., 59, 63–78.CrossRefGoogle Scholar
Lee, M.R., Waldron, K.A., Parsons, I. and Brown, W.L. (in prep) Mechanisms of fluid-feldspar interaction: pleated rims and the development of vein perthite. Contrib. Mineral. Petrol. Google Scholar
Lidiak, E.G. and Ceci, V.M. (1991) Authigenic K-feldspar in the Precambrian basement of Ohio and its effect on tectonic discrimination of the granitic rocks. Can. J. Earth Sci, 28, 1624–34.CrossRefGoogle Scholar
Lloyd, G.E. and Knipe, R.J. (1992) Deformation mechanisms accomodating faulting of quartzite under upper crustal conditions. J. Struct. Geol., 14, 127-43CrossRefGoogle Scholar
Lovera, O.M., Richter, F.M. and Harrison, T.M. (1989) The 40Ar/39Ar thermochronometry for slowly cooled samples having a distribution of diffusion domain sizes. J. Geophys. Res., 94, B12, 17917–35CrossRefGoogle Scholar
Lovera, O.M., Richter, F.M. and Harrison, T.M. (1990) Diffusion domains determined by 39Ar released during step heating. J. Geophys. Res., 96, B2, 2057-69Google Scholar
Lundstrom, I. (1974) Etch pattern and albite twinning in two plagioclases. Arkiv. Mineral. Geologi., 5, 63–91.Google Scholar
Manning, D.A.C., Rae, E.I.C. and Small, J.S. (1991) An exploratory study of acetate decomposition and dissolution of quartz and Pb-rich potassium feldspar at 150°C, 50 MPa (500 bars). Mineral. Mag., 55, 183–95.CrossRefGoogle Scholar
Mareschal, M., Fyfe, W.S., Percival, J. and Chan, T. (1992) Grain-boundary graphite in Kapuskasing gneisses and implications for lower crustal conductivity. Nature, 357, 674–6.CrossRefGoogle Scholar
McDowell, S.D. (1986) Compositional and structural state of coexisting feldspars, Salton Sea geothermal field. Mineral. Mag., 50, 75–84.CrossRefGoogle Scholar
Meike, A. (1990) A micromechanical perspective on the role of dislocations in selective dissolution. Geochim. Cosmochim. Ada, 54, 3347–52.CrossRefGoogle Scholar
Montgomery, C.W. and Brace, W.F. (1975) Micropores in plagioclase. Contrib. Mineral. Petrol., 52, 17–28.CrossRefGoogle Scholar
Murphy, W.M. (1989) Dislocations and feldspar dissolution. Euro. J. Min., 1, 315–26.CrossRefGoogle Scholar
Neretnieks, I. (1980) Diffusion in a rock matrix: an important factor in radionuclide retardation. J. Geophys. Res., 85, 4379–97.CrossRefGoogle Scholar
Nesbitt, H.W., MacRae, N.D. and Shotyk, W. (1991) Congruent and incongruent dissolution of labradorite in dilute, acidic, salt solutions. J. Geoi, 99, 429–42.CrossRefGoogle Scholar
Neumann, D. and Rutter, E.H. (1994) Experimental deformation of partially molten Westerly granite under vapour-absent conditions. Terra Abstracts, supplement No. 1 to Terra Nova, 6, 35.Google Scholar
Nixon, R.A. (1979) Differences in incongruent weathering of plagioclase and microcline-cation leaching versus precipitates. Geology, 7, 221–4.2.0.CO;2>CrossRefGoogle Scholar
O'Neill, J.R. and Taylor, H.P. (1967) The oxygen isotope and cation exchange chemistry of feldspars. Amer. Mineral, 52, 1414–37.Google Scholar
Parsons, I. (1978) Feldspars and fluids in cooling plutons. Mineral. Mag., 42, 1–17.CrossRefGoogle Scholar
Parsons, I. (1980) Alkali-feldspar and Fe-Ti oxide exsolution textures as indicators of the distribution and subsolidus effects of magmatic ‘water’ in the Klokken layered syenite intrusion, South Greenland. Trans. Roy. Soc. Edinburgh.: Earth Sci., 71, 1–12.CrossRefGoogle Scholar
Parsons, I. and Brown, W.L. (1984) Feldspars and the thermal history of igneous rocks. In Feldspars and feldspathoids: structure and occurrence. (Brown, W.L., ed.), NATO ASI Series, Reidel, Dordrecht, 317-71.Google Scholar
Parsons, I., Rex, D.C., Guise, P. and Halliday, A.N. (1988) Argon-loss by alkali feldspars. Geochim. Cosmochim. Ada, 52, 1097–112.CrossRefGoogle Scholar
Parsons, I., Mason, R.A., Becker, S.M. and Finch, A.A. (1991) Biotite equilibria and fluid circulation in the Klokken Intrusion. J. Petrol., 32, 1299–333.CrossRefGoogle Scholar
Poldervaart, A. and Gilkey, A.K. (1954) On clouded plagioclase. Amer. Mineral., 39,: 75-91Google Scholar
Richter, F.M., Lovera, O.M., Harrison, T.M. and Copeland, P. (1991) Tibetan tectonics from 40Ar/39Ar analysis of a single K-feldspar sample. Earth Plan. Sci. Lett., 105, 266–78.CrossRefGoogle Scholar
Rickert, P.G., Strickert, R.G. and Seitz, M.G. (1979) Nuclide migration in fractured or porous rock. In Radioactive Waste in Geologic Storage (Fried, S., ed.), American Chem Soc, Washington, 167-90.CrossRefGoogle Scholar
Roedder, E. (1984) Fluid Inclusions. Mineral. Soc. Amer. Reviews in Mineralogy, 12, 646.Google Scholar
Roedder, E. and Coombs, D.S. (1967) Immiscibility in granitic melts, indicated by fluid inclusions in ejected granite blocks from Ascension Island. J. Petrol., 8, 417-51.CrossRefGoogle Scholar
Saigal, G.C., Morad, S., Bj0rlykke, K., Egeberg, P.K. and Aagaard, P. (1988) Diagenetic albitization of detrital K-feldspar in Jurassic, Lower Cretaceous and Tertiary clastic reservoir rocks from offshore Norway, I: Textures and origin. J. Sediment. Petrol, 58, 1003–13.Google Scholar
Seifert, K.E. (1967) Electron microscopy of etched plagioclase feldspar. Journ. Amer. Ceram. Soc. 50, 660–1.CrossRefGoogle Scholar
Smith, J.V. and Brown, W.L. (1988) Feldspar Minerals 1. Crystal Structures, Physical, Chemical and Microtextural Properties. Springer-Verlag, Berlin, Heidelberg, New York, 828 pp.Google Scholar
Sprunt, E.S. and Brace, W.F. (1974) Direct observations of microcavities in crystalline rocks. Int. J. Rock Mech. Min. Sci. & Geomech. Abstr., 11, 139–50.CrossRefGoogle Scholar
Taylor, H.P. and Forester, R.W. (1971) Low-O18 igneous rocks from the intrusive complexes of Skye, Mull, and Ardnarmurchan, Western Scotland. J. Petrol, 12, 465-98CrossRefGoogle Scholar
Tazaki, K. and Fyfe, W.S. (1987) Primitive clay precursors formed on feldspars. Can. J. Earth Sci., 24, 506–27.CrossRefGoogle Scholar
Tchoubar, C. (1965) Formation de la kaolinite a partir d'albite alteree par l'eau a 200°C. Etude en microscopie et diffraction electroniques. Bull. Soc. Franc. Min. Crist., 88, 483–518.Google Scholar
Tullis, J. (1975) Elastic strain effects in coherent perthitic feldspars. Contrib. Mineral. Petrol, 49, 83–91.CrossRefGoogle Scholar
Tullis, J. and Yund, R.A. (1977) Experimental deformation of dry Westerly granite. J. Geophys. Res., 82, 5705–17.CrossRefGoogle Scholar
Tullis, J. and Yund, R.A. (1979) Calculation of coherent solvi for alkali feldspar, iron-free clinopyroxene, nepheline-kalsilite, and hematite-ilmenite. Amer. Min., 64, 1063-74Google Scholar
Tuttle, O.F. (1952) Origin of the contrasting mineralogy of extrusive and plutonic salic rocks. J. Geol, 60, 107–24.CrossRefGoogle Scholar
Velbel, M.A. (1986) Influence of surface area, surface characteristics and solution composition on feldspar weathering rates. In Geochemical processes at mineral surfaces (Davis, J.A. and Hayes, K.F., eds.), Amer. Chem. Soc, 615-34.Google Scholar
Villa, I.M. (1994) Multipath Ar transport in K-feldspar deduced from isothermal heating experiments. Earth Planet. Sci. Lett., 122, 393–401.CrossRefGoogle Scholar
Waldron, K.A. and Parsons, I. (1992) Feldspar microtextures and multistage thermal history of syenites from the Coldwell Complex, Ontario. Contrib. Mineral. Petrol, 111, 222–34.CrossRefGoogle Scholar
Waldron, K.A., Parsons, I. and Brown, W.L. (1993) Solution-redeposition and the orthoclase-microcline transformation: evidence from granulites and rele-vance to 18O exchange. Mineral. Mag., 57, 687–95.CrossRefGoogle Scholar
Waldron, K.A., Lee, M.R. and Parsons, I. (1994) The microstructures of perthitic alkali feldspars revealed by hydrofluoric acid etching. Contrib. Mineral. Petrol, 116, 360–64.CrossRefGoogle Scholar
Walker, F.D.L. (1990) Ion microprobe study of intragrain micropermeability in alkali feldspars. Contrib. Mineral. Petrol, 106, 124–8.Google Scholar
Walker, F.D.L. (1991) Micropores in Alkali Feldspars. Unpublished PhD thesis, University of Edinburgh. White, J.C. and Barnett, R.L. (1990) Microstructural signatures and glide twins in microcline, Hemlo, Ontario. Can. Mineral., 28, 757–69.Google Scholar
Wilson, M.J. (1975) Chemical weathering of some primary rock-forming minerals. Soil ScL, 119, 349-55.CrossRefGoogle Scholar
Wilson, M.J. and McHardy, W.J. (1980) Experimental etching of a microcline perthite and implications regarding natural weathering. J. Microscopy, 120, 291–302.CrossRefGoogle Scholar
Worden, R.H. and Rushton, J.C. (1992) Diagenetic K-feldspar textures: a TEM study and model for K-feldspar growth. J. Sediment. Petrol, 62, 779–89.Google Scholar
Worden, R.H., Walker, F.D.L., Parsons, I. and Brown, W.L. (1990) Development of microporosity, diffu-sion channels and deuteric coarsening in perthitic alkali feldspars. Contrib. Mineral. Petrol, 104, 507–15.CrossRefGoogle Scholar