Table of Contents
Textures and Microstructures
Volume 4 (1982), Issue 4, Pages 223-239

Reaction and Geometrical Softening in Granitoid Mylonites

Department of Geology, University College, P.O. Box 78, Cardiff CF1 1XL, United Kingdom

Received 24 June 1981; Accepted 15 July 1981

Copyright © 1982 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The microstructures of granitoid mylonites from Locquirec, N. Brittany; Ben Arnaboll, NW Scotland; and Cap de Creus, NE Spain show a similarity of development as a response to both geometric and reaction softening. A combination of these two softening processes leads to a concentration of deformation in the respective shear zones. Geometric softening leads to a rotation of quartz lattices for easy slip and is accompanied by dynamic recrystallization. Metamorphic reactions involving the breakdown of orthoclase and plagioclase feldspar to fine aggregates of muscovite plus quartz provide a secondary softening process which further concentrates deformation. These reactions indicate fluid mobility in the shear zones during deformation processes.