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A greenstone belt—basement relationship in the Tanganyika shield

Published online by Cambridge University Press:  01 May 2009

I. S. Haidutov
I. S. Haidutov
Affiliation:
Geological Institute, Bulgarian Academy of Sciences, Sofia — 13, Bulgaria
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Summary

An Archaean greenstone belt, occupied by rocks of the Nyanzian System, rests apparently unconformably on a basement composed of the metamorphites of the Dodoman System in the central part of the Tanganyika shield. The latter were originally metamorphosed in granulite facies. Two episodes of migmatization were imposed on this earlier crust producing two complexes of anatectic granitoids (Puma and Ikungi) which locally have a charnockitic character. Differences in structural setting suggest that they were developed in connection with two major tectonic events. A basin-like structure was built up during the second – Ikungi – in which the Nyanzian System occurs. The Nyanzian rocks are not migmatized and their juxtaposition with the migmatites suggests that they are of younger age. Another tectonism took place after deposition of the greenstones as a result of which they were intensely deformed. Two types of intrusive granites were emplaced in the greenschists upgrading them to hornfelses during this tectonism. An interesting feature is the coincidence of the general tectonic axes of these three events. For the successively established metamorphic processes in this Archaean nucleus a gradual downgrading of metamorphic facies is characteristic, showing its irreversible development.

Type
Articles
Information
Geological Magazine , Volume 113 , Issue 1 , January 1976 , pp. 53 - 60
Copyright
Copyright © Cambridge University Press 1976

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