Overprinting orogenic events, ductile extrusion and strain partitioning during Caledonian transpression, NW Mainland Shetland

Armitage, Timothy B.; Holdsworth, Robert E.; Strachan, Robin A.; Dempsey, Edward D.; Walker, Richard J.; Alvarez-Ruiz, Diana T.; Lloyd, Geoffrey E.

Abstract

A 3.6 km thick stack of mid-crustal deformed Precambrian rocks is associated with the North Roe Nappe (NRN) and Walls Boundary Fault in the northernmost Scottish Caledonides on NW Mainland Shetland. The greenschist- to amphibolite-facies rocks display unusually complex and heterogeneous combinations of coaxial and non-coaxial transpressional deformation. Previously published isotopic dating, together with new detailed field mapping and microstructural characterisation show that the NRN preserves a record of Neoarchaean, Neoproterozoic (Knoydartian) and Ordovician-Silurian (Caledonian) overprinting deformation and metamorphism. Neoarchaean events in the Uyea Gneiss Complex located in its footwall are reworked by younger events in the overlying nappe pile. The main ductile fabrics were formed during Caledonian top-to-the W/NW thrusting and top-to-the N sinistral shearing, with subordinate regions of top- to-the E extensional and NNE-SSW dextral shearing. In lower parts of the NRN, these different kinematic domains are texturally indistinguishable and overprinting relationships are absent. At higher levels, top-to-the-W/NW thrust-related fabrics are consistently overprinted by top-to-the-N/NE sinistral shearing. The highly partitioned transpressional deformation shows similarities with equivalent rocks of the Moine Nappe in NW Scotland.

Citation

Armitage, T. B., Holdsworth, R. E., Strachan, R. A., Dempsey, E. D., Walker, R. J., Alvarez-Ruiz, D. T., & Lloyd, G. E. (2024). Overprinting orogenic events, ductile extrusion and strain partitioning during Caledonian transpression, NW Mainland Shetland. Journal of Structural Geology, 180, Article 105088. https://doi.org/10.1016/j.jsg.2024.105088

• Journal Article Type: Article
• Acceptance Date: Feb 15, 2024
• Online Publication Date: Feb 21, 2024
• Publication Date: 2024-03
• Deposit Date: May 20, 2024
• Publicly Available Date: May 20, 2024
• Journal: Journal of Structural Geology
• Print ISSN: 0191-8141
• Electronic ISSN: 1873-1201
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 180
• Article Number: 105088
• DOI: https://doi.org/10.1016/j.jsg.2024.105088
• Public URL: https://durham-repository.worktribe.com/output/2454479