Quantitative chemical mapping of plagioclase as a tool for the interpretation of volcanic stratigraphy: an example from Saint Kitts, Lesser Antilles

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Authors

Oliver John Higgins, Tom Sheldrake , Luca Caricchi 

Abstract

Establishing a quantitative link between magmatic processes occurring at depth and volcanic eruption dynamics is essential to forecast the future behaviour of volcanoes, and to correctly interpret monitoring signals at active centres. Chemical zoning in minerals, which captures successive events or states within a magmatic system, can be exploited for such a purpose. However, to develop a quantitative understanding of magmatic systems requires an unbiased, reproducible method for characterising zoned crystals. We use image segmentation on thin section scale chemical maps to segment textural zones in plagioclase phenocrysts, and then correlate these zones throughout a stratigraphic sequence from Saint Kitts, Lesser Antilles. Both segmented phenocrysts and unsegmented matrix plagioclase are chemically decoupled from whole rock geochemical trends, with the latter showing a systematic temporal progression towards less chemically evolved magma (more anorthitic plagioclase). By working on a stratigraphic sequence, it is possible to track the chemical and textural complexity of segmented plagioclase in time, in this case on the order of millennia. In doing so, we find a relationship between the number of crystal populations, deposit thickness and time. Thicker deposits contain a larger number of crystal populations alongside an overall reduction in this number towards the top of the deposit. Our approach provides quantitative textural parameters for volcanic and plutonic rocks, including the ability to measure the amount of crystal fracturing. In combination with mineral chemistry, these parameters can strengthen the link between petrology and volcanology and pave the way towards a deeper understanding of the magmatic processes controlling eruptive dynamics.

DOI

https://doi.org/10.31223/X5RS39

Subjects

Earth Sciences, Geochemistry, Geology, Stratigraphy, Volcanology

Keywords

microprobe, zoning, crystal population, micropobe

Dates

Published: 2021-02-01 05:32

Last Updated: 2021-02-01 13:32

License

CC BY Attribution 4.0 International

Additional Metadata

Conflict of interest statement:
None

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