StraboTools: A Mobile App for Quantifying Fabric in Geology

Allen F. Glazner

Dept. of Geological Sciences, University of North Carolina, Chapel Hill, North Carolina 27599, USA, afg@unc.edu

J. Douglas Walker

Dept. of Geology, University of Kansas, Lawrence, Kansas 66045, USA

Abstract

Quantification of field observations is an essential step in making them reproducible and shareable, but field geologists have few tools for quantifying field observations of important features such as foliation intensity, crystal alignment, vesicle elongation, joint intensity, and mineral proportions. Here we describe a mobile app, StraboTools, which offers two ways to rapidly and objectively quantify these variables. The edge fabric tool examines grayscale gradients in a photograph and summarizes them with the edge fabric ellipse. For deformation of a homogeneous material with passive markers, this ellipse tracks the strain ellipse. Edge fabric ellipses can be determined on the outcrop and make quick work (5 seconds) of formerly time-consuming and subjective strain-analysis tasks (e.g., Fry and R_f /Φ analysis). They are remarkably sensitive to subtle deformations that are difficult to see by eye. The color index tool determines the proportion of any component in the photograph whose grayscale level can be isolated (e.g., dark minerals in a granitic rock, feldspar phenocrysts in a lava, or blue epoxy in a thin section). Estimating proportions by eye has poor precision and accuracy; the color index tool is both accurate and precise if a suitable rock face is available. These tools can be used with photomicrographs and aerial photographs as well as in the field.

Manuscript received 22 Feb. 2020. Revised manuscript received 19 May 2020. Manuscript accepted 22 May 2020. Posted 9 June 2020.

© The Geological Society of America, 2020. CC-BY-NC.

https://doi.org/10.1130/GSATG454A.1