NanoSIMS results from olivine-hosted melt embayments: Magma ascent rate during explosive basaltic eruptions

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dc.citation.firstpage1en_US
dc.citation.journalTitleJournal of Volcanology and Geothermal Researchen_US
dc.citation.lastpage18en_US
dc.citation.volumeNumber283en_US
dc.contributor.authorLloyd, Alexander S.en_US
dc.contributor.authorRuprecht, Philippen_US
dc.contributor.authorHauri, Erik H.en_US
dc.contributor.authorRose, Williamen_US
dc.contributor.authorGonnermann, Helge M.en_US
dc.contributor.authorPlank, Terryen_US
dc.date.accessioned2015-07-10T15:47:01Zen_US
dc.date.available2015-07-10T15:47:01Zen_US
dc.date.issued2014en_US
dc.description.abstractThe explosivity of volcanic eruptions is governed in part by the rate at which magma ascends and degasses. Because the time scales of eruptive processes can be exceptionally fast relative to standard geochronometers, magma ascent rate remains difficult to quantify. Here we use as a chronometer concentration gradients of volatile species along open melt embayments within olivine crystals. Continuous degassing of the external melt during magma ascent results in diffusion of volatile species from embayment interiors to the bubble located at their outlets. The novel aspect of this study is the measurement of concentration gradients in five volatile elements (CO2, H2O, S, Cl, F) at fine-scale (5–10 μm) using the NanoSIMS. The wide range in diffusivity and solubility of these different volatiles provides multiple constraints on ascent timescales over a range of depths. We focus on four 100–200 μm, olivine-hosted embayments erupted on October 17, 1974 during the sub-Plinian eruption of Volcán de Fuego. H2O, CO2, and S all decrease toward the embayment outlet bubble, while F and Cl increase or remain roughly constant. Compared to an extensive melt inclusion suite from the same day of the eruption, the embayments have lost both H2O and CO2 throughout the entire length of the embayment. We fit the profiles with a 1-D numerical diffusion model that allows varying diffusivities and external melt concentrations as a function of pressure. Assuming a constant decompression rate from the magma storage region at approximately 220 MPa to the surface, H2O, CO2 and S profiles for all embayments can be fit with a relatively narrow range in decompression rates of 0.3–0.5 MPa/s, equivalent to 11–17 m/s ascent velocity and an 8 to 12 minute duration of magma ascent from ~ 10 km depth. A two stage decompression model takes advantage of the different depth ranges over which CO2 and H2O degas, and produces good fits given an initial stage of slow decompression (0.05–0.3 MPa/s) at high pressure (> 145 MPa), with similar decompression rates to the single-stage model for the shallower stage. The magma ascent rates reported here are among the first for explosive basaltic eruptions and demonstrate the potential of the embayment method for quantifying magmatic timescales associated with eruptions of different vigor.en_US
dc.identifier.citationLloyd, Alexander S., Ruprecht, Philipp, Hauri, Erik H., et al.. "NanoSIMS results from olivine-hosted melt embayments: Magma ascent rate during explosive basaltic eruptions." <i>Journal of Volcanology and Geothermal Research,</i> 283, (2014) Elsevier: 1-18. http://dx.doi.org/10.1016/j.jvolgeores.2014.06.002.en_US
dc.identifier.doihttp://dx.doi.org/10.1016/j.jvolgeores.2014.06.002en_US
dc.identifier.urihttps://hdl.handle.net/1911/80881en_US
dc.language.isoengen_US
dc.publisherElsevieren_US
dc.rightsThis is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier.en_US
dc.subject.keywordmagma ascenten_US
dc.subject.keyworddiffusionen_US
dc.subject.keywordmelt inclusionsen_US
dc.subject.keywordvolatilesen_US
dc.subject.keywordexplosive eruptionsen_US
dc.subject.keywordbasalten_US
dc.titleNanoSIMS results from olivine-hosted melt embayments: Magma ascent rate during explosive basaltic eruptionsen_US
dc.typeJournal articleen_US
dc.type.dcmiTexten_US
dc.type.publicationpost-printen_US
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