Abstract

IT IS APPARENT that the study of Palaeozoic volcanism attracts a multi-disciplinary approach involving sedimentologists as closely as volcanologists, and utilizes techniques ranging from field mapping to the statistical handling of geochemical data. This interdependence was revealed by the list of contributions and even more by the discussion stimulated by the papers read at the September 1976 meeting of the Volcanic Studies Group, held in the Geology Department, Trinity College, Dublin. It is also clear that for a fair proportion of workers in both Caledonian and Hercynian volcanism, plate-tectonic models are now being invoked both to explain the petrogenesis of volcanic suites and to account for regional variations in petrochemistry.

Speakers who eschewed this 'armchair' approach were concerned with regional field aspects and emphasized the need for detailed field mapping as a basis for any interpretation. Dr Max described work in progress on the correlation, distribution and deformation of the South Connemara Group volcanics, including the extension of land-based studies by surveys of islands in Galway Bay. Dr Howells demonstrated the relationship between the Bedded Pyroclastic Formation of central Snowdonia, and the Middle Crafnant Volcanic Formation of eastern Snowdonia, and showed that, whilst synchronous, two very different volcanic facies derived their material from different sources––the Bedded Pyroclastics from the Snowdon area and the Middle Crafnants from sources east of Betwsy Coed. In the region of Dolwyddelan a rising submarine ridge is invoked to provide separation between the shallow-water, bedded basaltic tuff sequence of the former and the acid

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