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Department of Earth Sciences, CEMPEG, Uppsala University,
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- PublicationOpen AccessCO2 bubble generation and migration during magma-carbonate interaction(2015-04-17)
; ; ; ; ; ; ; ; ;Blythe, L. S. ;Deegan, F. M.; Department of Geological Sciences Stockolm University Sweden ;Freda, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Jolis, E. M.; CEMPEG, Uppsala University, Sweden ;Masotta, M.; Bahyerisches Geoinstitut Bahyretuh Germany ;Misiti, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Taddeucci, J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Troll, V. R.; CEMPEG, Uppsala University, Sweden ;; ; ; ; ; ; We conducted quantitative textural analysis of vesicles in high temperature and pressure carbonate assimilation experiments (1200 °C, 0.5 GPa) to investigate CO2 generation and subsequent bubble migration from carbonate into magma. We employed Mt. Merapi (Indonesia) and Mt. Vesuvius (Italy) compositions as magmatic starting materials and present three experimental series using (1) a dry basaltic-andesite, (2) a hydrous basaltic-andesite (2 wt% H2O), and (3) a hydrous shoshonite (2 wt% H2O). The duration of the experiments was varied from 0 to 300 s, and carbonate assimilation produced a CO2-rich fluid and CaO-enriched melts in all cases. The rate of carbonate assimilation, however, changed as a function of melt viscosity, which affected the 2D vesicle number, vesicle volume, and vesicle size distribution within each experiment. Relatively low-viscosity melts (i.e. Vesuvius experiments) facilitated efficient removal of bubbles from the reaction site. This allowed carbonate assimilation to continue unhindered and large volumes of CO2 to beliberated, a scenario thought to fuel sustained CO2-driven eruptions at the surface. Conversely, at higher viscosity (i.e. Merapi experiments), bubble migration became progressively inhibited and bubble concentration at the reaction site caused localised volatile over-pressure that can eventually trigger short-lived explosive outbursts. Melt viscosity therefore exerts a fundamental control on carbonate assimilation rates and, by consequence, the style of CO2-fuelled eruptions.330 316 - PublicationRestrictedExperimental simulation of magma–carbonate interaction beneath Mt. Vesuvius, Italy(2013)
; ; ; ; ; ; ; ;Jolis, E. M.; Department of Earth Sciences, CEMPEG, Uppsala University ;Freda, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Troll, V. R.; Department of Earth Sciences, CEMPEG, Uppsala University ;Deegan, F. M.; Department of Geosciences, Swedish Museum of Natural History ;Blythe, L. S.; Department of Earth Sciences, CEMPEG, Uppsala University, ;McLeod, C. L.; Department of Earth Sciences, Durham University, ;Davidson, J. P.; Department of Earth Sciences, Durham University,; ; ; ; ; ; We simulated the process of magma–carbonate interaction beneath Mt. Vesuvius in short duration piston-cylinder experiments under controlled magmatic conditions (from 0 to 300 s at 0.5 GPa and 1,200 C), using a Vesuvius shoshonite composition and upper crustal limestone and dolostone as starting materials. Backscattered electron images and chemical analysis (major and trace elements and Sr isotopes) of sequential experimental products allow us to identify the textural and chemical evolution of carbonated products during the assimilation process. We demonstrate that melt–carbonate interaction can be extremely fast (minutes), and results in dynamic contamination of the host melt with respect to Ca, Mg and87Sr/86Sr, coupled with intense CO2 vesiculation at the melt–carbonate interface. Binary mixing between carbon- ate and uncontaminated melt cannot explain the geochemical variations of the experimental charges in full and convection and diffusion likely also operated in the charges. Physical mixing and mingling driven by exsolving volatiles seems to be a key process to promote melt homogenisation. Our results reinforce hypotheses that magma–carbonate interaction is a relevant and ongoing process at Mt. Vesuvius and one that may operate not only on a geological, but on a human timescale.228 31