Relating Lattice Preferred Orientation to Deformational Process using Statistical Analysis of Symmetry in Orientation Distribution Space
Abstract
We introduce a new method for analyzing the statistical symmetry of lattice preferred orientation fabrics in deformed rocks. At present, these fabrics are usually analyzed in an empirical fashion, by comparison with experimental results and also by inspection for evidence of asymmetry in the fabrics (i.e. skeleton representation). Our approach is based on the idea of statistical symmetry, as originally suggested by Paterson and Weiss (1961), who were first to discuss how the symmetry elements in the structures or LPO fabrics in a deformed rock could be used to interpret the symmetry of the deformation, such as pure shear vs. simple shear, plane strain vs. flattening vs. constriction, and the sense of shear in noncoaxially deformed rocks. Our analysis focuses on finding the set of statistically significant mirror-planes in the LPO fabric. We expect a simple-shear deformation to contain only one mirror plane, parallel to the shear direction and perpendicular to the shear plane. In contrast, a coaxial flattening deformation would have a zonal distribution of parallel planes, with the zone axis equivalent to the maximum shortening direction. To estimate the mirror plane symmetry elements of an LPO data set, we search a grid of orientations in the lower hemisphere of a stereonet, and invert the LPO distribution to produce a mirrored version of the data. The original and mirrored distributions are compared in orientation distribution space using a Kolmogorov-Smirnov test to measure the probability that the distributions are similar, save for random variation. This analysis allows us to simultaneously consider the symmetry of all of the measured crystallographic directions. We illustrate our technique using LPO data from naturally deformed quartz mylonites from the Moine Thrust and sheared mantle xenoliths from Kamchatka. Ultimately, this technique is a step towards quantifying the deformation history of naturally deformed LPO fabrics.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMMR41A1852T
- Keywords:
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- 5112 PHYSICAL PROPERTIES OF ROCKS / Microstructure;
- 8011 STRUCTURAL GEOLOGY / Kinematics of crustal and mantle deformation;
- 8030 STRUCTURAL GEOLOGY / Microstructures;
- 8094 STRUCTURAL GEOLOGY / Instruments and techniques