The Geological Structure of the North-West Highlands of Scotland – revisited: Peach et al. 100 years on

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.

Henry Cadell's ‘Experimental researches in mountain building’: their lessons for interpreting thrust systems and fold–thrust structures

“…of the main rock sequences in the NW Highlands, especially in the Assynt district, was not that simple. The Torridonian strata that underlay the Cambrian rocks formed a wedge shape, tapering eastwardsand this was known to Cadell (see Butler 2010). The gneissic structure of the Lewisian basement that underlaid both the Torridonian and Cambro-Ordovician strata was highly inclined.…”

“…We now know it as the Moine Thrust Belt. Accounts of the Survey's mapping approaches are provided by Butler (2010) and the regional geology is extensively described, including detailed site descriptions, by Mendum et al (2009). Even recognizing the talent and numbers that Geikie directed to the mapping, the team made remarkable progress.…”

“…5). These have the appearance of communication tools, perhaps drawn to share knowledge with Cadell and other members of the Survey team (Butler 2010). In these sketches, imbricate thrusts are considered to be arrays of reverse faults that acted upon originally horizontally bedded strata.…”

“…Geological investigations were facilitated by the newly available topographic survey of Scotland so that the Survey team had access to state-of-the-art maps, at a scale of 1:10 560. The geologists did, however, draft their own topographic contours (see Butler 2010, for more details on the mapping strategies and approaches of the Survey team).…”

Structure of the Northern Moine thrust zone, Loch Eriboll, Scottish Caledonides

“…The Loch Eriboll region has been the focus of many detailed structural studies, and the area has been mapped extensively by many previous workers since the 1980s (see Field Guides by Butler ( , 2010a) and Butler et al, 2011) and Mendum et al (2009). McClay and Coward (1981) made a detailed map of the Heilam -Ben Arnaboll region and favoured the foreland-directed thrust sequence proposed initially by Elliott and Johnson (1980) for the Assynt region.…”