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Muscovite breakdown and corundum growth at anomalously low fH2o: a study of contact metamorphism and convective fluid movement around the Omey granite, Connemara, Ireland

Published online by Cambridge University Press:  05 July 2018

Colin C. Ferguson  and
Sanaa I. Al-Ameen
Colin C. Ferguson
Affiliation:
Kansas Geological Survey, University of Kansas, Lawrence, KS 66044, USA
Sanaa I. Al-Ameen
Affiliation:
Department of Geology, University of Nottingham, Nottingham NG7 2RD, UK
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Abstract

In the aureole of the late Caledonian Omey granite corundum develops in the Dalradian country rocks in a zone up to 250 m from the granite contact. The distribution of andalusite and K-feldspar in pelites and calcite+wollastonite+grossularite in marbles is consistent with inner-aureole metamorphic conditions of 615±25°C at 2.5±0.25 kbar, and ⋍ 0.85. Corundum develops from the reaction muscovite → corundum + K-feldspar+H2O and first appears over 100 m further from the granite than the assemblage wollastonite + grossularite + anorthite. Experimentally determined equilibria can be satisfied only if for the corundum-producing reaction was less than 0.6 and perhaps as low as 0.4. Corundum always grows within large muscovite crystals;fH2O within the crystal lattice is unrelated to that in the grain-boundary fluid of the surrounding rock.

Although whole-rock oxidation ratios are irregularly distributed within the aureole they are uniformly low in corundum-bearing rocks. Reducing conditions probably resulted from localized flow of H2O-rich fluid away from the granite in a diffuse channelway that contains most of the corundum localities and also a distinctive skarn. Although corundum growth within muscovite is sealed off from the external water vapour conditions, it is suggested that movement of H2O down a thermal gradient (and hence down an fH2O gradient at constant pressure) promotes the escape of (OH)− from the muscovite lattice and so allows the corundum reaction to proceed.

Keywords

muscovitecorundumcontact metamorphismOmey graniteConnemaraIreland
Type
Research Article
Information
Mineralogical Magazine , Volume 49 , Issue 353 , September 1985 , pp. 505 - 514
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1985

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Footnotes

*

Present address: Department of Geology, Birkbeck College (University of London), London WC1E 7HX, UK.

References

Boettcher, A. L., and Wyllie, P. J. (1968) J. Geol. 76, 235-44.CrossRefGoogle Scholar
Brown, G. C., and Fyfe, W. S. (1970) Contrib. Mineral. Petrol. 28, 310-18.CrossRefGoogle Scholar
Burnham, C. W., Holloway, J. R., and Davies, N. F. (1969) Geol. Soc. America Spec. Pap. 132.Google Scholar
Carslaw, H. S., and Jaeger, J. C. (1959) Conduction of Heat in Solids (2nd edn.). Oxford University Press, 510 pp.Google Scholar
Chatterjee, N. D., and Johannes, W. (1974) Contrib. Mineral. Petrol. 48, 89-114.CrossRefGoogle Scholar
Cheney, J. T., and Guidotti, C. V. (1979) Am. J. Sci. 279, 411-34.CrossRefGoogle Scholar
Cobbing, E. J. (1969) Proc. R. Irish Acad. 67(11), 303-25.Google Scholar
Evans, B. W. (1964) Geochim. et Cosmochim. Acta, 28, 127-56.CrossRefGoogle Scholar
Evans, B. W. (1965) Am. J. Sci. 263, 647-67.CrossRefGoogle Scholar
Evans, B. W. and Guidotti, C. V. (1966) Contrib. Mineral. Petrol. 12, 25–62.CrossRefGoogle Scholar
Evans, B. W. and Leake, B. E. (1970) Proc. R. Irish Acad. 70(B), 105-39.Google Scholar
Ferguson, C. C., and Harvey, P. K. (1979) Proc. Geol. Assoc. 90, 43-50.CrossRefGoogle Scholar
Grambling, J. A. (1981) Am. Mineral. 66, 702-22.Google Scholar
Holdaway, M. J. (1971) Am. J. Sci. 271, 97–131.CrossRefGoogle Scholar
Leake, B. E. (1978) Geol. J. Spec. Issue, 10, 221-48.Google Scholar
Leake, B. E. and Skirrow, G. (1960) J. Geol. 68, 23-41.CrossRefGoogle Scholar
Leake, B. E., Tanner, P. W. G., and Senior, A. (compilers) (1981) The Geology of Connemara (map, scale 1:63 360). University of Glasgow.Google Scholar
Leake, B. E., Tanner, P. W. G. and Singh, D. (1983) Nature, 305, 210-13.CrossRefGoogle Scholar
Luth, W. C., Jahns, R. H., and Tuttle, O. F. (1964) J. Geophys. Res. 64, 759-73.CrossRefGoogle Scholar
Norton, D., and Knight, J. (1977) Am. J. Sci. 277, 937-81.CrossRefGoogle Scholar
Robie, R. A., and Waldbaum, D. R. (1968) U.S. Geol. Surv. Bull. 1259.Google Scholar
Rosenfeld, J. L. (1970) Geol. Soc. America Spec. Pap. 129.Google Scholar
Steno, N. (1671) De Solidarum intra Solidum (Prodromus), translated by Henry Oldenburg, published in London between 1671 and 1673.Google Scholar
Tanner, P. W. G., and Shackleton, R. M. (1979) Spec. Publ. geol. Soc. Lond. 8, 243-56.CrossRefGoogle Scholar
Tanner, S. B., Kerrick, D. M., and Lasaga, A. C. (1983) Geol. Soc. Am. Abstr. with Programs, 15, 704.Google Scholar
Townend, R. (1966) Proc. R. Irish Acad. 65(B), 157–202.Google Scholar
Waldbaum, D. R., and Thompson, J. B. Jr., (1969) Am. Mineral. 54, 1274-98.Google Scholar
Winkler, H. G. F. (1978) Petrogenesis of Metamorphic Rocks (5th edn.), Springer-Verlag, New York.Google Scholar
Zen, E.-an (1963) Am. J. Sei. 261, 929-42.Google Scholar