Journal article
Reaction progress during mylonitization of basaltic dikes along the Sarv Thrust, Swedish Caledonides
Contributions to mineralogy and petrology, Vol.101(1), pp.30-45
1989
DOI: 10.1007/BF00387199
Abstract
The mylonite zone at the base of this thrust sheet contains diabase dykes which record intense deformation and syntectonic greenschist facies metamorphism. An angular shear strain of gamma approx 100 is calculated for a single dyke which can be followed for 50 m in the mylonite zone, and abundant cm-thick greenschist layers imply shear strains >1000. This amount of deformation is comparable to the largest strains attained during experimental superplastic deformation of metals and alloys, by analogy suggesting that dyke formation was macroscopically superplastic. The progress of five syntectonic reactions was measured as a function of increasing strain for the continuously exposed dyke in order to assess the contribution of reaction-enhanced ductility and fluid-rock interactions to strain localization along the thrust. Reaction progress calculations suggest that the breakdown of amphibole to form weaker phyllosilicates is the important strain-softening mechanism below gamma approx 100. The ultimate tectonite is a stable biotite-epidote schist comprised of a uniformly fine grain size (<200 mu m), constant grain shapes and strain-free grains. Below gamma approx 40, metamorphism was isochemical and shear strain was independent of H (sub 2) O in the reactions. Petrological fluid:rock ratios are low and suggest that deformation could have occurred under dry conditions. Deformation micromechamisms were probably dominated by diffusive mass transfer processes throughout the life of the shear zone. The absence of cataclasis and the fine grain size of the protolith basalt suggest that fluids were introduced via grain boundary diffusion. Incongruent P solution at low strains and K-metasomatism >gamma approx 40 also support diffusional flow. Diffusion-accommodated grain boundary sliding is thought to be the dominant micro- mechanism once the stable biotite-epidote tectonite forms.
Details
- Title: Subtitle
- Reaction progress during mylonitization of basaltic dikes along the Sarv Thrust, Swedish Caledonides
- Creators
- J. A Gilotti - Lund University
- Resource Type
- Journal article
- Publication Details
- Contributions to mineralogy and petrology, Vol.101(1), pp.30-45
- Publisher
- Springer International
- DOI
- 10.1007/BF00387199
- ISSN
- 0010-7999
- eISSN
- 1432-0967
- Language
- English
- Date published
- 1989
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984229304402771
Metrics
1 Record Views