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Ignimbrite vents in the Sabaloka cauldron, Sudan

Published online by Cambridge University Press:  01 May 2009

D. C. Almond
D. C. Almond
Affiliation:
School of Geology, Kingston Polytechnic, Penrhyn Road, Kingston upon Thames, Surrey
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Summary

Large ignimbrite dykes continuous with an overlying sheet of rhyolitic ignimbrite have been found at two localities in the centrally-subsided block of the Sabaloka cauldron. There is good evidence that these dykes fed ash-flow eruptions. Other possible feeder vents occur along the marginal fracture zone of the cauldron but evidence for the origin of some of these structures is ambiguous. Ignimbrites within the dyke-shaped feeders contain a very strong eutaxitic foliation oriented parallel to the contacts and this feature is thought to result from inwardly-directed pressures exerted by the dyke walls during a collapse which followed eruption of the ash-flows. Vents of this type are believed to originate by permissive intrusion through the roof of a shallow-seated magma chamber, in contrast to forcefully injected diatreme vents. A broad genetic classification of these bodies is suggested, based on their mode of emplacement.

Type
Articles
Information
Geological Magazine , Volume 108 , Issue 2 , May 1971 , pp. 159 - 176
Copyright
Copyright © Cambridge University Press 1971

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