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Some Investigations of the Roraima Formation Intrusives in British Guiana

Published online by Cambridge University Press:  01 May 2009

B. R. Rust
B. R. Rust
Affiliation:
Grant Institute of Geology, University of Edinburgh.
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Abstract

A traverse of a noritic gabbro sill (c. 1,000 feet thick) intruding the Roraima Formation showed no cryptic layering, but small-scale fractionation throughout the sill is indicated by the strongly-zoned plagioclase (An80→40), and orthopyroxene (En79→54) with outer rims of inverted pigeonite. Olivine (Fo80) is only present in the chilled margin.

New evidence on the age of the granites underlying the Roraima Formation is given by the discovery of post-Roraima felsite dykes, with high-quartz phenocrysts.

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Type
Articles
Information
Geological Magazine , Volume 100 , Issue 1 , February 1963 , pp. 24 - 32
Copyright
Copyright © Cambridge University Press 1963

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References

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