Discussion on the Glen Kyllachy Granite and its bearing on the nature of the Caledonian Orogeny in Scotland

Abstract

D rs A. L. H arris , A. J. H ighton A. M. R oberts & M. S. S toker write: A recent paper by van Breemen & Piasecki (1983) prompts some comments about correlation of lithostratigraphic units on either side of the Great Glen in Scotland, with its implications for displacements across the Great Glen Fault. Van Breemen & Piasecki (p. 47 and fig. 1) have followed the earlier work of Piasecki et al. 1981 in correlating the Grampian Division of the Grampian Highlands with the Loch Eil Division of the Northern Highlands, regarding both divisions as cover sequence to older gneisses which had undergone Precambrian (Grenville) deformation and metamorphism. Work by A. J. Highton in Upper Strathnairn, reported by Harris et al. 1981, has to a large extent confirmed the conclusion of Piasecki (1980) that a cover–basement relationship exists in the Grampian Highlands between older complexly deformed Central Highland Division gneisses of high metamorphic grade (basement) and younger, simply deformed, pebbly, cross-bedded Grampian Division psammites (cover). Both Piasecki (1980) and Mr Highton have concluded that a major ductile fault (the Grampian Slide of Piasecki, op. cit.) of unknown displacement separates the rocks of the 2 divisions. Piasecki (1980) regards the slid younger rocks as still overlying the older, while Mr Highton has demonstrated that older basement rocks have been thrust over the younger.