Explosion-breccias near Stob Mhic Mhartuin, Glen Coe, Argyll and their bearing on the origin of the nearby flinty crush-rock

Abstract

The petrology of a narrow belt of quartzite breccias lying inside the Glen Coe cauldron-subsidence is discussed. The rocks, previously mapped as an outlier of Lower O.R.S. sediments, are shown to be explosion-breccias possibly related to the volcanic rocks of the area. The crushed quartzite found in these breccias closely resembles some of the early stage developments of the nearby flinty crush-rock which is present locally along the boundary–fault of the cauldron. For this reason it is argued that the flinty crush-rock is a much modified explosion-breccia, and not a variety of mylonite produced by movement of the fault as hitherto believed.