Isotopic ages of dykes and pegmatitic gneiss from the southern islands of the Outer Hebrides

Abstract
Synopsis: Potassium-argon ages of 1720, 1565, and 1500 m.y. from dykes from South Uist and Benbecula confirm the existence of Laxfordian activity in the southern part of the Outer Hebrides. The pegmatitic gneiss of Ardivachar, South Uist, yields a whole-rock rubidium-strontium isochron age of 2560±80 m.y., closely correlating with the post-Scourie Group pegmatites of the mainland.