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. Ryan Thigpen, Sarah E. Mazza, Calvin A. Mako, Maarten Krabbendam, Brandon M. Spencer, Kyle T. Ashley, Robin A. Strachan, Ella F. Davis

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Moine metasedimentary rocks of northern Scotland are characterized by arcuate map patterns of mineral lineations that swing progressively clockwise from orogen‐perpendicular E‐trend-ing 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
JournalGeosciences (Switzerland)
Volume11
Issue number10
DOIs
StatePublished - Oct 2021

Bibliographical note

Funding Information:
is also indicative of a top down to the ESE shear sense and this interpretation is supported by the incipient alignment (Sb) of elongate recrystallized quartz grains.

Publisher Copyright:
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Keywords

  • Caledonian
  • Deformation temperature
  • Grampian
  • Microstructure
  • Moine thrust
  • Quartz c‐axis fabric
  • Scandian
  • Sgurr Beag thrust
  • Shear sense
  • Tectonic transport direction

ASJC Scopus subject areas

  • Earth and Planetary Sciences (all)

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