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.

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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/).

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This project was supported by National Science Foundation grants EAR 0538010, EAR 0711207 and EAR 1220138 to R.D.L.

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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.

geosciences-11-00411-s001.zip (1 kB)
Supplementary file