H2O diffusion in rhyolitic melts and glasses

Zhang, Youxue; Behrens, Harald

doi:10.1016/s0009-2541(99)00231-4

Cited by 233 publications

(157 citation statements)

References 28 publications

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“…D is based on Eq. 18 of Zhang et al (2007) for the basaltic eruptions and on Zhang and Behrens (2000) for the silicic eruptions. c R is the H 2 O concentration at the melt-vapor interface and depends on the solubility at P g .…”

Section: Bubble Growth Modelingmentioning

confidence: 99%

Relating vesicle shapes in pyroclasts to eruption styles

et al. 2013

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Vesicles in pyroclasts provide a direct record of conduit conditions during explosive volcanic eruptions. Although their numbers and sizes are used routinely to infer aspects of eruption dynamics, vesicle shape remains an underutilized parameter. We have quantified vesicle shapes in pyroclasts from fall deposits of seven explosive eruptions of different styles, using the dimensionless shape factor , a measure of the degree of complexity of the bounding surface of an object. For each of the seven eruptions, we have also estimated the capillary number, Ca, from the magma expansion velocity through coupled diffusive bubble growth and conduit flow modeling. We find that is smaller for eruptions with Ca 1 than for eruptions with Ca 1. Consistent with previous studies, we interpret these results as an expression of the relative importance of structural changes during magma decompression and bubble growth, such as coalescence and shape relaxation of bubbles by capillary stresses. Among the samples analyzed, Strombolian and Hawaiian fire-fountain eruptions have Ca 1, in contrast to Vulcanian, Plinian, and ultraplinian eruptions. Interestingly, the basaltic Plinian eruptions of Tarawera volcano, New Zealand in 1886 and Mt. Etna, Italy in 122 BC, for which the cause of intense explosive activity has

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Section: Bubble Growth Modelingmentioning

confidence: 99%

Relating vesicle shapes in pyroclasts to eruption styles

et al. 2013

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“…Zhang and Behrens (2000) showed that D OH (C,T,P) varies linearly with water concentration at low total water contents (less than about 2 wt%), and we account for this effect in our model. However, we do not include variations in D OH (C,T,P) with temperature and pressure-a simplifying assumption discussed later.…”

Section: Model For Spherulite Growthmentioning

confidence: 88%

“…Using D OH in rhyolite at conditions relevant to our samples (~0.1 wt% water and 0.1 MPa; Zhang and Behrens 2000), the time required to grow a spherulite of given radius comes from the scaling relationship (6) where R is the final radius of the spherulite. Results are summarized in Fig.…”

Section: Discussionmentioning

confidence: 99%

Diffusion-controlled spherulite growth in obsidian inferred from H2O concentration profiles

Watkins

Manga

Huber

et al. 2008

Contrib Mineral Petrol

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Spherulites are spherical clusters of radiating crystals that occur naturally in rhyolitic obsidian. The growth of spherulites requires diffusion and uptake of crystal forming components from the host rhyolite melt or glass, and rejection of non-crystal forming components from the crystallizing region. Water concentration profiles measured by synchrotron-source Fourier transform spectroscopy reveal that water is expelled into the surrounding matrix during spherulite growth, and that it diffuses outward ahead of the advancing crystalline front. We compare these profiles to models of water diffusion in rhyolite to estimate timescales for spherulite growth. Using a diffusion-controlled growth law, we find that spherulites can grow on the order of days to months at temperatures above the glass transition. The diffusion-controlled growth law also accounts for spherulite size distribution, spherulite growth below the glass transition, and why spherulitic glasses are not completely devitrified.

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“…The first thing to notice is that the fit for a constant (i.e., concentration independent) D(H 2 O) matches the data poorly. That a simple error function fits hydration profiles in silicate melts and glasses poorly is well known and is the basis for our understanding that D ( which water is assumed to be dissolved as both mobile water molecules (which are assumed to have a constant diffusion coefficient) and hydroxyl groups (which are assumed to be immobile) where the concentrations of the two species are related via the reaction H 2 O mol + O 2-= 2OH, which has a constant equilibrium constant, K (Behrens and Nowak, 1997;Zhang, 1999;Zhang and Behrens, 2000;. Figure 2) confirms that this is a robust feature of diffusion of water in silicate melts, extending from highly polymerized compositions such as rhyolite (in which this feature was first demonstrated by Shaw (1974)) to the relatively depolymerized basaltic composition shown here.…”

Section: ) Experimental Determination Of the Chemical Diffusion Of Wmentioning

confidence: 99%

“…We note, however, that despite the success of this relatively simple species-based approach, there are some complications. For example, some studies (Behrens and Zhang, 2001;Lyakhovsky et al, 1996;Zhang and Behrens, 2000; have suggested that the diffusion coefficient for molecular water increases with total water content, and the mobility of OH groups may be significant under some circumstances, especially at very low water contents . Although we have emphasized here the results on basaltic melts, our results on other compositions show similar overall behavior.…”

Section: ) Experimental Determination Of the Chemical Diffusion Of Wmentioning

confidence: 99%

Infrared Spectroscopy and Stable Isotope Geochemistry of Hydrous Silicate Glasses

Stolper¹

2007

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H2O diffusion in rhyolitic melts and glasses

Cited by 233 publications

References 28 publications

Relating vesicle shapes in pyroclasts to eruption styles

Relating vesicle shapes in pyroclasts to eruption styles

Diffusion-controlled spherulite growth in obsidian inferred from H2O concentration profiles

Infrared Spectroscopy and Stable Isotope Geochemistry of Hydrous Silicate Glasses

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