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Styles of basement involvement in the Moine Thrust Belt, NW Scotland

By
R.W.H. Butler
R.W.H. Butler
Institute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom
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R.E. Holdsworth
R.E. Holdsworth
Reactivation Research Group, Department of Earth Sciences, University of Durham, South Road, Durham DH1 3LE, United Kingdom
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S.J. Matthews
S.J. Matthews
BP Exploration plc, Chertsey Road, Sunbury on Thames, Middlesex TW16 7LN, United Kingdom
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Published:
January 01, 2006

The Moine Thrust Belt contains imbricate systems derived from Cambro-Ordovician sediments together with thrust sheets of their Lewisian basement. Correlation of Precambrian structures between these thrust sheets and the adjacent foreland demonstrates displacements >25 km, values confirmed and exceeded by restored cross sections constructed through the imbricated sedimentary cover. The basement-carrying thrust sheets display a wide variety of structural styles even though they have deformed under essentially the same metamorphic pressure and temperature conditions (lower greenschist facies). These include the translation of crystalline basement as sheets with no appreciable internal deformation apart from sparse quartz-epidote-filled fractures and ∼1 m of mylonites and related fault rocks along the basal thrusts. Thrust trajectories can run parallel to the regional, near-horizontal datum (the sub-Cambrian unconformity) even though there are no apparent preexisting surfaces that might have localized slip on these horizons within the basement. In other examples, however, parts of basement thrust trajectories appear to have located preferentially on preexisting faults. These features have been underemphasized in previous studies and can be inferred by the preservation of PrecambrianTorridonian strata beneath the sub-Cambrian unconformity within thrust sheets. Basin faults that controlled deposition and preservation of Torridonian strata may have promoted large-scale folding at the basement-cover interface that is manifest as the large-scale recumbent structures of the southern part of the thrust belt. These different styles are compared and discussed in terms of the propensity of the Lewisian basement to localize deformation at greenschist facies through reactivation and retrogression-enhanced weakening.

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Contents

GSA Special Papers

Styles of Continental Contraction

Stefano Mazzoli
Stefano Mazzoli
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Robert W.H. Butler
Robert W.H. Butler
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Geological Society of America
Volume
414
ISBN print:
9780813724140
Publication date:
January 01, 2006

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