In the Moine thrust zone, Proterozoic (Moine) metasedimentary rocks of the Caledonian belt are carried over the foreland sequence of Archaean to Proterozoic (Lewisian) gneiss, upper Proterozoic (Torridonian) sandstones, and the unconformable sequence of Cambro-Ordovician shelf quartzites and limestones. The thrust structures occur on all scales, from minor duplex zones a few centimeters across to large thrust sheets on a kilometer scale. The thrust sequence is generally piggy-back; thus, the easternmost (highest level) thrust formed first. The thrust direction was toward N65°W ±10°. The lower thrust sheets have produced folds by the stacking of imbricate slices, although in Eriboll on the north coast, buckle folds are common in the hanging wall and footwalls of minor thrusts. The higher thrust sheets contain buckle folds, which locally are sometimes large-scale structures and generally oblique to thrust transport. This suggests that the buckle folds formed by differential movement, with the northern part of the thrust zone moving farthest to the west-northwest. Textural studies suggest that this movement in the north occurred at a slower rate, under more ductile conditions. Back thrusts and break-back faults developed at tip zones where the resistance to movement and/or fault propagation was high. The amounts of displacement estimated from offsets of Lewisian structures are 35 to 45 km. Balanced cross sections in the region between Foinaven and Assynt show shortening values from 35 km + to 55 km + . The Foinaven imbricates do not affect the lowest Cambrian strata or their basement; that is, the basement rocks must continue back some 55 km beneath the Moines, the distance equivalent to the restored middle to upper Cambrian. This implies that any crustal ramp to the Moine thrust zone must lie more than 55 km east of the present outcrop of the thrust. However, off the north coast of Scotland, deep seismic reflection profiles show moderately dipping reflections much farther to the northwest, and if these represent the crustal-scale ramp, this ramp must be offset by a major tear or transfer fault along the north Scottish coast. In the southern part of Assynt, in the central part of the thrust zone, there are several extensional fault systems as well as a late (extensional?) fault at the local base of the Moines that cuts across earlier thrust and extensional faults. These extensional movements suggest a gravity-spreading mechanism for some Caledonide thrusting. The timing of thrusting can be bracketed by the 430-Ma age for the Borralan igneous intrusion, which predates most major thrust movements, and by the Devonian age of molasse deposits. It is difficult to find the driving mechanism for the Moine thrust at this time.

Abstract The Achnashellach Culmination is one of the major structures of the Moine Thrust Belt. As with other culminations in the belt, it is formed by a stack of imbricate thrusts. Up to 1 km of Torridon Group sediments, together with a further 200–250 m of Cambrian strata, are repeated up to 10 times, but with ramp-on-ramp thrust geometries. Thus structural thickening was chiefly achieved by thick thrust sheets with individually and aggregated displacements that are substantially lower than elsewhere in the thrust belt. The culmination is limited on its flanks by lateral ramps that climb section out of Torridon Group and up into Cambrian strata. To the north the imbricate thrusts may be deduced to branch onto the major Kinlochewe Thrust. To the south the imbricates are represented only by stacked Durness Limestone. The northward-climbing lateral ramp coincides with a major Precambrian structure, the Loch Maree Fault, which controls the thickness of Torridonian strata preserved beneath the sub-Cambrian unconformity, a rare example of basement influence on thrust system geometry within the Moine Thrust Belt. The imbricates of the Achnashellach Culmination show back-steepening and have bulged up the overriding Kishorn and Kinlochewe thrust sheets. However, these structurally higher level tectonic units slice across imbricate structures in their footwalls. Elsewhere high-level thrusts are folded by some parts of underlying imbricates. Collectively these relationships are not compatible with classical duplex models. They are explained better by models of quasi-synchronous slip on imbricate thrusts. Discordant relationships beneath major thrust sheets, including those that cut down stratigraphic section in the transport direction, can be explained by such models without necessitating low-angle extensional faulting within the thrust belt.

Abstract Following years of sporadic debate, in the early 1880s consensus was reached that thrust tectonics explained hitherto controversial geological field relationships in NW Scotland. This spawned a major research effort there by the Geological Survey of Great Britain that culminated in a series of highly detailed geological maps, preliminary research papers and, eventually, the publication of a memoir to the region. These works became highly influential to early-20th century geoscience, especially structural geology. Not only did they provide the first major synthesis of thrust belt structure, they also provided the basis for descriptions of fault and shear zone processes and deductive methods for unravelling tectonic histories in metamorphic basement. A common misconception is that the results arose from mapping alone, without regard to extant models and theory and this approach is held up as an ideal for fieldwork. Yet the notebooks and writings of the surveyors show the application of learning not only from other research groups but also between themselves. As with modern mapping, the Survey team created interpretations that built on contemporary knowledge. This work in turn has driven subsequent research for over 100 years, in the NW Highlands and in deformed rocks throughout the world.

Abstract The NW Highlands of Scotland have been an important test-bed for concepts in thrust tectonics. Here, research following the breakthrough publication of the 1907 memoir is reviewed, especially that relating to structural evolution in the Moine Thrust Belt. This belt was WNW-directed, involving cover sediments and thin sheets of crystalline basement. Displacements total 50–100 km within a branching array of thrusts. There are significant lateral variations in imbricate thrust geometry and localization behaviour. Following the application of linked thrust tectonic models in the 1980s significant attention has been directed at deducing thrust sequences, patterns of strain localization, folding styles and the significance of extensional tectonics as part of the structural evolution. The key has lain in deducing the kinematic linkages between thrusts and other structures, tracing displacements and examining the consequences of structural interpretations through geometric restoration. Thrusting models have been up-scaled to the crust. However, these linked kinematic approaches have been applied only hesitantly to the ductile structures of the Moine Thrust Sheet where structural research has focused on outcrop-scale deformation, especially of folds. Consequently, the larger-scale significance for Caledonian tectonics of thrust systems in the NW Highlands of Scotland has yet to be developed fully.

Abstract In 1888, inspired by fieldwork in what has become known as the Moine Thrust Belt, NW Scotland, Henry Cadell conducted a pioneering series of analogue deformation experiments to investigate the structural evolution of fold–thrust belts. Some experiments showed that imbricate thrusts build up thrust wedges of variable form, without requiring precursor folding. Others demonstrated a variety of fold–thrust structures and how heterogeneities in basement can localize thrust structures. These experiments are described here and used to draw lessons on how analogue deformation experiments are used to inform the interpretation of fold–thrust structures. Early adopters used Cadell's results as guides to structural styles when constructing cross-sections in thrust belts. His models and the host of others created since serve to illustrate part of the range of structural geometries in thrust belts. However, as with much subsequent work, Cadell's use of a deformation apparatus, with a fixed basal slip surface, biases perceptions of fold–thrust belts to be necessarily ‘thin-skinned’ (experimental design bias) and can simply reinforce established interpretations of natural systems (confirmation bias). So analogue deformation experiments may be unreliable guides to the deterministic interpretations of specific fold–thrust structures in the sub surface of the real world.