Abstract

A joint Tectonic Studies Group and Volcanic Studies Group meeting was held at the Department of Geology, University of Edinburgh on 20 May 1977, for the purpose of exploring the common ground between structural and petrological/volcanological interests in the subject of minor intrusives.

In the course of the eleven papers presented a wide range of ground was covered although, not surprisingly, the problems associated with the intrusion and congelation of basic magmatic sheets occupied the greater part of the meeting. By way of contrast, however, two of the papers presented were directed towards the deformation phenomena within and around granitic intrusions.

Basic sheet swarms were considered from a diversity of viewpoints ranging from petrochemical to structural. G. P. Durant highlighted the wide compositional range from transitional basalt to trachyte within the Islay and Jura dyke swarms and concentrated on their penological relationships. T. J. Halsall demonstrated that, from a detailed study of the south Arran dyke swarm, it is possible to recognise a sequence of emplacement episodes within which the change of magma type is a reflection of changing stress patterns. M. K. Wells, speaking of the Centre 2 intrusions of Ardnamurchan, indicated how the processes of cone-sheet intrusion, gabbro emplacement and updoming were intimately inter-related processes associated with the lateral spread of magma from a central feeder system. In a detailed treatment of the emplacement and crystallisation of a single sheet intrusion (the Dippin sill, Arran), F. G. F. Gibb and C. M. B. Henderson discussed the role of crystal fractionation

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