STRABOTOOLS: MEASURING THINGS IN THE FIELD THAT YOU COULDN'T MEASURE BEFORE

Field geologists have long awaited the development of a geo-tricorder that would give a rock's crystallization age, chemical composition, mineral composition, etc. in the field. Although this device is just a gleam in some developer's eye at the moment, we have developed an app, StraboTools (ST), that is a short step in this direction. ST currently contains two main tools. (1) The color index tool allows the user to make rapid, precise, and accurate measurements of the percentage of dark minerals (color index) or other components of a rock that can be isolated based on their grayscale value. The color index correlates strongly with bulk composition, so easy field determination allows mapping of, e.g., pluton zoning without laboratory analysis. (2) The edge fabric tool quantifies fabric in an image by examining the orientations of grayscale gradient vectors and determining an ellipse representing their orientations and magnitudes. For homogeneous deformation, this ellipse tracks the strain ellipse. The edge fabric tool can pick up remarkably subtle fabrics and can be used to rapidly quantify fabric orientation and intensity on the outcrop.

Two more tools are currently in development. (3) The mode tool uses unsupervised classification to determine the modal percentages of minerals in photos where different minerals are distinguishable based on color. In testing on granitoid rocks, it reproduces observed modes with surprising accuracy. This tool may also offer a method for mapping pluton zonation in the field. (4) The grain size tool uses autocorrelation to produce a representative grain size (or grain cluster size). Asking the grain size of a plutonic rock is an ill-posed question because the different crystal species generally have lognormal distributions with different means and dispersions; the grain size tool offers an objective measure of this important parameter.