Structural anisotropy: Using image analysis to quantify block-in-matrix fabrics

Block-in-matrix rock assemblages — such as mélanges — are structurally complex units whose fabric is primarily defined, not by planar or linear features as most rock units are, but by the orientation and aspect ratio of irregularly shaped blocks. Despite this, previous attempts to quantitatively characterize mélange fabrics have predominantly focused on measuring the foliation using traditional techniques. Here we introduce a method of characterizing block-in-matrix fabrics using image analysis of field photos to discern the aspect ratios and orientations of blocks and define the structural anisotropy of the rock unit. We also include the software to calculate structural anisotropy and the trend of the fabric from image analysis data.