Some Investigations of the Roraima Formation Intrusives in British Guiana
- 1 February 1963
- journal article
- research article
- Published by Cambridge University Press (CUP) in Geological Magazine
- Vol. 100 (1) , 24-32
- https://doi.org/10.1017/s0016756800055011
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.Keywords
This publication has 6 references indexed in Scilit:
- An X-ray study of exsolution phenomena in the Skaergaard pyroxenesMineralogical Magazine and Journal of the Mineralogical Society, 1960
- STILLWATER IGNEOUS COMPLEX, MONTANAPublished by Geological Society of America ,1960
- Pyroxenes from the early and middle stages of fractionation of the Skaergaard intrusion, East GreenlandMineralogical Magazine and Journal of the Mineralogical Society, 1957
- Geology of southeastern VenezuelaGSA Bulletin, 1942
- Lamellar structure in orthopyroxenes (With Plate IV)Mineralogical Magazine and Journal of the Mineralogical Society, 1942
- Differentiation of the Palisade diabase, New JerseyGSA Bulletin, 1940