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

<p>Infrared laserprobe <sup>40</sup>Ar/<sup>39</sup>Ar 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 <sup>40</sup>Ar/<sup>39</sup>Ar 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 (2σ). 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. </p>