Lamprophyric magmatism in the Sleat Group (Torridonian), Kyle of Lochalsh: Torridonian sill or ash-flow tuff, or Permo-Carboniferous intrusion?

Abstract

Synopsis A prominent bed which is concordant with its host Sleat Group (Torridonian) rocks near Kyle of Lochalsh, Highland Region, NW Scotland, has been categorized as an alkaline lamprophyre (sannaite). It consists mostly of a yellowish-grey crumbly material with marginal layers of competent rock which exhibit flow textures reminiscent of ash-flow tuffs. A central facies displays trachytic texture. The presence of sanidine, flow textures and pseudomorphed skeletal olivine phenocrysts supports a volcanic origin. The rock’s NE-SW trend is incompatible with local Tertiary NW–SE dyke swarms. While the evidence for this rock being a contemporary late-Mesoproterozoic ash-flow tuff or sill, or a Permo-Carboniferous sill may appear equivocal, the weight of evidence favours a Torridonian intrusive origin, contemporary with the Gardar Igneous Province of Greenland.