Hostname: page-component-77c89778f8-vsgnj Total loading time: 0 Render date: 2024-07-23T15:03:55.625Z Has data issue: false hasContentIssue false
  • English
  • Français

Cryptic variation in the Kapalagulu layered intrusion, western Tanzania

Published online by Cambridge University Press:  05 July 2018

W. J. Wadsworth ,
A. C. Dunham  and
A. A. Almohandis
W. J. Wadsworth
Affiliation:
Department of Geology, University of Manchester, Manchester M13 9PL, England
A. C. Dunham
Affiliation:
Department of Geology, University of Hull, Cottingham Road, Hull HU6 7RX, England
A. A. Almohandis
Affiliation:
Department of Geology, Riyadh University, Riyadh, Saudi Arabia
Get access Rights & Permissions [Opens in a new window]

Abstract

The Kapalagulu intrusion displays the following sequence of cumulus phase layering in a stratigraphic sequence of 1400 m: Basal Zone (BZ) olivine ± chromite → Intermediate Zone (IZ) olivine + plag + opx →, olivine + plag + opx + cpx → Main Zone (MZ) plag + opx + cpx → plag + cpx + Fe/Ti oxide + apatite. The corresponding cryptic variation is olivine Fo83 − 77 (limited to BZ and IZ), orthopyroxene En82 − 56, clinopyroxene Ca46Mg45Fe9 to Ca43Mg37Fe21 and plagioclase An88 − 80. Reversals of the cryptic variation occur at the base of MZ (minor reversal) and in the middle of MZ (major reversal), and are attributed to the influx of relatively primitive magma. The major reversal indicates that progressive mixing of fresh and residual magmas occurred. Because of the major reversal, inverted pigeonite appears twice in the layered sequence, but at different compositions (En65 and En56). Unlike the cumulus olivine and pyroxene, cumulus plagioclase exhibits a wide range of composition (5−10% An) in individual rocks and even in single crystals.

Type
Research Article
Information
Mineralogical Magazine , Volume 45 , Issue 337 , 1982 , pp. 227 - 236
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1982

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

Brown, G. M. (1956) Phil. Trans. R. Soc. B240, 1-53.Google Scholar
Cahen, L., and Snelling, N. J. (1966) The Geochronology of Equatorial Africa. Amsterdam, North Holland.Google Scholar
Campbell, I. H. (1977) J. Petrol. 18, 83-215.CrossRefGoogle Scholar
Cawthorn, R. G., Davies, G., Clubley-Armstrong, A., and McCarthy, T. S. (1981) Lithos, 14, 116.Google Scholar
Dunham, A. C., and Wadsworth, W. J. (1978) Mineral. Mag. 42, 347-56.CrossRefGoogle Scholar
Goode, A. D. T. (1976) J. Petrol. 17, 379-97.CrossRefGoogle Scholar
Henderson, P. (1975) Geochim. Cosmochim. Acta, 39, 1035-44.CrossRefGoogle Scholar
Irvine, T. N. (1980) In Physics of Magmatic Processes (Hargraves, R. B., ed.), Princeton University Press, 325-83.Google Scholar
Jackson, E. D. (1961) USGS Prof. Paper, 358, 1-106.Google Scholar
Jackson, E. D. (1970) Geol. Soc. S. Africa Spec. Publ. 1, 391-424.Google Scholar
Jackson, E. D. (1971) Fortschr. Mineral. 48, 128-74.Google Scholar
Piper, J. D. A. (1975) Tectonophysics, 26, 135-61.CrossRefGoogle Scholar
van Zyl, C. (1959) Trans. Geol. Soc. S. Africa, 62, 1-31.Google Scholar
Yon Gruenewaldt, G. (1973) Ibid. 76, 207-27.Google Scholar
Yon Gruenewaldt, G. (1979) Can. Mineral. 17, 233-56.Google Scholar
Wadsworth, W. J. (1961) Phil. Trans. R. Soc. B244, 2l-64.Google Scholar
Wadsworth, W. J. (1963) Mineral. Soc. Am. Spec. Paper, 1, 108-15.Google Scholar
Wager, L. R. (1959) Geol. Mag. 96, 7580.CrossRefGoogle Scholar
Wager, L. R. and Brown, G. M. (1968) Layered Igneous Rocks. Oliver & Boyd, Edinburgh.Google Scholar
Wager, L. R. and Deer, W. A. (1939) Meddels. Gronland, 105, No. 4.Google Scholar
Wager, L. R., Brown, G. M., and Wadsworth, W. J. (1960) J. Petrol. 1, 73-85.CrossRefGoogle Scholar