Moine Thrust zone mylonites at the Stack of Glencoul: II – results of vorticity analyses and their tectonic significance
Published:January 01, 2010
R. D. Law, 2010. "Moine Thrust zone mylonites at the Stack of Glencoul: II – results of vorticity analyses and their tectonic significance", Continental Tectonics and Mountain Building: The Legacy of Peach and Horne, R. D. Law, R. W. H. Butler, R. E. Holdsworth, M. Krabbendam, R. A. Strachan
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This paper presents quantitative data from the Stack of Glencoul on flow vorticities associated with mylonite generation in the hanging wall and footwall of the Moine Thrust, using samples collected in a vertical traverse from 80 m above the thrust plane to 8.5 m beneath the thrust. Estimated vorticity numbers (Wm) in Moine pelites and psammites above the thrust range from 0.775–0.725 (c. 43–47% pure shear component) increasing downwards to 0.83–0.75 (35–45% pure shear) at 10 cm above the thrust. Wm values in dynamically recrystallized Cambrian quartzites at 0.5–14.5 cm beneath the thrust range from 0.99–0.90 (10–30% pure shear). At 3.0–8.5 m beneath the thrust estimated Wm values are less than 0.75 in the quartzites, although there is some thin section-scale partitioning with Wm values of 0.75–0.65 (45–55% pure shear) in domains of dynamically recrystallized quartz and Wm values <0.65 (>55% pure shear) in domains of relict detrital quartz grains. Integration of strain and vorticity analyses indicates a vertical shortening of 50–75% in these gently dipping mylonites located at the base of the Moine Nappe. The tectonic implications of vertical shortening (thinning) and transport-parallel stretching at the base of the Moine Nappe are discussed.
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Continental Tectonics and Mountain Building: The Legacy of Peach and Horne
The world's mountain ranges are the clearest manifestations of long-term deformation of the continental crust. As such they have attracted geological investigations for centuries. Throughout this long history of research a few keynote publications stand out. One of the most important is the Geological Survey's 1907 Memoir on The Geological Structure of the North-West Highlands of Scotland. The Memoir summarized some of the Geological Survey's finest work, and outlined many of the principles of field-based structural and tectonic analysis that have subsequently guided generations of geologists working in other mountain belts, both ancient and modern. The thematic set of 32 papers in this Special Publication celebrate the 100th anniversary of the 1907 Memoir by placing the original findings in both historical and modern contexts, and juxtaposing them against present-day studies of deformation processes operating not only in the NW Highlands, but also in other mountain belts.