The Moine Thrust Belt contains imbricate systems derived from Cambro-Ordovician sediments together with thrust sheets of their Lewisian basement. Correlation of Precambrian structures between these thrust sheets and the adjacent foreland demonstrates displacements >25 km, values confirmed and exceeded by restored cross sections constructed through the imbricated sedimentary cover. The basement-carrying thrust sheets display a wide variety of structural styles even though they have deformed under essentially the same metamorphic pressure and temperature conditions (lower greenschist facies). These include the translation of crystalline basement as sheets with no appreciable internal deformation apart from sparse quartz-epidote-filled fractures and ∼1 m of mylonites and related fault rocks along the basal thrusts. Thrust trajectories can run parallel to the regional, near-horizontal datum (the sub-Cambrian unconformity) even though there are no apparent preexisting surfaces that might have localized slip on these horizons within the basement. In other examples, however, parts of basement thrust trajectories appear to have located preferentially on preexisting faults. These features have been underemphasized in previous studies and can be inferred by the preservation of PrecambrianTorridonian strata beneath the sub-Cambrian unconformity within thrust sheets. Basin faults that controlled deposition and preservation of Torridonian strata may have promoted large-scale folding at the basement-cover interface that is manifest as the large-scale recumbent structures of the southern part of the thrust belt. These different styles are compared and discussed in terms of the propensity of the Lewisian basement to localize deformation at greenschist facies through reactivation and retrogression-enhanced weakening.

Abstract Since the early descriptions published by Callaway in 1884, the gently dipping mylonites exposed along the Moine Thrust at the Stack of Glencoul have drawn generations of geologists to the northern part of the Assynt district. These mylonites, derived from Cambrian quartzites (footwall) and Moine pelites and psammites (hanging wall), have figured prominently in: a) early research into the influence of crystal plastic deformation and recrystallization on microstructural and crystal fabric evolution; b) debates on the kinematic interpretation of macro- and micro-structures and crystal fabrics; and c) debates on the tectonic significance of such kinematic data. In this paper first we briefly review the historical aspects of this research and then, using both previously published and unpublished data, document the finite strain and quartz fabric development at this classic mylonite locality. A tectonic interpretation of these data, together with quantitative estimates of flow vorticities associated with mylonite formation at the Stack of Glencoul, are presented in a companion paper by Law (2010) .

Abstract Abrupt lateral changes in thrust geometry occur in many fold-and-thrust belts along so-called transverse zones, commonly related to pre-existing basement faults. However, the causative structures are usually concealed. We analyse here the Traligill Transverse Zone in the Assynt Culmination of the Caledonian Moine Thrust Belt, NW Scotland. This transverse zone trends sub-parallel to the WNW transport direction and is associated with en echelon faults cutting thrusts, discontinuity of thrust architecture and oblique fold-and-thrust structures. Thick thrust sheets north of the Transverse Zone contain thick basement slices; thrust sheets to the south are thin and involve a thin-bedded sequence. The Traligill Transverse Zone developed above the Loch Assynt Fault, a basement cross-fault, and reactivated Proterozoic ductile shearzone. Piercing point analysis shows that the cross-fault was active both before and after thrusting. Thrusting thus affected strata that were already disrupted by steep faults. The amplitude of the disturbance in fold-and-thrust architecture along the Traligill Transverse Zone is much greater than the vertical displacement along the fault; this is attributed to localized transpressional thrust-stacking. Other basement cross-faults and their relationship with lateral variations within the Moine Thrust Belt and in other thrust belts are discussed.