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Journal of the Geological Society; 1974; v. 130; issue.3; p. 276-277;
DOI: 10.1144/gsjgs.130.3.0276
© 1974 Geological Society of London

DISCUSSION

PROFESSOR R. M. SHACKLETON: The valuable results obtained by the author still led to no definite solution to one of the major problems of this region. This is the relative ages of the granulite metamorphism of central and northern Uganda and the greenschist metamorphism of the Nyanzian of SE Uganda, W Kenya and central Tanzania. The Nyanzian is older than granites which are dated between 2400–2800 m.y. Dr Leggo’s granulite zircon ages are somewhat older, but not enough to demonstrate that the granulite metamorphism is pre-Nyanzian. A gradation from greenschist to granulite facies, comparable to that in the Archaean rocks of Mysore is not excluded by the age data. Structural evidence does suggest that the granulites are older because their east-west structures appear to be earlier than the north-south structures in the Aruan gneisses and it appears that this north-south grain must be truncated by the east-west Nyanzian structures. Unfortunately, there are no reliable maps of the badly-exposed critical area immediately north of the Nyanzian outcrops in southeast Uganda. It is, therefore, to be hoped that Dr Leggo will be able to extend zircon age work southwards into the Nyanzian.

DR K. A. DAVIES also congratulated the author and welcomed the considerable amount of information he had brought regarding the ages of Uganda’s metamorphic rocks. He was surprised however to hear him link the Masaba granite of the Kenya border with the 2500–2600 m.y. episode of the west and north. The main mass of the Masaba granite was

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