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

Allt na Cailliche

[NC 320 102]

Description

The Allt na Cailliche (Figure 7.2) flows into the SE corner of Loch Ailsh and can be reached easily using forestry roads. The first exposures, just above the gravel fan, are of mylonitized, almost flinty Moine rocks. Upstream from this point pink 'nordmarkite' can be seen, forming a waterfall. In the gorge above, exposures in the stream bed are of foliated and sheared 'nordmarkite' with conspicuous pink feldspars. The rock is quite mafic. The Geological Survey mapped three sills near the Moine Thrust in the Allt na Cailliche, and also at several points near the thrust plane between there and the A837.

Interpretation and conclusions

This moderately deformed and unusual alkaline rock type was clearly emplaced as a sill just above the plane of the Moine Thrust, which must lie just below the lowest exposures in the Allt na Cailliche. This close proximity to the thrust characterizes all of the known exposures of deformed 'nordmarkites', and it seems highly unlikely that the association is fortuitous. One can conclude that the emplacement of the 'nordmarkites' was controlled by the thrust plane, occurred late in the evolution of the thrust zone, and that the moderate deformation and recrystallization of the 'nordmarkites' was caused by late movements on the Moine thrust plane.

References