Hostname: page-component-cd9895bd7-jn8rn Total loading time: 0 Render date: 2024-12-25T07:47:55.103Z Has data issue: false hasContentIssue false
  • English
  • Français

Hybridization and the petrogenesis of composite intrusions: the dyke at An Cumhann, Isle of Arran, Scotland

Published online by Cambridge University Press:  01 May 2009

R. Kanaris-Sotiriou  and
F. G. F. Gibb
R. Kanaris-Sotiriou
Affiliation:
Department of Geology, University of Sheffield, S1 3JD, U.K.
F. G. F. Gibb
Affiliation:
Department of Geology, University of Sheffield, S1 3JD, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

The composite dyke at An Cumhann, Arran consists of a central unit of quartz-feldspar porphyry flanked by narrow marginal dolerites containing xenocrysts of quartz, plagioclase and alkali feldspar identical to the phenocrysts in the porphyry. The chemistry of the marginal dolerites indicates that they formed by the crystallization of a hybrid magma produced at depth by the incorporation of the porphyritic acid magma in a basic liquid. During the intrusion of the hybrid magma, flow caused a differential distribution of the xenocrysts across the initial basic dyke. Subsequent intrusion of the quartz-feldspar porphyry magma along the still unconsolidated centre of the basic dyke produced the wide central unit. A similar origin is proposed for other composite intrusions of the same type in the region. Whilst it is unlikely that the coexistence of the highly contrasting magmas necessary for the formation of these intrusions is entirely coincidental there is little likelihood that the two liquids were related as members of the same fractionation series.

Type
Articles
Information
Geological Magazine , Volume 122 , Issue 4 , July 1985 , pp. 361 - 372
Copyright
Copyright © Cambridge University Press 1985

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Blake, D. H., Elwell, R. W. D., Gibson, I. L., Skelhorn, R. R. & Walker, G. P. L. 1965. Some relationships resulting from the intimate association of acid and basic magmas. Quarterly Journal of the Geological Society of London 121, 31–49.CrossRefGoogle Scholar
Brown, G. M. 1963. Melting relations of Tertiary granitic rocks in Skye and Rhum. Mineralogical Magazine 33, 533–62.CrossRefGoogle Scholar
Bryan, W. B., Finger, L. W. & Chayes, F. 1969. Estimating proportions in petrographic mixing equations by least squares approximation. Science 163, 1926–7.CrossRefGoogle ScholarPubMed
Buist, D. S. 1952. A contribution to the petrochemistry and petrogenesis of the composite sill of South Bute. Transactions of the Edinburgh Geological Society 15, 52–68.CrossRefGoogle Scholar
Drever, H. I. & Johnston, R. 1958. The petrology of picritic rocks in minor intrusions - A Hebridean group. Transactions of the Royal Society of Edinburgh 63, 459–99.CrossRefGoogle Scholar
Drever, H. I. & Johnston, R. 1967. Picritic minor intrusions. In Ultramafic and Related Rocks (ed. Wyllie, P. J.), pp. 71–82. New York: Wiley.Google Scholar
Gibb, F. G. F. 1968. Flow differentiation in the xenolithic ultrabasic dykes of the Cuillins and the Strathaird Peninsula, Isle of Skye, Scotland. Journal of Petrology 9, 411–43.CrossRefGoogle Scholar
Judd, J. W. 1893. On composite dykes in Arran. Quarterly Journal of the Geological Society of London 49, 536–64.CrossRefGoogle Scholar
Macdonald, J. G. & Herriot, A. 1983. Macgregor's Excursion Guide to the Geology of Arran, 3rd ed. Geological Society of Glasgow. 210 pp.Google Scholar
Moorbath, S. & Bell, J. D. 1965. Strontium isotope abundance studies and rubidium-strontium age determinations on Tertiary igneous rocks from the Isle of Skye, Northwest Scotland. Journal of Petrology 6, 36–66.CrossRefGoogle Scholar
Smellie, W. R. 1913. The Tertiary composite sill of South Bute. Transactions of the Geological Society of Glasgow 15, 212–39.Google Scholar
Thorpe, R. S., Potts, P. J. & Sarre, M. B. 1977. Rare earth evidence concerning the origin of granites of the Isle of Skye, northwest Scotland. Earth and Planetary Science Letters 36, 111–20.CrossRefGoogle Scholar
Tomkeieff, S. I. & Marshall, C. E. 1935. The Mourne dyke swarm. Quarterly Journal of the Geological Society of London 91, 251–92.CrossRefGoogle Scholar
Tyrrell, G. W. 1928. The Geology of Arran. Memoir of the Geological Society of Great Britain. London: H.M.S.O.Google Scholar