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

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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.
Original languageEnglish
Number of pages16
JournalJournal of the Geological Society
Volume177
Issue number5
Early online date23 Oct 2020
DOIs
Publication statusEarly online - 23 Oct 2020

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