Analyzing sulfur and chlorine behavior in the 2006 eruption of Augustine volcano
Abstract
In this study, we look at the behavior of volatiles, specifically that of sulfur and chlorine, during the 2006 eruption of Augustine volcano, Alaska by combining the geochemistry of melt inclusions and modeling of S and Cl behavior during crystallization. Major elements, S, and Cl in the silicate plagioclase-hosted melt inclusions (MI) from three andesites of 2006 eruption were analyzed using electron microprobe analysis (EMPA). The MIs were dacitic-rhyolitic, with average SiO2 of 71.3 wt.%, S of 216 ppm and Cl of 3624 ppm, which are similar to the previously published MIs from 2006 eruption [1]. When compared to the minimally degassed basaltic MI data from Pleistocene Augustine eruptions [2], dacitic and rhyolitic MIs from 2006 eruptions have similar Cl contents (5445 vs 5867 ppm) and significantly less S content (609 ppm vs 5882 ppm). In order to investigate the S and Cl behavior during the magmatic differentiation, equilibrium crystallization paths were modelled in Rhyolite MELTS [3] from a dacitic starting composition at the pressures of 25-100 MPa, constrained by the apparent H2O concentration in the melt [4]. We then modelled the distribution of S and Cl between melt, fluid, and sulfur- or chlorine-bearing minerals along the crystallization path with initial S and Cl contents from Pleistocene MI [2]. S and Cl solubilities and their partition coefficients were calculated along the crystallization paths using the previous experimental constrained models [5-8]. When compared to our silicate MI data, the results indicated that S-bearing minerals precipitated in the melt during the 2006 eruption of Augustine and significantly reduced the concentration of S in both the fluid and the melt. In contrast, Cl-bearing minerals were most likely not precipitated, and Cl concentration in the melt is mainly controlled by partitioning between fluid and silicate melt, which is strongly affected by low pressure.
[1] Webster et al., 2010, The 2006 Eruption of Augustine Volcano, Alaska, USGS; [2] Zimmer et al, 2010, J Petrol; [3] Gualda and Ghiorso, 2014, G-Cubed; [4] Newman and Lowenstern, 2002, Comput Geosci-UK; [5] Masotta and Keppler, 2014, GCA; [6] Webster and Lange, 2015, AM Mineral; [7] Masotta et al., 2016, GCA; [8] Alletti et al., 2014, GeoResJ- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.V43I0244W
- Keywords:
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- 1030 Geochemical cycles;
- GEOCHEMISTRYDE: 4930 Greenhouse gases;
- PALEOCEANOGRAPHYDE: 8185 Volcanic arcs;
- TECTONOPHYSICSDE: 8408 Volcano/climate interactions;
- VOLCANOLOGYDE: 8412 Reactions and phase equilibria;
- VOLCANOLOGYDE: 8419 Volcano monitoring;
- VOLCANOLOGYDE: 8430 Volcanic gases;
- VOLCANOLOGY