Towards an Integrated Texture Toolkit, 1: Unveiling the Complex Relationship Between Crystal Size, Shape, and Fabric in EBSD Data

Abstract

Rock textures observed via thin section are skewed from their true 3D nature. This is due to a variety of cut effects—artifacts that are introduced due to the lower dimensional nature of the thin section relative to the rock. Typically, these methods invert crystal shape and crystal size, but with each process performed separately and in sequence. With the ongoing adoption of electron backscatter diffraction (EBSD) by petrologists, an additional data stream has now become available: the 3D orientation of 2D grain sections. For EBSD analysis, no stereological corrections are typically applied for interpreting the data. In this study, we test whether this orientational information is also skewed due to a fabric cut effect. We test this by numerically generating synthetic crystal datasets representative of a number of crystal shapes and population sizes. We find that EBSD orientational data does have a fabric cut effect since crystals oriented with long axes perpendicular to the thin section are more likely to be sampled compared to those with long axes oriented parallel to it. This effect needs to be accounted for to accurately interpret the true 3D fabric. Towards this end, we develop a method of inverting cut fabrics which provides robust error estimations and show its accuracy using a range of synthetic examples. When applied to natural samples, which are inherently more complex than the simplified, synthetic samples, we find that the inversion process does not always produce geologically plausible results. To more faithfully correct for the different cut effects, we argue that the stereological inversion process should not be performed separately or sequentially, as is commonly done at present. Instead, we need a new textural toolkit framework to correct for crystal shape, size, and orientation simultaneously with accurate uncertainty estimates.