SOFTWARE FOR THE QUANTIFICATION, ERROR ANALYSIS, AND VISUALIZATION OF STRAIN AND FOLD GEOMETRY IN UNDERGRADUATE FIELD AND STRUCTURAL GEOLOGY LABORATORY EXPERIENCES

Two free software tools are used for quantification and visualization of strain and fold geometry in undergraduate laboratory and field experiences at SUNY New Paltz. The software program Orient is used to plot directional data, such as bedding and cleavage measurements, calculate best-fit clusters and fold axes, and determine bootstrap confidence cones to illustrate error. As students collect measurements, they are input into the program to get visual feedback of the developing fold geometry and confidence regions. The data is displayed as Schmidt plots, which use the equal-area projection. However, the stereographic projection can be used to illustrate the density distortion on a stereonet and the importance of selecting the correct projection for data analysis. Additionally, the orthographic projection, with optional upper hemisphere transparency, gives an effective visualization of the fold geometry when plane normals are represented by rays emanating from the center of the sphere. All projections can be interactively rotated to visualize the data in three dimensions. Examples at different scales are given from three field sites: an outcrop of a fold pair near Highland NY, folds exposed at the Bear Valley Strip Mine near Shamokin PA, and map-scale folds near Rosendale NY. The software program EllipseFit is used for strain analysis laboratories and research projects, and includes the capabilities for digitizing clasts from images, calculating strain, bootstrap error analysis, and retro-deforming the images. Again, students can calculate the strain and bootstrap confidence regions while collecting data to get feedback during the process. Three examples at different scales are given: a thin-section of a deformed oolitic limestone, a hand sample of graptoliferous slate from the Taconic Mountains NY, and an outcrop exposure of deformed diamictite from below the Willard thrust on Antelope Island UT. The free software can be downloaded from: www.frederickvollmer.com