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 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.

Abstract The Moine Thrust Belt in NW Scotland is fundamental for developing an understanding of complex fault systems and continental tectonics. The high-quality geological mapping, exceptional structural interpretation and insight of the late nineteenth century that underpins this is chronicled here. The Geological Survey of Great Britain mapped the thrust belt over a 14 year period, at 1:10 560, but it took five decades for the individual 1:63 360 map sheets to be published. The mapping itself was hampered by access problems, illness and prevailing weather. The deployment of expert staff to this region of few apparent economic resources threatened the status of the Geological Survey. Map publication was hindered by the transition from hand-coloured to full-colour printing, together with the restrictions of publishing to a strict grid that incorporated complex geology outside the thrust belt itself. This history of fieldwork, publication and outreach by the Geological Survey is placed in an environmental and logistical context to identify the challenges not only for the mapping itself but also in sharing the results in publication. The execution of these activities provides lessons for developing coherent interpretation in complex geology and the challenges in charting their uncertainties and alternative explanations.

Abstract Archibald Geikie’s (1835–1924) field research led to better understanding of geological relationships and, ultimately, Earth processes. We consider three pieces of research in Scotland, from his early work on Skye through to the execution and impact of his 1860 expedition to the NW Highlands with Murchison, returning to Skye to consider arguments with Judd on igneous relationships. We describe the field locations and place modern interpretations in their historical context. We discuss how methods and approaches for building interpretations in the field were modified and improved through debates. Reliance on a few ‘critical outcrops’ served to anchor interpretation at the expense of understanding more complex exposures. Similar bias appears to have arisen from using simple exploratory transects which were only mitigated by proper mapping approaches. Significant misunderstandings between protagonists appear to have arisen through the reliance of text description rather than diagrammatic illustrations. The vitriolic nature of debate seems to have anchored misinterpretations, obscured interpretational uncertainty and promoted false-reasoning by inhibiting inclusive scientific engagement.

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.