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Irumide and post-Mozambiquian plutonism in Malawi

Published online by Cambridge University Press:  01 May 2009

H. W. Haslam
Affiliation:
Institute of Geological Sciences, 64/78 Gray's Inn Road, London WC1X 8NG, England
M. S. Brewer
Affiliation:
Bermuda College, Department of Academic Studies, Prospect, Devonshire 4-04, Bermuda (formerly at IGS, London)
D. P. F. Darbyshire
Affiliation:
Institute of Geological Sciences, 64/78 Gray's Inn Road, London WC1X 8NG, England
A. E. Davis
Affiliation:
Institute of Geological Sciences, 64/78 Gray's Inn Road, London WC1X 8NG, England

Summary

Rb-Sr whole-rock isochron ages of 443 ± 30 Ma, 449 ± 42 Ma and 489 ± 14 Ma with initial 87Sr/86Sr ratios of 0.70669 ± 0.00068, 0.70599 ± 0.00035 and 0.70658 ± 0.00025 were obtained, respectively, for the Cape Maclear granite, the surrounding Cape Maclear syenite and the Senga Bay granitic body. The results confirm previous estimates of the age of the post-Mozambiquian Lake Malawi Granitic Province, of which these plutons are part. Data from the Dzalanyama granite have excess scatter, but indicate an Irumide age of about 1000 Ma. This batholith is therefore much older than the Lake Malawi Granitic Province but much younger than the Nyika granite of northern Malawi, contrary to earlier suggestions. The porphyritic foliated granite of Mcezi Hill gave an age of 1016 ± 55 Ma and an initial ratio of 0.70522 ± 0.00084. Irumide plutonism in the region includes several dissimilar groups of intrusions, all with low initial87Sr/86Sr ratios. The Irumide age of the Dzalanyama granite makes it possible that the metasediments of the Mchinji Group are wholly post-Ubendian.

Type
Articles
Copyright
Copyright © Cambridge University Press 1983

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References

REFERENCES

Andrew, E. M. 1974. Gravity survey of Malawi: fieldwork and processing. Rep. Inst. Geol. Sci. No. 74/15.Google Scholar
Bloomfield, K. 1965(a). A reconnaissance survey of alkaline rocks in the northern and central regions. Rec. geol. Surv. Malawi (1963) 5, 1763.Google Scholar
Bloomfield, K. 1965(b). The Cape Maclear granitic complex. Rec. geol. Surv. Malawi (1963), 5, 6479.Google Scholar
Bloomfield, K. 1968. The pre-Karroo geology of Malawi. Mem. geol. Surv. Malawi No. 5.Google Scholar
Brewer, M. S., Haslam, H. W., Darbyshire, D. P. F. & Davis, A. E. 1979(a). The petrology and geochronology of hypersthene granites in the Mchinji area, Malawi. Rep. Inst. Geol. Sci. No. 79/1.Google Scholar
Brewer, M. S., Haslam, H. W., Darbyshire, D. P. F. & Davis, A. E. 1979(b). Rb-Sr age determinations in the Bangweulu Block, Luapula province, Zambia. Rep. Inst. Geol. Sci. No. 79/5.Google Scholar
Cannon, R. T., Hopkins, D. A., Thatcher, E. C., Peters, E. R., Kemp, J., Gaskell, J. L. & Ray, G. E. 1969. Polyphase deformation in the Mozambique belt, northern Malawi. Bull. geol. Soc. Am. 80, 2615–22.CrossRefGoogle Scholar
Carter, G. S. & Bennett, J. D. 1973. The geology and mineral resources of Malawi. 2nd revised edition. Bull. geol. Surv. Malawi No. 6.Google Scholar
Carter, G. S., Haslam, H. W. & Smith, S. H. 1973. Regional geochemical reconnaissance of Malawi. Bull. geol. Surv. Malawi No. 43.Google Scholar
Dawson, A. L. & Kirkpatrick, I. M. 1968. The geology of the Cape Maclear Peninsula and Lower Bwanje Valley. Bull. geol. Surv. Malawi No. 28.Google Scholar
Dodson, M. H., Cavanagh, B. J., Thatcher, E. C. & Aftalion, M. 1975. Age limits for the Ubendian metamorphic episode in northern Malawi. Geol. Mag. 112, 403–10.CrossRefGoogle Scholar
Halliday, A. N., Stephens, W. E. & Harmon, R. S. 1980. Rb-Sr and O isotopic relationships in 3 zoned Caledonian granitic plutons, Southern Uplands, Scotland: evidence for varied sources and hybridization of magmas. Jl geol. Soc. Lond. 137, 329–48.CrossRefGoogle Scholar
Haslam, H. W., Brewer, M. S., Davis, A. E. & Darbyshire, D. P. F. 1980. Anatexis and high-grade metamorphism in the Champira Dome, Malawi: petrological and Rb-Sr studies. Mineralog. Mag. 43, 701–14.CrossRefGoogle Scholar
Holt, D. N. 1961. The geology of part of Fort Johnston District, east of Lake Nyasa. Rec. Geol. Surv. Nyasaland (1959) 1, 2329.Google Scholar
Kemp, J. 1970. Basement geology of two areas in Malawi; their essentially similar histories. 14th Annu. Rep. Inst. Afr. Geol. Univ. Leeds, 1218.Google Scholar
Kemp, J. 1974. The geology of the Dwangwa area. Bull. geol. Surv. Malawi No. 31.Google Scholar
Peters, E. R. 1975. The geology of the south Viphya area. Bull. geol. Surv. Malawi No. 36.Google Scholar
Ray, G. E. 1974. The structural and metamorphic geology of northern Malawi. Jl. geol. Soc. Lond. 130, 427–40.Google Scholar
Ray, G. E. 1975. The geology of the Chitipa-Karonga area. Bull. geol. Surv. Malawi No.42.Google Scholar
Ray, G. E. & Crow, M. J. 1975. A review of some age determinations from the Misuku Belt of northern Malawi. Rec. geol. Surv. Malawi 8, 4966.Google Scholar
Snelling, N. J. 1963. Age determination unit. Rep. Overseas Geol. Surv. for 1962, 30–9.Google Scholar
Thatcher, E. C. 1973. Gneisses and granites in the Malawi Province of the Mozambique belt. Spec. Publ. geol. Soc. S. Afr. 3, 149–55.Google Scholar
Thatcher, E. C. & Walter, M. J. 1968. The geology of the South Lilongwe Plain and Dzalanyama Range. Bull. geol. Surv. Malawi No.23.Google Scholar
Walshaw, R. D. 1965. The geology of the Ncheu-Balaka area. Bull. geol. Surv. Malawi No.19.Google Scholar
Walter, M. J. 1972. The geology of the Salima-Mvera Mission area. Bull. geol. Surv. Malawi No.30.Google Scholar