A cross correlation method for chemical profiles in minerals, with an application to zircons of the Kilgore Tuff (USA)

Magmatic crystals are characterised by chemical zonation patterns that reflect the thermal and chemical conditions within magma reservoirs in which they grew. Crystals that exhibit similar patterns of zonation are often interpreted to have experienced similar conditions of growth. These patterns of zonation may represent continuous processes such as cooling, or more instantaneous events such as magma injection, and provide an insight into the structure and evolution of a magmatic system, both temporally and spatially. We have developed an algorithm that is objectively able to quantify the similarity within and between suites of magmatic crystals from different samples. Significantly, the algorithm is able to identify correlation that occurs between the interiors of two crystals, but does not extend to the rim, which provides an opportunity to understand the long-term evolution of magmatic systems. We develop and explain the mathematical basis for our algorithm and introduce its application using cathodoluminescence images of zircons from the Kilgore Tuff (USA). The results allow us to correlate samples from two different outcrops that are found over 80 km apart.