Statistical Comparison Of Crystal Orientation Fabrics With Particular Reference To The Fabrics Of Heterogeneously Deformed Quartzite Pebbles Of The Conglomerate From The Tyson Formation, Vermont

Abstract

A highly deformed conglomerate from the Tyson Formation in central Vermont, U.S.A. is the focus of the analysis of the internal fabric of individual, heterogeneously deformed quartzite pebbles. The quartz crystallographic fabric is measured using the optical universal stage and X-ray fabric camera. The grain shape fabric is measured using digitized video camera images.;For the purpose of comparing quartz c-axis orientation patterns, nonparametric tests are investigated. This study is based on a suite of 132 measured quartz c-axis patterns which are representative of all possible types provided by Dr. John Starkey. The insights gained from this study are applied to the more subtle variations in the quartz c-axis patterns displayed by the heterogeneously deformed pebbles.;The c-axis fabrics of the quartzite pebbles show single girdle and crossed-girdle patterns which can be reconciled with plane strain deformation. Further, the crossed-girdle patterns are symmetrically oriented relative to the foliation which therefore indicates coaxial deformation. However, in some crossed-girdle patterns, one girdle is stronger suggesting local non-coaxial deformation. Both strain paths probably developed under conditions of plane strain.;The Mann-Whitney, Kolmogorov-Smirnov and Squared rank test statistics are derived by comparing 32 selected, recognizable types of measured quartz c-axis orientation patterns with the uniform reference pattern. Two groups of test statistics were found, a group of clustered pattern types and a group of dispersed pattern types. The data for all pattern types can be grouped according to their statistics, except cleft girdles and double maxima.;The nonparametric statistical tests are also used to compare two measured orientation patterns in an objective and reproducible manner. The Mann-Whitney and Kolmogorov-Smirnov tests confirmed the similarity of patterns which visual comparison would show as similar. However, the Squared ranks test proved to be too sensitive in comparing the measured orientation patterns with each other.;The comparison of the orientation patterns from the heterogeneously deformed pebbles of the Tyson conglomerate showed that the orientation patterns were similar in almost every case. However, the orientation patterns were found to be different between the different pebbles