Abstract
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.
Highlights
Deformation experiments using rheologically contrasting materials as analogues for rock are widely used and cited to illustrate the evolution of largescale geological structures
Cadell’s experiments, in common with those conducted by previous researchers, used laterally continuous layers of material. This arrangement was appropriate for models that might inform understanding of thrust structures developed in the Cambro-Ordovician strata of NW Scotland – stratigraphy that is remarkably layer-cake over tens of kilometres
There is little discussion of how these insights should be integrated into a workflow to reduce uncertainty in the interpretation of structural geometry in the natural world
Summary
Unconformably by quartz sandstones of Lower Cambrian age (Eriboll Quartzite Formation) These strata are stacked and repeated by thrusts – especially evident on the mountain ridges of Conamheall and Foinaven (Fig. 6a). He noted that the top of the Lewisian basement passed beneath the repeated Cambrian strata without being offset by faults He was able to map out the base of the deformed quartz sandstones – later designated as the Sole Thrust (Peach et al 1907; Fig. 4). Cadell’s perception of the characteristic structure of his study area is shown, a diagram from his notebook that is a proof copy destined for his book on Sutherland’s geology (Cadell 1896) It shows the structure created by thrusts of different displacement and dip, all repeating stratigraphic units. As he states (Cadell 1889, p. 339), these ‘images tell their own tale, and require but little description’
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