Experimental constraints on magma mixing: case studies from Phlegrean Fields and Montserrat
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Abstract
The mixing process in nature is observed at different scales in the rock record, evident through variable structural and textural patterns and morphologies such as filament-like structures, enclaves, and mineral phases showing physico-chemical disequilibrium. The type and geometry of these structures strongly depends on the mixing dynamics (e.g. Morgavi et al., 2012 Perugini et al., 2012). The quantification of the morphology and the compositional variability of these structures are essential to understand this fundamental igneous process and require detailed analytical and experimental studies. Although mixing between mafic and felsic magmas is regarded as a major process affecting compositional variability of igneous rocks in the Earth system and eruption trigger, the mechanisms acting to promote melt interaction, both from the physical and chemical point of view, are still poorly understood.
We will perform the first set of chaotic mixing experiments using trachytic and phonolitic magma from the Phlegraean Fields volcanic area and andesitic and basaltic magmas from the Soufriere Hills Volcano, Montserrat.The mixing process will be trigged by a recently developed apparatus that generates chaotic streamlines in the melts, mimicking the development of magma mixing in nature. The study of the interplay of physical dynamics and chemical exchanges between melts it will be carried out by time series mixing experiments under controlled chaotic dynamic conditions. The variation of major and trace elements it will be studied in detail by electron microprobe (EMPA) and Laser Ablation ICP-MS (LA-ICP-MS).
The aim of our work is to quantify how different chemical elements homogenize in the magmas at differing rates. The mobility of each element during mixing it will be estimated by calculating the decrease of concentration variance in time. These results will constitute a robust basis for determining the timescale of the mixing process at Phlegrean Fields and Soufriere volcano using the differential mobility of chemical elements.
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