Textural segmentation of magmatic minerals to compare geochemical zoning in elemental maps: assessing changes in plagioclase zoning based on the size of pyroclasts

Abstract:

Magmatic minerals crystallised in igneous systems commonly show textural zoning patterns, which can be related to changes in the state of the host magma. Large-scale textural features can often be identified by eye in backscatter-electron (BSE) or cathodoluminescent (CL) images. Using statistical methods that have been designed to segment optical images, we have developed a procedure to segment textural zones within magmatic minerals and correlate zones between multiple crystals using elemental maps. This allows us to characterise the complexity and variability of chemical zoning between different geological samples. We provide an example using the mineral phase plagioclase. Using two contemporaneous samples from an eruptive unit on the island of St. Kitts we show that a volcanic bomb (~10cm) and scoria (~2cm) have distinct phenocryst assemblages even though their bulk geochemistry is identical.