Gravitational sorting of phenocrysts in some Icelandic intrusive sheets

• Published in: Geological Magazine
• Main Author: Blake, D. H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1968
• Subjects: Iceland
• Online Access: http://dx.doi.org/10.1017/s0016756800052511; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800052511

SUMMARY Some thin basaltic intrusive sheets in south-eastern Iceland consist in cross-section of a porphyritic central zone sharply bounded by non-porphyritic margins. Within the porphyritic zone phenocrysts of plagioclase, augite and olivine are arranged in two main layers, an upper layer containing mostly plagioclase phenocrysts, and a lower layer containing concentrations of augite and olivine phenocrysts. The phenocrysts are considered to have been gravitationally sorted during the passage through the sheets of a highly fluid and strongly flowing porphyritic basalt magma.