Quantitative fabric analysis of experimentally deformed volcanic rocks

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Gerik, Axel۱; Lavallée, Yan۲; Kruhl, Jِrn H.۱
Holding Date 08 September 2008

The quantitative analysis of patterns as a geometric arrangement of material domains with specific geometric or crystallographic properties such as shape, size or crystallographic orientation has been shown to be a valuable tool with a wide field of applications in geo- and material sciences. We have developed a collection of automated methods that can easily be applied for different problems.
For example, in experimental volcanology an adequate description of the ductile-brittle transition of highly crystalline lavas is crucial to a better understanding of explosive eruptions at dome-building volcanoes. During lava emplacement, ductile shearing and brittle fracturing of these highly crystalline melts may produce complex crystal and fracture fabrics. Such fabrics can be reproduced in experiments (Lavallée et al., in press) and have been quantitatively analyzed with respect to anisotropy of fabric complexity and fabric inhomogeneity (Gerik & Kruhl, in press). Such analyses are important since they provide valuable information on the material behavior at different stages of deformation.
Experimentally deformed volcanic rock samples showed an anisotropy increase in the groundmass pattern whereas the anisotropy decreased in the crystal pattern. This can be explained by fracturing of platy plagioclase crystals, which leads to more equant fragment shapes and, consequently, to a decrease in crystal pattern anisotropy. The increase in groundmass anisotropy results from an alignment of the original crystals perpendicular to the direction of compression.
Such a quantitative approach also allows for a comparison of natural rocks and experimentally deformed samples and, therefore, potentially enables a deeper-rooted investigation of natural processes, based on experiments.