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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.
Document Type
Article
Publication Date
9-30-2021
Digital Object Identifier (DOI)
https://doi.org/10.3390/geosciences11100411
Funding Information
This project was supported by National Science Foundation grants EAR 0538010, EAR 0711207 and EAR 1220138 to R.D.L.
Related Content
The following are available at https://www.mdpi.com/article/10.3390/geosciences11100411/s1, Supplementary File S1: Location, lineation and foliation orientation, quartz c-axis fabric opening angle, deformation temperature and shear sense data for all samples, plus publication versus field sample numbers, Supplementary File S2: quartz recrystallization regime and recrystallized grain size data for all samples, Supplementary File S3: summary of 40Ar/39Ar analytical methods employed for sample MT-10, Supplementary File S4: 40Ar/39Ar data for sample MT-10.
The above materials are also available for download as the additional file listed at the end of this record.
Repository Citation
Law, Richard D.; Thigpen, J. Ryan; Mazza, Sarah E.; Mako, Calvin A.; Krabbendam, Maarten; Spencer, Brandon M.; Ashley, Kyle T.; Strachan, Robin A.; and Davis, Ella F., "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" (2021). Earth and Environmental Sciences Faculty Publications. 24.
https://uknowledge.uky.edu/ees_facpub/24
Supplementary file
Notes/Citation Information
Published in Geosciences, v. 11, issue 10, 411.
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.
This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).