Reconstruction of 3D grain boundaries from rock thin sections, using an advanced polarised‐light microscopy method

Abstract

Summary Grain boundaries play a significant role in materials by initiating reactions and collecting impurities. Here we present FAGO (Fabric Analyser Grain boundary recOnstruction), a first step towards the automatic determination of three‐dimensional (3D) grain boundary geometry using polarised light. The trace of the grain boundaries from 2D rock thin sections are determined primarily from data acquired using an automatic fabric analyser microscope and the FAME software (fabric analyser‐based microstructure evaluation; Peternell and colleagues and Hammes and Peternell). Based on the Fabric Analyser G50's unique arrangement of nine differently oriented light sources the retardation can be determined independently for each light direction and at each pixel in the field of view. FAGO combines these retardation datasets for each individual pixel together with retardation profiles across grain boundaries, to determine the orientations of the boundaries. The grain boundary traces are then broken up into segments of equal orientation, using the profile‐obtained orientation data. Finally, a 3D grain boundary model is reconstructed. The data processing is almost fully automatic using the MATLAB® environment. Only minor manual inputs are required.

Using the traditional microscope for mineral grain orientation determination: A prototype image analysis pipeline for optic‐axis mapping (POAM)

“…58 It has also been used for 3D optical mapping of grain boundaries using the independent retardation estimations of oriented light sources. 59 A prominent application of the G50 system was the semiautomated identification of pristine apatite crystal areas for 238 U fission-track dating in thermochronology. This was achieved at a rate of ∼15 min/mount, 15 providing very significant time savings over conventional petrography.…”

“…MiFa has been integrated with software for postprocessing microstructure analysis (grain size and SPO) 16 and numerical simulation of 2D microstructural development 58 . It has also been used for 3D optical mapping of grain boundaries using the independent retardation estimations of oriented light sources 59 …”