Grenville-age pseudotachylite in the Lewisian: laserprobe Ar-40/Ar-39 ages from the Gairloch region of Scotland (UK)

摘要

Infrared laserprobe Ar-40/Ar-39 dating has been used to date pseudotachylite and host-rock minerals from a crush belt in the Lewisian basement of Scotland. It has revealed complexity in the pseudotachylite data that is attributable to the presence of refractory host-rock clasts and mineral fragments in the pseudotachylite. In conjunction with the host-rock mineral laserprobe Ar-40/Ar-39 data it has been possible to simplify the pseudotachylite data for the samples, and the preferred ages for these are: 980 +/- 39 Ma, 999 +/- 31 Ma and 1024 +/- 30 Ma (2 sigma). These ages are the first record of Grenville-aged brittle deformation in the Lewisian. Further, this study serves to illustrate the complexity of dating pseudotachylites, and the advantages and limitations of the IR laserprobe applied to such materials.