A computer program for the calcite strain-gauge technique

Abstract

The calcite strain-gauge technique has been used successfully to determine strains in slightly to moderately deformed limestones. The technique involves the use of a universal stage to collect calcite twin orientation, thickness and frequency data. The data are reduced by a least-squares method to give the orientations and magnitudes of the principal strains. The purpose of this paper is to describe an easy-to-use computer program for the technique, and an accompanying manual on collecting data for the strain-gauge analysis. The program calculates principal strain magnitudes and orientations, total strain due to twinning ( J 2 0.5), standard errors for the strains, average twin-width, twin intensity and percent negative expected values. In addition, the program can plot stereonets with compression axes, tension axes, poles to e twin planes, crystallographic c-axes, g-axes, average twin-widths per twin set, twin intensity per twin set, and positive and negative expected values. The stereonets may also be rotated. All calculated orientation data may be saved in a computer file for later input into a stereonet contouring program. The user may choose automatically to remove 20% of the twin sets with the largest deviation, or manually to remove selected twin sets from the data being analyzed, in order to ‘clean’ the data. Twin sets that give positive or negative expected values may also be analyzed separately.