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Upper-mantle metasomatism beneath a continental rift: clinopyroxenes in alkali mafic lavas and nodules from Sruth West Uganda

Published online by Cambridge University Press:  05 July 2018

F. E. Lloyd
F. E. Lloyd*
Affiliation:
Department of Geology, University of Reading
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Abstract

Clinopyroxenes are dominant in highly potassic, silica undersaturated mafic volcanics occurring on the western rim of the uplifted, rifted East African craton. A kimbcrlite style of eruption provides nodules of alkali clinopyroxenite (clinopyroxene + titaniferous phlogopite+titanomagnetite, apatite, sphene, and rare corroded olivine) which have similar bulk chemistry to the feldspathoid-bearing lavas. Many nodules display metasomatic textures supporting a formation from the alteration of pre-existing material; clinopyroxene growth is characterized by complex, non-oscillatory colour zoning. Comparison of natural clinopyroxene chemistry with published data for elinopyroxenes crystallized from synthetic potassium-rich mafic material, suggests that a significant proportion of the nodules crystallized at upper-mantle pressures. Neither garnet- nor orthopyroxene-bearing nodules have ever been recorded from south-west Uganda, suggesting that metasomatism of the local mantle has proceeded far enough to obliterate all recognizable remnants of four-phase lherzolite.

Type
Research Article
Information
Mineralogical Magazine , Volume 44 , Issue 335 , September 1981 , pp. 315 - 323
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1981

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References

Aoki, K. and Kushiro, I. (1968). Contrib. Mineral. Petrol. 18, 326.CrossRefGoogle Scholar
Bailey, D. K. (1964). J. Geophys. Res. 69, 1103.CrossRefGoogle Scholar
Bailey, D. K. (1972). J. Earth Sci. (Leeds), 8, 225.Google Scholar
Bailey, D. K. (1974). The Alkaline Rocks (J. Wiley & Sons, New York), 53.Google Scholar
Willis, Bailey (1936). Carnegie Inst. of Washington Publication. Google Scholar
Borley, G. D. (1967). Mineral. Mag. 36, 364.Google Scholar
Bultitude, R. J. and Green, D. H. (1971). J. Petrol. 12, 121.CrossRefGoogle Scholar
Carmichael, I. S. E. (1967). Contrib. Mineral. Petrol. 15, 24.CrossRefGoogle Scholar
Den Tex, E. (1971). Fortschr. Mineral. 48, 69.Google Scholar
Edgar, A. D., Green, D. H., and Hibberson, W. O. (1976). J. Petrol. 17, 339.CrossRefGoogle Scholar
Green, D. H. (1973a). Earth Planet. Sci. Lett. 17, 456.CrossRefGoogle Scholar
Green, D. H. (1973b). Tectonophysics, 17, 285.CrossRefGoogle Scholar
Holmes, A. (1950). Am. Mineral. 35, 772.Google Scholar
Holmes, A. (1965). Principles of Physical Geology (Thomas Nelson Ltd., London and Edinburgh, new and fully revised edn.).Google Scholar
Hough, F. E. (1972). Ph.D. thesis, Reading.Google Scholar
King, L. C. (1962). The Morphology of the Earth (Oliver & Boyd, Edinburgh).Google Scholar
Kushiro, I. (1970). Carnegie Inst. Washington Yearb. 68, 245.Google Scholar
Lloyd, F. E. (1972). See Hough (1972).Google Scholar
Lloyd, F. E. and Bailey, D. K. (1975). Phys. and Chem. of the Earth 9, 389.CrossRefGoogle Scholar
Long, R. R, Backhouse, R. W., Maguire, P. K. H., and Sundaralingham, K. (1972). Tectonophysics, 15, Special Issue—East African Rifts, 165.CrossRefGoogle Scholar
Mueiler, St., Petersmitt, E., Fuehs, K., and Ansorge, J. (1969). Tectonophysics, 8, 529.CrossRefGoogle Scholar
Poldervaart, A. and Hess, H. H. (1951). J. Geol. 59, 472.CrossRefGoogle Scholar
Savelli, C. (1968). Contrib. Mineral. Petrol. 16, 328.Google Scholar
Thompson, J. B. (1947). Bull. Geol. Soc. Am. 58, 1232.Google Scholar
Wade, A. and Prider, R. T. (1940). Q.J. Geol. Soc. Lond. 96, 39.CrossRefGoogle Scholar