Abstract Details
(2020) A Geochemical and Textural Cross-Section of a Compositionally Zoned Magma Reservoir
Zayac J & Longpré M-A
https://doi.org/10.46427/gold2020.3072
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05i: Plenary Hall, Thursday 25th June 06:48 - 06:51
John Zayac
Marc-Antoine Longpré View all 7 abstracts at Goldschmidt2020 View abstracts at 9 conferences in series
Marc-Antoine Longpré View all 7 abstracts at Goldschmidt2020 View abstracts at 9 conferences in series
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Submitted by Michael Rowe on Wednesday 24th June 05:58
Clear and concise presentation! You've presented phenocryst proportions but don't quantify groundmass crystallinity. I'm particularly interested in how the groundmass crystallinity varies as a function of volatile loss (phenocryst - groundmass), and how much of your groundmass glass chemical variation is dictated by late stage groundmass crystallization rather than an actual change in bulk liquid composition (residual glass between crystals as opposed to a mostly glass material).
Thanks for the encouragement and the great question - one I'll be sure to keep in mind as I am preparing this manuscript. I am currently working on quantifying the groundmass crystallinity across the eruption. In general, if microlite crystallization controlled the compositional gradient, one would expect a positive correlation between SiO2 and microlite content, which we see the opposite of. We have also measured the bulk rock chemistry of both the dacite and the andesite end-members for this eruption (and four others). As expected, the microlite poor dacite has less variation between bulk rock and glass chemistry than the microlith-rich andesite, but the compositional gap between the early eruptive products and the late persists, which suggests that the gap is present in the pre-erutpive system, and not solely a product of degassing-induced crystallization
Clear and concise presentation! You've presented phenocryst proportions but don't quantify groundmass crystallinity. I'm particularly interested in how the groundmass crystallinity varies as a function of volatile loss (phenocryst - groundmass), and how much of your groundmass glass chemical variation is dictated by late stage groundmass crystallization rather than an actual change in bulk liquid composition (residual glass between crystals as opposed to a mostly glass material).
Thanks for the encouragement and the great question - one I'll be sure to keep in mind as I am preparing this manuscript. I am currently working on quantifying the groundmass crystallinity across the eruption. In general, if microlite crystallization controlled the compositional gradient, one would expect a positive correlation between SiO2 and microlite content, which we see the opposite of. We have also measured the bulk rock chemistry of both the dacite and the andesite end-members for this eruption (and four others). As expected, the microlite poor dacite has less variation between bulk rock and glass chemistry than the microlith-rich andesite, but the compositional gap between the early eruptive products and the late persists, which suggests that the gap is present in the pre-erutpive system, and not solely a product of degassing-induced crystallization
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