Protomylonite, Mylonite and Ultramylonite

  • Rudolph A. J. TrouwEmail author
  • Cees W. Passchier
  • Dirk J. Wiersma


The objective of this chapter is to show how variation of strain intensity can be judged in thin section. Usually this kind of variation can best be observed in low-grade mylonites where the percentage of porphyroclasts decreases progressively with strain intensity. However, the percentage of matrix is highly dependent on mineralogical composition (e.g. quartz and biotite tend to convert to matrix readily). Compositional banding in gneiss can therefore result in mylonitic banding of apparent strain variation, which in fact only reflects variation in composition of the parent rock. Several examples of ultramylonite are derived from quartzitic rocks that tend to form few or no porphyroclasts at all.


Shear Band Strain Intensity Mylonitic Foliation Quartz Lens Undulose Extinction 
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Copyright information

© Springer-Verlag Berlin Heidelberg 2010

Authors and Affiliations

  • Rudolph A. J. Trouw
    • 1
    Email author
  • Cees W. Passchier
    • 2
  • Dirk J. Wiersma
    • 3
  1. 1.Depto. Geologia Ilha do FundaoUniversidade Federal do Rio de JaneiroRio de Janeiro-RJBrazil
  2. 2.Institut für GeowissenschaftenUniversität MainzMainzGermany
  3. 3.UtrechtThe Netherlands

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