Goals

Microfabrics contain important information about the physical conditions, the kinematics and the processes of deformation. The kinematics of deformation (i.e., the shear sense), for example, are often inferred from the asymmetry of microstructural and textural features in deformed rocks. In order to gain a better understanding of kinematic indicators and the deformational behavior of minerals at different physical conditions, researchers have studied the mechanical properties and microfabrics of most common rock-forming minerals (e.g., quartz, calcite, feldspar, olivine).  The study of naturally deformed rocks, experimental rock deformation, and computer modeling have all played complementary roles in improving our knowledge of mineral physics.

We chose an experimental approach involving the deformation of polycrystalline norcamphor in a see-through, Means-Urai deformation apparatus under simple shear conditions. The main advantage of this method is that it allows continuous observation of the microfabric evolution during progressive deformation. We monitored this evolution with photographs, video tapes and computer integrated polarization microscopy (CIP, see Panozzo Heilbronner, R. & Pauli, C.  1993. Integrated spatial and orientation analysis of quartz c-axes by computer-aided microscopy. J. Struct. Geol. 15, 369-383). With CIP, the c-axis orientations are visualized directly with specific reference colors. Strain was calculated with help of  passive marker particles and the computer program Marker Analysis (Bons, P., Jessell, M.W. & Passchier, C.W. 1993. The analysis of progressive deformation in rock analogues. J. Struct. Geol. 15, 403-412.)  This allowed us to relate the microstructure, the texture and the localization of strain in each experiment.

If desired, more information about the applied techniques and the results of  these experiments can be found in:

Herwegh, M. 1996. Microfabric Evolution in Monomineralic Mylonites: An Experimental Approach Using See-Through Analogue Materials. Unpublished Ph.D. thesis, University of Berne.

Herwegh, M. & Handy, M.R. 1996. The evolution of high temperature mylonitic microfabrics: evidence from simple shearing of a quartz analogue (Norcamphor). J. Struct. Geol., 18, 689-710.

Herwegh, M. & Handy, M. R. 1998. The origin of shape preferred orientations in mylonite: inferences from in-situ experiments on polycrystalline Norcamphor. J. Struct. Geol. 20, 681-694.

Herwegh, M., Handy, M.R. & Panozzo Heilbronner, R. 1997. Temperature and strain rate dependent microfabric evolution in monomineralic mylonite: evidence from in situ deformation of Norcamphor. Tectonophysics 280, 83-106.

Herwegh, M., Handy, M.R. & Panozzo Heilbronner, R. 1999. Evolution of mylonitc microfabrics (EMM), a computer application for educational purposes. Tectonophysics 303, 141-146.

Panozzo Heilbronner, R., & Herwegh, M. 1997. Time slicing, an image processing technique to visualize temporal development of fabrics. J. Struct. Geol. 19, 861-874.
 

This work was taken from the Ph.D. thesis of Marco Herwegh which was generously supported by the Swiss National Sciences Foundation (Nr. 21-33814.92).