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

Robert William Hope Butler, Robert Holdsworth, Stephen Matthews

Research output: Contribution to journalArticle

Abstract

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 c1 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.
Original languageEnglish
Pages (from-to)133-150
JournalGeological Society of America Special Paper
Volume414
Publication statusPublished - 2006

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thrust
Lewisian
greenschist facies
unconformity
Torridonian
trajectory
retrogression
epidote
reactivation
folding
Ordovician
Precambrian
cross section
quartz
basin
rock
sediment
temperature

Cite this

Styles of basement involvement in the Moine thrust Belt, NW Scotland. / Butler, Robert William Hope; Holdsworth, Robert; Matthews, Stephen.

In: Geological Society of America Special Paper, Vol. 414, 2006, p. 133-150.

Research output: Contribution to journalArticle

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N2 - 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 c1 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 ofPrecambrianTorridonian 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 tolocalize deformation at greenschist facies through reactivation and retrogression-enhanced weakening.

AB - 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 c1 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 ofPrecambrianTorridonian 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 tolocalize deformation at greenschist facies through reactivation and retrogression-enhanced weakening.

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