Numerical Dynamic Analysis of Quartz Deformation Lamellae and Calcite and Dolomite Twin Lamellae

Abstract

The method of numerical dynamic analysis has been applied successfully to samples of naturally deformed carbonate-cemented sandstone in which the quartz grains exhibit deformation lamellae and both calcite and dolomite grains exhibit twin lamellae. The naturally deformed samples are from the Foothills and Front Range subprovinces of the Canadian Rocky Mountains. The analysis of the quartz deformation lamellae assumes that the plane of the lamellae is a plane of high resolved shear stress, the sense of shear is negative, and the gliding direction is determined from the c axis and the pole to the lamellae. Using these assumptions, the existing methods of numerical dynamic analysis and the standard (graphic) dynamic analysis have been applied. Existing graphic techniques for the analysis of deformation lamellae yield essentially the same results as does the technique of numerical dynamic analysis. In this study, the correlation of the principal axes derived from numerical analysis of the quartz, calcite, and dolomite is both internally consistent and consistent with the geologic framework from which the samples were collected. It reflects the statistical homogeneity of the stress orientations during the deformation of these rocks. The samples all show a nearly layer-parallel compression of the layer with a range of orientations for the maximum principal stress that agrees well with maximum principal stress orientations calculated from analysis of macroscopic and megascopic structures related to the same thrust.