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The Mull Palaeogene dyke swarm: insights into the evolution of the Mull igneous centre and dyke-emplacement mechanisms

Published online by Cambridge University Press:  05 July 2018

R. MacDonald*
Affiliation:
IGMiP Faculty of Geology, University of Warsaw, al. Żwirki i Wigury 93, 02-089 Warszawa, Poland Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK
B. Bagiński
Affiliation:
IGMiP Faculty of Geology, University of Warsaw, al. Żwirki i Wigury 93, 02-089 Warszawa, Poland
B. G. J. Upton
Affiliation:
School of Geosciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK
H. Pinkerton
Affiliation:
Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK
D. A. MacInnes
Affiliation:
3 Stirling Road, Kilsyth, Glasgow G65 0JF, UK
J. C. MacGillivray
Affiliation:
Hollandbush, 4 Meadowbank Avenue, Strathaven, Lanarkshire ML10 6JS, UK

Abstract

Geochemical data are presented for five large Palaeogene dykes, members of the Mull swarm in southern Scotland and northern England (the Moneyacres, Hawick-Acklington, Barrmill, Muirkirk- Hartfell and Dalraith-Linburn dykes). The rock types range from basalt through andesite to dacite, although the range in individual intrusions is more restricted. The dykes are divisible into two groups; those where the compositional variation was generated by fractional crystallization of basaltic magmas, and those where it resulted from variable degrees of mixing of basaltic and silicic magmas. Several dykes are composite; the marginal facies can be more or less evolved than the central facies. The dyke magmas are thought to have originated from stratified magma chambers beneath the Mull centre and models are presented to show how the different components were derived from the chambers. Some dykes appear to have been terminated at or near the Southern Upland Fault, perhaps as a result of the chilling of early magma pulses by water in the fault. The Palaeogene dyke swarm is considerably more complex than previously recognized and has a significant input to models of the evolution of the Mull magmatic system.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2010

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