The effects of tectonic strain on crystallinity, apparent mean crystallite size and lattice strain of phyllosilicates in low-temperature metamorphic rocks. A case study from the Glarus overthrust, Switzerland

P. Árkai, K. Balogh, Martin Frey

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

The relationship between tectonic shearing strain and crystal structural features of illite-muscovite and chlorite has been investigated in a series of metasedimentary rocks (slates, mylonitized conglomerate and calc-mylonite) from two profiles traversing the classic Glarus overthrust, Swiss Helvetic Alps. In addition to the conventional X-ray diffractometric crystallinity measurements of illite-muscovite (IC) and chlorite (ChC), the apparent mean crystallite size and lattice strain were also calculated by the Voigt method, using single-line Fourier analysis. Small-scale variations in IC and ChC occur as a function of the distance from the Glarus overthrust. In contrast, the apparent mean crystallite size of illite-muscovite decreases while the lattice strain increases towards the overthrust in the Permian Verrucano within an interval of ca. 100-130 m. The reduction in crystallite size caused by increased shearing strain was not followed by recrystallization of illite-muscovite. Opposite trends for chlorite may be explained by syn- and post-overthrusting crystallization. Results from illite-muscovite and chlorite in the calc-mylonite are similar to those of the underlying Tertiary Flysch, in which no systematic changes were found as a function of the distance from the overthrust plane. Correlation between the crystallinity indices and the apparent mean crystallite size are stronger than those between the crystallinity indices and lattice strain. As crystallite size increases, lattice strain - with large fluctuations - tends to decrease with enhancing crystallinity. In general, lattice strain decreases with increasing crystallite size, although there are considerable differences between the various sample groups. Recrystallization of illite-muscovite caused by the overthrusting could be observed only within a several dm-wide zone above and below the gliding plane, as indicated by K-Ar dates of the <2 μm grain-size fraction of illite-muscovite.

Original languageEnglish
Pages (from-to)27-40
Number of pages14
JournalSchweizerische Mineralogische und Petrographische Mitteilungen
Volume77
Issue number1
Publication statusPublished - 1997

Fingerprint

Metamorphic rocks
phyllosilicate
Tectonics
crystallinity
Crystallite size
muscovite
illite
metamorphic rock
tectonics
chlorite
mylonite
Temperature
Shearing
gliding
Fourier analysis
metasedimentary rock
flysch
Crystallization
effect
conglomerate

Keywords

  • Chlorite crystallinity
  • Crystallite size
  • Glarus overthrust
  • Illite crystallinity
  • Lattice strain
  • Switzerland
  • Tectonic strain

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geology

Cite this

@article{791e7cd028ab42648452f923cc7ee675,
title = "The effects of tectonic strain on crystallinity, apparent mean crystallite size and lattice strain of phyllosilicates in low-temperature metamorphic rocks. A case study from the Glarus overthrust, Switzerland",
abstract = "The relationship between tectonic shearing strain and crystal structural features of illite-muscovite and chlorite has been investigated in a series of metasedimentary rocks (slates, mylonitized conglomerate and calc-mylonite) from two profiles traversing the classic Glarus overthrust, Swiss Helvetic Alps. In addition to the conventional X-ray diffractometric crystallinity measurements of illite-muscovite (IC) and chlorite (ChC), the apparent mean crystallite size and lattice strain were also calculated by the Voigt method, using single-line Fourier analysis. Small-scale variations in IC and ChC occur as a function of the distance from the Glarus overthrust. In contrast, the apparent mean crystallite size of illite-muscovite decreases while the lattice strain increases towards the overthrust in the Permian Verrucano within an interval of ca. 100-130 m. The reduction in crystallite size caused by increased shearing strain was not followed by recrystallization of illite-muscovite. Opposite trends for chlorite may be explained by syn- and post-overthrusting crystallization. Results from illite-muscovite and chlorite in the calc-mylonite are similar to those of the underlying Tertiary Flysch, in which no systematic changes were found as a function of the distance from the overthrust plane. Correlation between the crystallinity indices and the apparent mean crystallite size are stronger than those between the crystallinity indices and lattice strain. As crystallite size increases, lattice strain - with large fluctuations - tends to decrease with enhancing crystallinity. In general, lattice strain decreases with increasing crystallite size, although there are considerable differences between the various sample groups. Recrystallization of illite-muscovite caused by the overthrusting could be observed only within a several dm-wide zone above and below the gliding plane, as indicated by K-Ar dates of the <2 μm grain-size fraction of illite-muscovite.",
keywords = "Chlorite crystallinity, Crystallite size, Glarus overthrust, Illite crystallinity, Lattice strain, Switzerland, Tectonic strain",
author = "P. {\'A}rkai and K. Balogh and Martin Frey",
year = "1997",
language = "English",
volume = "77",
pages = "27--40",
journal = "Schweizerische Mineralogische und Petrographische Mitteilungen",
issn = "0036-7699",
publisher = "Staeubi Verlag AG",
number = "1",

}

TY - JOUR

T1 - The effects of tectonic strain on crystallinity, apparent mean crystallite size and lattice strain of phyllosilicates in low-temperature metamorphic rocks. A case study from the Glarus overthrust, Switzerland

AU - Árkai, P.

AU - Balogh, K.

AU - Frey, Martin

PY - 1997

Y1 - 1997

N2 - The relationship between tectonic shearing strain and crystal structural features of illite-muscovite and chlorite has been investigated in a series of metasedimentary rocks (slates, mylonitized conglomerate and calc-mylonite) from two profiles traversing the classic Glarus overthrust, Swiss Helvetic Alps. In addition to the conventional X-ray diffractometric crystallinity measurements of illite-muscovite (IC) and chlorite (ChC), the apparent mean crystallite size and lattice strain were also calculated by the Voigt method, using single-line Fourier analysis. Small-scale variations in IC and ChC occur as a function of the distance from the Glarus overthrust. In contrast, the apparent mean crystallite size of illite-muscovite decreases while the lattice strain increases towards the overthrust in the Permian Verrucano within an interval of ca. 100-130 m. The reduction in crystallite size caused by increased shearing strain was not followed by recrystallization of illite-muscovite. Opposite trends for chlorite may be explained by syn- and post-overthrusting crystallization. Results from illite-muscovite and chlorite in the calc-mylonite are similar to those of the underlying Tertiary Flysch, in which no systematic changes were found as a function of the distance from the overthrust plane. Correlation between the crystallinity indices and the apparent mean crystallite size are stronger than those between the crystallinity indices and lattice strain. As crystallite size increases, lattice strain - with large fluctuations - tends to decrease with enhancing crystallinity. In general, lattice strain decreases with increasing crystallite size, although there are considerable differences between the various sample groups. Recrystallization of illite-muscovite caused by the overthrusting could be observed only within a several dm-wide zone above and below the gliding plane, as indicated by K-Ar dates of the <2 μm grain-size fraction of illite-muscovite.

AB - The relationship between tectonic shearing strain and crystal structural features of illite-muscovite and chlorite has been investigated in a series of metasedimentary rocks (slates, mylonitized conglomerate and calc-mylonite) from two profiles traversing the classic Glarus overthrust, Swiss Helvetic Alps. In addition to the conventional X-ray diffractometric crystallinity measurements of illite-muscovite (IC) and chlorite (ChC), the apparent mean crystallite size and lattice strain were also calculated by the Voigt method, using single-line Fourier analysis. Small-scale variations in IC and ChC occur as a function of the distance from the Glarus overthrust. In contrast, the apparent mean crystallite size of illite-muscovite decreases while the lattice strain increases towards the overthrust in the Permian Verrucano within an interval of ca. 100-130 m. The reduction in crystallite size caused by increased shearing strain was not followed by recrystallization of illite-muscovite. Opposite trends for chlorite may be explained by syn- and post-overthrusting crystallization. Results from illite-muscovite and chlorite in the calc-mylonite are similar to those of the underlying Tertiary Flysch, in which no systematic changes were found as a function of the distance from the overthrust plane. Correlation between the crystallinity indices and the apparent mean crystallite size are stronger than those between the crystallinity indices and lattice strain. As crystallite size increases, lattice strain - with large fluctuations - tends to decrease with enhancing crystallinity. In general, lattice strain decreases with increasing crystallite size, although there are considerable differences between the various sample groups. Recrystallization of illite-muscovite caused by the overthrusting could be observed only within a several dm-wide zone above and below the gliding plane, as indicated by K-Ar dates of the <2 μm grain-size fraction of illite-muscovite.

KW - Chlorite crystallinity

KW - Crystallite size

KW - Glarus overthrust

KW - Illite crystallinity

KW - Lattice strain

KW - Switzerland

KW - Tectonic strain

UR - http://www.scopus.com/inward/record.url?scp=0030828012&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0030828012&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0030828012

VL - 77

SP - 27

EP - 40

JO - Schweizerische Mineralogische und Petrographische Mitteilungen

JF - Schweizerische Mineralogische und Petrographische Mitteilungen

SN - 0036-7699

IS - 1

ER -