Lattice strain across Na-K interdiffusion fronts in alkali feldspar: an electron backscatter diffraction study.
- Author(s)
- Anne-Kathrin Schäffer, Tom Jaepel, Stefan Zäfferer, Rainer Abart, Dieter Rhede
- Abstract
Cation exchange experiments between gem quality sanidine (X
Or = 0.85) and KCl melt produced chemical alteration of alkali feldspar starting at the grain surface and propagating inwards by highly anisotropic Na–K interdiffusion on the alkali sublattice. Diffusion fronts developing in b-direction are very sharp, while diffusion fronts within the a–c-plane are comparatively broad. Due to the composition dependence of the lattice parameters of alkali feldspar, the diffusion induced compositional heterogeneity induces coherency stress and elastic strain. Electron back-scatter diffraction combined with the cross-correlation technique was employed to determine the lattice strain distribution across the Na–K interdiffusion fronts in partially exchanged single crystals of alkali feldspar. The strain changes gradually across the broad fronts within the a–c-plane, with a successive extension primarily in a-direction conferring to the composition strain in unstressed alkali feldspar. In contrast, lattice strain characterised by pronounced extension in b-direction is localised at the sharp diffusion fronts parallel to b, followed by a slight expansion in a-direction in the orthoclase-rich rim. This strain pattern does not confer with the composition induced lattice strain in a stress-free alkali feldspar. It may rather be explained by the mechanical coupling of the exchanged surface layer and the mechanically strong substratum. The lattice distortion localised at the sharp diffusion front may have an influence on the diffusion process and appears to produce a self-sharpening feedback, leading to a local reduction of component mobilities.
- Organisation(s)
- Department of Lithospheric Research
- External organisation(s)
- Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum, Max-Planck-Institut für Eisenforschung
- Journal
- Physics and Chemistry of Minerals
- Volume
- 41
- Pages
- 795-804
- No. of pages
- 10
- ISSN
- 0342-1791
- DOI
- https://doi.org/10.1007/s00269-014-0692-y
- Publication date
- 11-2014
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105116 Mineralogy, 105120 Petrology
- Keywords
- ASJC Scopus subject areas
- Geochemistry and Petrology, General Materials Science
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/d7ae289f-c901-4302-b2d5-9741edb415a4