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

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

Research output: Contribution to journalArticlepeer-review

6 Downloads (Pure)

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.
Original languageEnglish
Article number105088
Number of pages29
JournalJournal of Structural Geology
Volume180
Early online date21 Feb 2024
DOIs
Publication statusPublished - 1 Mar 2024

Keywords

  • Transpression
  • Strain partitioning
  • Overprinting events
  • Quartz petrofabric analysis
  • EBSD
  • UKRI
  • NERC
  • NE/L002590/1

Cite this