Tectonic transport directions, shear senses and deformation temperatures indicated by Quartz c-axis fabrics and microstructures in a NW-SE transect across the moine and sgurr beag thrust sheets, Caledonian Orogen of Northern Scotland

Richard D. Law*, J. R. Thigpen, Sarah E. Mazza, Calvin A. Mako, Maarten Krabbendam, Brandon M. Spencer, Kyle T. Ashley, Robin A. Strachan, Ella F. Davis

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Downloads (Pure)

Abstract

Moine metasedimentary rocks of northern Scotland are characterized by arcuate map patterns of mineral lineations that swing progressively clockwise from orogen-perpendicular E-trending lineations in greenschist facies mylonites above the Moine thrust on the foreland edge of the Caledonian Orogen, to S-trending lineations at higher structural levels and metamorphic grades in the hinterland. Quartz c-axis fabrics measured on a west to east coast transect demonstrate that the lineations developed parallel to the maximum principal extension direction and therefore track the local tectonic transport direction. Microstructures and c-axis fabrics document a progressive change from top to the N shearing in the hinterland to top to the W shearing on the foreland edge. Field relationships indicate that the domain of top to the N shearing was at least 55 km wide before later horizontal shortening on km-scale W-vergent folds that detach on the underlying Moine thrust. Previously published data from the Moine thrust mylonites demonstrate that top to the W shearing had largely ceased by 430 Ma, while preliminary isotopic age data suggest top to the N shearing occurred at ~470–450 Ma. In addition, data from the east coast end of our transect indicate normal-sense top down-SE shearing at close to peak temperatures at ~420 Ma that may be related to the closing stages of Scandian deformation, metamorphism and cooling/exhumation.
Original languageEnglish
Article number411
Number of pages62
JournalGeosciences
Volume11
Issue number10
DOIs
Publication statusPublished - 30 Sep 2021

Keywords

  • tectonic transport direction
  • shear sense
  • deformation temperature
  • quartz c-axis fabric
  • microstructure
  • Caledonian
  • Grampian
  • Scandian
  • Moine thrust
  • Sgurr Beag thrust

Fingerprint

Dive into the research topics of 'Tectonic transport directions, shear senses and deformation temperatures indicated by Quartz c-axis fabrics and microstructures in a NW-SE transect across the moine and sgurr beag thrust sheets, Caledonian Orogen of Northern Scotland'. Together they form a unique fingerprint.

Cite this