Stephenson, D., Bevins, R.E., Millward, D., Highton, A.J., Parsons, I., Stone, P. & Wadsworth, W.J. 1999. Caledonian Igneous Rocks of Great Britain. Geological Conservation Review Series No. 17, JNCC, Peterborough, ISBN 1 86107 471 9. The original source material for these web pages has been made available by the JNCC under the Open Government Licence 3.0. Full details in the JNCC Open Data Policy

Creag na h-Innse Ruaidhe

[NC 224 140]

Description

A fine-grained, red 'grorudite' dyke, about 1 m thick, striking at outcrop NNE–SSW cuts the Cambrian 'false-bedded quartzite' in a GCR site that is also notified for structural reasons, the Cam Loch Klippe ((Figure 7.2), locality 2; and see the GCR volume Lewisian, Torridonian and Moine Rocks of Scotland). The Lewisian–Cambrian unconformity occurs about 200 m to the SE, and is in part inverted in the lower limb of a fold that is truncated below the 'grorudite' exposure by the Ben More thrust plane.

Interpretation

The interpretation of Peach et al. (1907) of the structure of the Moine thrust zone in Assynt is a classic of British, and indeed world, geology. They interpreted an area of Le,wisian rocks overlain unconformably by Cambrian quartzites to the east of the Cam Loch as forming an outlier, or klippe, of the Ben More thrust sheet (Figure 7.2). This interpretation has been supported by modern re-interpretations of the geology of the western part of the thrust belt in Assynt (Elliott and Johnson, 1980; Coward, 1985) although the latter author considers the eastern edge of the klippe to be a fault, not a thrust. As noted for the Glen Oykel South GCR site, 'grorudites' occur only in the rocks above the Ben More thrust plane, and the elegant and robust interpretation of Peach et al. (1907) is supported by the 'grorudite' at Creag na h-Innse Ruadh.

Conclusions

The Creag na h-Innse Ruaidhe GCR site demonstrates the presence of 'grorudite' in one of the outlying thrust slices (klippen) of the Ben More Nappe, providing support for the internationally well-known and historically important structural interpretation.

References