| Popis: |
Characterization of texture using population statistics neglects spatial and temporal relations of the grains within the sample which provide valuable information about process and history. Despite the importance of space and time in textural analysis, little has been done to analyze the spatial variability of textures. In order to investigate the question of textural heterogeneity at a thin section scale in detail, the Standard Deviational Ellipse (ME) function from ArcGIS was used to create an extensive database from two different samples: an Elle simulation of crystal-plastic deformation and a weakly deformed quartz arenite photomicrograph. Both samples were deformed by the same increments of simple shear (γ = 0.00 - 0.87); the Elle sample by the deformation simulation and the quartz arenite by passively displacing grain boundaries according to the geometry of simple shear. Each sample was divided into nine cells and the textures in each was analyzed in the GIS using the Standard Deviational Ellipse as well as other parameters such as grain perimeter, area, ellipticity, and long axis orientation. In addition to using the Standard Deviational Ellipse to characterize textural variations, this tool was also evaluated for use as a finite strain marker.The study revealed non-systematic spatial and temporal variation in the change of the ME long axis orientations and ellipticity for the Elle simulation and systematic variation for the quartz arenite. The spatial variation in the texture categorized by the ME is partly due to the variations of grain distribution, shape, and grain position in the undeformed state and partly due to the nature of the deformation. The systematic variations in the quartz arenite are to be expected because of the way in which the sample was passively deformed. While analyzing the ME as a strain marker, it was found to correlate with the grain strain for quartz arenite, but varies significantly from the strains in the Elle simulation. Furthermore, the geometry of the ME is affected by the shape of the sampling area. Therefore, the ME cannot be explicitly used as strain marker. |
