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An electron microscopy study of deformation microstructures in granitic mylonites from southwestern Sweden, with special emphasis on the micas

Ooteman, A; Ferrow, Embaie LU and Lindh, Anders LU (2003) In Mineralogy and Petrology 78(3-4). p.255-268
Abstract
The lithology, age, geological setting, structural and metamorphic history of the granitic mylonites from the Mylonite Zone (MZ) in southwestern Sweden have been studied extensively. The deformation history, growth of microstructures, intensity of deformation, changes in mineral compositions, and pressure-temperature conditions of deformation have, however, not been addressed. In this study, powder X-ray diffraction, optical microscopy, electron microprobe analysis and transmission electron microscopy of micas, chlorite, and plagioclase are combined to understand the physical and textural changes experienced by the rocks during mylonitization. It is shown that the occurrence of foliated micas in shear bands, recrystallization of quartz and... (More)
The lithology, age, geological setting, structural and metamorphic history of the granitic mylonites from the Mylonite Zone (MZ) in southwestern Sweden have been studied extensively. The deformation history, growth of microstructures, intensity of deformation, changes in mineral compositions, and pressure-temperature conditions of deformation have, however, not been addressed. In this study, powder X-ray diffraction, optical microscopy, electron microprobe analysis and transmission electron microscopy of micas, chlorite, and plagioclase are combined to understand the physical and textural changes experienced by the rocks during mylonitization. It is shown that the occurrence of foliated micas in shear bands, recrystallization of quartz and biotite, and undulatory extinction in quartz grains were not uniform throughout the samples studied. Occurrence of dislocations and low-angle grain boundaries confirm that deformation occurred largely by glide dislocations. The low-angle grain boundaries observed are formed by the re-arrangement of these dislocations during grain size reduction processes. The micas show a high degree of spatial stacking order, but spatial stacking disorder in micas and chlorites has also been found. Ordered stacking faults are formed during low strain while disordered stacking faults are formed under high strain conditions. Occurrence of both ordered and disordered stacking faults indicates that the intensity of deformation was not uniform through the entire MZ. Moreover, the chemical composition of plagioclase shows that the exsolution lamellae observed with optical and electron microscopy are due to Ca-subsolidus reactions during low temperature deformation. Several substitution reactions occurring in the micas indicate that deformation took place between 0.3 and 0.4 GPa, at a temperature higher than 500degreesC. (Less)
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author
organization
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Contribution to journal
publication status
published
subject
in
Mineralogy and Petrology
volume
78
issue
3-4
pages
255 - 268
publisher
Springer
external identifiers
  • wos:000184734500006
  • scopus:0345765143
ISSN
0930-0708
DOI
language
English
LU publication?
yes
id
f6f62614-528f-4c01-bf86-94399c1875dc (old id 303813)
date added to LUP
2007-08-03 14:39:53
date last changed
2018-05-29 11:35:05
@article{f6f62614-528f-4c01-bf86-94399c1875dc,
  abstract     = {The lithology, age, geological setting, structural and metamorphic history of the granitic mylonites from the Mylonite Zone (MZ) in southwestern Sweden have been studied extensively. The deformation history, growth of microstructures, intensity of deformation, changes in mineral compositions, and pressure-temperature conditions of deformation have, however, not been addressed. In this study, powder X-ray diffraction, optical microscopy, electron microprobe analysis and transmission electron microscopy of micas, chlorite, and plagioclase are combined to understand the physical and textural changes experienced by the rocks during mylonitization. It is shown that the occurrence of foliated micas in shear bands, recrystallization of quartz and biotite, and undulatory extinction in quartz grains were not uniform throughout the samples studied. Occurrence of dislocations and low-angle grain boundaries confirm that deformation occurred largely by glide dislocations. The low-angle grain boundaries observed are formed by the re-arrangement of these dislocations during grain size reduction processes. The micas show a high degree of spatial stacking order, but spatial stacking disorder in micas and chlorites has also been found. Ordered stacking faults are formed during low strain while disordered stacking faults are formed under high strain conditions. Occurrence of both ordered and disordered stacking faults indicates that the intensity of deformation was not uniform through the entire MZ. Moreover, the chemical composition of plagioclase shows that the exsolution lamellae observed with optical and electron microscopy are due to Ca-subsolidus reactions during low temperature deformation. Several substitution reactions occurring in the micas indicate that deformation took place between 0.3 and 0.4 GPa, at a temperature higher than 500degreesC.},
  author       = {Ooteman, A and Ferrow, Embaie and Lindh, Anders},
  issn         = {0930-0708},
  language     = {eng},
  number       = {3-4},
  pages        = {255--268},
  publisher    = {Springer},
  series       = {Mineralogy and Petrology},
  title        = {An electron microscopy study of deformation microstructures in granitic mylonites from southwestern Sweden, with special emphasis on the micas},
  url          = {http://dx.doi.org/},
  volume       = {78},
  year         = {2003},
}