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Crystallographic Controls on the Alteration of Microcline Perthites from the Spruce Pine District, North Carolina

Published online by Cambridge University Press:  28 February 2024

Julia M. Sheets  and
Rodney T. Tettenhorst
Julia M. Sheets*
Affiliation:
Department of Geological Sciences, Ohio State University, Columbus, Ohio 43210-1110
Rodney T. Tettenhorst
Affiliation:
Department of Geological Sciences, Ohio State University, Columbus, Ohio 43210-1110
*
†Present address: Wittenberg University, Springfield, Ohio 45501.
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Abstract

Altered perthites from a weathered pegmatite in the Spruce Pine District, North Carolina, were characterized by electron microprobe as a K-rich microcline host with lesser Na-rich plagioclase having a lamellar morphology. Light-optical and transmission electron microscopy (TEM) show microtextural elements such as phase boundaries, holes and microfractures that could serve as potential nucleation sites for alteration to clay minerals.

The host microcline contains albite and pericline twinning textures that vary in character; the amount of each twinning type and/or the size of twin individuals changes on a μm scale. Plagioclase ranges from large lamellar vein and film albite (visible in the light microscope) to cryptoperthite whose size ranges from μm to perhaps 100 Å. The smallest-scale albite appears to be a late-stage phase of exsolution in which lamellae have nucleated heterogeneously on albite-twin composition planes in the microcline.

Alteration is concentrated in vein and film albite, especially along grain boundaries with microcline. Powder X-ray diffraction (XRD) patterns of intensely altered pegmatite show halloysite. Holes, microfractures, vein albite/host microcline boundaries and microcline/halloysite boundaries trend parallel to the traces of (010) and {110}, suggesting that these directions are pathways along which fluids migrate. Cleavage and microfractures occur along, and holes are bounded by, these directions. Holes are associated with dislocations and the latter are observed at feldspar/clay boundaries. Twin domains and cryptoperthitic albite are less susceptible to alteration than coarse lamellar albite and regions containing negative crystals and microfractures. However, microtextures in some areas containing halloysite suggest that once fluids penetrate the crystal, alteration may proceed preferentially in more strongly twinned regions.

Keywords

AlbiteAlterationCrystallographic ControlDefectsHalloysiteHolesMicroclineMicrofracturesMicrotextural ElementsPerthitePhase BoundariesTwinning
Type
Research Article
Information
Clays and Clay Minerals , Volume 45 , Issue 3 , June 1997 , pp. 404 - 417
Copyright
Copyright © 1997, The Clay Minerals Society

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References

Andersen, O., (1928) The genesis of some types of feldspar from granite pegmatites Nor Geol Tidsskr 10 10–207.Google Scholar
Akizuki, M., (1972) Electron-microscopic investigation of microcline twinning Am Mineral 57 57–808.Google Scholar
Banfield, J.F. and Eggleton, R.A., (1990) Analytical transmission electron microscope studies of plagioclase, muscovite, and K-feldspar weathering Clays Clay Miner 38 77–89 10.1346/CCMN.1990.0380111.CrossRefGoogle Scholar
Berner, R.A., (1981) Kinetics of weathering and diagenesis, Chapter 3 Kinetics of geochemical processes. Rev Mineral 8 111–133 10.1515/9781501508233-007.CrossRefGoogle Scholar
Berner, R.A. and Holdren, G.R. Jr., (1977) Mechanism of feldspar weathering: I. Some observational evidence Geology 5 5–372 10.1130/0091-7613(1977)5<369:MOFWSO>2.0.CO;2.2.0.CO;2>CrossRefGoogle Scholar
Brindley, G.W. and Brindley, G.W., (1951) The kaolin minerals X-ray identification and crystal structures of clay minerals London Mineral Soc. 32–75.Google Scholar
Brobst, D.A.. 1962. Geology of the Spruce Pine district, Avery, Mitchell, and Yancey counties, North Carolina. US Geol Surv Bull 1122A. 26 p.Google Scholar
Brown, W.L. and Macaudiere, J., (1984) Microfracturing in relation to atomic structure of plagioclase from a deformed metaanorthosite J Struct Geol 6 6–586 10.1016/0191-8141(84)90067-1.CrossRefGoogle Scholar
Brown, W.L. and Parsons, I., (1983) Nucleation on perthite-perthite boundaries and exsolution mechanisms in alkali feldspars Phys Chem Mineral 10 10–61 10.1007/BF00309585.CrossRefGoogle Scholar
Brown, W.L. and Parsons, I., (1984) Exsolution and coarsening mechanisms and kinetics in an ordered cryptoperthite series Contrib Mineral Petrol 86 86 18.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 109 147–167 10.1016/0012-821X(92)90080-F.CrossRefGoogle Scholar
Butler, J.R., (1973) Paleozoic deformation and metamorphism in the Blue Ridge Thrust Sheet near Spruce Pine, North Carolina [abstract] Geol Soc Am Abstr with Prog 5 382.Google Scholar
Casey, W.H. Banfield, J.F. Westrich, H.R. and McLaughlin, L., (1993) What do dissolution experiments tell us about natural weathering? Chem Geol 105 1–15 10.1016/0009-2541(93)90115-Y.CrossRefGoogle Scholar
David, F. and Walker, L., (1990) Ion microprobe study of intragrain micropermeability in alkali feldspars Contrib Mineral Petrol 106 106–128 10.1007/BF00306413.CrossRefGoogle Scholar
Debat, P. Soula, J.-C. Kubin, L. and Vidal, J.-L., (1978) Optical studies of natural deformation microstructures in feldspars (gneiss and pegmatites from Occitania, southern France) Lithos 11 11–145 10.1016/0024-4937(78)90004-X.CrossRefGoogle Scholar
Eggleton, R.A., Coleman, S. M. and Dethier, D. P., (1986) The relation between crystal structure and silicate weathering rates Rates of chemical weathering of rocks and minerals London Academic Pr. 21–39.Google Scholar
Eggleton, R.A. and Buseck, P.R., (1980) High-resolution electron microscopy of feldspar weathering Clays Clay Miner 28 28–178 10.1346/CCMN.1980.0280302.CrossRefGoogle Scholar
Fitz Gerald, J.D., (1993) Slowly-cooled, orthoclase-rich alkali feldspars: Microstructures and implications for Ar-Diffusion [abstract] .Google Scholar
Fitz Gerald, J.D. and Harrison, T.M., (1993) Argon diffusion domains in K-feldspar I: Microstructures in MH-10 Contrib Mineral Petrol 113 113–380 10.1007/BF00286928.CrossRefGoogle Scholar
Fitz Gerald, J.D. and McLaren, A.C., (1982) The microstructures of microcline from some granitic rocks and pegmatites Contrib Mineral Petrol 80 80–229.Google Scholar
Gandais, M. Williame, C. and Brown, W.L., (1984) Mechanical properties of feldspars Feldspars and feldspathoids, NATO ASI Series C 137 Dordrecht D. Reidel 207–246 10.1007/978-94-015-6929-3_6.CrossRefGoogle Scholar
Gard, J.A., (1972) The electron-optical investigation of clays Mineral Soc Monograph 3 (Clay Miner Group) Oxford Alden Pr..Google Scholar
Goldberg, S.A. Trupe, C.H. and Adams, M.G., (1992) Pressure-temperature-time constraints for a segment of the Spruce Pine thrust sheet, North Carolina Blue Ridge [abstract] Geol Soc Am Abstr with Prog 24 17.Google Scholar
Kohyama, N. Fukushima, K. and Fukami, A., (1978) Observation of the hydrated form of tubular halloysite by an electron microscope equipped with an environmental cell Clays Clay Miner 26 26–40 10.1346/CCMN.1978.0260103.CrossRefGoogle Scholar
McLaren, A.C., (1978) Defects and microstructures in feldspars Chem Phys Solids Surf Chem Soc 7 7–30.Google Scholar
Parham, W.E., (1969) Formation of halloysite from feldspar: Low temperature artificial weathering versus natural weathering Clays Clay Miner 17 17–22 10.1346/CCMN.1969.0170104.CrossRefGoogle Scholar
Parker, J.M. III. 1949. Geology and structure of part of the Spruce Pine District, North Carolina. NC Dept Conserv and Devel Bull 65. 26 p.Google Scholar
Parsons, I. and Brown, W.L., (1984) Feldspars and the thermal history of igneous rocks NATO ASI Series C137 317 71.Google Scholar
Parsons, I., (1993) Fast routes for isotopic exchange in alkali feldspars [abstract] .Google Scholar
Rowe, G.L. Jr. and Brantley, S.L., (1993) Estimation of the dissolution rates of andesitic glass, plagioclase and pyroxene in a flank aquifer of Poas Volcano, Costa Rica Chem Geol 105 71–87 10.1016/0009-2541(93)90119-4.CrossRefGoogle Scholar
Smith, J.V. and Brown, W.L.. 1988. Feldspar Minerals, vol. 1. New York: Springer-Verlag. 828 p.CrossRefGoogle Scholar
Sverdrup, H.U., (1990) The kinetics of base cation release due to chemical weathering Sweden Lund University Pr..Google Scholar
Swoboda-Colberg, N.G. and Drever, J., (1993) Mineral dissolution rates in plot-scale field and laboratory experiments Chem Geol 105 105 69 10.1016/0009-2541(93)90118-3.CrossRefGoogle Scholar
Tibballs, J.E. and Olsen, A., (1977) An electron microscopic study of some twinning and exsolution textures in microcline amazonites Phys Chem Miner 1 1–324 10.1007/BF00307570.CrossRefGoogle Scholar
Worden, R.H. Walker, F.D.L. Parsons, I. and Brown, W.L., (1990) Development of microporosity diffusion channels and deuteric coarsening in perthitic alkali feldspars Contrib Mineral Petrol 104 104–515 10.1007/BF00306660.CrossRefGoogle Scholar
Zeitler, P.K. and Fitz Gerald, J.D., (1986) Saddle-shaped 40Ar/39Ar age spectra from young, microstructurally complex potassium feldspars Geochim Cosmochim Acta 50 1185–1199 10.1016/0016-7037(86)90401-1.CrossRefGoogle Scholar