Mylonites: lessons from Eriboll
Published:January 01, 2010
S. H. White, 2010. "Mylonites: lessons from Eriboll", 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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Eriboll has been an important area in understanding the geology and structure of the NW Highlands of Scotland. It came to prominence during the Highland Controversy between Nicol and Murchison in the 1850s. Nicol recognized a major regional, or grand, dislocation (the Moine Thrust Zone) at Eriboll whereas Murchison denied its existence. An important element in the resolution of the controversy was the repeated observation of a distinctive schistose rock that often marked Nicol's dislocation. Lapworth named it a ‘mylonite’ and related its development to mechanical metamorphism resulting from tectonic (milling) movements along the dislocation. Peach, Horne and co-workers, whose contributions to early mylonite studies are often overlooked, described the effects of increasing strain on mylonite development, recorded the prominent lineation within mylonites and identified its kinematic significance via thrust geometries and a first use of shear sense indicators. In this contribution those elements of the Highland Controversy that led to the identification of mylonites will be reviewed, concentrating on the contributions of Lapworth and of Peach, Horne and co-workers. It will include an examination and discussion of the mylonites from Lapworth's locality and of the mylonitized Moine schists at Eriboll. It will conclude with comments on mylonite classification and nomenclature.
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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.