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A Study of the Potash Felspar Gneisses of Connemara and Felspar Comparison with the Galway Granite

Published online by Cambridge University Press:  01 May 2009

P. J. Leggo
P. J. Leggo
Affiliation:
Department of Earth Sciences, University of Leeds, Leeds, 2.
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Abstract

Eighteen potash felspars from the potash felspar gneisses of the Connemara migmatite belt have been partially analysed and the associated plagioclase optically determined. Comparisons have been made with seventeen similar felspar pairs from the Galway Granite. Albite components are expressed graphically in an attempt to illustrate sodium distribution between associated felspar phases. On such a plot it is possible to contrast the “magmatic” felspars of the Galway Granite with those of the migmatitic gneisses; the separation of the two fields being a function of total rock chemistry. Crystallization temperatures have been determined by the two felspar method and the range 460 to 480° C. is thought to represent retrograde amphibolite conditions in the migmatitic gneisses, while petrographic evidence supports 550° C. as the temperature of amphibolite facies metamorphism in these rocks. Triclinicity measurements have also been made on the analysed potash felspars.

Type
Articles
Information
Geological Magazine , Volume 103 , Issue 6 , December 1966 , pp. 522 - 533
Copyright
Copyright © Cambridge University Press 1966

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References

REFERENCES

Barth, T. F. W., 1934. Temperatur i lava — magmamasser, somt et nytt geologish termometer. Naturen, 1934, pp. 187–92.Google Scholar
Barth, T. F. W., 1951. The Felspar Geologic Thermometers. Neues Jahrb. Miner., Abb. Bd., 82, 143–54.Google Scholar
Barth, T. F. W., 1956. Studies in Gneiss and Granite. Skr. Det Norske Vid. Akad. Oslo. Mat. — Naturv. Kl. No. 1.Google Scholar
Burke, K. C, 1957. An outline of the structure of the Galway Granite. Geol. Mag., 94, 452–64.CrossRefGoogle Scholar
Coombs, D. S., 1954. Ferriferous orthoclase from Madagascar. Miner. Mag., 30, 409–27.Google Scholar
Deer, W. A., Howie, R. A., and Zussman, J., 1963. Rock Forming Minerals, vol. IV. Longmans, Green and Co. Ltd., London.Google Scholar
Dietrich, R. V., 1960. Banded Gneisses of the Randesund area, southeastern Norway. Norsk. geol. Tidsskr., 40, 13–63.Google Scholar
Dietrich, R. V., 1961. Comments on the Two feldspar geothermometer and K-feldspar obliquity. Instit. “Lucas Mallada” C.S.I.C. (Spain) Cursillos y Conferen Fasc., 8, 15.Google Scholar
Faust, G. T., 1936. The fusion relations of iron-orthoclase. Am. Miner., 21, 735–63.Google Scholar
Goldschmidt, J. R., and Laves, F., 1954. Potassium felspar structurally intermediate between microcline and sanidine. Geochim. et Cosmochim. Acta., 6, 100–18.Google Scholar
Heier, K. S., 1961. The amphibolite-granulite facies transition reflected in the mineralogy of potassium feldspars. Instit. “Lucas Mallada” C.S.I.C. (Spain) Cursillos y Conferen Fasc., 8, 665.Google Scholar
Leake, B. E., and Leggo, P. J., 1963. On the Age Relations of the Connemara Migmatites and the Galway Granite, West of Ireland. Geol. Mag., 100, 193–204.CrossRefGoogle Scholar
Leggo, P. J., Compston, W., and Leake, B. E., 1966. Geochronology of the Connemara granites and its bearing on the antiquity of the Dalradian Series. Q. Jl geol. Soc. Lond., 122, 91–118.CrossRefGoogle Scholar
Mackenzie, M. S., and Smith, J. V., 1956. The alkali feldspars, III—An optical and X-ray study of high temperature feldspars. Am. Miner., 41, 406–27.Google Scholar
Poldervaart, A., 1950. Correlation of Physical Properties and Chemical Composition in the Plagioclase, Olivine and Orthopyroxene Series. Am. Miner., 35, 1067–79.Google Scholar
Ramberg, H., 1952. Origin of metamorphic and metasomatic rocks. University of Chicago Press. p. 317.Google Scholar
Read, H. H., 1931. The Geology of Central Sutherland. Mem. geol. Surv. U.K., pp. 125–28.Google Scholar
Riley, J. P., 1958. The rapid analysis of silicate rocks and minerals. Anal. Chem. Acta., 413–28.CrossRefGoogle Scholar
Rosenquist, I. Th., 1952. The Metamorphic Facies and the felspar minerals. Univ. Bergen. Arbok. Naturv. rekke, 4.Google Scholar
Turner, F. J., 1951. Observations of Twinning of Plagioclase in Metamorphic rocks. Am. Miner., 36, 581–89.Google Scholar
Winkler, H. G. F., 1961. On coexisting felspars and their temperatures of crystallization. Instit. “Lucas Mallada” C.S.I.C. (Spain) Cursillos y Conferen Fasc., 8, 9–13.Google Scholar
Wright, P. C., 1964. The petrology, chemistry, and structure of the Galway Granite of the Carna Area, County Galway. Proc. R. Ir. Acad., B, 63, 239–64.Google Scholar