Isotopic evidence for the age and origin of pitchstones and felsites, Isle of Eigg, NW Scotland

An 8 point whole-rock and mineral Rb-Sr isochron for the Sgurr of Eigg yields an age of 52.1 ± 1.0 Ma (2σ). This is the youngest accurate date yet reported for igneous activity in the British Tertiary Province, and indicates that sub-acid rocks of the Small Isles represent one of the latest episodes of Hebridean magmatism. Pb-isotope compositions of these rocks yield an apparent age of 2660 ± 75 Ma (2σ), interpreted as a mixing line between …