Microstructural and crystal fabric evolution during shear zone formation

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doi: 10.1016/0191-8141(92)90037-W
Authors:Lloyd, G. E.; Law, R. D.; Mainprice, David; Wheeler, J.
Author Affiliations:Primary:
University of Leeds, Department of Earth Sciences, Leeds, United Kingdom
Virginia Polytechnic Institute and State University, United States
Universite des Sciences et Techniques du Languedoc, France
University of Liverpool, United Kingdom
Volume Title:Mechanical instabilities in rocks and tectonics; a selection of papers
Volume Authors:Burg, Jean-Pierre, editor; Petit, Jean-Pierre
Source:Journal of Structural Geology, 14(8-9), p.1079-1100; International conference on Mechanical instabilities in rocks and tectonics, Montpellier, France, Sept. 3-6, 1991, edited by Jean-Pierre Burg, David Mainprice and Jean-Pierre Petit. Publisher: Pergamon, Oxford-New York, International. ISSN: 0191-8141
Publication Date:1992
Note:In English. 37 refs.; 4 plates
Summary:The microstructures and crystal fabrics associated with the development of an amphibolite-faciesquartzo-feldspathic mylonitic shear zone (Torridon, NW Scotland) were investigated using SEM electron channelling. The results illustrate a variety of microstructures and fabrics which attest to a complex shear zone deformation history. The microstructures suggest that the principal deformation mechanism was intracrystalline plasticity (with contributions from grain-size reduction via dynamic recrystallization, grain boundary migration and grain boundary sliding). Crystal fabrics measured from the shear zone vary with position depending on the shear strain involved, and are consistent with the operation of several crystal slip systems (e.g. prism, basal, rhomb and acute rhomb planes) in a consistent direction (probably a and/or m). They also reveal Dauphine twinning and suggest that this may be a significant process in quartz deformation. A single crystal fabric evolution path linking the shear zone margin fabric with the mylonitic fabric was not observed. Rather, the mylonitic fabric reflects the instantaneous fabric which developed at a particular location for a particular shear strain and original parental grain orientation. The mature shear zone therefore consists of a series of deformed original grains stacked on top of each other in a manner which preserves original grain boundaries and intragranular features which developed during shear zone evolution. [J.M.H.]
Subjects:Amphibolite facies; Deformation; Facies; Metamorphic rocks; Microstructure; Mylonites; Petrofabrics; SEM data; Shear; Shear zones; Structural geology; Theoretical studies; Europe; Great Britain; Scotland; United Kingdom; Western Europe; Northwestern Scotland; Torridon
Abstract Numbers:93M/2396
Record ID:1992061506
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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