Structure of the Lewisian rocks between Strath Dionard and Rhiconich, Sutherland, Scotland

Abstract

Synopsis The Lewisian rocks of the Strath Dionard–Rhiconich district consist essentially of acid gneiss, amphibolite and calc-silicate rock (Rhiconich group) with pegmatitic, granitic and basic minor intrusions (post-Rhiconich group rocks). The earliest structural element in the Rhiconich group is a lithological layering, possibly an original sedimentary feature, now largely obscured due to the subsequent deformation and metamorphism. Penetrative foliation associated with small intrafolial folds and mineral lineation related to the deformation of the Gualin phase are affected by generally asymmetrical folds including the large Strath Dionard antiform and the associated structures related to the Dionard phase of deformation. The later open folds, pseudotachylitic crush-rock and joints are related to the Leacach phase of deformation. The three phases of deformation were variously accompanied by recrystallisation and migmatitic activity and developed in a series of rocks comparable with those of the southern belt of Lewisian at a crustal level above that of the pyroxene-granulites of the central belt.