Post-Caledonian contractional structures are few and modest within the readily deformable Devonian sedimentary rocks of the northern British Isles (Scotland). This contrasts with the situation to the south in the southern UK and Europe (the Variscan orogen) and to the north in North East Greenland (Payer Land; Guarnieri, 2020), as well as Northern Greenland and Svalbard (Ellesmere/Svalbardian orogen; e.g., Manby and Lyberis, 1992).
The intervening areas, where the Caledonian Orogen merged the Baltican and Laurentian continents during the early stages of Pangaea amalgamation (Silurian-Devonian), have generally been thought to have escaped compressional tectonics during the later phases of Pangaea assembly, although some exceptions have been recorded, particularly in the Midland Valley area and in the Orcadian Basin, Scotland (e.g., Richie et al., 2003; Hippler, 1989).
A recent MSc thesis (Rian, 2018) documented E-W oriented contractional structures affecting Mid-Devonian sedimentary rocks of the Orcadian Basin in the Orkneys, although these structures have not been studied in detail. They are intersected by a late Carboniferous dike swarm and an overprinting extensional deformation phase, which also lacks thorough documentation. One hypothesis posits that the observed compressional deformation was synchronous with the Variscan Orogeny. If these structures formed as a result of deformation in the distal foreland of the Variscan Orogen, the E-W orientation suggests that they were either rotated after formation or that they developed through strain partitioning associated with strike-slip displacement along the Great Glen Fault and related strike-slip faults.
This thesis aims to document the post-mid-Devonian contractional structures and the overprinting extensional structures, to better constrain their timing and explore whether the contractional and overprinting extensional structures are related to the Variscan orogen or to some unrelated, hitherto unrecognized regional compressional and subsequent extensional tectonic event(s).
References
- Guarnieri, P. (2021). Devonian–Early Carboniferous thrust tectonics in the Old Red Sandstone Molasse Basin, North‐East Greenland. Terra Nova, 33(5), 521-528.
- Hippler, S. J. (1989). Fault rock evolution and fluid flow in sedimentary basins (Doctoral dissertation, University of Leeds).
- Manby, G., & Lyberis, N. (1992). Tectonic evolution of the Devonian Basin of northern Svalbard. Norsk Geologisk Tidsskrift, 72(1), 7-19.
- Ritchie, J. D., Johnson, H., Browne, M. A. E., & Monaghan, A. A. (2003). Late Devonian–Carboniferous tectonic evolution within the Firth of Forth, Midland Valley; as revealed from 2D seismic reflection data. Scottish Journal of Geology, 39(2), 121-134.