Norbert Toth , John Maclennan

Textural information, such as crystal size distributions (CSDs) or crystal aspect ratios are powerful tools in igneous petrography for interrogating the thermal history of rocks. They facilitate the investigation of crystal nucleation, growth and mixing as well as the cooling rate of the rock. However, they require large volumes of crystal segmentations and measurements that are often obtained with manual methods. Here a deep learning-based computer vision technique, termed instance segmentation, is proposed to automate the pixel-by-pixel detection of each plagioclase crystal in thin section images. Using predictions from a re-trained model the physical properties of the detected crystals, such as size and aspect ratio, can be rapidly generated to provide textural insights. The present segmentations are validated against published results from manual approaches to prove the method's accuracy. The power and efficiency of this automated approach is showcased by analysing an entire sample suite, segmenting over 48,000 crystals in only a matter of days. Widescale use of this method is expected to drive significant developments in the igneous petrography and related fields