Late Carboniferous dextral transpressional reactivation of the crustal-scale Walls Boundary Fault, Shetland: the role of pre-existing structures and lithological heterogeneities

Armitage, Timothy B.; Watts, Lee M.; Holdsworth, Robert E.; Strachan, Robin A.

Abstract

The Walls Boundary Fault (WBF) in Shetland, Scotland, formed during the Ordovician-Devonian Caledonian orogeny and underwent dextral reactivation in the Late Carboniferous. In a well-exposed section at Ollaberry, westerly verging, gently plunging regional folds in the Neoproterozoic Queyfirth Group on the western side of the WBF are overprinted by faults and steeply-plunging Z-shaped brittle-ductile folds that indicate contemporaneous right-lateral and top-to-the W reverse displacement. East of the WBF, the Early Silurian Graven granodiorite complex exhibits fault-parallel fractures with Riedel, P and conjugate shears indicating N-S striking dextral deformation and an additional contemporaneous component of E-W shortening. In the Queyfirth Group, the structures are arranged in geometrically and kinematically distinct fault-bounded domains that are interpreted to result from two superimposed tectonic events, the youngest of which displays evidence for bulk dextral transpressional strain partitioning into end-member wrench and contractional strain domains. During dextral transpressional deformation, strain was focussed into pelite horizons and favourably aligned pre-existing structures, leaving relics of older deformation in more competent lithologies. This study highlights the importance of pre-existing structures and lithological heterogeneity during reactivation and suggests the development of a regional transpressional tectonic environment during the Late Carboniferous on the Shetland Platform.

Citation

Armitage, T. B., Watts, L. M., Holdsworth, R. E., & Strachan, R. A. (2020). Late Carboniferous dextral transpressional reactivation of the crustal-scale Walls Boundary Fault, Shetland: the role of pre-existing structures and lithological heterogeneities. Journal of the Geological Society, 178, Article jgs2020-078. https://doi.org/10.1144/jgs2020-078

• Journal Article Type: Article
• Acceptance Date: Sep 22, 2020
• Online Publication Date: Sep 30, 2020
• Publication Date: Oct 23, 2020
• Deposit Date: Sep 28, 2020
• Publicly Available Date: Dec 3, 2020
• Journal: Journal of the Geological Society
• Print ISSN: 0016-7649
• Electronic ISSN: 2041-479X
• Publisher: The Geological Society
• Peer Reviewed: Peer Reviewed
• Volume: 178
• Article Number: jgs2020-078
• DOI: https://doi.org/10.1144/jgs2020-078
• Public URL: https://durham-repository.worktribe.com/output/1291553